Anisotropic glide-symmetric substrate-integrated-holey metasurface for a compressed ultrawideband Luneburg lens

An anisotropic unit cell based on glide symmetry is proposed for tailoring a metasurface that engineers an optically transformed Luneburg lens. Thanks to the optical transformation, the size of the lens is reduced by 25%. The proposed lens is ultrawideband, and it covers multi-octave frequency bands. The required constitutive materials are achieved in an air gap bounded by top and bottom glide-symmetric metasurfaces; i.e., they are off-shifted by half the period. Each surface is implemented in standard printed-circuit-board technology, and its unit cell consists of a grounded substrate with an elliptical holey top cladding surrounded by metalized through-vias. This technology, known as substrate-integrated-holes (SIHs), mimics the operation of holes drilled in a parallel plate but provides the higher effective refractive index required for lens compression. The SIH is attractive for practical applications since most of the energy propagates in the air gap between the two surfaces and, therefore, it features low dielectric losses. Thanks to glide symmetry, the proposed metasurface demonstrates a further enhanced effective refractive index with lower dispersion over an ultra-wide bandwidth in comparison to its non-glide counterpart. A multimodal transfer-matrix approach is here employed to carry out the Bloch analysis of the proposed SIH.