Broadband circularly polarized antenna by using polarization conversion metasurface

A compact and broadband circularly polarized antenna is proposed. A linear-to-circular polarization conversion metasurface is designed to broaden the 3-dB axial ratio bandwidth and the impedance bandwidth of the proposed antenna, with the mechanism of the metasurface investigated. Different with the conventional metasurface antenna designed by using uniform unit cells, this design makes use of two metasurface arrays with different unit cells. Full wave simulations show that the 10-dB impedance bandwidth of the proposed antenna is from 4.32 to 6.5 GHz (40.3%), and the 3-dB AR bandwidth is from 5 to 5.61 GHz (11.5%). Compared with that using the uniform elemental array, this design leads to more than 10% improvement in the 10-dB impedance bandwidth and more than 11.7% improvement in the axial ratio bandwidth. The proposed antenna has been fabricated and the simulated results have been verified with the measurements.