DESIGN OF A HIGH-EFFICIENCY BROADBAND ASYMMETRIC DOHERTY POWER AMPLIFIER

This study proposes a broadband asymmetric Doherty power amplifier (A-DPA) with a broadband matching network and an improved power combination network (PCN). A broadband matching network in the form of a low-pass filter is analyzed and applied in this work. With the narrowband characteristic of a 1/4 wavelength transmission line, an improved PCN is also analyzed and applied to decrease the impedance transformation ratio of the 1/4 wavelength transmission line and then extend the working bandwidth of the DPA. In the design process, GaN HEMTs from Cree are selected to be the main and auxiliary power amplifier transistors, and the ADS software is used to complete the entire design process. In the working frequency band of 3.3 GHz–3.6 GHz, simulated results show that the gain is approximately 13 dB when the output power is lower than 40 dBm and that the power-added efficiency (PAE) is 39%–51% within the 9 dB power back-off (PBO) region. Measured results indicate that the proposed A-DPA exhibits a 36%-45% PAE within the 9 dB PBO region. The saturated PAE is between 58% and 62%, and the saturated output power is approximately 42 dBm.