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Design of a high-efficiency Doherty GaN power amplifier

An S-band power amplifier (PA)was designed with a three-stage cascade structure in this paper. To achieve high efficiency up to 6 dB output power back-off (OPBO) and high linearity, GaN devices of high gain and efficiency were chosen for the driver amplifier, Doherty power amplifier (DPA) based on CREE CGH40025 was designed for the last stage amplifier. GaN high electron mobility transistors (HEMTs) have attracted great attention because of the outstanding material properties and an excellent trade-of between output power and efficiency, the research of the DPA based on GaN devices has become a hotspot. The DPA was designed to achieve high average efficiency for digitally modulated signals with high peak to average power ratio (PAR) used in mobile and satellite communication system. The PA provides peak output power of 47.22dBm, gain of 43dB and 64% power added efficiency (PAE). It exhibits a PAE of 38% at 6dB output power back-off and -21.5 dBc IM3 at 3dB output power back-off. The measured results show that Doherty amplifiers have high efficiency and good linearity to solve the problem on linearity and efficiency of the RF power amplifiers.