VYSOKÉ UČENÍ TECHNICKÉ V BRNĚ BRNO UNIVERSITY OF TECHNOLOGY FAKULTA ELEKTROTECHNIKY A KOMUNIKAČNÍCH TECHNOLOGIÍ ÚSTAV RADIOELEKTRONIKY FACULTY OF ELECTRICAL ENGINEERING AND COMMUNICATION DEPARTMENT OF RADIO ELECTRONICS NUMERICAL SYNTHESIS OF FILTERING ANTENNAS DOCTORAL THESIS DOKTORSKÁ PRÁCE AUTHOR AUTOR PRÁCE Ing. MARTIN KUFA BRNO, 2015
VYSOKÉ UČENÍ TECHNICKÉ V BRNĚ BRNO UNIVERSITY OF TECHNOLOGY FAKULTA ELEKTROTECHNIKY A KOMUNIKAČNÍCH TECHNOLOGIÍ ÚSTAV RADIOELEKTRONIKY FACULTY OF ELECTRICAL ENGINEERING AND COMMUNICATION DEPARTMENT OF RADIO ELECTRONIC NUMERICAL SYNTHESIS OF FILTERING ANTENNAS NUMERICKÁ SYNTÉZA FILTRUJÍCÍCH ANTÉN DOCTORAL THESIS DOKTORSKÁ PRÁCE AUTHOR AUTOR PRÁCE SUPERVISOR Ing. MARTIN KUFA Prof. ZBYNĚK RAIDA VEDOUCÍ PRÁCE BRNO 2015
ABSTRACT The dissertation thesis is focused on a complete design methodology of a three and four-element patch antenna arrays which are without any filtering parts and yet behave like a filtering antenna (filtenna). This design combines filter and antenna approaches and includes shaping the frequency response of the reflection coefficient and the modelling of the frequency response of the normalized realized gain. The frequency response of the main lobe direction is controlled as well. In order to control the shape of these responses, a set of g i coefficients for designing the filtering antenna array are obtained. The design methodology was verified on the three-element and four-element filtennas over the frequency range from 4.8 GHz to 6.8 GHz; for fractional bandwidth from 7 % to 14 % and for level of the reflection coefficient from 10 db to 20 db. The whole design methodology was supported by manufacturing and measuring six test cases of the filtering antenna array with different configurations. Simulated and measured results show a good agreement in all cases. KEYWORDS Filtering antenna array; filtenna; band-pass filter; low-pass prototype filter; lowpass transformation; g i coefficients; normalized realized gain. ABSTRAKT Dizertační práce je zaměřena na kompletní metodiku návrhu tří a čtyř prvkových flíčkových anténních řad, které neobsahují žádné filtrující části a přesto se chovají jako filtrující antény (filtény). Návrhová metodika kombinuje přístup pro návrh filtrů s přístupem pro anténní řady a zahrnuje tvarování frekvenčních odezev činitele odrazu a normovaného realizovaného zisku. Směr hlavního laloku přes pracovní pásmo je kontrolován také. S cílem kontrolovat tvary uvedených charakteristik, nové g i koeficienty jsou představeny pro návrh filtrujících anténních řad. Návrhová metodika byla ověřena na tří a čtyř prvkové filtrující anténní řadě přes frekvenční pásmo od 4,8 GHz do 6,8 GHz, pro šířku pásma celé struktury od 7 % do 14 % a pro požadovanou úroveň činitele odrazu od 10 db do 20 db. Celá metodika byla podpořena výrobou a měřením šesti testovacích vzorků filtrujících anténních řad s rozdílnými konfiguracemi. Ve všech případech se simulované a naměřené výsledky dobře shodují. KLÍČOVÁ SLOVA Filtrující anténní řada; filténa; filtr typu pásmová propust; prototypový filtr typu dolní propust; transformace na filtr typu dolní propust; g i koeficienty; normovaný realizovaný zisk. - ii -
BIBLIOGRAPHIC CITATION KUFA, M. Numerical synthesis of filtering antennas. Doctoral dissertation thesis. Brno: Brno University of Technology, Faculty of Electrical Engineering and Communication, 2015. 106 p. ACKNOWLEDGEMENT I would like to express my gratitude to my supervisor Prof. Dr. Ing. Zbyněk Raida for giving me an opportunity to work with him, and for his advice and invaluable guidance throughout my research. Brno, the 21 st of August, 2015 Martin Kufa The research described in my thesis was performed in laboratories of the SIX Research Center, the registration number CZ.1.05/2.1.00/03.0072, the operational program Research and Development for Innovation. - iii -
Contents CONTENTS 1 Introduction... 17 2 State of the Art... 18 2.1 Combination of band-pass filter and antenna... 18 2.2 Integration of radiating element into filter... 20 2.3 Filtering antennas with synthesized realized gain... 25 2.4 Summary... 26 3 Dissertation Objectives... 28 4 Planar filtering antenna array... 30 4.1 Comparison of properties of planar antenna arrays... 30 4.2 Patch antenna fed by aperture... 31 4.3 Parameters versus dimensions of antenna... 32 4.4 Antenna array fed by apertures... 41 4.5 Summary... 43 5 Equivalent circuit of filtering antenna array fed by apertures... 45 5.1 Equivalent circuit of single patch antenna fed by aperture... 45 5.2 Equivalent circuit of filtering patch array fed by apertures... 46 5.3 Low-pass transformation... 49 5.4 Summary... 51 6 Synthesis of filtering antenna array fed by apertures... 52 6.1 Main idea of synthesis of filtering antenna array fed by apertures... 52 6.2 Filter approach for obtain values of the equivalent circuit... 52 6.3 Synthesis of frequency response of normalized realized gain... 53 6.4 New g i coefficients for filtering antenna arrays... 55 - iv -
Contents 6.4.1 Three-element filtering antenna array and g i coefficients... 55 6.4.2 Four-element filtering antenna array and g i coefficients... 62 6.5 Dimensions of the full-wave model... 69 6.6 Comparison of theoretical results and full-wave results... 69 6.6.1 Full-wave verification of the three-element filtering antenna array... 70 6.6.2 Full-wave verification of the four-element filtering antenna array... 77 6.7 Summary... 83 7 Verification by measurement... 85 7.1 Verification of the three-element filtering antenna array... 85 7.2 Verification of the four-element filtering antenna array... 91 7.3 Summary... 98 8 Conclusions... 99 References... 102 Curriculum vitae... 105 Selected publications... 106 - v -
List of figures LIST OF FIGURES Figure 2.1 The structure of the SIW two-slot filtenna [1]... 18 Figure 2.2 The structure of the SIW filter Yagi filtenna [2]... 19 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 The layout of the top side (upper) and the layout of the bottom side (below) of the SIW filter COCO filtenna [3]... 19 A top layer (left side) and the bottom layer (right side) of the Vivaldi filtenna with varactor [6]... 20 The combination of two bandstop filters with binomical balun and single dipole antenna [7]... 20 The structure of the three square open-loops filter (on the left side) and the structure of the two square open-loops filtenna (on the right side) [8]... 21 Figure 2.7 The photo of the filtenna with the hairpin filter [10]... 21 Figure 2.8 Figure 2.9 The equivalent circuit including the patch as the last resonator of the filter [10]... 21 The equivalent circuit (left side) and the layout (right side) of the filtering U-shaped antenna [11]... 22 Figure 2.10 The equivalent circuit (left side) and the layout (right side) of the filtering U-shaped antenna array [12]... 22 Figure 2.11 The structure of the meander-line filtenna [14]... 23 Figure 2.12 The layout of the Γ-shaped filtenna with DGS designed in [15] (left side) and [16] (right side)... 23 Figure 2.13 The structure of the inverted L-shaped filtering antenna [17]... 24 Figure 2.14 The structure of the N-order filtering antenna [18]... 24 Figure 2.15 Filtenna based on the low-pass filter with reduced fractal defected ground structure (DGS) [22]... 25 Figure 2.16 Series fed five patch antenna array [7]... 25 Figure 2.17 Idealized antenna array [7]... 26 Figure 2.18 Dipole antenna array without feeders (left) and with feeders (right) [24]... 26 Figure 4.1 Parallel feeding of filtering array [25]... 30 Figure 4.2 Serial feeding of filtering array [25]... 30 Figure 4.3 Out-of-line serial feeding of antenna array [25]... 31 Figure 4.4 Filtering antenna array fed by apertures... 31 Figure 4.5 The structure of the patch fed by aperture... 32 - vi -
Figure 4.6 Figure 4.7 Figure 4.8 Figure 4.9 List of figures Frequency responses of reflection coefficient at the antenna input for different widths of the slot W s at the frequency 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 33 Variation of the width of the slot W s at the frequency 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart... 33 Influence of the width of the slot W s on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm... 34 Influence of the width of the slot W s on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 34 Figure 4.10 Mutual capacitance as a function of the width of the slot W s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 35 Figure 4.11 Value of the inverter simulating coupling between patch and feeder as a function of the width of the aperture W s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 35 Figure 4.12 Frequency responses of the reflection coefficient at the antenna input for different lengths of the slot L s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 36 Figure 4.13 Variation of the length of the slot L s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart... 36 Figure 4.14 Influence of the length of the slot L s on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm... 37 Figure 4.15 Influence of the length of the slot L s on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 37 Figure 4.16 Influence of the length of the slot L s on the mutual capacitance at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 38 Figure 4.17 Influence of the length of the slot L s on the value of the inverter at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 38 Figure 4.18 Frequency responses of the reflection coefficient at the antenna input for different lengths of the open end l o at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 39 Figure 4.19 Variation of the length of the open end l o at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart... 39 Figure 4.20 Influence of the length of the open end l o on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm... 40 Figure 4.21 Influence of the length of the open end l o on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 40 Figure 4.22 Influence of the length of the open end l o on the mutual capacitance at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 41 Figure 4.23 Influence of the length of the open end l o on the value of the inverter at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm... 41 - vii -
List of figures Figure 4.24 Three-element patch array fed by apertures... 42 Figure 4.25 Frequency response of reflection coefficient (blue line) and frequency response of normalized realized gain in direction perpendicular to substrate (green line) of three-element filtering patch array fed by apertures... 42 Figure 4.26 The frequency response of the main lobe direction in the detail (a larger figure) and over the whole range (a smaller figure)... 43 Figure 5.1 Figure 5.2 Figure 5.3 Figure 5.4 Figure 5.5 Figure 5.6 Figure 5.7 Figure 6.1 Figure 6.2 Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 The equivalent circuit of the patch fed by aperture: ANSYS Designer model... 45 Comparison of the reflection coefficient of the full-wave model (blue line) versus equivalent circuit (red line)... 46 Equivalent circuit of three-element filtering patch array fed by apertures: ANSYS Designer model... 47 Comparison of the full-wave model implemented in CST Microwave Studio (dotted green line), the equivalent-circuit model implemented in ANSYS Designer (dashed red line), and the equivalent-circuit model implemented in MATLAB (solid blue line)... 48 The equivalent circuit of the filtering array transformed to the lowpass prototype filter... 49 Equivalent circuit of the low-pass prototype filter with the capacitances g shifted before the J-inverters... 50 Comparison of the frequency response of the reflection coefficient of the equivalent circuit with the response of the low-pass prototype filter... 50 Comparison of the frequency response of the normalized realized gain obtained by CST Microwave Studio (blue) and by MATLAB (red)... 55 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 56 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 57 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 57 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 58 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 58 - viii -
Figure 6.7 Figure 6.8 Figure 6.9 List of figures Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 59 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 59 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 60 Figure 6.10 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 60 Figure 6.11 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db... 61 Figure 6.12 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db... 61 Figure 6.13 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db... 62 Figure 6.14 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 63 Figure 6.15 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 63 Figure 6.16 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db... 64 Figure 6.17 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 64 Figure 6.18 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 65 Figure 6.19 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db... 65 Figure 6.20 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 66 - ix -
List of figures Figure 6.21 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 66 Figure 6.22 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db... 67 Figure 6.23 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 25dB... 68 Figure 6.24 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 25 db... 68 Figure 6.25 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 25 db... 69 Figure 6.26 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 71 Figure 6.27 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 71 Figure 6.28 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 73 Figure 6.29 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 73 Figure 6.30 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 75 Figure 6.31 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 75 Figure 6.32 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent - x -
List of figures circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 78 Figure 6.33 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 78 Figure 6.34 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 80 Figure 6.35 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 80 Figure 6.36 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 82 Figure 6.37 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 82 Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Figure 7.5 Figure 7.6 Figure 7.7 Comparison of the simulated results and measured ones for the case: three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 85 Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the three-element filtenna at frequency 4.8 GHz... 86 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 4.8 GHz... 86 Comparison of simulated results and measured ones for the case: three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 87 Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the three-element filtenna at frequency 5.8 GHz... 87 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 5.8 GHz... 88 Comparison of simulated results and measured ones for the case: three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 89 - xi -
