A high-relative-bandwidth Doherty power amplifier with modified load modulation network for wireless communications

This paper presents a novel load modulation network to realize a broadband Doherty power amplifier (DPA). The proposed load modulation network consists of two generalized transmission lines and a modified coupler. A comprehensive theoretical analysis is carried out to explain the operation principles of the proposed DPA. The analysis of the normalized frequency bandwidth characteristic shows that a theoretical relative bandwidth of approximately 86% can be obtained across a normalized frequency range of 0.4-1.0. The complete design process that allows the design of the large-relative-bandwidth DPA based on derived parameter solutions is presented. A broadband DPA operating between 1.0 GHz and 2.5 GHz was fabricated for validation. Measurements demonstrate that the DPA can deliver an output power of 43.9-44.5 dBm with a drain efficiency of 63.7-71.6% in the 1.0-2.5 GHz frequency band at the saturation level. Moreover, a drain efficiency of 45.2-53.7% can be obtained at the 6 dB power back-off level.