Generating Vortex Beam with Tunable Divergence Radiation by High-efficient Broadband Metasurface

Vortex beam carrying orbital angular momentum (OAM) can significantly promote the transmission capacity since the unlimited orthogonal eigenstates of OAM increase the channels of wireless communications. However, the nature of divergence characteristics makes it difficult for receiving and demodulating with the increase of topological charge and propagation distance. The traditional methods for generating vortex beam include spiral phase plate, ring array antenna, computer-generated holograms, all of which suffer from large volume and complicated fabrication. Metasurface exhibits excellent electromagnetic control ability and has the advantages of small size and high integration. In this paper, a high-efficiency broadband metasurface vortex beam generator is proposed with three-layer complementary square ring resonator (CSRR) arrays. By judicious design the phase distribution of the metasurface, vortex beam with different topological charges $(l = \pm 1, \pm 2, \pm 3)$ can be concentrated in the same region at microwave frequencies. By engineering the expanding phase distribution with different topological charges, the proposed method has potential to address the challenges of practical applications with vortex beam.