High-Transmission Quasi-Optical Faraday Rotators Based on Multilayer Matching

Due to the inherent nonreciprocity of magnetic materials, Faraday rotators constructed based on these materials are the optimal passive isolation solution for compact range systems. In this letter, we propose a theoretical method of multisection matching transformation to analyze the reflection characteristics of anisotropic magnetic ferrite coated with multilayer isotropic dielectric layers. Utilizing this approach, a bilayer-matching transmission-type broadband quasi-optical Faraday rotator (QOFR) is designed to achieve reflection coefficient below 20$\text{ dB}$ in the 86 GHz to 141 GHz range. Compared to quarter-wave matching designs, it improves the operational bandwidth by 30% and stabilizes the ferrite rotation angle at 45° ± 0.7°. A transceiver isolation system for the compact range is constructed based on this QOFR. Its performance is measured on a quasi-optical platform. Additional theoretical analysis aims to identify factors that influence measured performance, especially the impact of gaps in multilayer dielectric materials. The CST and HFSS simulation results align with measurements and verify the accuracy of the proposed theoretical approach and design.