22 THE BELL SYSTEM TECHXICAL JOURXAL, JAXUARY 1952 



Hence the transmitted wave at this point is almost completely circularly- 

 polarized, even though the appHed magnetic field would indicate that 

 the resonance absorption f requeue}^ was far removed from 9000 mc. 

 Table I gives the data taken on several ferrites at 9000 mc. 



APPLICATIONS OF THE FERROMAGNETIC FARADAY EFFECT THE MICRO- 

 WAVE GYRATOR 



As pointed out in the introduction, the Faraday rotation affords an 

 anti-reciprocal phenomenon from which a microwave gyrator can be 

 constructed. Such a gyrator is illustrated in Fig. 11 along with diagrams 

 which help explain its action. Beneath the gyrator are construction lines 

 which indicate the plane of polarization of a wave as it travels through 

 the gyrator in either direction. On each diagram is a dotted sine wave 

 which is for reference purpose only and indicates the constant plane of 

 polarization of an unrotated wave. It is noticed that for propagation 

 from left to right in Fig. 11, the screw rotation introduced by the twisted 

 rectangular guide adds to the 90° rotation given to the wave by the 

 ferrite element making a total rotation of 180°. For a wave travelling 

 in the reverse direction, these two rotations cancel each other, producing 

 a net zero rotation through the complete element. The unique property 

 of the Faraday rotation becomes immediately apparent from this dia- 

 gram. In the case of the rotation induced by the twisted rectangular 

 guide, the wave rotates in one direction in going from left to right through 

 the twisted section, and rotates in the opposite direction when it trans- 

 verses the section from right to left. For the case of the rotation induced 

 by the ferrite element, the direction of rotation is indicated by the 

 arrow in the upper figure for either direction of propagation. The im- 

 portant characteristic of the element is the time phase relation between 

 two points such as A and B in the upper diagram. It is seen with the help 

 of the diagrams illustrating the rotating waves that the field variations 

 are in phase at points .4 and B for propagation from left to right, and 

 they are 180° out of phase for propagation from right to left. In other 

 words the transmission line is an integral number of wavelengths long 

 between A and B for propagation from left to right and is an odd integral 

 number of half wavelengths long for propagation from right to left. 



From the above description of the properties of the gyrator, many 

 of its applications in microwave technology become immediately ap- 

 parent. Before discussing these applications in more detail, however, 

 it is advantageous to introduce standardized terminology and circuit 

 symbols which apply to the gyrator and to other circuit elements 

 derivable from it. 



