High efficiency microwave FET power amplifiers

An experimental study was performed on a variety of GaAs FETs from different companies to identify device and circuit parameters that lead to high efficiency operation of microwave FET amplifiers. FETs were characterized by means of a unique system that measures the current and voltage waveforms of the device operating at microwave frequencies under large signal conditions. It is found that some characteristics of the gate - namely gate resistance and breakdown voltage of the Schottky barrier - have a large effect on the maximum operating efficiency and output power. A device, whose circuit was optimized for highest efficiency, operated with a power-added efficiency of 72% and an output power of 1.2 W at 2.4 GHz.