Figure 7.8 Figure 7.9 List of figures Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the three-element filtenna at frequency 6.8 GHz... 89 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 6.8 GHz... 89 Figure 7.10 Top layers of the manufactured test cases of the three-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz... 90 Figure 7.11 Bottom layers of the manufactured test cases of the three-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz... 91 Figure 7.12 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 92 Figure 7.13 Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the four-element filtenna at frequency 4.8 GHz... 92 Figure 7.14 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 4.8 GHz... 92 Figure 7.15 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 93 Figure 7.16 Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the four-element filtenna at frequency 5.8 GHz... 94 Figure 7.17 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 5.8 GHz... 94 Figure 7.18 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 95 Figure 7.19 Comparison of simulated and measured co and cross polarizations in E-plane (left) and H-plane (right) of the four-element filtenna at the frequency 6.8 GHz... 95 Figure 7.20 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 6.8 GHz... 96 Figure 7.21 Top layers of manufactured test cases of the four-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz... 97 Figure 7.22 Bottom layers of manufactured test cases of the four-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz... 97 - xii -
List of tables Table 6.1 Table 6.2 Table 6.3 Table 6.4 Table 6.5 Table 6.6 Table 6.7 Table 6.8 Table 6.9 LIST OF TABLES Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 70 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 72 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 72 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 74 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 74 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 76 Comparison of resonant frequency, fractional bandwidth and reflection coefficient of three-element filtenna: equivalent circuit model (MATLAB) versus full-wave model (CST)... 76 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 77 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); fourelement filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 79 Table 6.10 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 79 - xiii -
List of tables Table 6.11 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); fourelement filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 81 Table 6.12 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 81 Table 6.13 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); fourelement filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 83 Table 7.1 Table 7.2 Table 7.3 Table 7.4 Table 7.5 Table 7.6 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db... 86 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db... 88 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db... 90 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db... 93 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db... 94 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db... 96 - xiv -
List of symbols LIST OF SYMBOLS AF Array factor c Speed of light in free space C m Mutual capacitance COCO Coaxial collinear antenna D Direction of the single patch antenna d Distance between two neighboring radiation elements E Θ E Φ f 0 f 0a FBW FBW a FBW s g i h J k 0 l L a l o L s MPB MTL N n P r S 11 S 21 S 21RG SIW w Radiation pattern of the patch antenna in the E-plane Radiation pattern of the patch antenna in the H-plane Resonant frequency Fractional bandwidth of a single patch fed by an aperture Frequency bandwidth Frequency bandwidth of the whole structure Frequency bandwidth of the whole structure Normalized value of low-pass prototype filter Thickness of substrate Admittance inverter Free-space wave number Length of feeder Length of patch Length of open end Length of slot ABCD matrices of parallel branch ABCD matrix of transmission line Number of radiation elements Order of filtering antenna array Radiated power Frequency response of reflection coefficient Losses in dielectrics and losses by radiation Frequency response of the normalized realized gain Substrate integrated waveguide Width of transmission line - xv -
W a W N W s Y 0 Z 0 β γ Δ ε eff ε r List of symbols Width of patch Normalized value of the width of aperture Width of slot Characteristic admittance of feeder Characteristic impedance of feeder Phase constant Complex propagation constant Fringing field Effective dielectric constant Relative permittivity η 0 Impedance of the free space (120π Ω) ξ Phase shift between two adjacent patches ω 0 Ω c Center angular frequency Cutoff angular frequency - xvi -
Introduction 1 INTRODUCTION Nowadays, wireless devices play an increasingly important role. We use such devices in daily life almost continuously. In future, more and more new devices will use wireless connections. With the proliferation of new devices, we start to face two problems. First, existing frequency bands are overcrowded, and therefore, higher and higher frequency bands have to be used (that way, the growing demands on the transmission speed and the amount of data transferred can be met also). Second, flexibility and mobility of wireless devices have to be improved. In order to minimize dimensions of mobile devices, we can implement fractal theory to the design of an antenna. The fractal design can also reduce the size of filters. Further reduction of the filter size can be achieved by using the concept of defected ground structures. Finally, an antenna and a filter can be integrated into a single, compact structure of minimal dimensions. The combination of an antenna and a filter into a single, compact structure is called filtering antenna or filtenna. A simultaneous frequency and space filtering is the main task of the filtenna. In an ideal case, a band-pass filter does not need to be used on the receiving side because the filtering is done by the filtenna. In this report, we discuss the methodology of the design of filtering antennas which do not contain filter elements. Filtering abilities are here achieved by suitably designed structure of an antenna array. In Chapter 2, we analyze state of the art of the synthesis of filtering antennas. Different approaches are mutually compared, and problems to be solved are identified. Considering results of the analysis, we define objectives of the dissertation in Chapter 3. In Chapters 4, planar filtering antenna array fed by apertures is presented and its equivalent circuit and low-pass transformation are described in Chapter 5. Chapter 6 is focused on the complete synthesis approach of the filtering antenna array and in the Chapter 7, the confrontation of the simulated and measured results of the filtennas are mentioned. Chapter 8 concludes the report. - 17 -
State of the art 2 STATE OF THE ART This Section reviews recent developments in the field of filtering antennas (filtennas). We will concentrate on three main approaches to the design of filtennas: A separate planar filter and a separate planar antenna are integrated. As a planar filter, a microstrip band-pass filter or a SIW (substrate integrated waveguide) band-pass filter are used. As a planar antenna, a patch antenna or a patch array are exploited. In the structure of a planar filter, the last resonator of a filter is replaced by a patch antenna or a monopole. Such a structure can be designed by a filter synthesis approach. The filtering antenna (the filtenna) is created only by radiating elements without any filtering parts. The frequency response of the realized gain is synthesized by optimization of all radiating elements, distances of the neighboring elements and amplitude and phase excitations of each individual element. The following Chapters describe the methods in detail. 2.1 Combination of band-pass filter and antenna The first part of the filtering antenna is created by a band-pass filter and the second one is formed by any radiating element. In this case, a band-pass filter and an antenna or antenna array are designed absolutely separately on one common substrate. Several papers using a combination of a band-pass filter integrated into SIW technology will be introduced in a following sub-section. In [1], authors have described a third-order SIW inductive window filter which is coupled with a slot antenna or two-slot antenna array. The structure is called a SIW oneslot filtenna or a SIW two-slot filtenna, respectively. In [1], the slot antenna array without the SIW filter is shown it does not behave like a filtenna. A SIW two-slot filtenna is depicted in Figure 2.1. Figure 2.1 The structure of the SIW two-slot filtenna [1] - 18 -
State of the art The SIW filter can be combined with a Yagi antenna. In [2], a five-cavity SIW filter was connected with a six-element printed Yagi antenna consisting of a reflector, a dipole and four directors. Layout of the described filtenna is shown in Figure 2.2. Figure 2.2 The structure of the SIW filter Yagi filtenna [2] A structure consisting of a third-order cavity window band-pass filter integrated into SIW and a planar coaxial collinear (COCO) radiation element was described in [3]. In the first instance, authors presented a conventional planar COCO antenna which is created by serially fed patch antennas on both sides of a substrate. In the second instance, the third-order SIW band-pass filter was added before the COCO antenna. In the paper, the authors did not address the question of a frequency response of gain and space filtering. A top and a bottom layout of the SIW filter COCO filtenna is depicted in Figure 2.3. Figure 2.3 The layout of the top side (upper) and the layout of the bottom side (lower) of the SIW filter COCO filtenna [3] A tunable filtennas using a band-pass filter with a varactor were discussed in [4], [5] and [6]. In these papers, a microstrip band-pass filter with a varactor is connected with a wideband dual-side Vivaldi antenna. Thanks to the varactor, the filtenna can be tuned at required frequency in the frequency range from 6.1 GHz to 6.5 GHz. But authors did not discuss a spatial filtering in the frequency range. An example of the Vivaldi filtenna with the varactor is shown in Figure 2.4. - 19 -
State of the art Figure 2.4 A top layer (left side) and the bottom layer (right side) of the Vivaldi filtenna with varactor [6] Slightly different approach to design of the filtering antenna was presented in [7]. In this case, authors combine two third-order stopband filters with binomical balun and single dipole antenna. The filters were created by spiral resonators and were integrated into microstrip feeder (left part in Figure 2.5). Due to this combination, the frequency response of the realized gain was suppressed out of the working band. The structure is shown in Figure 2.5. Figure 2.5 The combination of two bandstop filters with binomical balun and single dipole antenna [7] 2.2 Integration of radiating element into filter Several papers describe a design of filtennas using a filter synthesis approach. Filtennas consist of a band-pass filter with an integrated radiating element as a last resonator of the filter. In this case, the filtenna is designed as complete device, but filtering and radiating parts can be clearly identified. In [8], a filter consisting of three microstrip square open-loops was designed first. Second, the last open-loop resonator and an output port were replaced by a coupled line and a Γ-shaped antenna [8] or by center fed circular patch antenna and a coupled annular ring [9]. The coupled line was used as an admittance inverter with the length close to quarter of wavelength. The three square open-loops filter and the corresponding two square open-loops filtenna are shown in Figure 2.6. - 20 -
State of the art Figure 2.6 The structure of the three square open-loops filter (on the left side) and the structure of the two square open-loops filtenna (on the right side) [8] In [10], authors presented a microstrip patch antenna integrated into a band-pass filter. The band-pass filter was created by a three-pole hairpin filter and connected to a patch antenna representing the fourth pole. The patch plays the role of the last resonator of the filter. In [10], an equivalent circuit including a patch and filter approach for design of the filtenna was designed. That way, dimensions of the whole structure were partially reduced. A layout of this filtenna is shown in Figure 2.7 and the equivalent circuit of the filtenna is given in Figure 2.8. Figure 2.7 The photo of the filtenna with the hairpin filter [10] Figure 2.8 The equivalent circuit including the patch as the last resonator of the filter [10] In [11], a filtering microstrip U-shaped antenna with a T-shaped resonator in a feeder was published. A gain response of the combination of a U-shaped antenna and a T-shaped resonator behaves like a second-order quasi-elliptic band-pass filter with two zeroes at the band edges. The U-shaped antenna works as a radiation element and as well as the second resonator in a filter structure. A gap between the T-shaped resonator and U-shaped antenna forms an admittance inverter (J-inverter). The design of the filtering antenna was based on a circuit approach and a synthesis of a band-pass filter. The equivalent circuit and the layout of the U-shaped filtenna are shown in Figure 2.9. - 21 -
State of the art Figure 2.9 The equivalent circuit (left side) and the layout (right side) of the filtering U-shaped antenna [11] The design of a filtering microstrip antenna array based on [11] was described in [12] and [13]. A filtering array is created by four U-shaped patch antennas and a very sophisticated feeder which together behaves like a third-order band-pass filter. The first pole is formed by an E-shaped power divider which is coupled with an external 50 Ω feeder by the first gap (first J-inverter). The second pole is created by a half-wavelength balun which is attached by the second gap with the E-shaped divider (second J-inverter). And the last pole is generated by U-shaped patch antennas coupled with the balun by a gap (last J-invertor). Design of the filtering U-shaped antenna array is based on a circuit approach and synthesis of a band-pass filter. An equivalent circuit of the filtering antenna array and a layout are depicted in Figure 2.10. In [12] we can found a comparison of the filtering U-shaped antenna array and a conventional antenna array which is connected with a hairpin band-pass filter. Figure 2.10 The equivalent circuit (left side) and the layout (right side) of the filtering U-shaped antenna array [12] A printed meander-line antenna with quarter-wavelength resonator filter which operate together as the second-order filtenna was published in [14]. The meander-line antenna plays the role of radiating element but also the last segment of the band-pass filter. The first segment of the band-pass filter is designed as a shunt resonator. Thanks to the shunt resonator, a frequency response of antenna gain has two extra transmission zeroes. A structure of the meander-line filtenna is depicted in Figure 2.11. - 22 -
