Ultra-Wideband Millimeter-Wave Vortex Beam Generation Based on Reflective Pancharatnam-Berry Phase Metasurface

Due to the gradual scarcity of spectrum resources, orbital angular momentum (OAM) technology has been proposed and developed continuously to broaden channel capacity. To solve this problem, some ultra-wideband reflective phase metasurface antennas working in millimeter band are designed to generate high purity vortex waves which carry OAM. Based on the Pancharatnam-Berry (PB) phase concept, the unit cell is composed of a metasurface, dielectric, metal grounding layer. Through the optimization design of the unit structure parameters, the reflected wave efficiency can be as high as 95% when covering 2π rotating phase, which realizes the basic requirements of PB phase concept and the relative bandwidth of 116%. Then the metasurface arrays are arranged according to vortex wave generation formula and phase compensation principle. In the 25 GHz to 35 GHz frequency wide band, integer (l = ±1, ±2, ±3) decimal (l = ±1.5) and high-mode (l = ±8) OAM vortex beams are generated, respectively. The OAM purity analysis shows that the antennas can generate millimeter wave OAM beams with high purity in a wide band range, and with a maximum gain of up to 23.6 dBi.