Behavior and applications of ferrites in the microwave region

The behavior and applications of ferrites in microwave circuits have been studied at the Holmdel Radio Laboratory with particular emphasis on non-reciprocal properties. There are numerous ways of building non-reciprocal devices which accomplish the same function, and the authors propose at the outset that a terminology based on function be adopted. Definitions of the gyrator, circulator and isolator are given. A qualitative method of deducing the properties of new ferrite-loaded circuits, termed “point-field” analysis, has been particularly fruitful, in that it permitted the exploration of a wide variety of ferrite-loaded circuits despite the absence of precise mathematical analyses. Faraday rotation in longitudinally-magnetized ferrite-loaded circuits has been studied; the effects of higher-order modes, the reasons for variation in Faraday rotation as a function of frequency, and the optimum geometry for the ferrite loading are discussed. In transversely-magnetized ferrite-loaded rectangular waveguide it is shown that the single mode medium may be non-reciprocal as to phase constant, attenuation constant, or distribution of field components in the cross-section. The latter effect is called the “field-displacement” effect. In transversely-magnetized ferrite-loaded round waveguide, either reciprocal or non-reciprocal birefringence may be achieved and examples are given. Some non-reciprocal ferrite-loaded dielectric waveguides are discussed. In all of these forms of non-reciprocal transmission media, gyrators, circulators and isolators may be built, and experimental data are reported on some of the possibilities. A brief review of prospective uses for these non-reciprocal elements is given.