Design of Doherty power amplifier with power back-off extension based on harmonic tuning and output combining network optimization

This paper proposes a Doherty power amplifier (DPA) design method based on harmonic tuning and output combining network (OCN) optimization to extend the power back-off (PBO) range. Firstly, based on the optimal harmonic load impedance, a harmonic tuning optimization method is used to design the harmonic tuning network of the amplifiers, effectively improving the efficiency at saturation and PBO. Secondly, the fundamental output matching network and the post-matching network are considered as an OCN. The Sparameters of the OCN are calculated and utilized in the DPA design. To further expand the PBO range, the carrier load impedance at PBO is determined by considering the relationship between PBO range and reflection coefficient. Finally, a multi-objective evolutionary algorithm combined with the theory of solution set is used to optimize the OCN design, simplifying the design process of the output matching network. For verification, a high-efficiency DPA operating at 1.68 GHz with a large PBO range of 9.5 dB is designed and measured. Results indicate that the proposed DPA achieves a saturated output power greater than 44 dBm, with a peak efficiency of up to 75.2%. The efficiencies are 68.5% and 61.0% at 6 and 9.5 dB back-off powers, respectively.