2018 Volume 15 Issue 3 Pages 20171222
This paper proposes a method for extending the bandwidth of a three-device Doherty power amplifier (DPA) based on symmetric devices. λ/4 transmission lines are inserted between each peaking amplifier output and carrier amplifier output to compensate load impedance of carrier amplifier. In order to achieve perfect load modulation, carrier amplifier output circuit total electrical length is designed to 90 degrees, and the peak amplifier output total electrical length is designed to 180 degrees. The proposed method is demonstrated by designing a three-device broadband DPA using three 10-W packaged GaN HEMT devices. Measurement results show that over 40% drain efficiency is achieved at 9-dB back-off power, over the frequency band of 1.45–2.35 GHz, accounting for 46% fractional bandwidth.