Design of Broadband Reflecting Luneburg Lenses by Higher Symmetries

This work reports the application of higher symmetries to the design of a Reflecting Luneburg Lens (RLL) with broadband response. RLLs consist of two stacked parallel plate waveguides (PPW) of circular shape, where the bottom PPW is filled with an azimuthally symmetric graded index (GRIN) medium, so that the fields coupled to the top PPW take the form of a plane wave. In this work, the GRIN medium in the bottom PPW is implemented by unitcells consisting of metallic inclusions with higher symmetry. This type of unit cell achieves the required equivalent refractive index profile with reduced frequency dispersion, thus increasing the operational bandwidth of the lens. The proposed architecture can be used as beam-former for complete azimuthal scanning in a wide frequency range, while benefiting from the robustness and low-losses of metal-only structures.