DESIGN OF SELF-BIASED HEXAFERRITE WAVE-GUIDE CIRCULATORS

Self-biased millimeter-wave circulators can be built using hexaferrite materials with high internal anisotropy field, thus avoiding the use of large and heavy permanent magnets. The design principles of these d evices are considered thoroughly in the article for both below- and ab ove-resonance circulators. The article treats the classical structure of a half-wave-long ferrite cylinder, two dielectric spacers, and two metal transformers. A simple microwave technique for the measurement o f the necessary parameters of the hexaferrite material is used. The ch oice of an adequate material with a proper value of the internal aniso tropy field is discussed. An accurate procedure for the dimensioning o f the ferrite insert and the spacers that eliminates the tedious cut-a nd-try work is described. A way to find the effective internal magneti c field is shown. Simple relations for the calculation of the matching elements are also given. Results on an above-resonance 33 GHz self-bi ased circulator that support the theory are presented.