Research and Development of Wideband Ferrite Waveguide Circulators for Industrial Applications: Realistic Magnetic Field Integrated with Electromagnetic Modeling

Circulators are used to safeguard microwave sources in plasma processing systems and separate electromagnetic (EM) signals in radar and communication systems. Despite introductory materials on the fundamental principles of circulators being available in the literature, research and development (R&D) in some specific companies and research labs have been confidential, limiting public access to advanced technologies and know-how. This study examines nine configurations of WR340 waveguide circulators using the finite element method (FEM), assuming a saturated magnetization with a uniform magnetic bias as considered by other R&D groups in the literature survey for comparison and optimization purposes. A T-shape geometry employing circular metal stages and partial height cylindrical ferrite disks with a bandwidth of 190 MHz, insertion loss less than 0.21 dB, reflection, and isolation better than -20 dB was selected for industrial prototyping and optimized with ten types of ferrites. However, during prototype testing, the transmission was lower than expected, and the loss was high. To overcome these issues a methodology involving a magnetic circuit design using a magnetostatic solver coupled with an EM solver was done. The simulations revealed that the magnetic field inside the ferrite disks was non-uniform, and two strategies were proposed to mitigate non-saturated magnetization. The proposed methodology can achieve a bandwidth of over 100 MHz, isolation better than -20 dB, and transmission up to 95%. The study highlights the importance of considering a realistic magnetic field and magnetization inside the ferrite disks and its relevance to advancing the research and development of ferrite circulators.