Broadband reflecting Luneburg lens beam-former at Ka-band

This papes describes the application of higher symmetries to enable broadband operation of Reflecting Luneburg lenses (RLL) at Ka-band. RLLs are a new type of beam-former, consisting of two vertically stacked parallel plate waveguides (PPWs) of circular shape, of which the bottom one is filled with a graded index (GRIN) medium with azimuthal symmetry. The rays launched by a source in the bottom PPW follow curvilinear paths such that they emerge collimated in the top PPW after encountering a reflecting boundary. Owing to the lens' symmetry, one can generate plane waves with arbitrary directions by simply changing the azimuthal position of the source in the bottom layer. In this paper, the GRIN medium is implemented by loading the bottom PPW with higher symmetric unit-cells consisting of metallic posts. This solution offers a double benefit: it allows one to synthesize the somehow high refractive indexes in the RLL profile and it also mitigates frequency dispersion, thus increasing the lens operational bandwidth. The proposed architecture constitutes a metal-only, low-profile beam-former that can provide full azimuthal scanning in the whole Ka-band.