A Highly Selective Third-Order Filtering Cross-Polarization Converter Using Guided- Wave-Inspired Metasurface

This work proposes a polarization-independent third order filtering polarization converter with enhanced frequency selectivity (sharp roll-off) in the S-band. The design employs an L-shaped guided-wave structure on the bottom layer to efficiently convert linearly polarized incident waves into cross-polarized waves. The meandered metallic line and defected ground structure individually introduce one cross-polarized reflection zero at separate frequencies, collectively forming a third-order filtering response that enhances passband flatness while achieving sharp roll-off characteristics. An equivalent circuit model is established to analyze and validate the design mechanism. The proposed unit cell exhibits an insertion loss of 0.71 dB within the passband, out-of-band rejection exceeding 20 dB in both lower and upper transition bands, and the polarization conversion ratio (PCR) achieving 99.7% at 2.7 GHz. Simulated and measured results validate the superior frequency selective and polarization-conversion performance, indicating its potential for radar systems and satellite communications.