I 



The Field Displacement Isolator 



By S. WEISBAUM and H. SEIDEL 



(Manuscript received February 7, 1956) 



A nonreciprocal ferrite device (field displacement isolator) has been con- 

 structed with reverse to forward loss ratios of about 150 in the region from 

 5,925 to 6,425 mc/sec. The forward loss is of the order of 0.2 dh while the 

 reverse loss is 30 dh. These results are obtained by using a single ferrite 

 element, spaced from the sidewall of the guide. The low forward loss suggests 

 the existence of an electric field nidi at the location of a resistance strip on 

 one face of the ferrite. We discuss the various conditions, derived theoretically, 

 under which the electric field null may be obtained and utilized. Further- 

 more, a method of scaling is demonstrated which permits ready design to 

 other frequencies. 



I. INTRODUCTION 



The need for passive nonreciprocal structures has long been recog- 

 nized.^ In the microwave field, Hogan's gyrator' paved the way for an 

 increasingly important class of such devices. The isolator, in particular, 

 has emerged as one of the more useful ferrite components. It performs 

 the function, as its name implies, of isolating the generator from spurious 

 mismatch effects of the load. Unlike lossy pads, which consume generator 

 power, the isolater provides a unidirectionally low loss transmission 

 path. 



A. G. Fox, S. E. IMiller and M. T. Weiss'' have pointed out that non- 

 reciprocal ferrite devices may exploit any of the following waveguide 

 effects : 



1. Faraday rotation 



2. Gyromagnetic resonance 



3. Field displacement 



4. Nonreciprocal phase shift 



In the present paper we shall discuss an isolator, based upon the field 

 displacement effect, which was developed to meet the following require- 

 ments for a proposed microwave relay system (5,925-6,425 mc/sec): 

 1 . Forward loss 0.2 db 



877 



