Analysis of elliptical microstrip antennas with and without a circular slot

The wall admittance of an arbitrarily shaped microstrip antenna is generall y formulated. As examples, elliptical microstrip antennas with and without a circular slot are calculated. The wall admittance is determined by the sp ectral domain analysis in order to consider the effect of the dielectric su bstrate. The electromagnetic fields within the cavity are expanded in terms of the eigenfunctions in the cylindrical coordinate system and their expan sion coefficients are determined by applying the impedance boundary conditi on at the aperture in the sense of the least squares. The calculated input impedance and axial ratio agree fairly well with the experimental data. The proposed method is valid for the microstrip antennas with a patch whose ge ometry deviates from the particular coordinate system, such as single-feed circularly polarized microstrip antennas.