878 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



2. Reverse loss 20 db 



3. Return loss 30 db 

 The field displacement isolator employs an ordinary rectangular | 



waveguide and requires no specialized adaptation to the rest of the 

 guide system. It is relatively compact and does not require excessive 

 magnetic fields. In contrast to the field displacement structure of Ref- 

 erence 3, in which a symmetrically disposed pair of ferrite slabs is used, 

 the present unit (see Fig. 1) contains only a single slab. Other differences 

 of a more substantial nature may be noted — in the present case the 

 slab is displaced from the guide wall, it occupies a partial height of the 

 waveguide, and it employs a novel disposition of the absorption material 

 on one face. These features result in a broadband device. 



In the analysis presented in this paper the isolator field characteristics 

 for a full height slab are determined by exact solution of Maxwell's 

 equations, as opposed to the "point-field" perturbation approximation 

 used in Reference 3. An exact solution of the partial height geometry of 

 the experimental device would be exceedingly difficult to obtain. How- 

 ever, such a solution did not appear to be essential for this investigation 

 since good correspondence has been obtained between the experimental 

 results and the idealized full height slab calculations. 



The following performance of the isolator was obtained from 5,925- 

 6,425 mc/sec: 



1. Forward loss --^ 0.2 db 



PERMANENT 

 MAGNET 



V/y/////y/^y>/// ////y///y///////////y'////y^A 



._FERRITE 



^ RESISTANCE 

 I ""COATING 



L- 



'////////////////////////////////////////y'yy//A 



h = 0.550 IN. 

 ^■ = 0. 180 IN. 

 b = 0.074 IN. 

 L= 1.590 IN. 

 3 = 0.795 IN. 



T 



I 

 I 

 I 

 I 

 I 



S 



I 



Fig. 1 — Field displacement isolator. 



