Application of X-parameter model of gallium nitride device for a continuous broadband Doherty power amplifier design

The design of a continuous broadband Doherty power amplifier (DPA) based on an X-parameter model is presented in this work. The broadband load-pull X-parameter model is extracted at both the package plane and current generate plane of the device under test. The model cannot only predict the fundamental and harmonic nonlinear behavioral accurately, but also find the optimal output power and drain efficiency (DE) region of the Smith chart precisely, thereby assisting DPA design. A 10-W gallium nitride packaged transistor from Wolfspeed is utilized in this design. The fabricated DPA reached a saturation output power of 44.3 dBm, with a saturation DE over 68% and a 6 dB output power back-off efficiency over 51% in the frequency range of 1.1-1.8 GHz, verifying experimentally the effectiveness of the proposed design methodology.