A Broadband Doherty Power Amplifier for Sub-6GHz 5G Applications

This paper presents a novel and accurate procedure for designing a Doherty power amplifier (DPA) for wireless systems. The method is based on a systematic approach to designing the matching networks of both Main and Auxiliary devices, which employs an optimization process to set their input impedance in the corresponding optimal regions obtained from the standard load- and source-pull simulations. To import the optimum regions of each device into the optimization algorithm, mathematical expressions are derived and graphically reported on the Smith chart. Besides this, we have developed an accurate method to account for the loading effect of the Auxiliary amplifier on the Main one at back-off when designing the Main PA. As a proof of concept, a symmetric DPA is designed, fabricated, and tested. The measurements showed a working frequency band of 3.3-3.9GHz (aimed at n78 band of 5G-NR), a minimum peak output power of 36W, drain efficiency between 48%-53.2% at peak and 34.6%-44.5% at 6dB back-off.