State of the art Figure 2.11 The structure of the meander-line filtenna [14] The described issue was followed in [15] and [16]. The design procedure was identical with [14] but the meander-line antenna was replaced by the Γ-shaped antenna and the quarter-wavelength resonator was replaced by a defected ground plane (DGS) resonator. The DGS resonator created the first segment of the second-order filtering antenna and the Γ-shaped antenna formed the last segment of the filter (see Figure 2.12). Figure 2.12 The layout of the Γ-shaped filtenna with DGS designed in [15] (left side) and [16] (right side) A similar design of a filtering antenna was presented in [17]. The filtering antenna was created by an inverted L-shaped antenna and a quarter-wavelength resonator. The structure was placed on one side of a substrate and the resonator was separated from the ground plane by a slot as shown in Figure 2.13. - 23 -
State of the art Figure 2.13 The structure of the inverted L-shaped filtering antenna [17] In [18], authors designed a filtering antenna which was composed by a parallel coupled microstrip line band-pass filter and an inverted L-shaped antenna. The inverted L-shaped antenna was designed as the last resonator of the parallel coupled microstrip line band-pass filter. Authors compared results of the filtering antenna and the combination of a parallel coupled microstrip line filter which is conventionally connected with the inverted L-shaped antenna. A structure of the N-order filtering antenna is shown in Figure 2.14. Figure 2.14 The structure of the N-order filtering antenna [18] A low-pass filter with reduced fractal defected ground structure (DGS) [19] [21] can be used as a basic element to design of a filtenna [22]. The low-pass filter consisted of the 11 th order low-pass filter with stubs separated by transmission lines on the top side of the substrate and six units of reduced fractal Minkowski DGS connected by narrow slots on the bottom side of the substrate. This filter exhibits two passband ranges and owing to the addition of three capacitive elements at the end of the first, third and fifth stubs and removed the second output port, the filter behaves like the filtenna at the second operating band (Figure 2.15) [22]. - 24 -
State of the art Figure 2.15 Filtenna based on the low-pass filter with reduced fractal defected ground structure (DGS) [22] 2.3 Filtering antennas with synthesized realized gain The last main approach to the design of filtennas is based on the antenna array, where the frequency response of the realized gain is synthesized by optimization of the dimensions, amplitude and phase excitations and distances between neighboring radiating elements. Due to described approach, authors could shape the frequency response of the realized gain and obtain the required response. In [7], authors described the series fed patch antenna array consisting of five radiating elements (Figure 2.16). In the structure, each patch antenna (length and width of the patches) and each transmission line (length and width of the feeders) have different dimensions, which were the subjects of the optimization process. The optimized whole structure behaves like filtering antenna at the band 5 GHz. Figure 2.16 Series fed five patch antenna array [7] Another way to synthesis of the realized gain of the antenna array was presented in [7] and [23] as well. In this case, authors assumed an idealized antenna model without couplings between neighboring radiating elements. The idealized antenna array was optimized by particle swarm optimization and the objects of the optimization were: distances among radiating elements, amplitudes of all elements and phases of the excitations sources. The idealized antenna array is illustrated in Figure 2.17. - 25 -
State of the art Figure 2.17 Idealized antenna array [7] The synthesis of a dipole antenna array was described in [23] and [24]. In this case, authors used a multi-objectives self-organizing algorithm. The synthesis of the dipole antenna array was divided into two main parts. Firstly, authors optimized the antenna array without any feeders among neighboring dipoles (Figure 2.18 left). The objects of the optimization were amplitudes and phases on inputs of the each dipole and its length. Distance between array and a ground plane was set to fixed length equals to quarter of a wavelength. Secondly, the feeders among the dipoles were considered to the model (Figure 2.18 right). In this configuration, goals of the optimization were achieved owing to changes of the amplitudes and phases of the excitation current, distances among neighboring dipoles and its lengths. Distance between antenna array and the ground plane was same as in the previous model. Due to described models, authors could shape gain and level of side lobes (in the first case) and control the responses of the gain and the reflection coefficient (in the second case). Figure 2.18 Dipole antenna array without feeders (left) and with feeders (right) [24] 2.4 Summary State of the art clearly shows that approaches to the design of filtering antennas can be divided into three branches: The first class of approaches connects a band-pass filter and an antenna into a compact device on a common substrate. In some cases, the authors do not address the question of space filtering, and the filtenna is a device connecting the filter and the antenna on common substrate only. In the second class of approaches, the filtering antenna is created by a band-pass filter with a radiating element on the position of the last resonator in the filter topology. These filtering antennas are designed using a band-pass filter synthesis approach. But even in this case, filtering and radiating parts of the structure can be identified. The third class of approaches, the filtering antenna array is consisted only from radiating elements (patches or dipoles) and frequency filtering is obtained by - 26 -
State of the art optimization of all parameters in the whole antenna array. Described approach does not include the filtering theory into the design of the filtering antennas or the filtennas. Up to now, authors have not used the band-pass synthesis for the design of the filtering antenna without filter parts. And in this case of approach, the synthesis of the shape of the frequency responses of the realized gain and reflection coefficient and control of the direction of the main lobe can be a new topic for research too. - 27 -
Dissertation objectives 3 DISSERTATION OBJECTIVES In Chapter 2, the recent developments in the field of filtering antennas were presented. The analysis clearly identified new directions of the research in the field of filtering antennas: Methodologies for the design of filtering arrays without filter modules have not been published yet. The filtering array should be designed such a way so that the excitation current is reflected from the input port in the stop band or enters the antenna in the pass-band. Proper equivalent circuits of filtering antennas to be used for filtenna synthesis are missing. A design based on an equivalent circuit can significantly improve synthesis of filtennas. Synthesis approaches applying a band-pass filter design to the synthesis of filtering arrays have not been developed yet. A filter design procedure following the line from a low-pass prototype to a band-pass filter is attractive to be exploited for the design of filtennas. Methods of controlling the frequency response of the realized gain have not been satisfactorily described yet. In case of a filter, the output voltage is related to time derivatives of the input voltage. In case of a filtenna, the output gain is related to the integral of current distributions (amplitudes and phases) on the planar structure. Therefore, advanced techniques have to be developed to make frequency dependencies of gain sharper, and to suppress variations of the main-lobe direction. Therefore, we can define the following objectives of the dissertation: A methodology of selecting an appropriate geometry of a filtering array will be worked out and verified. In the thesis, we will investigate various geometries of antenna arrays. The geometries will be evaluated from the viewpoint of resonances. A suitable antenna array should show a single resonance without parasitic ones in the operation band. In the frequency region of resonance, the filtering array should be matched (the excitation power passes from the feeder to the main lobe direction) and the main lobe direction should be stable. Applying optimization techniques, the width of the operation band should be maximized. We will develop methodology of synthesizing filtering antennas based on an equivalent circuit concept. An equivalent circuit of a single antenna element and the entire antenna array should be suitable for the application of the band-pass filter approach. In an ideal case, the equivalent circuit will consist of R, L and C lumped components, an impedance inverter or an admittance inverter only. The filtering antenna will be synthesized by using the band-pass filter approach. Starting from normalized values of a low-pass prototype filter, the band-pass filter can be designed. That way, an equivalent circuit of a filtenna is obtained. In the - 28 -
Dissertation objectives final step, the equivalent circuit is converted to the geometry of the filtering antenna. Methods of stabilizing the direction and the shape of the main lobe in the operation band of the filtenna will be developed and verified. For space filtering, the direction of the main lobe should be perpendicular to the substrate with small variations. The frequency response of the realized gain is asked to behave like a transmission coefficient of a band-pass filter. Since the frequency response of the realized gain is related to the integral of current distributions on the filtenna layout, the requested stability of parameters has to be achieved by a proper feeding (a stable amplitude and phase of currents at elements within the operation band), or by compensation techniques (influences of feeding network and antenna elements should exhibit opposite effects. In the following Chapter, so-far achievements are summarized. - 29 -
Planar filtering antenna array 4 PLANAR FILTERING ANTENNA ARRAY In this Section, the selection of an appropriate structure of a filtering antenna array will be discussed. We will concentrate on a planar antenna array fed by apertures which is a good candidate for the implementation of filtering antennas. An influence of dimensions of an aperture and length of an open end on the mutual capacitance and coupling will be investigated. The influence of these parameters will be described by equations in order to easily implement these dependencies. 4.1 Comparison of properties of planar antenna arrays When choosing a suitable configuration of an antenna array to be used for the design of the filtering array, following demands have to be considered: The antenna array should operate without parasitic resonances. The direction of the main lobe should not depend on the frequency and should be perpendicular to the antenna array (z-direction in Figure 4.4). The feeding network should not affect radiation patterns and the main lobe direction. The first two conditions can be met by using a parallel feeding network (Figure 4.1) [25]. However, this solution is not suitable for shaping the frequency response of the realized gain since the selectivity of the gain response is low. Figure 4.1 Parallel feeding of filtering array [25] The selectivity of the gain response can be improved by using a serial feeding of the array (Figure 4.2) [25]. Nevertheless, the feeders between the neighboring patches cause parasitic resonances around the main resonance of the array. In addition, the direction of the main lobe is unstable, depending on frequency. Figure 4.2 Serial feeding of filtering array [25] As a compromise, we can use the out-of-line serial feeding network of the antenna array which is shown in Figure 4.3 [25]. In this case, the feeding network has - 30 -
Planar filtering antenna array a minimal effect on radiation patterns and the direction of the main lobe. The final selectivity of the gain is very good. Figure 4.3 Out-of-line serial feeding of antenna array [25] In order to minimize the influence of the feeder on the radiation patters and the main lobe direction, the antenna array fed by apertures was selected for the final design of the filtering antenna array. Due to this solution, two substrates have to be used. Nevertheless, all the requirements are sufficiently met. The filtering antenna array fed by apertures is shown in Figure 4.4. Figure 4.4 Filtering antenna array fed by apertures The array is fabricated from two dielectric substrates covered by a metallic foil on both the surfaces. The central metallic layer is shared by both the substrates. On the bottom of the substrate, the 50 Ω metallic feeder is created (see Figure 4.4). On the centre metallic layer, apertures are etched into the ground plane. On the top layer, metallic rectangular patches play the role of radiators (see Figure 4.4). 4.2 Patch antenna fed by aperture In the first step, we designed a single patch at the frequency 5.80 GHz [26] [30] W a c 2 f 0, (1) r 1 2 1 1 10 r r h eff 1 2 2. (2) Wa An antenna was designed for the substrate ARLON 25N with relative permittivity r = 3.38, thickness h = 1.524 mm and negligible losses. In equations, W a is the width of a patch antenna, c is the speed of the light in free space, f 0 is resonant frequency, ε r is - 31 -
Planar filtering antenna array relative permittivity, ε eff is an effective dielectric constant and h is a thickness of the substrate. We can calculate length of the patch [26] [30] L a c 2, (3) f 2 0 eff where Δ represents fringing fields which can be calculated by [26] [30] Wa eff 0.3 0.262 h 0.412 h. (4) Wa 0.258 0.813 eff h Using equations (1) to (3), we can obtain the width of the patch 14.10 mm and the length of the patch 13.50 mm. But these dimensions of the patch do not correspond to the resonant frequency 5.80 GHz. Therefore, the width of the patch has to be parametrically changed to reach the resonance L 0. 957. (5) a W a The new value of the width of the patch for the frequency 5.80 GHz is 13.28 mm and the length equals to 12.70 mm. In the next step, we add an aperture and a feeder under the patch antenna. A final structure of the antenna fed by aperture is shown in Figure 4.5. The width of the feeder is w = 3.30 mm, and the length of the open end l o equals to the quarter of the wavelength, approximately. Figure 4.5 The structure of the patch fed by aperture 4.3 Parameters versus dimensions of antenna For an easier design of the filtering array fed by apertures, we have to understand the influence of dimensions of the antenna structure on a resonant frequency, a frequency bandwidth, a coupling between the feeder and the patch and a mutual capacitance between the feeder and the patch. In the following parts, we will vary the length and the width of the aperture (slot) and the length of the open end of the feeder. - 32 -
