An active pulsed RF and pulsed DC load-pull system for the characterization of HBT power amplifiers used in coherent radar and communication systems

This paper presents a new automated and vector error-corrected active load- pull system allowing the characterization of microwave power transistors un der coherent pulsed RF and pulsed de operating conditions. In this paper, t he use of this system is focused on the characterization of a 240-mum(2) Ga InP/GaAs heterojunction bipolar transistor (HBT) (Thomson CSF-LCR, Orsay, F rance). On one hand, source and load-pull measurements of such a transistor are reported for different pulsewidths, On the other hand, nonlinear simul ations based on an electrothermal model of an HBT have been performed and a re compared with experiments. Power variations and RF carrier phase shift w ithin the pulse versus input power and junction temperature of the transist or are shown.