Theoretical study on a broadband, high cross-polarization conversion efficiency metalens based on phase discontinuity

In this paper, a novel unit cell for the metalens in a microwave band based on the principle of phase discontinuity at the interface is suggested and theoretically investigated. It has a broad bandwidth of 25%, in which the cross-polarization conversion efficiency approaches the theoretical limit. The Pancharatnam-Berry phase is adopted to achieve the desired abrupt phase change for the transmitted cross-polarized wave, then an anomalous refraction metalens and a bi-functional metalens are proposed. The simulated results show that the anomalous refraction metalens can bend the transmitted cross-polarized wave with a specific angle predicted by the generalized laws of refraction, and the bi-functional metalens can diverge or converge the circularly polarized incident wave with a focal length of 10λ, determined by the helicity of the incident wave. Our designs provide a promising approach to planarize microwave components.