Measured and Simulated Impact of Irregular Radar Pulse Trains on the Pulse-to-Pulse Stability of Microwave Power Amplifiers

This paper investigates the impact of irregular pulsed RF signals on the pulse-to-pulse (P2P) stability of a microwave power GaN HEMT amplifier. This study is based on both the time-domain envelope measurements and nonlinear circuit envelope simulations of P2P stabilities. Measurements and simulations are performed with an irregular pulse train that integrates a long silence (i.e., off-time) between each periodic burst of RF pulses because of its influence on temperature and trap behaviors of GaN HEMTs. The first aim is to experimentally characterize the impact of silence durations and output mismatching on the amplitude and phase P2P stabilities of a 10-W S-band GaN HEMT amplifier. The second objective is to assess the ability of nonlinear HEMT models to fit the time-domain measurements of pulse-to-pulse stabilities. This final part of the paper is focused on the relative impact of electrothermal and drain-lag models on the nonlinear circuit envelope simulations of pulse-to-pulse stabilities. It is demonstrated that both the thermal and trapping effects have to be considered to fit the complex behavior of measured pulse-to-pulse stabilities for microwave GaN HEMT power amplifiers.