Nonlinear operating characteristics of IMPATT diodes

The nonlinear equations which describe the current and field in a Read-type IMPATT have been solved in closed form by assuming that the transit time of the carriers through the drift region is small compared with the period of the microwave oscillation. Using this solution the large-signal impedance of the diode is obtained. Impedance-plane plots for large-signal operation are presented. For small r-f voltages the results reduce to those obtained by Gilden and Hines. Larger voltages result in a decrease in the negative resistance of the diode and this leads to stable oscillator operation. A region of unstable operation similar to that found by Read is also predicted. The large-signal analysis predicts, a marked change in the current tuning of IMPATT diodes as compared to the small-signal case. Experiments have been performed on an IMPATT diode in a reentrant coaxial cavity. The experimental results on frequency tuning, impedance and other operating characteristics of the oscillator are in good agreement with the theoritical predictions. The experimental and theoretical results will be presented and compared.