Optimum loading for relaxation l.s.a. diode

In the relaxation l.s.a. mode, the r.f. waveform across the loaded diode reaches very high voltages and then approaches, in part, the first cycle of a damped oscillation. The degree of damping depends on the loading of the circuit. It is shown theoretically that, for typical drive voltages, if the load is greater than G0/120 where G0 is the low-field device conductance, the voltage will not ultimately fall below threshold, accumulated space charge will not be dispersed and the diode will suffer avalanche breakdown owing to domain formation. Conversely, the loading must approach G0/120 to obtain maximum efficiency. These effects have been demonstrated in a pseudolumped circuit, using vapour-epitaxial metal-contacted devices. 400 W of peak power with 13.6% efficiency at 6.1 GHz has been obtained.