Ultra-wideband unidirectional pseudospin-polarized waveguide with dual boundary conditions.

This study presents a novel pseudospin-polarized waveguide with closed boundaries, designed using complementary metasurfaces with dual surface impedances. By enforcing electromagnetic duality, the proposed structure establishes mirror reflection symmetry, significantly reducing backscattering and ensuring robust one-way wave propagation. The waveguide effectively suppresses backward-propagating modes, even in the presence of bends and structural discontinuities, making it a highly stable and efficient platform for guided-wave applications. With an ultra-wide operating bandwidth spanning 7-350 GHz, the waveguide exhibits exceptional isolation levels exceeding - 0.5 dB, ensuring minimal signal loss. To achieve precise performance predictions, we employ a rigorous variational method to calculate the surface impedance of the metasurfaces, enhancing the accuracy of analytical and numerical results. Leveraging these unique propagation characteristics, we design a high-performance ultra-wideband filter based on complementary split-ring resonators. It offers strong stopband attenuation with minimal insertion loss. This makes the proposed filter an excellent candidate for next-generation microwave and millimeter-wave systems, including wireless communications, radar, and high-frequency signal processing. By integrating pseudospin physics with electromagnetic duality, this work establishes a new paradigm in waveguide design, demonstrating how complementary metasurfaces can enable low-loss, broadband, and highly efficient unidirectional wave propagation for advanced electromagnetic applications.