Ultra-wideband Luneburg lens with high performance based on gradient metamaterials

Based on the perspective of a wide scanning range and ultra-broad bandwidth, Luneburg lenses are highly anticipated to be an outstanding option for multibeam radiation. However, owing to the lack of low-loss continuously varying permittivity materials, the practical application of Luneburg lenses is far below the expected level. In this paper, an ultra-wideband planar Luneburg lens (PLL) is proposed. Due to the novel design of an all dielectric lightweight radially symmetric periodic gradient metamaterial, the presented lens is able to yield highly directional emission with side lobes all below -8 dB and achromatic sub-diffraction focusing with full width at half maximum about 0.4λ from 4 GHz to 22 GHz. The prototype of the lens is manufactured by computer-numerical controlled machining. The measured data of the near field and far field agree well with that of the simulated data, verifying the effectiveness of the proposed design methodology. The superiority of the presented approach to design a Luneburg lens is demonstrated. Therefore, the PLL has the advantages of being lightweight, with a compact structure, low profile, ultrabroadband function, high resolution, and convenient fabrication, giving it great potential to be practically deployed.