Planar filtering antenna array The initial dimensions of the whole structure are W a = 13.28 mm, L a = 12.70 mm, W s = 1.00 mm, L s = 7.60 mm, w = 3.30 mm, and l o = 8.80 mm. These dimensions of the patch antenna fed by aperture correspond to the critical coupling (the best matching). Including the aperture and the feeder into the structure, the resonant frequency was shifted from the original value 5.80 GHz to the frequency 5.40 GHz, approximately. This frequency shift of resonance is caused by a coupling and a mutual capacitance between the feeder and the patch. The width of the aperture (slot) was varied form 0.60 mm to 2.60 mm with the step 0.20 mm. Figure 4.6 shows that the width of the slot W s has no a dramatic effect on the shift of the resonant frequency. Figure 4.7 shows that W s mainly influences the coupling between the patch and the feeder: increasing width of the slot W s, the coupling between the patch and the feeder changes from under-coupled to over-coupled. Figure 4.6 Frequency responses of reflection coefficient at the antenna input for different widths of the slot W s at the frequency 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.7 Variation of the width of the slot W s at the frequency 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart Influence of the width of the slot W s on the resonant frequency and the frequency bandwidth is illustrated by Figure 4.8 and Figure 4.9. If increasing the width of the slot - 33 -
Planar filtering antenna array W s, the resonant frequency decreases. The decrease of the frequency can be approximated by 2 2 f 0 3.54310 W s 2.039W s 5.546. (6) If increasing the width of the slot W s, the frequency bandwidth increases also. For W s > 1.80 mm, the frequency bandwidth stagnates 4 3 2 FBW 12.382W 104.981W 346.331W 524.725W 39.059. (7) s s s s Figure 4.8 Influence of the width of the slot W s on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.9 Influence of the width of the slot W s on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm In order to use the equivalent circuit for the synthesis of the filtering antenna, we have to know the specific value of the mutual capacitance and the value of the inverter simulating the coupling. Figure 4.10 shows the effect of the width of the slot W s on the mutual capacitance 2 2 1 C 1.64010 W 1.07010 W 2.026, (8) m and Figure 4.11 illustrates the influence on the value of the inverter N N 1 2 J 7.89410 WN 1.11510. (9) - 34 -
Planar filtering antenna array Figure 4.7 and Figure 4.11 show that the increasing width of the slot W s increases the coupling and therefore, the value of the inverter is increased too. With respect to easier future implementation, the width of the aperture W s is normalized by width of the patch antenna W N = W s / W a in equations (8) and (9). Figure 4.10 Mutual capacitance as a function of the width of the slot W s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.11 Value of the inverter simulating coupling between patch and feeder as a function of the width of the aperture W s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm The length of the slot L s was varied too. The starting value was 6.60 mm and the stop value was 9.00 mm with the step 0.20 mm. The influence of the length of the slot L s on the reflection coefficient is shown in Figure 4.12. The variation of the parameter L s has a similar effect on the reflection coefficient as the parameter W s. The resonant frequency is shifted in a small range only. But the dominant effect comprises the coupling between the patch antenna and the feeder. Figure 4.13 shows that the increasing length of the slot L s changes the coupling between the patch antenna and the feeder from under-coupled to over-coupled. - 35 -
Planar filtering antenna array Figure 4.12 Frequency responses of the reflection coefficient at the antenna input for different lengths of the slot L s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.13 Variation of the length of the slot L s at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart The shift of the resonant frequency caused by the variation of the length of the slot L s is illustrated by Figure 4.14, and the variation of the frequency bandwidth is shown in Figure 4.15. The value of the resonant frequency linearly decreases with the increasing length of the slot L s 1 f 1.10810 6.211. (10) 0 L s The frequency bandwidth grows with the increasing length of the slot up the length 8.5 mm; then it decreases 3 2 FBW 4.516 L 75.314 L 300.996 L 153.938. (11) s s s - 36 -
Planar filtering antenna array Figure 4.14 Influence of the length of the slot L s on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.15 Influence of the length of the slot L s on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.16 shows the dependence of the mutual capacitance on the slot length L s. Obviously, the mutual capacitance is about 2.10 pf up to the length of the slot 7.40 mm and then the mutual capacitance falls sharply with the increasing length of the slot L s 1 3 2 C 3.98910 L 8.076 L 54.307 L 123.356. (12) m s The effect of the slot length L s on the value of the inverter is depicted in Figure 4.17. The value of the inverter is slowly increasing with the growing length of the slot L s but not linearly as in the case of the slot width W s s 2 2 1 J 2.34810 L s 3.12010 L s 1.061. (13) s - 37 -
Planar filtering antenna array Figure 4.16 Influence of the length of the slot L s on the mutual capacitance at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.17 Influence of the length of the slot L s on the value of the inverter at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm The length of the open end l o of the feeder under the patch antenna is the last important parameter. We have varied l o from 6.50 mm to 11.50 mm with the step 0.50 mm. The dependence of frequency response of the reflection coefficient on the open end length l o is illustrated by Figure 4.18. Obviously, the resonant frequency does not depend on the length of the open end l o. The parameter l o significantly influences the coupling between the patch antenna and the feeder. Figure 4.19 shows that the increasing length of the open end l o enforces the coupling between the patch antenna and the feeder to move slowly from over-coupled to under-coupled. - 38 -
Planar filtering antenna array Figure 4.18 Frequency responses of the reflection coefficient at the antenna input for different lengths of the open end l o at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.19 Variation of the length of the open end l o at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm in Smith chart Figure 4.20 shows the minimal shift of the resonant frequency (from 5.33 GHz to 5.38 GHz) 4 3 2 2 1 f 5.59410 l 1.82410 l 1.97810 l 4.664. (14) 0 o o o In case of the frequency bandwidth, the increasing value l o lets the bandwidth slowly fall from the value 260 MHz to the value 140 MHz 2 FBW 4.718l o 59.397l 76.473. (15) o - 39 -
Planar filtering antenna array Figure 4.20 Influence of the length of the open end l o on the resonant frequency for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.21 Influence of the length of the open end l o on the frequency bandwidth at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm The length of the open end of the feeder l o influences the mutual capacitance and the value of the inverter (see Figure 4.22 and Figure 4.23). If increasing the length l o, the mutual capacitance grows but the value of the inverter falls down. The effect of the parameter l o on the mutual capacitance can be described by 2 2 Cm 5.30110 lo 1.228l0 4.777, (16) and dependence of the value of the inverter can be approximated by 3 2 2 1 J 1.81810 l o 4.85110 lo 3.32010. (17) - 40 -
Planar filtering antenna array Figure 4.22 Influence of the length of the open end l o on the mutual capacitance at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm Figure 4.23 Influence of the length of the open end l o on the value of the inverter at 5.80 GHz for the substrate with ε r = 3.38 and h = 1.524 mm 4.4 Antenna array fed by apertures In order to verify the properties of the structure of interest, we designed a synchronously tuned three-element filtering antenna array fed by apertures (all the patch antennas are tuned at the same frequency and all the apertures have the same dimensions as well). The array did not exhibit parasitic resonances and the main lobe direction stayed perpendicular to the substrate within the operation band (see Figure 4.25 and Figure 4.26). The array was designed for the substrate ARLON 25N (relative permittivity r = 3.38, thickness h = 1.524 mm, negligible losses). Figure 4.24 shows that the bottom layer is created by a 50 Ω transmission line. The ground plane with rectangular apertures is located in the middle layer and patch antennas are placed on the top layer. A distance between neighboring patches is one wavelength, approximately. In phase feeding of patches ensures the main lobe direction being perpendicular to the substrate. The length of patches is L a = 12.7 mm, and the - 41 -
Planar filtering antenna array width of patches equals to W a = 13.3 mm. Slots are L s = 6.4 mm long and W s = 0.6 mm wide. The microstrip feeder is designed to exhibit the characteristic impedance Z 0 = 50 Ω. The width of the transmission line is w = 3.3 mm, and the length of the open end l o equals to the quarter of the wavelength, approximately. Figure 4.24 Three-element patch array fed by apertures The designed antenna array fed by apertures was analyzed by CST Microwave Studio. Figure 4.25 shows that the array is designed for the frequency 5.58 GHz. The 10 db frequency bandwidth of the array is about 3 % and reflection coefficient is better than 42 db. No parasitic resonances appear in the operation band. The frequency response of a normalized realized gain creates an equivalent of a band-pass filter (green line in Figure 4.25). For the gain, the 3 db frequency bandwidth is 8 % wide, and the maximal realized gain is 10.8 dbi. Figure 4.25 Frequency response of reflection coefficient (blue line) and frequency response of normalized realized gain in direction perpendicular to substrate (green line) of three-element filtering patch array fed by apertures - 42 -
Planar filtering antenna array Selectivity of the equivalent band-pass filter is better than 36.6 db/ghz. Suppression in the stop band equals to 20 db. Figure 4.25 shows that the three-element filtering patch antenna array fed by apertures radiates in the frequency range from 5.15 GHz to 6.14 GHz only. The main lobe direction varies from 5 to 0 (see Figure 4.26). Figure 4.26 The frequency response of the main lobe direction in the detail (a larger figure) and over the whole range (a smaller figure) As demonstrated in this Section, the antenna array fed by apertures is a good candidate for future design of the filtering array since this structure meets our demands on the number of resonances, frequency selectivity and direction of the main lobe very well. 4.5 Summary In this Section, we discussed properties of different feeding networks to be used for the implementation of a filtering array. The out-of-line serial antenna array fed by apertures was chosen since providing an optimum compromise among all requirements. Due to this configuration, the antenna array exhibits a single main resonance without any parasitic one, and its main lobe is directed perpendicularly to the substrate. We also investigated the influence of the dimensions of the aperture (the slot) and the length of the feeder on the reflection coefficient and coupling. None of the investigated parameters has a dominant effect on the resonant frequency and the frequency bandwidth. On the other hand, the dominant influence on the coupling between the patch antenna and the feeder was obtained by varying dimensions of the slot (both the width W s and the length L s ). The length of the open end of the feeder l o has no effect on the resonant frequency, but influences coupling between the patch and the feeder. Considering influence of structure dimensions on the mutual capacitance and value of the inverter, the width of the aperture (the slot W s ) was chosen for the future implementation of the filtering array design methodology. Finally, we focused on the synchronously tuned three-element antenna array fed by apertures which exhibits the one resonance only, and the frequency response of the - 43 -
Planar filtering antenna array normalized realized gain behaves like the band-pass filter. The main lobe direction is oriented perpendicularly to the substrate with small deviations only. Due to these facts, the antenna array fed by apertures is a good candidate for the design of the filtering antenna to be presented in the next Section. - 44 -
Equvalient circuit of filtering antenna array fed by apertures 5 EQUIVALENT CIRCUIT OF FILTERING ANTENNA ARRAY FED BY APERTURES In this Section, we will introduce an equivalent circuit of the single patch antenna fed by aperture which will be compared with the results of the full-wave simulation of the same structure. The equivalent circuit of the three-element filtering patch antenna array fed by apertures will be introduced as well and we will derive formulas for obtaining the requested frequency response of the reflection coefficient. Derived formulas will be implemented in MATLAB. The results calculated in MATLAB, simulated as the equivalent circuit and the full-wave model will be mutually compared. A transformation of an equivalent-circuit model of the filtering patch array fed by apertures to a normalized low-pass prototype filter will be introduced. 5.1 Equivalent circuit of single patch antenna fed by aperture An equivalent circuit of the patch fed by aperture is depicted in Figure 5.1. Values of a parallel resonant circuit RLC represent the patch antenna only. The capacitance C m is a mutual capacitance between the feeder and the patch, and JINV denotes an admittance inverter (J-inverter) between the feeder and the patch. Figure 5.1 The equivalent circuit of the patch fed by aperture: ANSYS Designer model The comparison of the reflection coefficient of the full-wave model of the single patch antenna fed by aperture from CST Microwave Studio with the equivalent circuit is depicted in Figure 5.2. The results are in a good agreement, and therefore, the equivalent circuit can be used as a complete equivalent model of the filtering array for future filter design approach. - 45 -
Equvalient circuit of filtering antenna array fed by apertures Figure 5.2 Comparison of the reflection coefficient of the full-wave model (blue line) versus equivalent circuit (red line) 5.2 Equivalent circuit of filtering patch array fed by apertures An equivalent model of the filtering antenna will be derived for the three-element filtering patch array fed by apertures which is shown in Figure 5.3. This equivalent circuit can be extended to higher orders by following the same principle. The equivalent circuit is composed of three parallel RLC resonant circuits, three mutual capacitances C m, three J-inverters and four segments of a transmission line. The parallel RLC resonant circuits simulate the behavior of the patches. In order to meet outputs of fullwave simulations, parameters of the RLC resonator were set to R = 50.4 Ω, L = 66.2 ph, C = 11.4 pf and C m = 1.8 pf. The J-inverter simulates coupling between the microstrip transmission line (feeder) and the individual patch. The coupling equals to 0.0162. The width of the microstrip feeder is 3.3 mm, and its characteristic impedance equals to 50 Ω. The length of the first segment of the feeder (from the source to the first patch) is 30 mm. The lengths of the second segment and the third segment of the feeder equal to 30 mm. The length of the last segment of the feeder (from the last patch to the open end) is 8.8 mm. - 46 -
