CHAPTER 5 MODIFIED MINKOWSKI FRACTAL ANTENNA

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$DOVRSUHVHQWHG 5.1 Modified Minkowski fractal antenna The modified Minkowski fractal antenna is investigated in this chapter, which originates from the plane square shapedpatch antenna.$ In this case, Minkowski iterations produce a cross-like actal fr patch with even fine details at the edges.

In this case, Minkowski iterations produce a cross-like actal fr patch with even fine details at the edges.

1 CHAPTER 5 MODIFIED MINKOWSKI FRACTAL ANTENNA &KDSWHUSUHVHQWVWKHGHVLJQDQGIDEULFDW LRQRIPRGLILHG0LQNRZVNLIUDFWDODQWHQQD IRUZLUHOHVVFRPPXQLFDWLRQ7KHVLPXODWHG DQGPHDVXUHGUHVXOWVRIWKLVDQWHQQDDUH DOVRSUHVHQWHG 5.1 Modified Minkowski fractal antenna The modified Minkowski fractal antenna is investigated in this chapter, which originates from the plane square shapedpatch antenna. In this case, Minkowski iterations produce a cross-like actal fr patch with even fine details at the edges. This antenna is designed by giving the first iteration at the center of each side of the square patch [ ]. This discussed below in detail. 5.2 Antenna design The modified Minkowski fractal antenna i shown in Fig 5.1. The IE3D software based on method of moment (MoM) is used simulate to this fractal antenna. Similar to diamond shaped fractal antenna discussed chapter in 4, the FR4 material is used as a substrate for this antenna. The thickness of the substrate is 1.575mm and the dielectric constant is 4.3. The side lengt h of this fractal antenna is 30mm (without iteration) and after 1 st LWHUDWLRQµLQGHQWDWLRQ VL]HLV 2mm 8mm and square size is 14mm. Figure 5.1: Modified Minkowski fractal antenna with zero iteration. 62

5.3 Antenna structure used in simulator Fig. 5.

The port locations for 1 st iteration and 2 nd iteration are (-2, 9)

4 5.3 Antenna structure used in simulator Fig. 5.4 and Fig. 5.5 respectively depicts e th actual structure with port location of the antenna in simulator for 1 st and 2 nd iteration. The port locations for 1 st iteration and 2 nd iteration are (-2, 9) and (7, 2.5) respectively. Figure 5.4: Structure of antenna in simulator after st iteration. 1 Figure 5.5: Structure of antenna in simulator after nd iteration. 2 65

5 5.4 Simulation results of antenna for 1 st iteration Return loss (S 11 ) Return loss is usually measured at the junc tion of a transmission line and terminating impedance. It is defined as the ratio of the amplitude of reflected wave to the amplitude of incident wave. More specifically, the return loss value describes the reduction in the amplitude of reflected energy, as compared to the forward energy. Fig. 5.6 depicts the return loss of antenna for st iteration. 1 Figure 5.6: Variation of return loss (S 11 ) with frequency for 1 st iteration. From Fig. 5.6, it can be observed that e thresonant frequencies are 4.9GHz, 9.5GHz and 12.8GHz, and the return loss is less than -10dBi at these resonant frequencies. Thus, the designed antenna is best ited sufor these resonant frequencies Radiation pattern The radiation pattern of an antenna provide s the information that describes how the antenna directs the energy it radiates. All tennas, an if are 100% efficient, will radiate the same total energy for equal input power regardless of pattern shape. Radiation patterns are generally presented on a relative power db scale. 66

6 The elevation radiation pattern of an antenna shows the gain of antenna at resonant frequencies in the elevation plane. Fig. 5.7 and Fig. 5.8 depicts the elevation radiation patterns of the designed antenna at resonant frequencies of 4.9GHz and 9.5GHz respectively. Figure 5.7: Elevation radiation pattern at 4.9GHz. Figure 5.8: Elevation radiation pattern at 9.5GHz. Fig. 5.9 depicts the combined elevation diation ra pattern of the designed antenna at both resonant frequencies. 67

7 Figure 5.9: Combined Elevation radiation pattern at both resonant frequencies Total field gain vs frequency Fig depicts the total field gain vs. frequency plot. It can be observed from Fig that the gain of the antenna is 5dBi, 6.4dBi and 2.5dBi at resonant frequencies of 4.9GHz, 9.5GHz and 12.8GHz respectively. Figure 5.10: Total field gain vs frequency of the designed antenna. 68

