  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.
