MAGNETRON AS GENERATOR OF CENTIMETER WAVES 303 



corporated in the high power designs with immediate improvement in 

 performance. The output circuits used were simple loop to coaxial lead 

 combinations like those in use on the 706A-C. 



Radar needs for higher power near 10 cm. had developed to the point of 

 a specific requirement for a magnetron of not less than 350 kw. output. 

 Since it was believed that the best one could obtain from the 718AY-EY was 

 250 kw. even at the risk of shortened cathode life, the requirement made 

 necessary a new design. In the work on higher power magnetrons, better 

 than 300 kw. had been obtained at efficiencies greater than 50 per cent at 

 maximum loading with what was essentially a double length 718AY-EY 



Fig. 62 — An external view of a 720A-E magnetron (1000 kw., ^^2800 mc/s). 



type. Thus it appeared that the new power requirement could be met with 

 such a design. The press of time made it necessary to concentrate further 

 efforts on improving this design, with not much if any time to be devoted 

 to further experimentation along other lines. The chief drawback of the 

 double length magnetron was the large magnet it required. Several months 

 later an equally efficient magnetron, shorter, and having a larger number of 

 circuit elements might have been produced, but the original program had 

 advanced beyond the stage at which it could be changed. The improve- 

 ments in design of the double length 718AY-EY type magnetron resulted 

 in the 720A-E series. 



An external view of the 720 A-E magnetron is shown in Fig. 62. A cut- 

 away model is shown in Fig. 63 in which may be seen the nature of the 



