Behavior and Applications of Ferrites in the Microwave Region

16 16 17 20 20 21 22 26 30 31 32 33 33 34 36 37 40 42 49 53 55 59 61 65 65 71 72 73 75 76 78 86 88 90 93 93 94 96 98 Iii the history of the communication art there has never been available any passive circuit element or waveguide medium which was not reciprocal. After Polder, 1 Beljers, 2 and Roberts 3 demonstrated the gyromagnetic nature of ferrites at microwave frequencies, passive non-reciprocal devices for the first time became possible. Such non-reciprocal devices have great immediate and potential value in the microwave art. Additionally, ferrites have reciprocal properties which are under the control BEHAVIOR AND APPLICATIONS OF F E R R I T F . K 3 of an applied magnetic field and which lead to new forms of modulators, variable attenuators, and variable reciprocal phase-changers in the microwave range. Since C. L. Hogan*, 4 demonstrated the practical importance of ferrites to the microwave art by making use of microwave Faraday rotation to build a gyrator, the authors have studied, at the Holmdel Kadio Laboratory, the behavior and applications of ferrites with emphasis on their non-reciprocal properties. It soon became apparent that ferrites can manifest non-reciprocal properties in a variety of ways other than by Faraday rotation. Thus, they may produce non-reciprocal birefringence, nonreciprocal phase shift, non-reciprocal field displacement, non-reciprocal coupling through apertures, as well as non-reciprocal rotation of polarization. Any one of these non-reciprocal properties can be used, together with conventional reciprocal circuit elements, to obtain all of the nonreciprocal circuit functions which have so far been devised.