1368 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



having a loss characteristic such as is shown in Fig. 5, Curve C, in which 

 the loss differential becomes great as soon as the material is saturated, 

 then the bandwidth would be as shown in Fig. 21. Of all the materials 

 which have been measured in the past two years only one sample has 

 shown this effect. At the time such behavior was regarded as the an- 

 tithesis of the ideal, and no further investigation was made. Now that 

 there is a use for such a material, effort is being directed toward maximiz- 

 ing the effect. Since the effect is thought quite definitely to be due to a 

 very high effective anisotropy field arising either from crystalline aniso- 

 tropy or demagnetizing effects, the problem of creating the proper ma- 

 terial should be quite straightforward. 



At this point we should consider the relative merits of the transverse 

 field non-reciprocal devices and those employing the Faraday rotation. 

 We have seen that it is possible to construct a simple isolator using the 

 non-reciprocal absorption in rectangular waveguide. Such an isolator 

 has a minimum forward loss of more than 0.5 db for 20 db reverse loss 

 where an isolator employing the Faraday Rotation can be made with 

 less than 0.1 db forward loss for 30 db return loss. On the other hand 

 the transverse field isolator is much simpler, more compact and easier to 



.FERRITE 



'DC 



-FERRITE 



LOSS 

 FORWARD RETURN 



LOSS 

 FORWARD RETURN 



10,000 

 6000 

 4000 



0.7 DB 

 0.8 DB 



22 DB 

 22 DB 



10,000 

 6000 

 4000 



0.1 DB 

 0.2 DB 



25-30 DB 

 25-30 DB 



ISOLATORS 



^FERRITE 



CIRCULATORS 



Fig. 22 — Comparison of two basic non-reciprocal elements of the Faraday 

 eflfect and transverse field effect types. 



