Annular Ferrite Circulator in Stripline Technology

A new type of ferrite circulator, with annular nucleus, in stripline technology, and operating under the saturating level of magnetization has been developed by means of a suitable model that makes use of Green´s functions for generalized planar structures and ensures continuity of the boundary conditions at the interface ferrite-dielectric, even for the circularly symmetric resonant mode. The annular geometry of the nucleus makes feasible the miniaturization of the biasing magnetic circuit and the losses are reduced as there are no metallic conductors near the axis of the structure, where the tangential components of the magnetic field are intense. A prototype was built and measurements showed insertion loss of 0.25 dB and isolation loss better than 20 dB over a bandwidth of 16% around the frequency of circulation of 2.544 GHz. Its performance compares favourably with circulators of other geometries of nucleus, reported in the literature.