A 3.5-GHz 350-W Black-Box Doherty Amplifier Design Method Without Using Transistor Models

Abstract

This paper presents a newly developed realistic design method of a Doherty power amplifier (PA) having an output combiner network treated as a black-box. The method optimizes a realistic output network based on ideal output network parameters with the black-box design by using large-signal load-pull and S-parameter measurement results without transistor nonlinear models, which was necessity by the previous approach. The optimization considers the load modulations of a main amplifier and an auxiliary amplifier at back-off and peak output power level. To verify the method experimentally, a 3.5 GHz 350 W Doherty PA using GaN-HEMT transistors is fabricated and measured. The PA exhibits a drain efficiency greater than 50% at 7 dB back-off level and the peak drain efficiency of 57% at 6 dB back-off level.