Design Formulas for Planar Fabry–Pérot Cavity Antennas Formed by Thick Partially Reflective Surfaces

Simple closed-form formulas are proposed to estimate the broadside radiation performance of planar Fabry-Pérot-cavity (FPC) antennas formed by an arbitrary thick partially reflective-surface (PRS). The new formulas also estimate the attenuation and propagation constant of the leaky waves excited in the FPC when covered by such a thick PRS. When the PRS thickness vanishes the derived formulas reduce to those previously derived for FPC formed by infinitesimally thin PRS. Notably, we demonstrate that the same fundamental limit for the figure of merit defined as the pattern bandwidth-directivity product holds, as that for FPC with thin PRS, under the approximation that the phase variation of the PRS scattering parameters is not too rapid. The accuracy of the proposed formulas is verified with comparisons to numerical full-wave simulations.