Integrated Self-Biased Circulators for C-Band and X-Band RF Applications

The circulator is an important RF component for phased array radar and telecommunication systems. It enables full-duplex communications — simultaneous transmission and reception of signals with a shared antenna. Defense-related applications have even stricter requirements for size, weight, and power density (SWaP). Therefore, a self-biased circulator is particularly attractive with its size to be potentially reduced by over 1000 times by removing bulky permanent magnets. This makes it possible to develop an approach to monolithically integrate a circulator within current GaN T/R MMIC modules. So far most self-biased circulators have been reported to operate in the range of Ku-V band relying on hexaferrite materials to provide nonreciprocity. Pushing these devices to operate at lower frequencies are highly desired by both military and commercial radar, satellite and wireless communication systems. Qorvo has developed a monolithic process flow for self-biased circulators which is compatible with our current GaN production MMIC process flow (3 metal interconnects, 3 capacitor types, capacitor over via). In this talk, for the first time, we present the results of both C-band and X-band self-biased circulators fabricated by Qorvo’s 4-mil GaN process. This effort illustrates a path to further miniaturize RF front-end modules at a higher integration level.