168 BELL SYSTEM TECHNICAL JOURNAL 



operating life satisfactory? Could its efficiency and output power be sub- 

 stantially increased? Could one construct similar magnetrons at forty 

 centimeters, at three centimeters, even at one centimeter? Could the mag- 

 netron oscillator be tuned conveniently? One by one, during the war years, 

 all of these questions have been answered in the affirmative. In many in- 

 stances, but not without detours and delays, results have been better than 

 expected or hoped for. 



The British magnetron was first reproduced in America at the Bell 

 Telephone Laboratories for use in its radar developments and those at 

 the Radiation Laboratory of the National Defense Research Committee 

 which was then being formed at the Massachusetts Institute of Technology. 

 Since that time, extensive research and development work has been carried 

 on in our Laboratories, in other industrial laboratories, and in the laboratories 

 of the National Defense Research Committee. Several manufacturers have 

 produced the resultant designs. Magnetron research and development was 

 also carried on in Great Britain by governmental and industrial laboratories. 

 There has been continuous interchange of information among all these 

 laboratories through visits and written reports. Magnetron and radar de- 

 velopments have been greatly accelerated by this interchange. 



Multicavity magnetron oscillators are iiow available for use as pulsed and 

 continuous wave generators at wavelengths from approximately 0.5 to 50 

 centimeters. The upper limit of peak power is now about 100 kilowatts at 

 1 centimeter, 3 megawatts at 10 centimeters. Operating voltages may be 

 less than 1 kilovolt or more than 40 kilovolts. The magnetic fields essential 

 to operation range from 600 to 15,000 gauss. Tunable magnetrons now 

 exist for many parts of the centimeter wave region. The tuning range for 

 pulsed operation at high voltage is about ±5%. It is as much as ±20% 

 for low voltage magnetrons. Magnetrons may now be tuned electronically, 

 making frequency modulation possible. Present magnetron cathodes are 

 rugged and have long life. Even for high frequency magnetrons where cur- 

 rent density requkements are most severe, research has made available 

 rugged cathodes with adequate life. Magnetrons are built to withstand 

 shock and vibration without change in characteristics. Designs have been 

 compressed and in some cases the magnet has been incorporated in the 

 magnetron structure in the interest of light weight for airborne radar equip- 

 ments. 



PART I of this paper is a general discussion of present knowledge con- 

 cerning the magnetron oscillator. As such it is largely a discussion of what 

 has come to be common knowledge among those who have carried out 

 wartime developments. It brings together in one place results of work 

 done by all the magnetron research groups including that at our Labora- 

 tories. PART I supplies the background necessary to understanding the 



