Low-profile high-gain broadband circularly polarized slot antenna with RCS reduction using polarization conversion metasurface

A novel design of circularly polarized broadband slot antenna with high gain, low profile, and low radar cross-section (RCS) is proposed by employing polarization conversion metasurface (MS). By introducing sawtooth corner-truncated square MS with diagonal gaps, a compact circularly polarized antenna composed of 4 × 4 unit cells is presented. It is found that a smaller MS slot antenna can achieve an impedance bandwidth of 42.9% (3.7–5.72 GHz) and a 3-dB axial ratio (AR) bandwidth of 22.8% (4.55–5.72 GHz). Simultaneously, the MS can realize polarization conversion. The MS and its orthogonal units were arranged in a chessboard-type pattern and applied as the radiator of a larger MS slot antenna, which was fed by a sequentially rotated feeding network. In addition, owing to the anti-phase cancellation and scattering, the 5-dB average RCS reduction can be obtained within the frequency range from 3.8 to 6.9 GHz. For verification, the proposed larger circularly polarized antenna was fabricated and tested. The operating bandwidth was measured as 44% (3.78–5.91 GHz) with a 3-dB AR bandwidth of 39.6% and a high gain of 10.3 dBic. Furthermore, the larger antenna produces a useful RCS reduction from 3.7 to 6.7 GHz. The simulated and measured results are in good agreement.