SOME INVESTIGATIONS ON A WAVEGUIDE FEED PATCH ANTENNA

Abstract

The microstrip antennas in recent years, are gaining wide publicity due to their numerous advantages. The versatility of this class of antennas at microwave frequencies suggests a potential usefulness at millimeter-wave frequencies. However, it has become apparant that feed structures which operate quite well at microwave frequencies are not viable with millimeter-waves, since the losses become significant in microstrip lines and co-axial feed components are not available above about 50 GHz. For this reason, a new feeding technique for patch antenna, namely, 'waveguide feed', has been studied in this dissertation. In this work, a moment method analysis has been presented for a microstrip patch antenna coupled to a waveguide via an aperture in its ground plane. Equivalence theorem, in conjunction with the boundary conditions, has been used to set up two coupled integro-differential equations. These are then reduced to matrix form using the method of moments. Though the analysis is quite general, in the sense that no restrictions have been imposed on the shape and size of the patch and the aperture, analytical expressions have been derived for the particular case of a rectangular patch fed by a rectangular waveguide via a rectangular aperture in the ground plane. Based on the above analysis, a computer program has been developed in FORTRAN, to analyse the structure. Numerical results obtained from the program have been checked for the convergence and compared with the published work for a number of different problems. Some test data have also been presented for a waveguide fed microstrip patch antenna. Some experimental investigations were also carried out on the waveguide feed patch antenna which was constructed using RT/Duroid 5880. Experimental results have been reported here on the input characteristics, gain, and the radiation pattern of this antenna. Further, the effect of using a slide screw tuner for reducing the impedance mismatch and increasing the size of the ground plane has also been studied