RF current and voltage waveform during start-up of pulsed TRAPATT oscillators

Efficient TRAPATT oscillators have been demonstrated with p⁺-p-n-n⁺mesa diodes. The starting transients have been studied in a simple circuit with only a single discontinuity in a 50-ohm line. A rapidly rising bias pulse has been used to start the oscillations and current and voltage waveforms have been measured with a time resolution of about 50 picoseconds. The results show that in a low-Q circuit steady oscillation is established in less than one cycle and no initial IMPATT oscillation is required. With this circuit less than optimum efficiency is obtained. With higher-Q circuits several periods are required to establish equilibrium, but higher efficiencies are obtained. Even in this case no IMPATT oscillation is seen. These results are obtained at a frequency that can be mechanically tuned from about 0.4-2 GHz.