Angular independency of a parallel-plate Luneburg lens with hexagonal lattice and circular metal posts

An asymmetric parallel-plate waveguide Luneburg (1964) lens (APWLL) is developed using a periodic regular circular metal post structure, which acts as a metallic artificial dielectric. The effect of metal post shapes and lattices on the angularly independent performance of the structure is investigated and then for the best angular independency a circular metal post shape and a hexagonal lattice are chosen. A prototype APWLL is designed for an adaptive cruise control (ACC) radar at 76-77 GHz. Measurement and simulation show that the structure with a hexagonal lattice and circular metal posts has not only better performance, but also functions as well as an actual isotropic homogeneous dielectric with angular independency.