Design of GaN Doherty Power Amplifiers for Broadband Applications

This letter presents a modified Doherty power amplifier (DPA) architecture to release bandwidth limitation of the conventional DPA. The proposed DPA structure eliminates two quarter wavelength impedance inverters used in the conventional DPAs. Instead, both the carrier and peak amplifiers in the proposed DPA are matched to 70 Ω at the output ports, which enables an easier implementation of broadband matching networks. Broadband input matching network (IMN) and output matching network (OMN) are then designed to achieve wideband DPA with enhanced performance. To verify the design concept, a broadband DPA is designed, fabricated, and measured on a RT/Duroid 5880 substrate with 2.2 dielectric constant and 0.787 mm substrate thickness. In the working frequency bands (0.8 to 1.2 GHz), the designed DPA provides 50.8% to 78.5% power-added efficiency (PAE) at full output power, 30.3% to 40.1% PAE at 6 dB of output power back-off (OBO), 10.8 to 14.8 dB gain (the gain variation is within 2.6 dB over different input power levels at each specific frequency), and maximum output power between 40.2 and 42.9 dBm.