10-16] MICROWAVE FERRITE DEVICES AND THEIR APPLICATION 563 



B 



01- 02=90° 



Fig. 10-37 Schematic of a DiflFerential Phase-Shift Circulator. 



Electronically controlled quarter-wave and half-wave plates for circularly- 

 polarized applications can be made using ferrites in circular or square 

 waveguide. An electronically driven ferrite half-wave plate, in conjunction 

 with two conventional quarter-wave plates, can be employed as an elec- 

 tronically controlled continuous phase shifter or single-sideband generator^^ 

 for such applications as generating doppler frequencies. 



Isolators. The first nonreciprocal component to achieve almost 

 universal adoption in radar systems is the ferrite isolator. An isolator is a 

 unidirectional attenuator having low loss in the forward direction and high 

 loss in the reverse direction. Having gained a reputation as a panacea for 

 many magnetron ills, this very effective component commands considera- 

 tion in any new system design. 



The resonance absorption isolator ^^•'^^ one of the most important types 

 for high-power applications, is an ingenious device which exploits the 

 absorption differential between positive and negative circularly polarized 

 waves in a ferrite which is magnetically biased into the resonance region. 

 The cross-sectional geometry of such an isolator is essentially the same as 

 the differential phase shift section of Fig. 10-36a, but magnetic field 

 strength, generally provided by an external permanent magnet, must be 

 higher in the isolator. The ferrite is intimately bonded to the waveguide to 

 provide for dissipation of the heat generated in the ferrite by the RF power 

 absorbed. A typical commercial resonance absorption isolator is shown in 

 Fig. 10-38. There are many other ferrite devices, both low and high power, 

 which also can function as load isolators.^^ 



56J. Cacheris, "Microwave Single-sideband Modulator Using Ferrites," Proc. IRE 42, 

 UAl-llAl (1954). 



S'^See, for example, Alvin Clavin, "High-Power Ferrite Load Isolators," IRE Trans. MTT-3 

 No. 5, 38-43 (October 1955). 



