High Gain and High Isolation SIW-Based Dual-Circularly Polarized Metasurface Antenna Using CMA-Based Mode Control for MMW Applications

A SIW-based dual-circularly polarized (CP) metasurface antenna with high gain and high isolation is proposed in this paper for millimeter-wave (MMW) applications. The orthogonal higher-order modes (HOMs) TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">230</sub>/TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">320</sub> are utilized to generate CP. A dual CP cavity-backed antenna with curved slots serves as the primary radiator, whereas a 4 × 4 square patch metasurface is employed as a superstrate. The characteristic mode analysis (CMA) of the antenna is utilized to identify and align the HOMs with a 90° phase difference to enable dual CP radiation. CMA is also applied to the metasurface to synthesize modal phase differences of the primary antenna’s modes, enabling broadband phase compensation. The metasurface height is optimized to induce a 180° phase-shifted reflection, canceling undesired coupled fields and enhancing port isolation. Additionally, the symmetric electric field distribution across the metasurface improves broadside gain and suppresses cross-polarization. The fabricated antenna achieves a peak gain of 13.0 dBic, isolation >38 dB at 30.2 GHz, and broadside cross-polarization not exceeding –30 dB with a maximum cross-polarization of less than –18 dB. These results confirm the antenna’s potential for advanced MMW applications requiring efficient, dual-CP performance.