▎ 摘　　要

In this paper, we propose a tunable broadband terahertz (THz) linear polarization conversion switch (LPCS) and linear-to circular polarization (LTCP) metamaterial. By tuning the Fermi energy level of graphene from EF = 0 eV to EF = 1 eV at 2.70-5.62 THz, it is possible to adjust the proposed structure from the linear polarization conversion (LPC) ON state to the LPC OFF state and also to tune the polarization conversion rate (PCR) from 1% to 99.99%. When E-F = 0.5 eV and is in the range of 5.56-5.96 THz, the structure can achieve LTCP function with ellipticity ( q ) exceeding 0.97 and an axial ratio (AR) of less than 1.5 dB. Based on the surface current and U-V decomposition, the LPC ON state, LPC OFF state and LTCP function are analyzed and well corroborated. Investigating graphene surface impedance at different fermi energy levels proves the polarization state tunable. The proposed structure can be applied to various fields of wireless communication, sensing and imaging.