Equvalient circuit of filtering antenna array fed by apertures Figure 5.3 Equivalent circuit of three-element filtering patch array fed by apertures: ANSYS Designer model The equivalent circuit was verified in a circuit simulator of ANSYS Designer and in MATLAB by a script exploiting ABCD matrices [31] [35]. The ABCD matrix of the transmission line follows [31] A C B cosh D Yc sinh l Zc sinh l l cosh l. (18) Here, Z c is the characteristic impedance of the feeder, and Y c is the characteristic admittance of the feeder, l is the length of the feeder and γ is the complex propagation constant. For the lossless transmission line [31], [32] where is the phase constant. Following [32], equation (18) can be rewritten to A C B cos D j Yc j. (19) l j Zc sin l sin l cos l The J-inverter can be described by the ABCD matrix [31], [32] A C B 0 D j J 1 j J 0. (20) and finally, using the matrix for the general impedance [31], we obtain the ABCD matrix of the parallel RLC circuit described by A C B D 0 (21) j R L R R LC j L. (22) 1 1 2 The filtering antenna array fed by apertures can be quickly designed by a script implementing equations (20) to (22). Using equations (21), (22) and considering the condition for the short end of a one-port network [31], the ABCD matrix for a parallel combination of resonant circuits can be obtained - 47 -
Equvalient circuit of filtering antenna array fed by apertures A C B 1 0 2 j R L J. (23) D 1 2 R R LC j L In the next step, we can calculate the total ABCD matrix of the equivalent circuit of the whole antenna structure by multiplying equations (20) and (23): TOTAL 3 MTLs MPB 1 MTL1 MPB 2 MTL2 MPB MTL o. (24) Here, MTL s is the ABCD matrix of the transmission line from the source to the first patch and MTL o is the ABCD matrix of the transmission line from the last patch to the open end of the transmission line. MTL 1 is the ABCD matrix of the transmission line between the first patch and the second patch, and MTL 2 is the ABCD matrix of the transmission line between the second patch and the third patch. MPB 1, MPB 2 and MPB 3 are ABCD matrices of parallel branches (patches). The reflection coefficient of the equivalent circuit may be calculated from the total ABCD matrix (24) by using [31], [32] S 11 A B Y0 C Z0 D. (25) A B Y C Z D 0 Figure 5.4 compares results of full-wave analysis in CST Microwave Studio (green line), results of circuit analysis in ANSYS Designer (red line) and results of MATLAB computations (blue line). Obviously, frequency responses of reflection coefficient computed in ANSYS Designer and MATLAB script agree well. The frequency shift between the full-wave model and the equivalent circuit from MATLAB is 2.5 %, approximately. Matching of the full-wave model is better about 15 db compared with the equivalent-circuit model implemented in MATLAB. Hence, the equivalent circuit model is proven to fully replace the full-wave model in faster, less accurate calculations. 0 Figure 5.4 Comparison of the full-wave model implemented in CST Microwave Studio (dotted green line), the equivalent-circuit model implemented in ANSYS Designer (dashed red line), and the equivalent-circuit model implemented in MATLAB (solid blue line) - 48 -
Equvalient circuit of filtering antenna array fed by apertures 5.3 Low-pass transformation In this Chapter, we present a transformation of an equivalent-circuit model of the patch array fed by apertures to a normalized low-pass prototype filter. The frequency transformation is given by the relation [31] and [32] C 0. (26) FBW 0 The transformation from the low-pass filter to the band-pass filter can be calculated using [31] jg j C g FBW 0 0 C g. (27) j FBW Here, Ω C is cut-off angular frequency of the low-pass prototype filter, ω 0 denotes the center angular frequency, FBW is the fractional bandwidth and g is the normalized value of the low-pass prototype filter. After several mathematic operations, the equation (27) can result in the relationship for the transformation from the band-pass filter to the low-pass prototype filter [31]. The transformed one-port low-pass prototype filter is shown in Figure 5.5. Here, the second port is replaced by the radiation into the environment. In Figure 5.5, g denotes the value of the low-pass prototype filter which was calculated by g FBW C. (28) 0 C Figure 5.5 The equivalent circuit of the filtering array transformed to the low-pass prototype filter Using the above-described process and considering (28), we can move the capacitances g before the J-inverters. Thanks to this change, the capacitances g will be transformed to the inductances gg (see Figure 5.6). Now, the frequency response of the reflection coefficient of the one-port configuration of the low-pass prototype filter can be calculated by a script in MATLAB (see Figure 5.7). The environment plays the role of the second port as in the previous case. - 49 -
Equvalient circuit of filtering antenna array fed by apertures Figure 5.6 Equivalent circuit of the low-pass prototype filter with the capacitances g shifted before the J-inverters Figure 5.7 shows the frequency response of the reflection coefficient of the equivalent circuit of the three-element filtering array (see Figure 5.3) which was calculated by the script in MATLAB using equations and principles described above. This response is depicted by the doted blue line and corresponding scales are shown in blue. The frequency response of the reflection coefficient of the recalculated low-pass prototype filter (solid red line) which was calculated by script in MATLAB and which corresponds with Figure 5.6 is illustrated in Figure 5.7 as well. The response is located to bottom and left axes. Figure 5.7 Comparison of the frequency response of the reflection coefficient of the equivalent circuit with the response of the low-pass prototype filter Figure 5.7 shows that the frequency response of the reflection coefficient of the equivalent circuit is identical with the response of the low-pass prototype filter. Therefore, the proposed process can be used for the complete design of the filtering antenna array which will be introduced in the next Section. - 50 -
5.4 Summary Equvalient circuit of filtering antenna array fed by apertures In this Section, we presented an equivalent circuit of the single patch antenna fed by aperture and compared results with the simulation of the full-wave model of this structure. The obtained results were identical. Moreover, we presented the equivalent circuit of the three-element filtering patch array fed by apertures, and we derived formulas for obtaining the requested frequency response of the reflection coefficient (to be implemented in MATLAB). The results calculated in MATLAB, simulated as the equivalent circuit in ANSYS Designer and simulated as the full-wave model in CST Microwave Studio were shown as well. Finally, we introduced a transformation of an equivalent-circuit model of the filtering patch array fed by apertures to a normalized low-pass prototype filter. This transformation was successfully verified. The described process can be used for the complete design of the filtering antenna array fed by apertures. - 51 -
Synthesis of filtering antenna array fed by apertures 6 SYNTHESIS OF FILTERING ANTENNA ARRAY FED BY APERTURES In this Section, we introduce a main idea for a comprehensive synthesis of the filtering antenna array. The synthesis procedure combines the frequency filter design and the antenna design approaches. The frequency response of the reflection coefficient at the antenna input, the frequency response of the normalized realized gain, and the direction of the main lobe are objectives of this synthesis. The desired center frequency, the requested fractional bandwidth of the filtenna and the prescribed magnitude of the reflection coefficient at the input of the filtenna have to be given to evaluate objectives. 6.1 Main idea of synthesis of filtering antenna array fed by apertures The main idea of synthesis of the filtering array is based on the equation [26] 2 S21 RG D AF 1 S 11. (29) Here, S 21RG is the frequency response of the normalized realized gain, which is understood as an equivalent of the frequency response of the transmission coefficient of the frequency filter (the second port of the filter is replaced by the radiation of the antenna to the surrounding environment). Equation (29) shows that the parameter S 21RG depends on the directivity of the single antenna D [25] [28], on the array factor AF of the whole structure [36] [38] and on the frequency response of the reflection coefficient at the antenna input S 11 [31], [39]. The formula (29) can be rewritten to the equation [26] 21 21 2 S RG D AF S. (30) Here, S 21 corresponds to losses in dielectrics and losses by the radiation [25] and [26]. When synthesizing a filter, g i coefficients of the low-pass prototype filter can shape the frequency response of the reflection coefficient S 11 and the transmission coefficient S 21. Obviously, we can shape the frequency response of the normalized realized gain S 21RG a similar way. Since conventional approximations of filter characteristics (Chebyshev, Butterworth, etc.) are not applicable in case of filtering arrays, alternative coefficients will be derived in the next Section. 6.2 Filter approach for obtain values of the equivalent circuit In this Section, we discuss the filter approach and equations which are necessary to design of the filtering antenna array and for control of the shapes of the frequency response of the reflection coefficient. - 52 -
Synthesis of filtering antenna array fed by apertures For computing the filtering antenna array, where each individual patch antenna, (combination of RLC in the equivalent circuit) are tuned at different frequencies (asynchronously tuned resonant circuit) f 0a (i), we use theory implemented on asynchronously tuned filters [31] f0 a i FBW f0 f0, (31) 2 where f 0a (i) is individual asynchronously tuned resonant frequency, FBW is the fractional bandwidth between resonant frequencies f 0a (i) and f 0 is the center frequency of the whole filtering antenna array. Capacitances and inductances of parallel resonant circuits modeling patches in the filtering array can be evaluated by [31] C i 2 f L i 0a 1 R FBW i 1 2 0a 2 f i Ci a, (32). (33) For evaluating J-inverters among individual patches and feeder, we can use [31] J i Y0 C i FBW 2 f g C 0 g i 0. (34) From the value of the J-inverters (34) and the dependencies of the mutual capacitance and coupling on the width of the aperture W s, we can calculate mutual capacitances between patch antenna and feeder by using (8) and (9) C m i i i 2 2 J 1.11510 1 J 1.11510 1.64010 1.07010 1 1 7.894 10 7.894 10 2 2 2.026, (35) where R denotes value of the resistor, C(i) and L(i) are individual capacitance and individual inductance and C m (i) is individual mutual capacitance in the parallel combination of RLC in Figure 5.3. The value of the fractional frequency bandwidth of a single patch antenna fed by an aperture is denoted as FBW a, Y 0 represents the characteristic admittance of the microstrip feeder, g 0 and g i are coefficients of the lowpass prototype filter and Ω C is the cutoff angular frequency of the filter. 6.3 Synthesis of frequency response of normalized realized gain The equivalent model of the filtering antenna array fed by apertures and synthesis of the reflection coefficient were described in the detail in previous Section and in [39], [40]. In this Section, the synthesis of the frequency response of the normalized realized gain based on the equivalent model, the frequency response of the reflection coefficient and calculation of a radiation pattern based on the electric surface current is presented. This approach is calculated by script in MATLAB and compared with the results from CST Microwave Studio. In order to calculate the frequency response of the normalized realized gain of the filtering antenna, we have to consider [28] - 53 -
Synthesis of filtering antenna array fed by apertures E 2 2 2 cos k0 La sin / 2 eff 1 r cot k0 h r 2 2 eff sin 2 2 sin cos eff 2 2 2 2 2 eff sin r cos cot k 0 h r sin to describe the radiation pattern of a patch antenna in the E-plane, and [28] E 2 2 2 1 cot k h sin c k W sin / 2 2 2 2 2 sin cot k h sin cos r r to describe the radiation pattern of a patch antenna in the H-plane. 0 cos 2 0 r Here, ε r denotes a relative permittivity of the substrate, h is a thickness of the substrate, ε eff is an effective dielectric constant, k 0 is the free-space wave number, L a is the length of the patch and W a is the width of the patch. Following [28], directivity can be calculated by equation 4 r D 2 E r 2 2 using equations (36) and (37). Here, r corresponds to a distance of some point outside the patch antenna, E Θ is the radiation pattern of the patch antenna in the E-plane and E Φ is the radiation pattern of the patch antenna in the H-plane, η 0 is the impedance of the free space (120π Ω) and P r is a radiated power. In order to calculate a total radiation pattern of the filtering array represented by the equivalent circuit (Figure 4.24 and Figure 5.3) [39], an array factor has to be defined [25], [26] 0 N E P r 2 2 0 0 a...... (36) (37) (38) sin / AF, (39) sin / 2 where N is a number of the radiation elements and the definition of Ψ is following [25] k cos. (40) 0 d In equation (40), k 0 is the free-space wave number, d is a distance between two neighboring radiation elements and ξ describes a phase shift between two adjacent patches. In order to obtain the frequency response of the normalized realized gain, the frequency response of the reflection coefficient [31], [39] has to be included. Figure 6.1 shows a comparison of the frequency response of the normalized realized gain obtained by the full-wave model in CST Microwave Studio with the result achieved by script in MATLAB which was described above. Obviously, the center frequency of the equivalent circuit is shifted down about 280 MHz. The dynamics of the filtering antenna array is approximately same in both the cases as well as the 3 db fractional frequency bandwidth. - 54 -
Synthesis of filtering antenna array fed by apertures Figure 6.1 Comparison of the frequency response of the normalized realized gain obtained by CST Microwave Studio (blue) and by MATLAB (red) 6.4 New g i coefficients for filtering antenna arrays This Section is focused on the definition of new g i coefficients of three-element and four-element filtering antenna arrays fed by apertures. New g i coefficients enable us to control frequency responses of the reflection coefficient and the normalized realized gain. The coefficients are extracted for a specific value of the reflection coefficient and an acceptable value of the fractional bandwidth of the filtering array. The g i coefficients are obtained by the optimization of the shape of the frequency responses of the reflection coefficient and the normalized realized gain by using a script in MATLAB which includes the equations described in the previous Sections. 6.4.1 Three-element filtering antenna array and g i coefficients The new g i coefficients for the three-element filtering antenna array fed by apertures, which are defined for several input parameters, are published in this Subsection. The equation 1 2 2 5.59810 46.303 6.80910 1 5.59810 FBW FBW s (41) 26.303 describes the relationship between the fractional bandwidth of the whole structure FBW s and the fractional bandwidth between the resonant frequencies f 0a (i) of the individual patches (FBW). The equation (41) is derived for the acceptable reflection coefficient (in this case S 11 < 10 db). In (41), FBW s represents the fractional bandwidth of the whole structure, which is related to the frequency response of the normalized realized gain (transmission - 55 -
