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THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



polarization circulator actually has four output branches corresponding 

 to the two different polarizations at each end. The polarizations of the 

 four output branches are indicated in Fig. 13. It is noticed that power 

 sent into the polarization circulator with polarization a is turned into 

 polarization h, also h is turned into c, c is turned into d, and d is turned 

 into yninus a. This property is indicated very clearly by the circuit sym- 

 bol suggested in Fig. 13, the phase inversion between arms d and a being 

 indicated by the minus sign between the d and a arms. 



Another one-way transmission system can be created by combining 

 the gyrator with two-normal hybrids. This combination is indicated in 

 Fig. 14. Since this device has all of the fundamental properties of the 



CIRCULATOR 



Fig. 14 — Schematic diagram of circulator. 



CIRCUIT SYMBOL 

 FOR CIRCULATOR 



polarization circulator with the exception of the phase inversion be- 

 tween arms d and a it is suggested that it be called a "circulator" and 

 the circuit symbol suggested w^hich indicates its properties is also given 

 in Fig. 14. 



This list of applications is obviously not complete since it includes 

 only the fundamental elements from which innumerable specific applica- 

 tions can be made. 



In addition to the applications discussed above, which depend upon 

 the anti-reciprocal property of the element for their operation there 

 are several simple applications which are based only upon the fact that 

 the amount of rotation can be controlled externally by adjusting the 

 magnetic field. Among these uses are electrically controlled attenuators, 

 modulators, and microwave switches. 



ACKNOWLEDGMENTS 



The author is indebted to a rmmber of persons for aid in developing 

 this circuit element. In particular, he wishes to thank A. G. Fox for 



