▎ 摘　　要

A graphene-based metamaterial transmitarray antenna is proposed to generate tunable orbital angular momentum (OAM) vortex waves in terahertz. Theoretical design of the transmitarray antenna has been developed by using the transmission line network model, and a multilayer graphene-based metamaterial element has been designed. By changing the chemical potentials of the graphene sheets, the 360 0 transmission phase range of the element is achieved in a broad band from 4.2 THz to 5.6 THz. By arranging the metamaterial element into a transmitarray, the OAM waves with tunable modes including l=0, +/- 1, +/- 2 and the mode purity greater than 0.96 are generated. Simulation results are given to demonstrate good performance of the proposed design, which provides a feasible way to the efficient generation and manipulation of the OAM vortex waves in terahertz. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement