Broadband Doherty-Like Power Amplifier Using Paralleled Right- and Left-Handed Impedance Transformers

Previously, the bandwidth of conventional Doherty power amplifiers (DPAs) is limited by the phase dispersion of the microstrip impedance transformer (IT). To overcome this phase dispersion, minimization of the phase delay of the IT is required, however at the expense of load modulation bandwidth, which limits further bandwidth extension. In this article, we present a broadband Doherty-like PA topology that, for the first time, uses parallel right- and left-handed ITs. This satisfies the minimal phase delay requirement while simultaneously maintaining wideband load modulation. Consequently, the frequency range for load modulation can be significantly extended. For demonstration purposes, a Doherty-like PA prototype is realized using two identical 10-W GaN HEMTs. Measurement results show that a drain efficiency of at least 40% is achieved at 5.2-6-dB back-off from 1.25 to 2.30 GHz, which corresponds to a very wide bandwidth of ~60%.