An extended symmetric doherty power amplifier with high efficiency over a wide power range

We propose an extended range Doherty power amplifier (DPA) to achieve high efficiency at 9-dB power back-off (PBO) using a novel loading impedance range. The proposed loading impedance range enables the auxiliary transistor to deliver more current so that symmetric devices can be used in the DPA and results in a compact and low loss output combining circuit. A 20-Watt DPA using Gallium nitride high electron mobility transistors (GaN HEMTs) at 3.5 GHz has been developed to demonstrate the concept. Measurements show power added efficiency (PAE) of 69% at 42.9 dBm saturation output power, PAE of 55% at 9-dB PBO, and gain of 12 dB. We believe our proposed DPA has the highest 9-dB PBO PAE of 55% among reported GaN DPA's.

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