Synthesis of filtering antenna array fed by apertures coefficient in the filter theory) for the decrease by 3 db. In this case, the fractional bandwidth FBW s can be set in the interval from 7 % up to 14 %. Equations g g 1, (42) 0 4 2 2 1 2 g 1 g3 4.77810 FBW 5.50610 FBW 5.33310, (43) 2 2 1 1 g 5.09710 FBW 5.53610 FBW 1.533 (44) 2 10 provide us the definition of the g i coefficients of the three-element filtering antenna array. Equation (42) has the same validity for all cases of the acceptable levels of the reflection coefficient. The influence of the fractional bandwidth FBW between the neighboring resonant frequencies f 0a (i) on the fractional bandwidth of the whole structure FBW s and on the parameters g 1 and g 3 are shown in Figure 6.2 and Figure 6.3. The influence of the fractional bandwidth on the parameter g 2 is depicted in Figure 6.4. In equations (42) to (44), the value of the coefficient g 0 is related to a normalized impedance of the feeder (transmission line), and the value of the coefficient g 4 corresponds to the impedance of the open end of the transmission line. Thanks to coefficients g 1 and g 3, we can influence the final value of the first and the third J- inverter (the shape of the required parameters such as S 11 and S 21RG ). Thanks to the coefficient g 2, final value of the second J-inverter can be reached (the shape of S 11 and S 21RG ). Figure 6.2 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db - 56 -
Synthesis of filtering antenna array fed by apertures Figure 6.3 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db Figure 6.4 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 10 db The formulas -1 2-2 5.49510 46.261 7.445 10-1 5.49510 FBW FBW s, (45) 26.261 2 2 1 2 g 1 g3 3.72710 FBW 4.40210 FBW 5.73310, (46) 2 2 1 1 g 3.32910 FBW 4.14910 FBW 2.510 (47) 2 10 can be used for the calculation of the fractional bandwidth of the whole structure, and g i coefficients can be exploited for case of the acceptable level of the reflection coefficient better than minus 15 db (S 11 < 15 db). All variable coefficients have the - 57 -
Synthesis of filtering antenna array fed by apertures same meaning as in the previous equations. Figure 6.5 shows the influence of the fractional bandwidth between the neighboring resonant frequencies f 0a (i) on the fractional bandwidth of the whole structure FBW s. Figure 6.6 represents the behavior of the coefficients g 1 and g 3 in the dependence on the value of the fractional bandwidth FBW as well as Figure 6.7 behavior of the coefficient g 2. Figure 6.5 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db Figure 6.6 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db - 58 -
Synthesis of filtering antenna array fed by apertures Figure 6.7 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 15 db The formulas where the reflection coefficient is requested being better than minus 20 db (S 11 < 20 db) follow below (all variables coefficients have the same meaning as in the previous equations) -1 2-2 5.20910 46.344 7.942 10-1 5.20910 FBW FBW s, (48) 26.344 2 2 1 3 g 1 g3 2.83510 FBW 3.59210 FBW 5.33310, (49) 2 2 1 2 g 4.48410 FBW 5.04410 FBW 1.117. (50) 2 10 Equations (48), (49) and (50) have been extracted form Figure 6.8, Figure 6.9 and Figure 6.10. Figure 6.8 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db - 59 -
Synthesis of filtering antenna array fed by apertures Figure 6.9 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db Figure 6.10 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 20 db The last three equations in this Section are focused on calculation the fractional bandwidth (Figure 6.11) and g i coefficients (Figure 6.12 and Figure 6.13) for reflection coefficient better than minus 25 db (S 11 < 25 db) and of course all variables coefficients have again the same meaning. -1 2 1-1 7.00110 42.01310 1.070 10-1 7.00110 FBW FBW s (51) 1 22.01310 1 2 1 1 g 1 g3 2.75310 FBW 1.20710 FBW 4.36310 (52) 2 2 1 1 g 2.56610 FBW 3.22510 FBW 3.460 (53) 2 10-60 -
Synthesis of filtering antenna array fed by apertures Figure 6.11 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db Figure 6.12 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 3 for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db - 61 -
Synthesis of filtering antenna array fed by apertures Figure 6.13 Influence of the fractional bandwidth FBW on the value of the parameter g 2 for the three-element filtenna and the acceptable reflection coefficient S 11 < 25 db 6.4.2 Four-element filtering antenna array and g i coefficients New g i coefficients for the four-element filtering antenna array fed by apertures are presented is this Section. As in the case of the three-element filtering antenna array, the g i coefficients are defined for several cases of the input parameters. Concretely, the fractional bandwidth and level of the reflection coefficient are changed. The equation 1 2 1.77010 6.89210 FBW s 1 1.77010 2 1.981 1.981 4 FBW (54) 2 describes the relationship between the fractional bandwidth of the whole structure FBW s and the fractional bandwidth between the resonant frequencies f 0a (i) of individual patches (FBW) for case of the four-element filtering antenna array and the acceptable level of the reflection coefficient better than minus 10 db (S 11 < 10 db). In equation g g 1, (55) 0 5 the values of coefficients g 0 and g 5 correspond to a normalized impedance of the feeder (transmission line) and the impedance of the open end of the transmission line. The equation (55) is shared for all cases of the acceptable level of the reflection coefficient which are presented in the next part of this Section. Thanks to the coefficients g 1 and g 4 2 2 1 1 g 1 g4 1.35410 FBW 1.17310 FBW 3.14310, (56) we can influence the final value of the first and the fourth J-inverter (the shape of the required parameters S 11 and S 21RG ). Thanks to the coefficients g 2 and g 3-62 -
Synthesis of filtering antenna array fed by apertures 2 2 1 g 2 g3 3.25710 FBW 1.759 FBW 3.70810, (57) the final value of the second and third J-inverter can be reached, and the shape of S 11 and S 21RG can be formed. The equations (54), (56) and (57) describe the dependence of the fractional bandwidth of the whole structure FBW s (Figure 6.14), the coefficients g 1 and g 4 (Figure 6.15), and the coefficients g 2 and g 3 (Figure 6.16) on the fractional bandwidth FBW between two resonant frequencies f 0a (i). Figure 6.14 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db Figure 6.15 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db - 63 -
Synthesis of filtering antenna array fed by apertures Figure 6.16 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 10 db Equations (54), (56) and (57) have to be recalculated if the requested matching should be better than S 11 < 15 db. In this case, the equations 1.429 FBW 1.429 2 4 2 1 2 1.10510 7.17110 FBW s 1 1.10510, (58) 2 2 1 2 g 1 g4 1.77910 FBW 3.60010 FBW 7.76210, (59) 2 2 1 1 g 2 g3 1.64710 FBW 1.64310 FBW 2.33110 (60) are derived from Figure 6.17, Figure 6.18 and Figure 6.19. Figure 6.17 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db - 64 -
Synthesis of filtering antenna array fed by apertures Figure 6.18 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db Figure 6.19 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 15 db Dependency of the fractional bandwidth of the whole structure FBW s g i coefficients 1 2 2 8.41710 4 2.931 7.60810 1 8.41710 FBW FBW s, (61) 2 2.931 2 2 1 2 g 1 g4 3.03810 FBW 4.87210 FBW 3.90510, (62) 1 2 1 1 g 2 g3 6.07510 FBW 2.70110 FBW 1.47110 (63) - 65 -
Synthesis of filtering antenna array fed by apertures on the fractional bandwidth between two neighboring resonant frequencies FBW can be derived from Figure 6.20, Figure 6.21 and Figure 6.22. In this case, the acceptable level of the reflection coefficient has to be better than minus 20 db (S 11 < 20 db). Figure 6.20 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db Figure 6.21 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db - 66 -
Synthesis of filtering antenna array fed by apertures Figure 6.22 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 20 db And finally, the last three equations are focused on the relationship between the fractional bandwidth of the whole filtering antenna array FBW s and g i coefficients 1 2 1 2 5.97810 41.41210 7.83110 1 5.97810 FBW FBW s (64) 1 21.41210 2 2 1 2 g 1 g4 3.68210 FBW 5.52110 FBW 9.71410, (65) 1 2 1 1 g 2 g3 4.91510 FBW 2.97210 FBW 1.27910 (66) on the fractional bandwidth of two neighboring resonant frequencies FBW for case of the acceptable reflection coefficient better than minus 25 db (S 11 < 25 db). The formulas (64) to (66) describe the dependencies which are presented in Figure 6.23, Figure 6.24 and Figure 6.25. - 67 -
Synthesis of filtering antenna array fed by apertures Figure 6.23 Influence of the fractional bandwidth FBW on the fractional bandwidth of the whole structure FBW s for the four-element filtenna and the acceptable reflection coefficient S 11 < 25 db Figure 6.24 Influence of the fractional bandwidth FBW on the value of the parameters g 1 and g 4 for the four-element filtenna and the acceptable reflection coefficient S 11 < 25 db - 68 -
Synthesis of filtering antenna array fed by apertures Figure 6.25 Influence of the fractional bandwidth FBW on the value of the parameters g 2 and g 3 for the four-element filtenna and the acceptable reflection coefficient S 11 < 25 db 6.5 Dimensions of the full-wave model The following paragraphs are focused on the way to obtain the final dimensions of the filtering antenna array fed by apertures. The length and the width of the each individual patch antenna can be calculated by equations (1) and (5), which were presented in Section 4.2. The width of the each aperture (slot) can be calculated by W and the length of the aperture by s i i c J 1.11510 1 7.894 10 2 f i L s i 0 0 a r 2 a r (67) 0.572 c. (68) 2 f i Other parameters (the width of the feeder, the distance between two neighboring patch antennas and the length of the open end of the feeder) can be calculated to using fundamental equations from [31], [32]. 6.6 Comparison of theoretical results and full-wave results In this Section, the complete synthesis of the filtering antenna array fed by apertures is confronted with the full-wave results obtained by CST Microwave Studio. These comparisons are done for the three-element filtenna and for the four-element filtering array. In comparisons, several cases of input settings with different values of the center frequency f 0, the fractional bandwidth of the whole structure FBW s and the acceptable level of the reflection coefficient S 11 are assumed. Compared models do not consider a connector, losses in the dielectrics and adhesives between substrates. - 69 -
Synthesis of filtering antenna array fed by apertures 6.6.1 Full-wave verification of the three-element filtering antenna array The described process of the design methodology of the three-element filtering antenna array is verified on three different test cases over the frequency band from 4.8 GHz to 6.8 GHz; for the fractional bandwidth from 7 % to 14 % and for the level of the reflection coefficient from 10 db to 20 db. The first verification of the design methodology was carried out for the center frequency f 0 = 4.8 GHz, the fractional bandwidth of the whole structure FBW s = 10 % and the acceptable level of the reflection coefficient S 11 < 10 db. For the specified requirements, parameters of the equivalent circuit model have been computed (the left column in Table 6.1). Considering ARLON 25N (h = 1.524 mm, r = 3.38) as a substrate for the fabrication of the filtenna, dimensions of the antenna layout can be obtained (the central column in Table 6.1). In order to improve results, a built-in optimizer of CST was used to improve the design (the right column in Table 6.1). Table 6.1 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db Equivalent circuit Dimensions from script CST optimized R 1 R 3 [Ω] 50.37 W a1, W a3 [mm] 15.15 W a1, W a3 [mm] 15.15 L 1, L 3 [ph] 74.45 W a2 [mm] 15.76 W a2 [mm] 15.76 L 2 [ph] 77.44 L a1, L a3 [mm] 14.50 L a1, L a3 [mm] 14.50 C 1, C 3 [pf] 11.74 L a2 [mm] 15.09 L a2 [mm] 15.09 C 2 [pf] 12.21 W s1, W s3 [mm] 0.50 W s1, W s3 [mm] 0.50 C m1 C m3 [pf] 2.20 W s2 [mm] 0.51 W s2 [mm] 0.51 J 1, J 3 [ms] 14.90 L s1, L s3 [mm] 8.67 L s1, L s3 [mm] 8.35 J 2 [ms] 14.40 L s2 [mm] 9.02 L s2 [mm] 8.67 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 32.20 d [mm] 32.20 d [mm] 34.70 l o [mm] 9.50 l o [mm] 9.50 l o [mm] 9.51 In Figure 6.26, frequency responses of reflection coefficient at the filtenna input S 11 and transmission coefficient (normalized realized gain RG) are depicted. MATLAB stands for the equivalent circuit approach, CST stands for full-wave simulation of the equivalent planar implementation, and CST opt. is the optimized planar implementation. Obviously, all frequency responses exhibit a sufficient agreement. - 70 -
Synthesis of filtering antenna array fed by apertures Figure 6.26 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db Comparison of the main lobe direction calculated by script in MATLAB with the result obtained by CST Microwave Studio is shown in Figure 6.27. In the case of the MATLAB script, the main lobe direction is exactly perpendicular in the required band. In the case of the full-wave result, the maximal deviation is 5 in the same range. Figure 6.27 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db In the following step, numerical values of the resonant frequency f 0, the fractional bandwidth FWB, the magnitude of the reflection coefficient S 11 at the resonant frequency, maximal deviation and the selectivity have been compared (see Table 6.2). We can see a reasonable match here. - 71 -
