Design of a Circularly Polarized Metasurface Antenna with Characteristic Mode Theory

A circularly polarized metasurface antenna based on characteristic mode theory is proposed in this paper. The characteristic modes of the metasurface structure were solved. And two mutually orthogonal characteristic modes to realize circular polarization was determined. By adding rectangular slots on the metasurface to change the orthogonality of the mode currents, the axial ratio performance of the metasurface antenna is improved. The antenna with an overall size of 35×35×4 mm³ (0.72λ×0.72λ×0.08λ at 6.2 GHz) is presented. The simulated S₁₁ bandwidth and 3dB axial ratio bandwidth are 30% (5.1 GHz - 6.9 GHz) and 17.3% (5.8 GHz - 6.9 GHz), respectively.