Analytical method for a circularly polarised rectangular microstrip antenna

The paper proposes a formulation method for the wall admittance of an arbit rarily shaped microstrip antenna using spectral domain analysis. In the pap er, the wall admittance of the circularly polarised rectangular microstrip antenna is calculated. The circularly polarised rectangular microstrip ante nna is analysed using the cavity model. The electromagnetic fields within t he antenna cavity are expanded in terms of the eigenfunctions in the cavity with sides extended by the edge extension length. The edge extension lengt h is determined so that the eigenfunctions satisfy the Helmholtz equation a t all frequencies. Their expansion coefficients are determined by the imped ance boundary condition at the aperture. The calculated input impedance and axial ratio of the antenna agree fairly well with the measured data.