Equivalent Circuit Model for Square Ring Slot Frequency Selective Surface

An equivalent circuit model for predicting the frequency response of a square ring slot frequency selective surface (SRS-FSS) for normal incidence is described. The proposed FSS consists of an array of square patches centered within a wire grid. The presented circuit model is formed by the impedance of the wire grid that is parallel with the impedance of the patch array, also the mutual coupling between the wire grid and the patch array is taken into account in the patch impedance. Through using the provided relations, the values of circuit elements can be calculated. The proposed relations are applied to many SRS-FSSs with different dimensions and the results are compared to those of the simulations obtained from two well-known software packages, Ansoft HFSS and CST Microwave Studio. The results show that the proposed model well approximates the frequency behavior of the SRS-FSS.