A Wideband Quasi-Asymmetric Doherty Power Amplifier with a Two-Section Matching-Phase Difference Compensator Network Design Using GaAs Technology

Abstract: In this paper, a quasi-asymmetric Doherty power amplifier (PA) is designed without load modulation using the GaAs 0.25{\mu}m pHEMT technology to reach an enlarged output power back-off (OPBO) with circuitry solutions in order to overcome technology restrictions. To prevent power leakage in auxiliary PA (PAaux) due to its extremely large off-state impedance, a Wilkinson power combiner is added to the output. Moreover, an input asymmetric power divider is designed to guarantee that no considerable power is delivered to main PA (PAmain) in the high-power region to make it saturated. A two-section matching network is proposed for PAmain, which simultaneously compensates for phase differences of the main and auxiliary amplification paths. To control the significant impedance variation of PAaux versus sweeping power and the different impedance trajectories of the main and auxiliary amplification paths, the bias and dimension selection of PAaux are analyzed to reach the desired output power profile versus input power. These methods overcome impedance variations and linearity degradation. To achieve the aimed 10% fractional bandwidth, appropriate low-quality LC-networks are selected as matching networks. The simulation results indicate the utility of the proposed structure for microwave link applications. Continuous-wave simulations imply that the Doherty PA has a 33dBm maximum output power and a 13.5dB power gain with less than 1dB power gain compression in the desired frequency range (7.6-8.4GHz). The drain efficiency of 30% at the highest input power, minimum of second and third harmonic powers of -140dBm and -130dBm, respectively, and OPBO of 7.5dB are also obtained.