Theory of phenomenological models and measurements of the fluctuating output of CW magnetrons

A macroscopic theory yielding the significant parameters which describe the coherent and incoherent output of a CW magnetron(e.g., modulation and "pushing" factors, bandwidths, carrier and noise levels, modulation indices, etc.) is outlined. Also described is the theory on which measurement of these descriptive parameters depends, as it is closely related to the interpretation of the data from which the defining parameters of the phenomenological model are obtained. It is shown that the most satisfactory general model of CW operation is that of a carrier or primary oscillation simultaneously amplitude-and angle-modulated by a band of shot or "primary" noise and accompanied by a background noise essentially incoherent with the modulated carrier. The chief effect is produced by the mechanism of angle-modulation, which even for relatively noisy tubes occurs with a very low modulation index; the amplitude-modulation, while normally weak, can not be neglected and must be included in the analysis. A technique of direct measurement, employing a wave-guide filter and crystal detector for input waves of the above type, is briefly described, and it is shown how the descriptive parameters of the magnetron model may be observed experimentally. Particular attention is paid to the approximations and assumptions involved, and the theory is illustrated with a number of representative data from a standard magnetron; applications of this general approach to other microwave sources are briefly considered.