Optimized Broadband Load Network for Doherty Power Amplifier Based on Bandwidth Balancing

Abstract

This letter presents an optimized broadband load network for the Doherty power amplifier (DPA) based on bandwidth balancing between low- and peak-power levels. The optimized broadband load network is composed of a quasi-lumped $\lambda $ /4 impedance transformer (ITF), a modified multiple resonance circuit (MMRC), and a broadband postmatching network (PMN). The quasi-lumped ITF at the carrier amplifier has an optimized characteristic impedance for bandwidth balancing between low- and peak-power levels. The MMRC provides the quasi-lumped ITF with an appropriate susceptance for optimized bandwidth. It also matches the impedance for the peaking amplifier. To validate this design concept, the broadband DPA was implemented using 30-W gallium–nitride high electron mobility transistor (GaN-HEMT) for both carrier and peaking amplifiers. For the down-link long-term evolution (LTE) signal with a channel bandwidth of 10 MHz and a peak-to-average power ratio (PAPR) of 6.5 dB at the frequency range of 1.15–2.45 GHz, DE ranging from 38.4% to 52.2%, and the adjacent channel leakage power ratio (ACLR) ranging from −23.9 to −35.0 dBc at an average output power of from 39.7 to 41.7 dBm were achieved.