Design of Doherty Power Amplifier Using Load-pull X-Parameters

The design of Doherty power amplifier (DPA) using load-pull X-parameter model is demonstrated in this paper. A 10 W GaN HEMT transistor is employed for the PA designing. As soon as the X-parameter model is extracted, its performance is validated. Compared with the circuit model provided by the device manufacture, the used X-parameters gives an excellent prediction. The region of the load Smith chart leads to optimal output power and drain efficiency (DE) can be accurately identified as critical to amplifier design. The input and output matching networks are designed using a Chebyshev low-pass architecture, and a step-impedance converter structure is used to design the output synthesis network. Finally, a DPA was designed and fabricated. The realized DPA achieves a saturation output power over 41 dBm in the frequency band of 1.4 GHz - 1.6 GHz, a saturation DE over 58%, and 6dB output power back-off (OBO) efficiency over 46% The comparison between the measured results of the realized DPA and the used load-pull X-parameter model is also given, and it shows that the X-parameter model can be applied for DPA designing with high-fidelity.