Scattering properties of patch antennas loaded with inhomogeneous substrates via a combined spectral domain-moment method

In this paper a combined spectral domain-moment method is proposed in order to investigate the scattering properties of microstrip patch antennas with inhomogeneous substrates. The closed analytical expressions for the spectral dyadic Green's functions for diÿerent inhomogeneity pro®les both in the rigorous and in the asymptotic form are obtained. A method of moments (MoM) formulation involving these expressions and using roof-top subdomain expansions is developed in order to calculate the radar cross-section for the antennas under analysis. Finally, diÿerent rectangular geometry patch shapes are considered (rectangular itself, L-patch, cross-patch, rectangular ring, etc.) and, for all of them, the monostatic radar cross-sections, compared to those obtained by using homogeneous substrates, are improved.