Enhancement of the broadband efficiency of a class-j power amplifier with varactor-based dynamic load modulation

A broadband Class-J power amplifier (PA) with dynamic load modulation (DLM) is presented. It is theoretically shown that a PA with judicious variation of the load resistance and a purely reactive load modulation can maintain 70% drain efficiency over 73% fractional bandwidth and 8.5 dB dynamic range. The theory is verified by a demonstrator PA based on a gallium nitride (GaN) device and a varactor as the tuneable element. The load modulation shows good results from 1.7 GHz to 2.3 GHz and up to 50% of power added efficiency (PAE) is obtained. It is shown that the average PAE for a modulated signal with 7 dB peak-to-average ratio is improved by 15%.