Technique for analysing cascaded frequency selective surface screens with dissimilar lattice geometries

The paper presents an efficient technique for analysing cascaded frequency selective surfaces (FSS) with non-commensurate periodicities by using an iterative approach based on the discrete plane wave spectrum (PWS) expansion. In this method, the tangential electric fields at the interfaces of the screens are first expanded in a set of transverse electric and transverse magnetic waves, and the responses of the individual FSS screens are derived for each of these waves. The transmission and reflection characteristics of the composite structure are then computed in an iterative manner, circumventing the need for matrix inversions. Such inversions can be extremely expensive in terms of CPU time and memory for non-commensurate FSS, because the analysis of the structures can no longer be reduced to that of a single cell by invoking Floquet´s theorem. Representative numerical examples are presented to illustrate the computational advantage gained by using the proposed approach as apposed to a conventional scattering matrix cascading technique, which is strictly valid only for composites with commensurate periodicities.