Analysis and design of broadband Doherty power amplifier using parameterized load modulation network and complex combining load

Abstract

This paper presents a novel approach to design broadband Doherty power amplifiers (DPAs) with extended fractional bandwidth (FBW). A parameterized load modulation network (LMN) and complex combining loads are proposed that can extend the FBW while providing more accurate back-off impedance. To examine the influence of parameter variations in the LMN on the broadband performance of the DPA, we utilize the parameter scanning method and subsequently select the optimal parameters in the LMN. Additionally, three-dimensional computer visualization techniques is invoked to visually examine the impedance solution space of the complex combining loads. A DPA prototype with a bandwidth of 0.85–1.8 GHz is then designed and implemented using commercial GaN transistors to validate the proposed architecture. The fabricated DPA attains a measured gain of 14.2–15.7 dB and a saturated power of 43.0–44.9 dBm. Across the designed operation band, the measured drain efficiency reached 51.6%–73.6% at saturation and 43.7%–56.7% at 6 dB output power back-off. When driven by a 20 MHz modulated signal with a peak-to-average power ratio (PAPR) of 8 dB, the average efficiency of the fabricated DPA is higher than 46.7%.