Ultra-wideband anomalous reflection realised by a gradient metasurface

In this work, an ultra-wideband gradient metasurface (GM) is designed by using Pancharatnam–Berry (PB) phase. In the design process, a circular polarisation (CP)-maintaining metasurface (CMM) is proposed at first, which can realise ultra-wideband CP-maintaining reflection in the frequency band of 7.7–19.9 GHz, moreover, PB phase will be generated in its co-polarised reflection coefficient under CP incidence by rotating the anisotropic resonators in its unit cells. Thus, based on the CMM, an ultra-wideband GM is designed by using PB phase. Both the simulation and experiment show that the designed GM can realise ultra-wideband anomalous reflection under arbitrary polarised incidence, the reflected wave under CP incidence will be deflected to an anomalous direction and even be converted to a surface wave; but under linearly polarised and elliptically polarised incidences, the reflected wave will be separated into two beams. In addition, to design more anomalous reflection metasurfaces, the generation principle of PB phase, together with the root cause of the CP-maintaining reflection of the proposed CMM, has been analysed in detail in the designing process.