8 5.4.4 Directivity of the designed antenna Fig depicts the directivity vs. frequency plot. The directivity of the designed antenna obtained at resonant frequencies of 4.9GHz, 9.5GHz and 12.8GHz is 7.5dBi, 9.5dBi and 9.1dBi respectively. Figure 5.11: Directivity vs frequenc y graph of the designed antenna VSWR of the designed antenna Fig shows the Voltage Standing Wave Ratio (VSWR) of the designed antenna.vswr is the ratio between the maximum voltage and minimum voltage along transmission line. Figure 5.12: VSWR characteristics of the designed antenna st iteration. for 1 69

10 frequencies of 4.2GHz, 9.5GHz and 14.1GHz respectively. Fig depicts combined elevation radiation pattern at ree thresonant frequencies of the antenna. Figure 5.14: Elevation radiation pattern at 4.2GHz nd of iteration. 2 Figure 5.15: Elevation radiation pattern at 9.5GHz nd of iteration. 2 71

Figure 5.16: Elevation radiation pattern at 14.1GHz nd of iteration. 2 Figure 5.17: Combined Elevation radiation pattern nd for iteration. 2 As seen from Fig.5.17, all resonant freque ncies maintain a gain of 2dBi.

11 Figure 5.16: Elevation radiation pattern at 14.1GHz nd of iteration. 2 Figure 5.17: Combined Elevation radiation pattern nd for iteration. 2 As seen from Fig.5.17, all resonant freque ncies maintain a gain of 2dBi.This shows that these frequencies are not higher order modes as there is consistency in the gain. However, the radiation patterns get affected in shape due to variation in the current length for the respective resonance allowing different current density to wavelength ratio. 72

12 5.5.3 Total field gain vs frequency Fig shows the total field gain vs. equency fr of the modified Minkowski fractal antenna. The gain at three resonant frequencies (4.2GHz, 9.5GHz and 14.1GHz) of the 2 nd iteration is 1.27dBi, 5.44dBi and 7.76dBi respectively. Figure 5.18: Total field gain vs frequency of nd iteration 2 of the designed antenna Directivity of the designed antenna Fig depicts that the directivity of th e designed antenna is 6dBi, 11dBi and 12.9dBi at respective three resonant frequencies 4.2GHz, 9.5GHz and 14.1GHz. Figure 5.19: Directivity characteristics of the designed antenna. 73

The gain of the antenna at 14.1GHz is 7.76dBi and the dir ectivity is 12.9dBi. Calculating the efficiency, k = 7.76/12.9 = 0.6015 (5.28) From the above results, the efficiency of the antenna at 14.

16 The gain of the antenna at 14.1GHz is 7.76dBi and the dir ectivity is 12.9dBi. Calculating the efficiency, k = 7.76/12.9 = (5.28) From the above results, the efficiency of the antenna at 14.1GHz is 60.15%. Table 5.1: Summary of st 1iteration results. Resonant Return Gain Directivity Bandwidth % VSWR Efficiency Frequency loss (dbi) (dbi) (MHz) Bandwidth Coefficient (GHz) (db) (k) Resonant Frequency loss (GHz) Return Table 5.2: Summary of nd 2iteration results. Gain (dbi) Directivity (dbi) Bandwidth MHz % Bandwidth VSWR Efficiency Coefficient (k) 5.7 Measured return loss Fig shows the picture of the fabricated antenna of 2 nd iteration using FR4 substrate. Figure 5.21: Fabricated antenna nd of iteration 2 with dimensions 30mm x 30mm. 77

17 Fig depicts the resonant frequencies of fabricated antenna, i.e., 3.822GHz, 4.506GHz and 4.886GHz and its corresponding return loss. Figure 5.22: Measured return loss of the fabricated antenna using site analyzer. 5.8 Conclusion In this chapter, the modified Minkowski fractal antenna is simulated and fabricated. The designed antenna is found to resonate 4.9GHz, 9.5GHz and 12.8GHz with respective gain of 5dBi, 6.4dBi and 2.5dBi. The respective bandwidths obtained are 500MHz, 1000MHz, and 300MHz. at these resonant frequencies st for iteration. 1 The values of gain achieved are 1.27dBi, 5.44dBi and 7.76dBi at three resonant frequencies (4.2GHz, 9.5GHz and 14.1GHz) of 2 nd iteration respectively. The bandwidths obtained are 600MHz, 800MHz and 1000MHz at the above three resonant frequencies respectively. The fabricated ante nna is tested using ite s analyzer having frequency range of 6GHz. The measured bandwidths obtained are 100MHz, 50MHz and 60MHz at three measured resonant frequencies respectively. The measured results show that the designed antenna supports multiband and is thus, suitable for low powered devices for wireless communication applications. 78

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