Design of a 550W High-Efficiency Asymmetric Improved Three-Stage Doherty Power Amplifier Based on GaN HEMT

To meet the demands of 5G base stations in large PAPR signal environments, this paper presents the design of a 550W improved three-stage Doherty power amplifier with a 12 dB back-off range. GaN HEMT devices with gate widths of 18 mm, 27 mm, and 27 mm are selected for internal matching design to ensure ultra-high output power. The paper analyzes the active load modulation mechanism under an asymmetric architecture and proposes an impedance matching design method suitable for this configuration. Test results in the 2.5-2.7 GHz show that the linear region gain is between 10.5 and 13.4 dB, the saturated output power ranges from 57.2 to 57.6 dBm, and the saturated drain efficiency is between 69% and 73%. At a 12 dB power back-off, the drain efficiency is between 55% and 58%. When the power back-off is 6 dB, the drain efficiency ranges from 62.2% to 65.1%. After incorporating Digital Pre-Distortion (DPD) technology, the ACPR test result is -55.9 dBc. These results address the issues of insufficient back-off range and linearity degradation due to saturation, which are common in traditional three-way and three-stage Doherty power amplifiers.