To be compatible with future wireless communication systems, it is very necessary to extend the bandwidth of the Doherty power amplifier (DPA). In this paper, a modified combiner integrated with a complex combining impedance is adopted to enable an ultra-wideband DPA. Meanwhile, a comprehensive analysis is performed on the proposed method. It is illustrated that the proposed design methodology can provide power amplifier (PA) designers with more freedom in implementing ultra-wideband DPAs. As a concept of proof, a DPA working over 1.2-2.8 GHz (a relative bandwidth of 80%) is designed, fabricated and measured in this work. Experimental results showed that the fabricated DPA delivers a saturation output power of 43.2-44.7 dBm with a gain of 5.2-8.6 dB. Meantime, the fabricated DPA achieves a saturation drain efficiency (DE) of 44.3-70.4% and a 6 dB back-off DE of 38.7-57.6%.
Keywords: Doherty power amplifier; complex combiner; modified combiner; ultra-wideband.