Wall Admittance of a Circular Microstrip Antenna

The formulation of the wall admittance of a circular microstrip antenna by the spectral domain method is presented. The circular microstrip antenna is calculated using the cavity model. The electromagnetic fields within the antenna cavity are determined from the impedance boundary condition at the side aperture. The contribution from the region outside the antenna is taken into account by the wall admittance. The wall admittance is defined by the magnetic field produced by the equivalent, magnetic current at the aperture. The magnetic field is calculated by the spectral domain method. The wall admittances obtained by this method are compared with the results calculated by Shen. The calculated input impedances of the microstrip antenna agree fairly well with the experimental data for the substrate thickness of up to 0.048λ_g. The formulation of wall admittance presented here is easily applicable to arbitrarily shaped microstrip antennas