Analytical method for a circularly polarised rectangular microstrip antenna

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