Equivalent circuit method for analyzing frequency selective surface with ring patch in oblique angles of incidence

In this letter, we present a novel equivalent circuit for analyzing frequency selective surfaces with a ring patch. The equivalent circuit is based on a shifting unit. The ring patch could be considered as two inductances and a capacitance. The layer of support is equated with a transmission line. Based on this assumption, an example of a two-layer FSS is fabricated and measured, and the transmission coefficient compared to the equivalent circuit model and method of moment (MoM) is reasonable. The method can be used to design a prototype of FSS, and then the designer can do further optimization by full-wave solution.