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 $\mathrm{R}_{\text {opt }}$ under low power conditions. Therefore, the DPA achieves peak efficiency at back-off power of greater than $\mathbf{6 ~ d B}$. The fabricated DPA with $0.15-\mu \mathrm{m}$ GaAs pHEMT delivers a $P_{\text {sat }}$ of $28.1-28.7 \mathrm{dBm}$, linear gain of $13.2-15.7 \mathrm{~dB}$, 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 $P A E_{\text {avg }}$ of $27.8-33.1 \%$ and adjacent channel leakage power ratio (ACLR) of -25.5--24.3 dBc at $P_{\text {avg }}$ of $20.8-21.3 \mathrm{dBm}$ for a 5 G NR signal with 100 MHz bandwidth and PAPR of 7.5 dB peak to average power ratio.