Design of Load Combiner in Three-Stage Doherty Power Amplifier for Bandwidth Extension

This paper presents a design of modified load combiner for wideband three-stage Doherty power amplifier (DPA). The proposed design can employ the output impedance of the peaking amplifiers to compensate the effective load impedance of the carrier amplifier in the low-power region for extending the bandwidth. To verify the design method, a 1.7-2.6 GHz three-stage DPA was designed using three 10-W GaN HEMTs. Simulated results show about 50% drain efficiency at 9.5 dB output power back-off over the entire frequency range of operation (42% fractional bandwidth).