This paper presents the theoretical analysis of phase distortion (AM/PM) mechanisms in Gallium Nitride (GaN) Doherty power amplifiers (DPAs) and a novel approach to optimize the tradeoff between linearity and efficiency. In particular, it is demonstrated how it is possible to mitigate the AM/PM by designing a suitable mismatch at the input of the active devices, based on the identification of constant AM/PM and gain contour circles. The proposed theory is experimentally confirmed by source- and load-pull measurements and further validated through the design and realization of a 7 GHz 10 W DPA based on GaN monolithic technology.
