Crossover With Wideband Operation and High Isolation Using Anisotropy and Polarization-Sensitive Image Guides

This article presents a novel dielectric image guide crossover that exploits the engineered uniaxial anisotropic properties of subwavelength dielectric gratings for millimeter-wave (mmWave) and sub-terahertz (sub-THz) applications. The proposed structure exploits polarization differences in the dominant mode of orthogonal channels, utilizing anisotropic features to achieve a compact, high-isolation, and wideband crossover. Optimized parameters demonstrate competitive performances, including an ultrawide 30 dB isolation bandwidth from 22 to over 50 GHz, low insertion loss (~0.5 dB), and minimal group delay variations (~0.04 ns), and to the best of the authors’ knowledge, this is the first implementation of such an mmWave crossover. The design is highly versatile, adaptable to various frequency ranges and waveguide technologies, and compatible with CMOS fabrication, making it well-suited for next-generation radio frequency (RF) systems such as 6G. A fabricated prototype validates the analytical studies conducted via the finite-difference frequency-domain (FDFD) method and full-wave simulations. The combination of high isolation, low loss, compact size, minimal group delay variation, and wideband operation makes this crossover a promising solution for mmWave and sub-THz crossover circuit systems and other high-density transmission line (TL) scenarios.