Design & Analysis Of Fractal Microstrip Patch Antennas For Wireless Communication Systems

The advancement in wireless communication technology has drawn demands for integrated components including antennas.Antenna is a vital constituent of low profile integrated wireless communication systems.In particular,antenna on chip is a new demanding area of antenna research that requires infinitesimal size antenna,to accomplish optimal design for modern handheld wireless communication devices.Multiband operation and wider operating bandwidth is another requirement for these wireless devices.One of the solutions to achieve these characteristics is by incorporation of fractal geometries.Fractal geometry has the characteristics of inherent self-similarity or self-affinity,used to describe and model complex shapes found in nature such as mountain ranges,waves.This feature helps the researchers and antenna designers to dig out some novel geometries which are appropriate for designing small antennas.Incorporation of this fractal geometry to microstrip antenna is one of the emerging research areas which need to be evaluated to achieve optimal antenna response.In general,the use of antenna fractal geometries is inclined towards miniaturization and/or widening operational bandwidth and/or yielding multiband response.Numerous techniques have been proposed in recent years for size reduction,multiband response and bandwidth enhancement of microstrip patch antennas having applications in communication and radar systems.Still,there is a lot of room available to carry this research further in order to meet the challenging demands towards compact,highly efficient and low cost antennas.In this dissertation,two novel patch antenna designs using fractals have been proposed.In the first proposal,a novel hybrid fractal antenna based on the combination of Koch and Minkowski(K-M)fractal geometries is designed.A microstrip patch antenna(MPA)operating at 1.8 GHz is incorporated with novel K-M hybrid fractal geometry,which results in a decrement of operating frequency to 1.44 GHz.The third iteration of K-M fractal geometry results in achieving 20 percent size reduction as compared to an ordinary MPA for the same resonant frequency with an impedance bandwidth of 16.2499 MHz and a directional gain of 6.48 dBi,respectively.In order to further evaluate the benefit of the proposed hybrid fractal geometry,a comparison study has also been carried out with the conventional Koch fractal geometry.The results show that the percentage of size reduction of the proposed K-M hybrid fractal is more as compared to Koch fractal,and hence show the advantage over Koch geometry.In the second proposal,a novel compact tri-band fractal antenna based on the self-similar stair shaped fractal geometry is designed.The third iteration results in tri-band response and the novel stair shaped fractal antenna resonates at 3.564 GHz,4.8254 GHz and 6.3348 GHz with impedance bandwidths of 36 MHz,119.5 MHz and 210 MHz,respectively.The pattern of the antenna is directional and the antenna is radiating in broadside direction with gain of 6.3 dBi,6.73 dBi and 2.71 dBi at the corresponding operating frequencies,respectively.All the designs are carried out in CST microwave studio.The designed antennas are then fabricated using low cost and readily available FR-4 substrate with thickness,dielectric constant and loss tangent of 1.6 mm,4.3 and 0.025,respectively and are fed with 50-ohm microstrip line.The antennas are then tested through the vector network analyzer(VNA)for operating bands and the anechoic chamber for radiation patterns to validate the simulated results.For the first antenna design,the measured impedance bandwidth at the upper and lower frequencies of the K-M antenna is 14.375 MHz(1.428125 – 1.4425 GHz).Different parameters of the fractal antenna such as return loss,impedance bandwidth and far field characteristics at operating band are found well matched to the simulated results,which enables the miniaturized hybrid fractal antenna a good candidate for wireless communication applications.In the second proposed design,the measured impedance bandwidths at resonant frequencies of 3.5 GHz,4.7 GHz and 6.23 GHz are observed to be 134.4 MHz(3440.6 – 3575 MHz),56.25 MHz(4696.9 – 4753.1 MHz)and 200 MHz(6130 – 6330 MHz),respectively.Good agreement has been observed in the measured and simulated results of the proposed stair shaped antenna,which enables the designed fractal antenna a good candidate for multiband applications.