The relationship of frequency of operation to large-signal noise degradation in IMPATT diodes

A singly tuned X-band IMPATT amplifier is simulated on a hybrid computer and results are given for the amount of conduction current modulation present in the device as a function of the period, T, with the ac voltage across the diode held fixed, Using Sjolund's large-signal noise theory which relates the conduction current modulation to the noise measure, M, curves are presented showing a logarithmic relation between M and the period, T, with M increasing for larger T. An approximate theory is given to explain this behavior. These noise measure results are compared to the IMPATT power-output data to give a qualitative understanding of the rate of noise degradation with power output in relation to frequency of operation. It is shown that, for minimum noise degradation, the IMPATT should be operated at or above the frequency corresponding to maximum power output for a given ac voltage across the diode. This information can be used to establish a criterion for minimum noise degradation during intermediate and large signal operation.