10-16] MICROWAVE FERRITE DEVICES AND THEIR APPLICATION 



559 



control of polarization, is utilized in a number of different types of ferrite 

 devices. 



The Microwave Gyrator. One of the most fundamentally important 

 nonreciprocal ferrite elements is the microwave gyrator. ^"^ The gyrator is a 

 two-port circuit element, ideally 

 lossless, having an electrical length 

 which is greater by 180° in one di- 

 rection of transmission through it 

 than in the other. It can be repre- 

 sented schematically as in Fig. 10- 

 31. A 90° Faraday rotator has the 

 nonreciprocal property required of a 



gyrator, while another form of gyrator is based on a direct differential 

 phase shift of 180° obtainable in a rectangular waveguide ferrite component. 

 Several other microwave gyrator elements are known. 



The Circulator. One of the most important and valuable applications 

 of the gyrator is in a nonreciprocal network called a circulator. This 

 multiport network is characterized by nonreciprocal coupling properties 

 such that a signal entering one port is coupled out a second port, a signal 

 entering the second port is coupled out a succeeding port, etc., while a 

 signal entering the last or «-th port couples to the first port. This coupling 

 property is illustrated schematically in Fig. 10-32. Ideally there is no 



Fig. 10-31 Schematic Representation 

 ot the Gyrator. 



5 6 5 6 



(a) (b) 



Fig. 10-32 Symbolized Coupling Properties of a Six-Port Circulator. 



coupling between other ports of the circulator, but in practice coupling 

 between the several ports is finite though often exceedingly small. A 

 practical circulator has three or more ports; but the number is not limited, 

 and two or more circulators can be cascaded to increase the number of 

 ports available. 



51C. L. Hogan, "The Microwave Gyrator," Bell System Tech. J. 31, 1-31 (1952) 



