A unified formulation for the analysis of general frequency selective surfaces

In this paper we solve the problem of the scattering of an arbitrary field from a general Frequency Selective Surface (FSS). The keypoint of our approach is a functional equation in the spectral domain, which is solved numerically by the Calrkin Method of Moments. Two approaches are possible, according to whether one assumes as unknown the induced current on the metalilc patches or the, electric field in the complcnentpry aperatures. The former Is convenient when the patches have a simple shape (e.g. strips, rings,discs), the latter in the case of a perforatec screen (e.g. round or rectangular apertures). The formulation Is then extended to treat the case where the patches are not metallic, but constituted by an anysotropic imoodance surfacf. The computer program AHPA is based on this formulation and car. perform a spectral charecterization of multiple grid FSS, with metallic patches described as a collection of scrips. Sample results relative to tripoles and square loops are presented and discussed.