Synthesis of filtering antenna array fed by apertures Table 6.2 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db MATLAB CST 1 st run CST optimized f 0 [GHz] 4.85 4.75 4.78 FBW -3 db [%] 10.94 13.80 12.72 S 11 @ f 0 [db] 12.56 12.35 15.07 FBW -10 db [%] 4.86 6.58 6.72 S 21 suppression [db] 19.31 18.63 19.32 S 21 selectivity [db/ghz] 40.10 40.89 40.43 Maximal deviation [ ] 0.00 5.00 5.00 In the second test case, the filtenna was designed at the center frequency 5.8 GHz; the fractional bandwidth of the whole structure 13 % and the reflection coefficient better than 15 db. Table 6.3 summarizes component values of the equivalent circuit model (left), dimensions of planar implementation (center) and optimized implementation (right). Table 6.3 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db Equivalent circuit Dimensions from script CST optimized R 1 R 3 [Ω] 50.37 W a1, W a3 [mm] 12.42 W a1, W a3 [mm] 12.21 L 1, L 3 [ph] 61.00 W a2 [mm] 13.18 W a2 [mm] 12.96 L 2 [ph] 64.77 L a1, L a3 [mm] 11.88 L a1, L a3 [mm] 11.68 C 1, C 3 [pf] 9.62 L a2 [mm] 12.62 L a2 [mm] 12.40 C 2 [pf] 10.21 W s1, W s3 [mm] 0.48 W s1, W s3 [mm] 0.47 C m1 C m3 [pf] 2.19 W s2 [mm] 0.48 W s2 [mm] 0.46 J 1, J 3 [ms] 19.30 L s1, L s3 [mm] 7.11 L s1, L s3 [mm] 7.12 J 2 [ms] 17.90 L s2 [mm] 7.55 L s2 [mm] 7.32 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 27.10 d [mm] 27.10 d [mm] 28.60 l o [mm] 8.00 l o [mm] 8.00 l o [mm] 7.43 In Figure 6.28, frequency responses of reflections and transmissions coefficients of the equivalent circuit model (obtained by script in MATLAB), planar implementation (CST) and optimized implementation (CST opt.) show a good agreement. The maximal deviations of the main lobe from the perpendicular direction obtained by the script in - 72 -
Synthesis of filtering antenna array fed by apertures MATLAB and result from CST are shown in Figure 6.29. The most important corresponding parameters from comparison in Figure 6.28 and in Figure 6.29 are given in Table 6.4. Figure 6.28 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db Figure 6.29 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db - 73 -
Synthesis of filtering antenna array fed by apertures Table 6.4 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db MATLAB CST 1 st run CST optimized f 0 [GHz] 5.77 5.68 5.79 FBW -3 db [%] 14.91 14.85 14.37 S 11 @ f 0 [db] 16.79 14.34 16.53 FBW -10 db [%] 8.62 9.68 8.96 S 21 suppression [db] 17.53 17.95 19.08 S 21 selectivity [db/ghz] 56.09 52.97 54.27 Maximal deviation [ ] 0.00 5.00 5.00 In the third test case, the filtering antenna array fed by apertures was designed at the center frequency 6.8 GHz; the fractional bandwidth of the whole structure 10 % and the reflection coefficient better than 10 db. Table 6.5 summarizes component values of the equivalent circuit model (left), dimensions of planar implementation (center) and optimized implementation (right). Table 6.5 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db Equivalent circuit Dimensions from script CST optimized R 1 R 3 [Ω] 50.37 W a1, W a3 [mm] 10.70 W a1, W a3 [mm] 10.54 L 1, L 3 [ph] 52.55 W a2 [mm] 11.13 W a2 [mm] 10.97 L 2 [ph] 54.67 L a1, L a3 [mm] 10.24 L a1, L a3 [mm] 10.09 C 1, C 3 [pf] 8.29 L a2 [mm] 10.65 L a2 [mm] 10.50 C 2 [pf] 8.62 W s1, W s3 [mm] 0.35 W s1, W s3 [mm] 0.34 C m1 C m3 [pf] 2.20 W s2 [mm] 0.36 W s2 [mm] 0.37 J 1, J 3 [ms] 14.90 L s1, L s3 [mm] 6.12 L s1, L s3 [mm] 6.29 J 2 [ms] 14.40 L s2 [mm] 6.37 L s2 [mm] 6.24 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 23.40 d [mm] 23.40 d [mm] 25.50 l o [mm] 6.90 l o [mm] 6.90 l o [mm] 6.67 In Figure 6.30, frequency responses of reflections and transmissions coefficients of the equivalent circuit model (MATLAB), planar implementation (CST) and optimized implementation (CST opt.) show a good agreement. Figure 6.31 compares the frequency responses of the main lobe direction. Over the operating band, the result calculated by - 74 -
Synthesis of filtering antenna array fed by apertures script in MATLAB and result obtained by full-wave model in CST are without any deviations from the perpendicular direction. Corresponding parameters from Figure 6.30 and Figure 6.31 are listed in Table 6.6. Figure 6.30 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db Figure 6.31 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db The complex comparison is provided by Table 6.7 demonstrating functionality of the presented design methodology at frequencies from 4.8 GHz to 6.8 GHz. The fractional bandwidth was changed from 7 % to 13 % and the frequency response of the reflection coefficient varied from 10 db to 20 db. In all cases, results produced by the - 75 -
Synthesis of filtering antenna array fed by apertures equivalent circuit model showed a good agreement with numerical full-waves models in CST Microwave Studio. Table 6.6 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db MATLAB CST 1 st run CST optimized f 0 [GHz] 6.67 6.62 6.69 FBW -3 db [%] 10.62 10.76 10.88 S 11 @ f 0 [db] 12.52 11.85 11.80 FBW -10 db [%] 4.66 3.18 3.37 S 21 suppression [db] 19.57 18.86 19.27 S 21 selectivity [db/ghz] 38.91 35.33 35.43 Maximal deviation [ ] 0.00 0.00 0.00 Table 6.7 Comparison of resonant frequency, fractional bandwidth and reflection coefficient of three-element filtenna: equivalent circuit model (MATLAB) versus full-wave model (CST) f 0 [GHz] Setting MATLAB CST FBW s [%] S 11 < [db] f 0 [GHz] FBW s [%] S 11 < [db] f 0 [GHz] FBW s [%] S 11 < [db] 4.80 7.00 10.00 4.86 7.39 12.09 4.76 11.65 11.46 4.80 10.00 10.00 4.85 10.94 12.56 4.75 13.80 14.82 4.80 13.00 10.00 4.84 15.03 13.11 4.75 15.96 11.08 4.80 10.00 20.00 4.86 11.26 23.45 4.76 13.40 9.62 5.80 7.00 10.00 5.78 7.29 12.09 5.71 11.07 15.77 5.80 10.00 10.00 5.77 10.79 12.55 5.70 12.87 16.00 5.80 13.00 10.00 5.76 14.83 13.08 5.68 14.72 14.68 5.80 7.00 15.00 5.76 10.31 21.12 5.68 11.76 12.92 5.80 10.00 15.00 5.78 11.01 17.68 5.70 12.66 16.47 5.80 13.00 15.00 5.77 14.91 16.70 5.68 14.82 13.70 5.80 7.00 20.00 5.75 7.43 9.00 5.64 10.69 19.00 5.80 10.00 20.00 5.78 11.10 23.43 5.69 10.95 41.03 5.80 13.00 20.00 5.77 15.01 21.14 5.68 14.72 14.68 6.80 7.00 10.00 6.67 7.17 12.09 6.62 9.17 17.51 6.80 10.00 10.00 6.67 10.62 12.53 6.62 10.73 14.27 6.80 13.00 10.00 6.65 14.61 13.04 6.60 13.20 7.50-76 -
Synthesis of filtering antenna array fed by apertures 6.6.2 Full-wave verification of the four-element filtering antenna array The described process of the design methodology of the four-element filtering antenna array is verified on the three different test cases over the frequency band from 4.8 GHz to 6.8 GHz; the fractional bandwidth of the whole structure from 8 % to 12 % and the level of the reflection coefficient from 10 db to 20 db. The first verification of the design methodology was done for the center frequency f 0 = 4.8 GHz, the fractional bandwidth of the whole structure FBW s = 8 % and the acceptable level of the reflection coefficient S 11 < 15 db. For the specified requirements, parameters of the equivalent circuit model have been computed (the left column in Table 6.8). Considering ARLON 25N (h = 1.524 mm, r = 3.38) as a substrate for the fabrication of the filtenna, dimensions of the antenna layout can be obtained (the central column in Table 6.8). In order to improve results, a built-in optimizer of CST was used to improve the design (the right column in Table 6.8). Table 6.8 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db Equivalent circuit Dimensions from script CST optimized R 1 R 4 [Ω] 50.37 W a1, W a4 [mm] 15.41 W a1, W a4 [mm] 15.59 L 1, L 4 [ph] 75.68 W a2, W a3 [mm] 15.50 W a2, W a3 [mm] 15.99 L 2, L 3 [ph] 76.15 L a1, L a4 [mm] 14.74 L a1, L a4 [mm] 14.92 C 1, C 4 [pf] 11.93 L a2, L a3 [mm] 14.83 L a2, L a3 [mm] 15.30 C 2, C 3 [pf] 12.01 W s1, W s4 [mm] 0.47 W s1, W s4 [mm] 0.43 C m1 C m4 [pf] 2.20 W s2, W s3 [mm] 0.45 W s2, W s3 [mm] 0.43 J 1, J 4 [ms] 12.89 L s1, L s4 [mm] 8.82 L s1, L s4 [mm] 8.05 J 2, J 3 [ms] 11.96 L s2, L s3 [mm] 8.87 L s2, L s3 [mm] 8.76 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 34.08 d [mm] 34.08 d [mm] 38.20 l o [mm] 9.47 l o [mm] 9.47 l o [mm] 9.51 In Figure 6.32, frequency responses of reflection coefficient at the filtenna input S 11 and transmission coefficient (normalized realized gain RG) are depicted. MATLAB stands for the equivalent circuit approach, CST represents full-wave simulation of the equivalent planar implementation, and CST opt. is the optimized planar implementation. Obviously, all frequency responses exhibit a sufficient agreement. - 77 -
Synthesis of filtering antenna array fed by apertures Figure 6.32 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db Comparison of the main lobe direction calculated by script in MATLAB with the result obtained by CST Microwave Studio is shown in Figure 6.33. In the case of the MATLAB script, the main lobe direction is exactly perpendicular in the required band. In the case of the full-wave result, the maximal deviation is 3 in the same frequency range. Figure 6.33 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db In the following step, numerical values of the resonant frequency f 0, the fractional bandwidth FWB, the magnitude of the reflection coefficient S 11 at the resonant - 78 -
Synthesis of filtering antenna array fed by apertures frequency, the maximal deviation and the selectivity have been compared (see Table 6.9). We can see reasonable match here. Table 6.9 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db MATLAB CST 1 st run CST optimized f 0 [GHz] 4.84 4.90 4.84 FBW -3 db [%] 7.77 5.62 5.40 S 11 @ f 0 [db] 20.05 23.65 32.99 FBW -10 db [%] 3.49 1.85 2.27 S 21 suppression [db] 17.91 21.62 22.10 S 21 selectivity [db/ghz] 103.66 95.33 98.38 Maximal deviation [ ] 0.00 3.00 3.00 In the second test case, the four-element filtenna was tuned at the center frequency 5.8 GHz with the fractional bandwidth of the whole structure 12 % and the acceptable level of the reflection coefficient better than 10 db. Table 6.10 summarizes component values of the equivalent circuit model (left), dimensions of planar implementation (center) and optimized implementation (right). Table 6.10 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db Equivalent circuit Dimensions from script CST optimized R 1 R 4 [Ω] 50.37 W a1, W a4 [mm] 12.54 W a1, W a4 [mm] 12.61 L 1, L 4 [ph] 61.59 W a2, W a3 [mm] 13.05 W a2, W a3 [mm] 13.16 L 2, L 3 [ph] 64.12 L a1, L a4 [mm] 12.00 L a1, L a4 [mm] 12.07 C 1, C 4 [pf] 9.71 L a2, L a3 [mm] 12.49 L a2, L a3 [mm] 12.59 C 2, C 3 [pf] 10.11 W s1, W s4 [mm] 0.46 W s1, W s4 [mm] 0.48 C m1 C m4 [pf] 2.20 W s2, W s3 [mm] 0.49 W s2, W s3 [mm] 0.43 J 1, J 4 [ms] 17.65 L s1, L s4 [mm] 7.17 L s1, L s4 [mm] 6.67 J 2, J 3 [ms] 18.34 L s2, L s3 [mm] 7.47 L s2, L s3 [mm] 6.56 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 28.64 d [mm] 28.64 d [mm] 29.40 l o [mm] 7.96 l o [mm] 7.96 l o [mm] 8.00 The comparison of the results calculated by script in MATLAB with the results obtained by CST and with optimized results from CST is shown in Figure 6.34. There - 79 -
Synthesis of filtering antenna array fed by apertures are the blue lines for results from script in MATLAB, the green lines represent the CST results and the red lines are optimized results from CST. Figure 6.34 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db In the case of the response obtained by script in MATLAB, the direction of the main lobe is absolutely perpendicular to the structure and in the case of the results from CST, the maximal deviation from the perpendicular direction is 4. This confrontation illustrates Figure 6.35. Figure 6.35 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db All the relevant parameters as are the center frequency, the fractional bandwidth, the acceptable level of the reflection coefficient, the suppression in the stop band - 80 -
Synthesis of filtering antenna array fed by apertures and the deviation of the main lobe direction from the MATLAB script, from full-wave model in CST and optimized one are given in Table 6.11. All the parameters agree very well. Table 6.11 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db MATLAB CST 1 st run CST optimized f 0 [GHz] 5.73 5.73 5.77 FBW -3 db [%] 11.82 14.22 12.15 S 11 @ f 0 [db] 13.41 10.29 13.51 FBW -10 db [%] 8.67 10.59 8.24 S 21 suppression [db] 15.06 19.96 21.73 S 21 selectivity [db/ghz] 90.52 79.67 79.10 Maximal deviation [ ] 0.00 4.00 4.00 The last test case of the four-element filtering array is designed at the center frequency 6.8 GHz with fractional bandwidth of the whole structure 12 % and the acceptable level of the reflection coefficient better than 20 db. Table 6.12 summarizes component values of the equivalent circuit model (left), dimensions of planar implementation (center) and optimized implementation (right). Table 6.12 Values of elements in equivalent circuit of filtenna (left), dimensions of planar implementation of filtenna (center), dimensions of optimized filtenna (right); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db Equivalent circuit Dimensions from script CST optimized R 1 R 4 [Ω] 50.37 W a1, W a4 [mm] 10.55 W a1, W a4 [mm] 10.60 L 1, L 4 [ph] 51.81 W a2, W a3 [mm] 11.29 W a2, W a3 [mm] 11.33 L 2, L 3 [ph] 55.49 L a1, L a4 [mm] 10.09 L a1, L a4 [mm] 10.14 C 1, C 4 [pf] 8.17 L a2, L a3 [mm] 10.81 L a2, L a3 [mm] 10.84 C 2, C 3 [pf] 8.75 W s1, W s4 [mm] 0.37 W s1, W s4 [mm] 0.37 C m1 C m4 [pf] 2.20 W s2, W s3 [mm] 0.38 W s2, W s3 [mm] 0.36 J 1, J 4 [ms] 16.76 L s1, L s4 [mm] 6.04 L s1, L s4 [mm] 6.05 J 2, J 3 [ms] 15.71 L s2, L s3 [mm] 6.46 L s2, L s3 [mm] 6.10 w [mm] 3.30 w [mm] 3.30 w [mm] 3.30 d [mm] 24.82 d [mm] 24.82 d [mm] 25.40 l o [mm] 6.89 l o [mm] 6.89 l o [mm] 6.90-81 -
Synthesis of filtering antenna array fed by apertures The confrontation of the responses which are calculated by the script in MATLAB with results of the basic and optimized models in CST is shown in Figure 6.36. In Figure 6.36, MATLAB stands for the equivalent circuit approach, CST represents fullwave simulation of the equivalent planar implementation, and CST opt. is the optimized planar implementation. Obviously, all frequency responses exhibit sufficient agreement. Figure 6.36 Frequency responses of reflection coefficient S 11, transmission coefficient S 21 (or normalized realized gain RG) for equivalent circuit (MATLAB), planar implementation (CST) and optimized planar implementation (CST opt.); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db Figure 6.37 illustrates the frequency dependence of the main lobe direction over the operating range. The blue line represents response calculated by the script in MATLAB and the red points are obtained by full-wave model in the CST. Figure 6.37 Frequency responses of the main lobe direction computed by script of equivalent circuit (solid blue line) and computed by CST (red rings); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db - 82 -
