A BEVIEW OF NEW MAGNETIC PHENOMENA 



1169 



vary the characteristic impedance over a wide range, this effect has 

 possibilities of application in attenuators, modulators, and phase shifting 

 devices. 



XI. NEW MAGNETIC APPLICATIONS 



The engineer is naturally interested in some of the uses to which the 

 new magnetic phenomena may be put. Several applications will be 

 described briefly. 



1. The gyrator. This is a four pole element for which there is a 180° 

 phase difference between the two directions of propagation. In other 

 words, the transfer impedances in the two directions are equal in mag- 

 nitude but opposite in sign. Thus the device violates the reciprocity 

 theorem. 



Hogan built the first microwave gyrator using the arrangement shown 

 in Fig. 8. In this device, a wave traveling from left to right has its 

 polarization rotated 90° counter-clockwise in the twisted section and 

 another 90° in the same direction by the ferrite — a total rotation of 180°. 

 For a Avave traveling from right to left the two rotations, that in the 

 ferrite and that in the twisted section, cancel each other. Thus, if A and 

 B represent points of the same phase for a left-to-right wave, they 

 represent points of 180° phase difference for a right-to-left wave. 



2. One way transmission system. If the input and ouput waveguides 

 in Fig. 6 are oriented with their planes at 45° to each other and if the 

 solenoid current is adjusted for 45° rotation in the ferrite, the result is a 

 one-way transmission system.^^ Such a device is broadband. An arrange- 

 ment of this sort may be employed in a microwave system to isolate the 

 transmitter or receiver from the waveguide. It has the advantage that 

 loss in the forward direction can be made quite small by proper choice 

 of material. 



SOLENOIDAL 

 COIL 



Fig. 8 — Schematic diagram of a microwave gyrator. From left to right, the 

 plane of polarization is rotated 180°; corresponding to a phase shift of tt. From 

 right to left, the plane of polarization is not rotated and the phase shift is there- 

 fore zero. 



