A Ku-Band 2-Stage Differential Doherty Power Amplifier with Compact Asymmetric Doherty Combiner Based on Virtual Stub in 0.15-µm GaAs pHEMT

This paper presents Ku-band two-stage symmetric Doherty power amplifier (DPA) that utilizes a virtual stub-based combiner architecture. The new combiner design converts virtual stubs into a differential combiner and allows a carrier amplifier to operate at impedance values more than twice as high as Ropt under low power conditions. Therefore, the DPA achieves peak efficiency at back-off power of greater than 6 dB. The fabricated DPA with 0.15-µm GaAs pHEMT delivers a Psat of 28.1–28.7 dBm, linear gain of 13.2–15.7 dB, peak PAE of 39.8–44.0%, and 6 dB back-off PAE of 31.5–36.0% within the frequency bandwidth from 12.4 to 14.0 GHz. The designed DPA also achieves a PAEavg of 27.8–33.1% and adjacent channel leakage power ratio (ACLR) of -25.5–-24.3 dBc at Pavg of 20.8–21.3 dBm for a 5G NR signal with 100 MHz bandwidth and PAPR of 7.5 dB peak to average power ratio.