Broadband and Linearity Enhanced Doherty Power Amplifier using Complex-valued Load Modulation

This paper presents a novel output combining network to enable the extension of the bandwidth of the Doherty power amplifier (DPA) and improve its linearity. This combiner network brings about a complex-valued load modulation to take advantage of the continuous modes of operation for broadening the DPA bandwidth. It is also exploited to devise a nonlinear gain characteristic (AM/AM), which is complementary to the main transistor one and consequently improve the DPA linearity. Accordingly, a 50-W broadband DPA prototype with improved nonlinear gain characteristic is designed to operate over frequency band of 1.5-2.5 GHz while maintaining a drain efficiency in excess of 43% and small gain variation around 1dB over the entire 6dB Doherty region. Moreover, the linearizability of the designed DPA was verified under wideband (up to 80 MHz instantaneous bandwidth) and multi-band modulated stimuli using digital predistortion technique.