Relativistic backward-wave oscillators: Theory and experiment

Microwave sources based on backward-wave oscillators driven by relativistic electron beams are capable of producing high-power coherent radiation in cm and mm wavelength regime. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical models which can be compared in detail with the experimental data. This work is devoted to fill this need and applied to the University of Maryland backward-wave oscillator experiment. It is shown that the theoretical predictions for the threshold current to start the oscillations, the frequency characteristics, and the efficiency of the device compared favorably with the experimental data.