Metasurfaces for Generating Focusing Vortex Beam

Abstract

In this paper, we have designed two multifunctional metasurfaces which generate focusing vortex beams of+1 and +2 mode orbital angular momentum (OAM), respectively. Two metasurfaces contain 24*24 unit cells that could achieve high efficiency chirality rotation in reflection direction from 3.9GHz to 10.6GHz and with a suspended structure. Based on the principle of geometric phase, we achieve accurately phase control in this band. Then, by superimposing the phase of the generated +1 and +2 mode OAM with the phase distributions for focusing, the desired phase distributions of metasurfaces is obtained. The simulation results are found in good agreement with theoretical analysis that our designs can generate +1 and +2 mode OAM vortex beams and realize nearfield focusing at 9GHz.