A Dual Layer Frequency Selective Surface Reflector for Wideband Applications

A dual-layer, bandstop frequency selective surface (FSS) is presented in this paper for wideband applications. Each layer uses patch type FSS with slots for miniaturization and are cascaded with an air gap in between. The low-profile FSS with unit cell dimension on the order of 0.2λ0×0.2λ0 provides transmission coefficient below -10dB in the frequency range of 4-7 GHz with 56% bandwidth. The FSS exhibits a nearly linear phase variation with frequency in the operating band and can be used as a substrate below planar wide band antennas with bi-directional radiation for enhancing its gain, directivity in the broadside direction as well as shielding it against nearby conductive surfaces such as metal cases, other printed antennas. Detailed design method, equivalent circuit analysis and measurement results of the FSS are presented in this paper.