Ferrite-Based Multiport Circulators With RF Co-Designed Bandpass Filtering Capabilities

This article reports on the RF design and practical development of multiport circulators with RF co-designed bandpass filtering functionality. The proposed bandpass filter/circulator (BPFC) concept is based on a hybrid implementation approach, where dual-mode non-reciprocal ferrite-based resonators (FBRs) are cascaded with microwave resonators and mixed-electromagnetic (EM) couplings. In this manner, highly selective bandpass filtering transfer functions are created in the direction of propagation, and high RF signal cancellation is obtained in the reverse direction. A design methodology using coupled-resonator-based synthesis is proposed to facilitate the design of these components using well-known filter design techniques. Various electromagnetically simulated and synthesized examples are presented to demonstrate the operating principles of the BPFC approach alongside its applicability to high-order filtering responses. The BPFC concept is further expanded to the realization of multiport non-reciprocal components. For proof-of-concept demonstration, four multiport prototypes were designed, manufactured, and measured at S -band.