Synthesis of filtering antenna array fed by apertures All the most important parameters are summarized in Table 6.13, where the values from the script are located in the first column, the middle column summarizes results from the basic full-wave model in CST and values from the optimized structure in CST are given in the last one. Table 6.13 Comparison of resonant frequency, fractional bandwidth and reflection coefficient computed for equivalent circuit (left), planar implementation (center) and optimized implementation (right); four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db MATLAB CST 1 st run CST optimized f 0 [GHz] 6.62 6.67 6.68 FBW -3 db [%] 12.29 13.60 12.61 S 11 @ f 0 [db] 12.01 16.05 19.97 FBW -10 db [%] 10.04 10.20 9.04 S 21 suppression [db] 15.48 19.69 20.50 S 21 selectivity [db/ghz] 93.69 84.85 75.25 Maximal deviation [ ] 0.00 5.00 5.00 6.7 Summary In the previous Section, the comprehensive synthesis procedure for the design of the filtering antenna array was presented. The developed synthesis procedure for the filtering antenna has combined the design of a frequency filter and the design of an antenna array (Section 6.1). Equations for the calculation of numerical values of components of the equivalent circuit (capacitances, mutual capacitances, inductances and J-inverters) were derived on the basis of the frequency filter approach (Section 6.2). The antenna approach was used for the synthesis of the frequency response of the normalized realized gain (Section 6.3). We calculated the E-plane pattern and the H- plane pattern of a single patch antenna from the electric surface current, and subsequently, we evaluated the directivity of the patch antenna. For the comprehensive synthesis of the frequency response of the normalized realized gain, the antenna factor has to be calculated and the reflection coefficient (Section 5.2) has to be included. Moreover, this Section was focused on the definition of new g i coefficients for the three-element and the four-element filtering antenna array fed by apertures. In derivations, we assumed the substrate ARLON 25N. The g i coefficients were derived for an acceptable level of the reflection coefficient at the antenna input which was changed in the interval from 10 db to 20 db. Due to g i coefficients, the shape of the frequency responses of the reflection coefficient as well as the normalized realized gain could be altered and controlled. Outputs of the Section 4.3 allowed us to formulate relations for the calculation of the width and the length of the each individual aperture which depends on values of the J-inverters presented in Section 6.5. - 83 -
Synthesis of filtering antenna array fed by apertures The verification of the presented synthesis procedure and the validation of new g i coefficients were described in Section 6.6. Results produced by the MATLAB script were compared with results obtained by a full-wave model in CST Microwave Studio. Functionality of the described synthesis procedure was verified on three test cases of the three-element filtenna, and three test cases of the four-element filtering antenna array over the frequency range from 4.8 GHz to 6.8 GHz with the different fractional bandwidth of the whole structure. The bandwidth varied from 7 % to 14 % in the case of the three-element filtenna, and from 8 % to 12 % in the case of the four-element filtenna. And finally, the acceptable level of the reflection coefficient at the input of the filtenna was changed from 10 db to 20 db. All the verifications carried out on all six test cases were in a good agreement. - 84 -
Verification by measurement 7 VERIFICATION BY MEASUREMENT This Section is focused on the experimental verification of theoretical results. The verification compares a full-wave model simulated in CST Microwave Studio and experimental results obtained by measurements. All three test cases of the three-element filtenna as well as all three test cases of the four-element filtering array were manufactured and measured. The following Sections deal with comparisons. 7.1 Verification of the three-element filtering antenna array Three test cases characterized by different requirements were manufactured and measured. The first sample was designed at the center frequency 4.8 GHz with fractional bandwidth of the whole structure equal to 10 % and the acceptable level of the reflection coefficient better than 10 db. The comparison of simulated results from CST Microwave Studio, where the dielectric losses and the SMA connector were included, with measured results is shown in Figure 7.1. Figure 7.1 Comparison of the simulated results and measured ones for the case: three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db Figure 7.1 shows that simulated results and measured ones are in a good agreement. Only the measured frequency response of the normalized realized gain has a wider 3 db fractional bandwidth (about 3 %). The simulated and measured co-polarizations and cross-polarizations in the E- plane and the H-plane are shown in Figure 7.2. The E-plane corresponds with the x-z plane and the H-plane with the y-z plane in Figure 4.4. The frequency response of the main lobe direction is one of the most important parameters of filtering antennas. This dependence is illustrated by Figure 7.3. In the operating band, the simulated maximal deviation of the main lobe is only 4.9, and the measured one is 5.99. The realized gain of this filtering antenna array is about 9 dbi - 85 -
Verification by measurement over the operating range. All these dependencies are in a good agreement. The comparison of the most important values is summarized in Table 7.1. Figure 7.2 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the three-element filtenna at frequency 4.8 GHz Figure 7.3 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 4.8 GHz Table 7.1 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 4.8 GHz; FBW s = 10 % and S 11 < 10 db Simulation Measurement f 0 [GHz] 4.81 4.84 FBW -3 db [%] 13.50 16.52 S 11 @ f 0 [db] 9.37 7.73 FBW -10 db [%] S 21 suppression [db] 19.44 19.85 S 21 selectivity [db/ghz] 64.47 66.45 Maximal deviation [ ] 4.90 5.99-86 -
Verification by measurement As the second test case, the three-element filtering antenna array at the center frequency 5.8 GHz with the fractional bandwidth of the whole structure FBW s equals to 13 % and the acceptable level of the reflection coefficient better than 15 db was manufactured and measured. The comparison of the simulated and measured frequency responses of the reflection coefficient and the normalized realized gain are given in Figure 7.4. The simulated co-polarization and cross-polarization components in the E- plane and the H-plane are confronted with measured ones in Figure 7.5. Again, the E- plane represents the x-z plane in Figure 4.4 and the H-plane corresponds with the y-z plane in Figure 4.4. Figure 7.4 Comparison of simulated results and measured ones for the case: three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db Figure 7.5 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the three-element filtenna at frequency 5.8 GHz The frequency response of the main lobe direction is shown in Figure 7.6 where the simulated maximal deviation of the main lobe is only 6.2 and measured one is 5 in the operating band. The realized gain of the filtering antenna array is about 9 dbi over the operating range. The important values obtained by simulations and measurements are listed in Table 7.2. In this case, the results are in a good agreement. - 87 -
Verification by measurement Figure 7.6 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 5.8 GHz Table 7.2 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 5.8 GHz; FBW s = 13 % and S 11 < 15 db Simulation Measurement f 0 [GHz] 5.86 5.77 FBW -3 db [%] 14.00 14.89 S 11 @ f 0 [db] 11.88 11.85 FBW -10 db [%] 11.02 10.01 S 21 suppression [db] 18.01 21.92 S 21 selectivity [db/ghz] 51.13 49.68 Maximal deviation [ ]. 6.20 4.99 The last test case of the three-element filtenna at the centre frequency 6.8 GHz, the fractional bandwidth of the whole structure 10 % and the acceptable level of the reflection coefficient better than 10 db was manufactured and measured. The comparison of simulated and measured results is depicted in Figure 7.7. The copolarization and the cross-polarization components in the E-plane (x-z plane in Figure 4.4) and in the H-plane (y-z plane in Figure 4.4) are shown in Figure 7.8. The frequency response of the main lobe direction is illustrated by Figure 7.9 which shows the maximal simulated deviation of the main lobe equals to 4.2 and measured one 5 over the operating band. The maximal realized gain of the filtering antenna array is about 10 dbi. Figure 7.7 and Table 7.3 show that the results are in a good agreement. Only the measured 3 db fractional bandwidth is wider in comparison with the simulated one (about 5 %). - 88 -
Verification by measurement Figure 7.7 Comparison of simulated results and measured ones for the case: three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db Figure 7.8 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the three-element filtenna at frequency 6.8 GHz Figure 7.9 Comparison of simulated and measured frequency responses of the main lobe direction of the three-element filtenna designed at the center frequency 6.8 GHz - 89 -
Verification by measurement Table 7.3 Comparison of the most important simulated and measured results for the case: three-element filtenna; f 0 = 6.8 GHz; FBW s = 10 % and S 11 < 10 db Simulation Measurement f 0 [GHz] 6.73 6.64 FBW -3 db [%] 11.14 16.11 S 11 @ f 0 [db] 18.67 12.48 FBW -10 db [%] 5.74 5.73 S 21 suppression [db] 16.73 15.95 S 21 selectivity [db/ghz] 30.89 32.27 Maximal deviation [ ] 4.20 4.99 The differences between simulated and measured results are given by the accuracy of manufacturing. As mentioned, the filtering antenna array is composed from two dielectric substrates and is sensitive to the accuracy of assembling. Top layers of all three fabricated test cases of the three-element filtenna are shown in Figure 7.10. Corresponding bottom layers are given in Figure 7.11. Figure 7.10 Top layers of the manufactured test cases of the three-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz - 90 -
Verification by measurement Figure 7.11 Bottom layers of the manufactured test cases of the three-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz 7.2 Verification of the four-element filtering antenna array In this Section, simulated and measured results of the three test cases of the fourelement filtering antenna array are compared. The first test case was tuned at the center frequency 4.8 GHz with the fractional bandwidth of the whole structure 8 % and the acceptable level of the reflection coefficient better than 15 db. The test case was manufactured and measured. The comparison of simulated frequency responses of the reflection coefficient and the normalized realized gain with measured ones is shown in Figure 7.12. The simulated and measured co-polarization and cross-polarization components in the E-plane and the H-plane are shown in Figure 7.13. The E-plane corresponds with the x-z plane and the H-plane with y-z plane in Figure 4.4. The realized gain of the filtering antenna array over the operating range is about 11 dbi. In this case, the frequency response of the main lobe direction was measured and compared as well (see Figure 7.14). The most important parameters from all confrontations are listed in Table 7.4. - 91 -
Verification by measurement Figure 7.12 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db Figure 7.13 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the four-element filtenna at frequency 4.8 GHz Figure 7.14 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 4.8 GHz - 92 -
Verification by measurement Table 7.4 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 4.8 GHz; FBW s = 8 % and S 11 < 15 db Simulation Measurement f 0 [GHz] 4.84 4.82 FBW -3 db [%] 5.61 5.89 S 11 @ f 0 [db] 21.53 16.36 FBW -10 db [%] 2.67 2.46 S 21 suppression [db] 20.26 21.69 S 21 selectivity [db/ghz] 94.85 76.16 Maximal deviation [ ] 3.00 5.00 The second test case of the four-element filtenna at the center frequency 5.8 GHz with the fractional bandwidth of the whole structure 12 % and the acceptable level of S 11 better than 10 db was manufactured and measured as well. Figure 7.15 shows the comparison of measured frequency responses of the S 11 and the normalized realized gain with simulated ones. The simulated and measured E-plane patterns and H-plane patterns of the four-element filtenna at the frequency 5.8 GHz which correspond with the x-z plane and the y-z plane in Figure 4.4 are illustrated by Figure 7.16. The frequency dependencies of the main lobe direction over the operating range are shown in Figure 7.17. The maximal deviation of simulated results equals to 4, and measured ones to 5. The realized gain of the filtenna is about 11 dbi in the operating band. The values of the center frequency, the fractional bandwidth for 3 db and for 10 db as well as the level of the reflection coefficient, the suppression in the stop band and the selectivity of the filtenna are listed in Table 7.5. Figure 7.15 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db - 93 -
Verification by measurement Figure 7.16 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the four-element filtenna at frequency 5.8 GHz Figure 7.17 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 5.8 GHz Table 7.5 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 5.8 GHz; FBW s = 12 % and S 11 < 10 db Simulation Measurement f 0 [GHz] 5.78 5.68 FBW -3 db [%] 12.63 13.52 S 11 @ f 0 [db] 13.77 10.16 FBW -10 db [%] 9.24 10.28 S 21 suppression [db] 21.29 19.76 S 21 selectivity [db/ghz] 80.37 75.33 Maximal deviation [ ] 4.00 5.00 And the last test case of the four-element filtering antenna array at the center frequency 6.8 GHz with the fractional bandwidth of the whole structure of 12 % and the acceptable level of the reflection coefficient better than 20 db was manufactured and - 94 -
Verification by measurement measured as well. The comparison of simulated and measured frequency responses of the reflection coefficient and the normalized realized gain are shown in Figure 7.18. The simulated and measured E-plane patterns, and the H-plane patterns of the four-element filtenna at the frequency 6.8 GHz, which correspond with the x-z plane and the y-z plane in Figure 4.4, are illustrated in Figure 7.19. The frequency responses of the main lobe direction are illustrated in Figure 7.20, where the maximal simulated deviation of the main lobe is equal to 5.4 and measured one to 7.0. This filtering antenna array has a realized gain about 10 dbi over the operating range. The ripple losses in the pass band are equal to 1.4 db. The most important parameters of the four-element filtenna at the center frequency 6.8 GHz are listed in Table 7.6. Figure 7.18 Comparison of simulated results and measured ones for the case: four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db Figure 7.19 Comparison of simulated and measured co and cross polarizations in E- plane (left) and H-plane (right) of the four-element filtenna at the frequency 6.8 GHz - 95 -
Verification by measurement Figure 7.20 Comparison of simulated and measured frequency responses of the main lobe direction of the four-element filtenna designed at the center frequency 6.8 GHz Table 7.6 Comparison of the most important simulated and measured results for the case: four-element filtenna; f 0 = 6.8 GHz; FBW s = 12 % and S 11 < 20 db Simulation Measurement f 0 [GHz] 6.76 6.70 FBW -3 db [%] 13.13 8.59 S 11 @ f 0 [db] 27.73 25.01 FBW -10 db [%] 10.41 8.06 S 21 suppression [db] 22.76 15.74 S 21 selectivity [db/ghz] 82.23 98.08 Maximal deviation [ ] 5.40 7.00 The differences between simulated and measured results are given by the manufacturing accuracy. As mentioned, the filtering antenna arrays are composed from two dielectric substrates and are sensitive to the accuracy of assembling. Top layers of all three fabricated test cases of the four-element filtenna are shown in Figure 7.21, and bottom layers are given in Figure 7.22. - 96 -
Verification by measurement Figure 7.21 Top layers of manufactured test cases of the four-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz Figure 7.22 Bottom layers of manufactured test cases of the four-element filtennas: upper filtenna at the frequency 4.8 GHz; middle filtenna at 5.8 GHz and lower one at the frequency 6.8 GHz - 97 -