Low-RCS High-Gain Broadband Substrate-Integrated Waveguide Antenna Based on Elliptical Polarisation Conversion Metasurface

An elliptical polarisation conversion metasurface (PCM) is proposed for Ka-band applications, integrated with a high-gain substrate-integrated waveguide (SIW) antenna to achieve significant radar cross section (RCS) reduction. The PCM elements, arranged in a chessboard configuration, feature a simple yet efficient design with an elliptical pattern symmetric along the diagonal, enabling effective conversion of linearly polarised waves. The antenna employs a broadband dipole excited through SIW slot coupling. Simulation results demonstrate that the PCM unit achieves a polarisation conversion bandwidth of 80.38% (25.3–59.3 GHz) with a polarisation conversion ratio (PCR) exceeding 90%. When integrated with the dipole antenna, the design exhibits a −10 dB impedance bandwidth of 15.08% (33.7–39.2 GHz) and a maximum realised gain of 9.12 dBi, representing a 1.7 dB gain enhancement at 36 GHz. Moreover, the 16 × 16 PCM array configuration achieves an RCS reduction bandwidth of 77.98% (25.85–58.92 GHz), with RCS reduction values exceeding 9 dB across this bandwidth and an average reduction of 12 dB. The proposed antenna has been fabricated and tested, with measured results showing excellent agreement with simulations in terms of $S_{11}$ and gain performance.