572 



ANTENNAS AND RF COMPONENTS 



The ideal linear duplexer is a matched, lossless three-port device in which 

 the first port couples only to the second and the second couples only to the 

 third. Such an "impossible" duplexing device recently came into being as 

 the microwave circulator. A perfect circulator is the ideal linear duplexer. 

 In practice, one must settle for something less than ideal duplexing perform- 

 ance. The practical microwave circulator is, however, the best known 

 solution to the linear duplexing problem and does not suffer the loss which 

 is characteristic of other linear duplexers. Four-port circulators providing 

 isolation in excess of 30 db, and one-way insertion losses of a fraction of a 

 decibel are a practical reality for moderate-powered systems (see Fig. 

 10-34). As previously mentioned, the isolation achieved between trans- 



3.0 



1.5 



1.05 5 



1.02 



1.002 



20 30 40 



'RETURN LOSS"OR ISOLATION (db) 



50 



60 



Fig. 10-44 Return Loss or Receiver Isolation 



Coefficient. 



Affected by Load Reflection 



