High-power transit-time oscillators: Onset of oscillation and saturation

A simple circuit model is used to investigate the transit-time oscillator (TTO) driven by a high-current diode. A novel condition for the onset of oscillation is derived in terms of the diode impedance. It is shown that a low impedance is required for the production of high-power microwaves in a TTO. The initial growth is calculated, and the saturation level is numerically computed using the one-dimensional model. These one-dimensional (1-D) results are in excellent agreement with a full scale two-dimensional Particle-in-Cell simulation. The success of the much simpler 1-D model allows a close examination of the roles played by the convection current and by the displacement current, as well as the modification in the transit time due to the intense space charge within the gap. (C) 1997 American Institute of Physics.