A 20–500 MHz, 250W Adaptive Bias Class-G Balanced GaN Power Amplifier with Inherent Resilience to Antenna VSWR

A novel Class‑G balanced power amplifier architecture is presented that enhances efficiency and robustness under severe antenna VSWR by adaptively reducing the drain supply voltage when the RF voltage swing collapses. Two 28 V, 250 W GaN Class‑AB stages are combined through a broadband 3 dB, 90° hybrid and fed by independent current‑limited DC/DC converters that autonomously lower the branch rail in response to increased current under mismatch, preserving output power while reducing device dissipation. Mismatch formulation shows that when mismatch reduces the fundamental drain‑voltage swing without clipping, proportional VDD scaling recovers efficiency; measurements of a 20–500 MHz prototype demonstrate up to 8 percentage‑point efficiency improvement at up to 3:1 VSWR compared with a fixed‑supply balanced amplifier, without requiring ferrite isolators.