Design of self-Biased, wideband microstrip circulators for integrated antenna systems

The integration of microwave components into a radar antenna system to achieve high performance, low cost, light weight and compact size is of considerable importance to commercial and military applications [1]. One such component, namely the circulator, is difficult to integrate into such systems due to the specialized materials required (i.e. ferrite) and the need of external biasing magnets, the latter of which is responsible for placing the ferrite in a satura-ed state. In an effort to remove these bulky external magnets, so called ldquoself-biasedrdquo ferrites are a topic of current research. In this work we present a design methodology in which self-biased ferrites can be used in microstrip circulators. This methodology relates the effect of coercivity to bounds on the ferrite geometry, which is not typically done in traditional designs. Using these bounds, we employ a multiple stage parameter search to produce a broadband microstrip circulator design with a 10.7% bandwidth, as validated by simulation.