570 



ANTENNAS AND RF COMPONENTS 



echo signals follow the paths shown in Fig. 10-41 b. The dummy load on 

 the fourth arm of the duplexer serves only to absorb a small amount of 

 leakage power during transmission. 



The novel crossed guide duplexer pictured in Fig. 10-42 has a number of 

 features which make it attractive for certain airborne radar applications. 



Fig. 10-42 Cross-Guide Duplexer. (Courtesy of Bomac Laboratories, Inc.) 



A complete duplexer in itself, the device requires no ATR tube and does not 

 present a large mismatch to the magnetron before it ionizes. Compact, 

 lightweight, and convenient to apply, the device functions as a unity- 

 coupled directional coupler on reception; but on transmission, ionization 

 takes place in the region of the clover-leaf coupling iris and provides the 

 necessary receiver isolation. Its application is limited, largely because of 

 its restricted bandwidth. 



The gas tube duplexer, although universally used in pulse radar systems, 

 is by no means the only form of duplexing. FM and CW systems, as 

 described in Chapter 6, in fact require some linear form of duplexing to 

 permit simultaneous reception on a continuous basis. There are a number 

 of linear methods for isolating the receiver from the transmitter in a radar 

 system. The most direct solution of course is to employ separate trans- 

 mitting and receiving antennas and achieve isolation by physical separa- 



