Ultrathin Metasurface for Controlling Electromagnetic Wave with Broad Bandwidth

In this paper, ultrathin metasurface based on phase discontinuities is proposed to manipulate electromagnetic waves in the microwave region. The gradual phase changes accumulated along the transmission path in the conventional lens are substituted with abrupt phase changes at the interface of the metasurface, which are realized by the Pancharatnam-Berry phase element. An ultrathin metasurface with a linear phase gradient is designed, fabricated, and measured. The phenomenon of anomalous refraction can be observed in a broad bandwidth, in which the cross-polarization conversion efficiency keeps approaching the theoretical limit. The measured result shows that the anomalous refraction angle can be well predicted by the generalized Snell's laws, and the efficiency keeps >20% in a broad bandwidth of 24%. Our design makes a remarkable progress in the cross-polarization conversion efficiency of the transmission-type metasurface, which is beneficial to put metasurface into practical application.