Characterisation of an experimental gallium nitride microwave Doherty amplifier

The efficiency of microwave power amplifiers is highly dependent upon both amplifier architecture and the active device technology employed. This paper presents for the first time the combination of gallium nitride (GaN) device technology with the now well established efficiency enhancing Doherty power amplifier (PA) architecture. The amplifier is characterised at 1.8 GHz using both single-tone and modulated excitation through the use of a purpose built multi-port, multi-stimulus measurement system. Initial measurements are very positive and show how GaN devices can be highly effective within the Doherty amplifier, even with the limitations of the simple experimental structure used. Measurements show that efficiency is successfully extended over 6dB of dynamic range, and a power density of 0.9W/mm is demonstrated, while linearity remains comparable to that observed for a GaAs Doherty.