Experimental Validation of a Metasurface Luneburg Lens Antenna Implemented With Glide-Symmetric Substrate-Integrated Holes

In this letter, we present the experimental validation of a K_{a}-band Luneburg lens antenna based on a novel cost-effective metasurface. The metasurface is composed of a parallel plate waveguide (PPW) loaded with quasi-periodic inclusions in both conductors. The inclusions are square holes printed on a substrate, with vias placed around the holes. The vias connect the printed layer of the substrate to the ground. This configuration is named substrate-integrated hole (SIH). It is demonstrated that the SIH metasurface can obtain a higher effective refractive index, compared to the conventional holey metasurface. To further increase the effective refractive index, the SIHs in the two conductors of the PPW are glide-symmetrically arranged. The refractive index distribution of the Luneburg lens is realized by locally tuning the dimensions of the SIHs. The lens is fed with 11 waveguide feeds with an angular separation of 10^{\circ }. Thus, the antenna can steer its radiation in a 100° angular range. A flare is integrated with the PPW to match the antenna to the free-space impedance. Since the wave propagates mainly in the PPW air gap, the dielectric losses are low. The measured radiation efficiency of the antenna is roughly 80%.