The Magnetron as a Generator of Centimeter Waves

Late in the summer of 1940, a fire control radar operating at 700 megacycles per second was in an advanced state of development at the Bell Telephone Laboratories. The pulse power of this radar was generated by a pair of triodes operating near their upper limit of frequency. Even when driven to the point where tube life was short, the generator produced peak power in each pulse of only two kilowatts, a quantity usable but marginal. Although the triodes employed had not been designed for high voltage pulsed operation, they were the best available. This is an example of how development of radar in the centimeter wave region was circumscribed by the lack of a generator of adequate power and reasonable life expectancy. Moreover, the prospects of improvement of the triode as a power generator at these wavelengths and extension of its use to shorter wavelengths were not bright. Solution of the problem by means of power amplification was remote. A new source of centimeter wave power was urgently needed.