A New Formula for the Pattern Bandwidth of Fabry-Pérot Cavity Antennas Covered by Thin Frequency Selective Surfaces

A new closed form expression is introduced to estimate the 3 dB pattern bandwidth of a Fabry-Pérot cavity antenna covered by a thin frequency selective surface (FSS) radiating at the broadside direction. The new formula has been obtained by using reciprocity, transmission line theory, and the susceptance model of the FSS. This formula estimates the 3 dB pattern bandwidth more accurately than previous expressions.