Experimental Investigation of a Self-Biased Microstrip Circulator

An experimental investigation of an above-ferromagnetic resonant self-biased hexagonal ferrite circulator is detailed in this paper. The concept of the region of opportunity is invoked to establish a relationship between the ferrite's geometry and its MH large-signal data for self-biased operation. This concept is used to design a working three-port nonreciprocal device that will serve as a basis for experimentally ascertaining best case insertion losses (ILs), return losses (RLs), and/or isolations (ISs) for circulator applications. Furthermore, we show that this nonreciprocal device when externally tuned as a circulator exhibits RLs and ISs of better than 15 dB across a narrow band; the ILs are on the order of 1.5 dB within this same band. This IL is correlated to the best case IL. Results confirm the conclusion that a ferrite with H(c) = 4.0 kOe, 4 pi M(s) = 4.375 kG, and Delta H = 1.862 kOe is suitable for self-biased circulator applications.