Abstract
This study presents an X-band two-stage Doherty power amplifier (DPA) using pre-matched gallium-nitride high electron mobility transistors (GaN-HEMTs). The pre-matched GaN-HEMT includes partial matching circuits in the package using bond-wires and capacitors. To obtain broad bandwidth and low loss, the pre-matching circuits were carefully designed to have a low matching quality factor. The optimum second harmonic impedance, which was extracted from the harmonic source/load pull simulations, was applied to the pre-matching circuits for high efficiency. Using the pre-matched GaN-HEMTs, an X-band two-stage power amplifier (PA) was designed and implemented. By combining two two-stage PAs in parallel, a DPA was built. The implemented DPA exhibited a max gain of 25.5 dB and an output power from 42.5 to 45.8 dBm at the frequency band from 7.9 to 8.4 GHz. It also showed a high efficiency of 37.8% at the 6 dB back-off output power level of 39.6 dBm.
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