Reduced kernel IE's for MEN based analysis of multilayered FSS structures

Despite the fact that the general behavior of periodic structures has been investigated for many decades, the analysis and design of multilayered FSSs is still a very real and complicated problem. This is especially true for the stringent requirements, which rise, for example, when the FSS has to be integrated with a planar phased array. A multimode equivalent network (MEN) based approach has been developed to solve this specific kind of problem and successfully applied to a realistic design case (Monni, S. et al.). The key innovative notion introduced by the MEN method is the formalization of the scattering problem through a set of integral equations (IEs) with reduced kernel and corresponding reduced Green's function (GF). Originally, the pertinent method of moments (MoM) based IEs have been solved by expanding the unknowns in terms of sub-domain functions. However, when the frequency filtering performance required from the FSS includes steep roll offs and wide scan angles, the number of accessible (interacting) modes to be included in the analysis grows, and it turns out that, for expansions based on sub-domain functions, the MoM matrix tends to be ill-conditioned. This specific behavior is the subject of the paper.