A Bandwidth Enhanced Doherty Power Amplifier With a Compact Output Combiner

This letter introduces a broadband and compact output combiner for Doherty power amplifier (DPA). A grounded quarter Wavelength $(\lambda/4)$ line is added to the output of the peaking amplifier, which helps to compensate for the bandwidth limiting effect that happens in the conventional combiner. Frequency response analysis indicates that stable impedance is achieved across a wide band for the carrier PA. For demonstration, a DPA prototype based on the proposed structure is implemented using two 10 W GaN HEMT transistors. At 6 dB back-off power, over 42% drain efficiency is obtained from 1.5 GHz to 2.5 GHz, accounting for 50% fractional bandwidth. In addition, a minimum of 55% drain efficiency is maintained at saturation in the same frequency band.