Design of a Broadband Metasurface Luneburg Lens for Full-Angle Operation

We present a broadband metasurface Luneburg lens for full-angle operation. The design of the Luneburg lens is based on an inverted substrate parallel-plate-waveguide structure with nonuniform circular holes etched on the upper metallic plate. We show that this structure is superior to existing designs as it allows significant simplification of the fabrication process. To achieve a smooth variation of the effective refractive index profile as well as circular symmetry for the Luneburg lens, size-variable meta-atoms are used for synthesizing the metasurface. The effective refractive index profile can be tuned by varying just the hole diameters. By introducing tapered microstrip ports that are evenly distributed on the circumference of the Luneburg lens, full-angle operation of the lens can be achieved. A prototype with a diameter of 400 mm is fabricated and experimentally evaluated at operating frequencies ranging from 6 to 9 GHz. We show good conceptual agreement between the simulated and experimental results.