INVESTIGATIONS ON APERTURE-COUPLED U-SLOTMICROSTRIP ANTENNAS" which

Abstract

In this dissertation, an aperture-coupled feed has been investigated for a rectangular patch antenna with U-slot. In the U-slot microstrip antenna, there are number of geometrical and electrical parameters which can critically affect the antenna characteristics. An extensive parametric study of these parameters was done through rigorous simulation on Zeland's IE3D simulation. too]. During simulation, only one parameter was varied at a time keeping all others constant, which helped us in understanding the influence of each parameter in antenna characteristics. With the help of simulation, we obtained best possible antenna structure. Experimental verification of the optimized antenna was done and it is observed that simulation results are in good agreement with measurement. Experimental results show that the antenna can attain an impedance bandwidth of 25.7% with average gain of 7 dBi, and has stable radiation characteristics over the frequency band of interest. Addition of U-slot significantly affects the gain characteristics by increasing the gain nearly upto 12.1 dBi near U-slot resonance frequency. Wide impedance characteristics can also be changed into dual-band characteristics by merely changing the stub length. To clearly visualize the effect of the addition of U-slot, a reference aperture-coupled microstrip antenna without U-slot was also studied through simulation as well as experimentally. It was found that the addition of U-slot in the microstrip patch results in an improvement of about 5% in the impedance bandwidth. Since the aperture-coupled feed is especially attractive for array implementation, circularly polarized arrays using the proposed U-slot antenna have also been investigated by using two different feed networks. Circularly polarized radiation is obtained from an array composed of linearly polarized U-slot antenna elements having unique angular and phase arrangements. Simulation results on the array predict substantially increased impedance bandwidth (upto 38%) and average gain (uptol 1.5 dBi). In other words, the array configuration has a fairly high gain-bandwidth product. Obtained axial bandwidth is 3.5 % with the minimum axial ratio as 0.4 dB.