Wideband Planar Microwave Lenses Using Sub-Wavelength Spatial Phase Shifters

Abstract

We present a new technique for designing low-profile planar microwave lenses. The proposed lenses consist of numerous miniature spatial phase shifters distributed over a planar surface. The topology of each spatial phase shifter (SPS) is based on the design of a class of bandpass frequency selective surfaces composed entirely of sub-wavelength, non-resonant periodic structures. A procedure for designing the proposed lenses and their constituting spatial phase shifters is also presented in the paper. This design procedure is applied to two different planar lenses operating at X-band. Each lens is a low-profile structure with an overall thickness of 0.08λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and uses sub-wavelength SPSs with dimensions of 0.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at 10 GHz. These prototypes are fabricated and experimentally characterized using a free-space measurement system and the results are reported in the paper. The fabricated prototypes demonstrate relatively wide bandwidths of approximately 20%. Furthermore, the lenses demonstrate stable responses when illuminated under oblique angles of incidence. This feature is of practical importance if these lenses are to be used in beam-scanning antenna applications.