A 24-28 GHz Doherty Power Amplifier with 4 W Output Power and 32% PAE at 6 dB OPBO in 150 nm GaN Technology

A 24–28 GHz two-stage GaN Doherty power amplifier is designed and characterized. At mm-wave frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77 %. Even though, compared to symmetric Doherty power amplifiers, the load modulation of the main transistor is reduced, this amplifier still achieves 32 % and 23 % power added efficiency at 6 dB and 9 dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak power added efficiency of 42%.