THE BELL SYSTEM 

 TECHNICAL JOURNAL 



VOLUME XXXI JANUARY 1952 NUMBER 1 



The Ferromagnetic Faraday Effect 

 at Microwave Frequencies 

 and its Applications 



The Microwave Gyrator 



BY C. L. HOGAN 



A new microwave circuit element dependent on the Faraday rotation of a 

 polarized wave has been developed. The element violates the reciprocity 

 theorem and, because it shares this property with a gyroscope and because 

 it is dependent on gyromagnetic resonance absorption, it has been termed 

 a microwave gyrator. It is a loiv-loss broadband device with many applica- 

 tions. Among these are one-way transmission systems, microwave circula- 

 tors, microwave switches, electrically controlled variable attenuators and 

 modulators. 



The microwave gyrator has been realized by making use of the Faraday 

 rotation in pieces of ferrite placed in the waveguide. Polder has previously 

 shown, in his analysis of the gyromagnetic resonance phenomenon, that 

 ferromagnetic substances should show appreciable Faraday rotations at 

 microwave frequencies. In the present study, Polder^s analysis has been 

 extended to include a wave being propagated through a ferromagnetic sub- 

 stance with dielectric and magnetic loss, and data are presented which give 

 experimental verification of the theory. In addition an experimental tech- 

 nique is described which may be of some interest in studying the properties 

 of fer rites at microwave frequencies. 



