New output combiner design for broadband Doherty power amplifier

This paper introduces a broadband and compact output combiner for Doherty power amplifier. A grounded quarter-wavelength (λ/A) line is added to the output of the peaking amplifier, which helps to compensate the bandwidth limiting effect happened in the conventional combiner. Frequency response analysis indicates that stable impedance is achieved across a wide band for the carrier PA. For demonstration, a Doherty power amplifier prototype based on the proposed structure is implemented using two 10W GaN HEMT transistors. Good simulation and measurement results are achieved.