Co-Design of Highly Efficient Power Amplifier and High-Q Output Bandpass Filter

This paper reports the first co-design configuration of a power amplifier (PA) in cascade with a high-Q bandpass filter. By matching the filter's input port directly to the transistor's drain node, the conventional output matching network (OMN) of a PA is entirely eliminated. This leads to smaller size/volume, minimized loss, and enhanced overall performance. To enable this co-design method, the matching-filter synthesis theory is proposed and investigated in detail in this paper. Based on this theory, a 3% bandwidth (centered at 3.03 GHz) two-pole filter, implemented using high-Q evanescent-mode cavity resonators, is designed as the PA OMN to provide optimized fundamental and harmonic impedances for a commercial 10-W GaN transistor. Simulation and measured results show that the co-designed PA-filter module yields a desired Chybeshev filter behavior while maintaining excellent PA performance in the passband with 72% efficiency, 10-W output power, >10-dB gain, and 60-dBm output third-order intercept point. This co-designed module experimentally presents a 8% higher overall efficiency compared to a control group developed using a conventional independent PA and filter, which further validates the effectiveness of this method.