THE RADAR RECEIVER 



719 



The dielectric supporting rings shown form an RF by-pass element minimiz- 

 ing the loss of input signal power in the IV output network. In this design 

 the beating oscillator energy is introduced into the waveguide by mounting 

 the reflex oscillator tubes adjacent to the waveguide in such a fashion that 

 the output probe is inserted into the waveguide cavity at a point removed by 

 an odd one-quarter of a wavelength from the face of the TR output iris. 

 This assures reflection of the local oscillator energy which travels toward 

 the TR tube directing it toward the crystal element. The degree of coupling 

 of the reflex oscillator circuit is varied by adjustment of the distance that 

 the probe is inserted within the waveguide. For airborne applications an 

 additional oscillator tube is included for beacon reception. This basic form 



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Fig. 14. — 10,000-mc Crystal Converter. Schematic diagram. 



of radar converter was employed in large numbers in the military airborne 

 radar field during World War II. 



A third type of crystal converter design which was developed in the latter 

 period of the war is illustrated in Fig. 15. A basic difiference in this struc- 

 ture is found in the use of a waveguide hybrid junction often referred to as a 

 "magic tee." This junction has an electrical performance characteristic 

 at microwaves similar to that of the hybrid coil common to low frequency 

 communication circuits, i.e., a 4-pair terminal network with an internal 

 configuration such that power applied to any one pair of terminals will appear 

 equally at two other pairs of terminals, but will not be available at the re- 

 maining pair of terminals. Referring to Fig. 15, it should be noted that 

 power applied to the input waveguide will appear equally in the output 

 branches but is balanced out of the beat oscillator branch. In a similar 

 fashion, the beat oscillator power will appear equally in the two output 



