Design of broadband GaN doherty power amplifiers

Abstract

This paper 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 (one is after the output matching network of the carrier amplifier and the other one is before the load of the DPA). Instead, both the carrier and peak amplifiers in the proposed DPA are matched to 70 Ω (1.4*Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) at the output ports, which enables the easy implementation of broadband matching networks. Broadband input and output matching networks are then designed to achieve wideband Doherty power amplifiers with enhanced performance. To verify the design concept, a broadband microstrip DPA is designed, fabricated, and measured on a Duroid 5880 substrate with 2.2 dielectric constant and 0.787 mm substrate thickness. In the working frequency band (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.