Harmonic-Tuned High-Efficiency GaN HEMT Doherty Power Amplifier Based on Two-Power-Level Impedance Optimization

This paper presents a harmonic-tuned high-efficiency GaN HEMT Doherty power amplifier (DPA) without a quarter-wave transformer. The output matching circuits in the fabricated DPA were designed based on the dual-RF-input-power-level impedance optimization method instead of one with a quarter-wave transformer for load modulation. In addition, optimum harmonic reactive termination conditions to achieve high efficiency were maintained in the load modulation for both carrier and peaking amplifiers. The fabricated DPA achieved a maximum drain efficiency of 67% and a maximum power-added efficiency (PAID) of 61% with a saturation output power of 40 dBm at 4.7 GHz. Furthermore, in a 7-dB back-off condition, a drain efficiency of 66% and a PAE of 60% were obtained, which were comparable to the saturated output power efficiencies and had excellent backoff performance.