The Behaviour of Multiple Circuit Magnetrons in the Neighbourhood of the Critical Anode Voltage

Abstract

It is pointed out that the mechanism of operation of the multiple circuit magnetron oscillator in the region of minimum magnetic field and voltage, where the efficiency is commonly assumed to approach zero, should approach that of an oscillator of the travelling wave tube type, providing that a cathode of suitable size is used. Useful efficiencies should thus be obtainable under these conditions. Details of experiments are given in which an electronic efficiency of 12% was obtained at a wavelength of 3 cm. at values of magnetic field and voltage several times lower than those used for high efficiency operation. The mode of operation was determined by the value of the magnetic field, a given mode being maintained over a range of magnetic field of the order of 8% The anode voltage was about 70% of the critical value. The experimental results generally support the hypothesis and suggest that the minimum voltage regime should be of extreme importance for work at the highest radio frequencies.