Ferrites in Microwave Applications 



By J. H. ROWEN 



(Manuscript received May 26, 1953) 



Since Hogan's* exposition of the extreme usefulness of the microwave 

 Faraday effect numerous other laboratories have begun investigating propa- 

 gation through ferrites and have made significant contributions to the art. 

 In view of the tremendous interest which is being accorded this work this 

 paper has been prepared to summarize some of the observations and develop- 

 ments to date. The plane wave theory is reviewed briefly with special atten- 

 tion being given to the mechanisms by which power is absorbed by the ferrite. 

 The plane wave theory is then modified to describe various waveguide effects. 

 Finally experimental procedures and results are presented to illustrate the 

 theory and to provide general information regarding the design of devices 

 employing these effects. 



INTRODUCTION 



The ferromagnetic Faraday effect occurs at microwave frequencies 

 as a direct result of the dispersion in permeabiUty which is associated 

 with ferromagnetic resonance. The resonance can be explained most 

 simply by stating that the total magnetization vector of a magnetized 

 ferromagnetic material has associated with it an angular momentum 

 arising from the angular momenta of all of the spinning electrons con- 

 tributing to the magnetization. Because of this angular momentum 

 (which is directed along the same axis as is the magnetic moment but in 

 the opposite direction) the magnetization vector behaves as a top or 

 gyroscope. If it is displaced from its equilibrium position in a steady 

 magnetic field it will not rotate directly into alignment with the field 

 but will precess about the dc field direction at a frequency determined 

 by the strength of the dc field. In the absence of damping this preces- 

 sion would continue indefinitely, but damping losses are such that the 

 precession will damp out in approximately 10~* sec. 



* C. L. Hogan, The Ferromagnetic Faraday Effect at Microwave Frequencies 

 and Its Applications — The Microwave Gyrator, B.ST.J., 31, pp. 1-31, Jan., 

 1952. 



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