High Efficiency, Extended Back-off Range Doherty Power Amplifier Using A Three Port Harmonic Injection Network

In this paper, a high efficiency, extended back-off range Doherty power amplifier (DPA) using a three port harmonic injection network (HIN) is proposed. The proposed three-port HIN changes the drain termination impedance trajectory of the carrier device thus enabling optimal fundamental impedance of carrier device from back-off to saturation. This is aided by the proposed HIN, which allows the passage of second harmonic components, which enhances the voltage amplitude of both active devices. Meanwhile, the second harmonic drain terminations of the carrier device are located near the open circuit, which results in a near rectangular current waveform. Concurrently, the second harmonic drain termination of the peaking device sees a short circuit, which leads to an increase in efficiency and power. To validate the idea, a DPA was designed and fabricated based on commercially available gallium nitride HEMT (Cree CGH 40010F) devices for verification. Measured results of the proposed idea, demonstrates that operation at 9-9.5 dB back-off is possible between 1.6 - 1.95 GHz, with drain efficiency better than 62.5%.