Design of a Dual-Band Doherty Power Amplifier Using Single-Loop Network

This article presents a method of theoretical analysis and design of the Doherty power amplifier (DPA), which has good dual-band performance. A novel output combiner network architecture is proposed, which is named a single-loop network. The architecture effectively utilizes the dual-band characteristics of the T-shaped pattern, thereby enabling the combiner network to exhibit distinct load modulation paths at the chosen operating frequency points. The detailed analysis of the load modulation characteristics of this novel architecture highlights the flexibility of this DPA in achieving superior performance across different frequencies. This article presents a theoretical approach for determining the optimal T-shaped network parameters suitable for this combiner design. Numerical solutions for each individual parameter are provided, leading to a comprehensive understanding of the system's performance and optimal configuration. To verify the proposed architecture, two GaN transistors with different powers are used to design and implement a dual-band DPA with a bandwidth of 1.75/2.70 GHz. The fabricated DPA presents 55.7%–69.5% efficiency at the saturation level. The drain efficiency measured at 9.5-dB output back-off (OBO) power level is 42.3%–62.0% at the designed frequency band.