Power Amplifiers with Frequency-Selective Matching Networks

In this article, we demonstrate a method for codesign of filtering matching networks for power amplifiers (PAs) with the desired frequency response, improved efficiency, and reduced footprint. The microwave transistor operates with high efficiency with a specific complex-impedance load, and this requires the development of a theory for filter matching network design with arbitrary complex-impedance ports. The formulation is first developed and then applied to a simple second-order filter and a fourth-order filter with cross couplings and transmission zeros and verified in the experiment. A single-stage high-efficiency 4.7-GHz, 4-W hybrid GaN filter-PA (FPA) within a sub-6-GHz 5G band is designed, built, and characterized. The port impedances are determined by load- and source-pull for an efficiency-power tradeoff. The measured performance shows a gain of 15 dB, PAE = 55% with 9% fractional bandwidth, and 10-dB rejection at 4.5 and 5 GHz. Comparison with a cascaded PA-filter circuit shows a 25% lower loss with the same rejection and a reduced footprint with the same rejection. A GaAs monolithic microwave integrated circuit (MMIC) FPA at 28 GHz (millimeter-wave 5G FR2 band) is also designed and measured with a second-order output matching filter, demonstrating 8-dB gain, 200 mW of output power, and PAE = 30% with a rejection of 8 dB at 26.5 and 29.6 GHz.