Double-Fed multilevel frequency selective surface for low-profile planar lens

A multilevel frequency selective surface (FSS) with double feeding is presented in this paper. The FSS is formed by a non-uniform distribution of square holes on several metallic layers. The resulting structure works as a low-profile planar lens that enhances the radiation of the feeding open waveguides. This behavior provides a large rectangular amplitude distribution and a constant phase on the upper plane of the lens. As a result, a high gain and a good side lobe levels are obtained along a wide bandwidth. The gain pattern on main planes at 20.5 GHz and the S-parameters on the input ports for a 3-layer structure are shown in this paper. These results confirm the validity of the proposed structure as a starting point for larger arrays.