An Octave High Power Push-Pull Doherty Amplifier With Broadband 2nd Harmonic Termination Control

This paper presents a push-pull Doherty power amplifier (PPDPA) with an octave bandwidth. It includes balanced to unbalanced (balun) transformers, which are custom designed to limit the dispersion of the second harmonic terminations seen by the main and auxiliary transistors. When integrated into the broadband impedance inverter, the resulting combiner network allows for maintaining proper load modulation and consequently high efficiency at back-off (BO) for more than an octave bandwidth. A mixed-signal PPDPA demonstrator was successfully designed using two packaged 90 Watt GaN transistors. It demonstrated drain efficiencies (DEs) of 52-64% and 51-58% at full and 6 dB BO powers, respectively, across a fractional bandwidth of 80% (0.6 GHz-1.4 GHz). It also maintained an output power of about 51.5 dBm +/- 1.5 dB.