Dual-Band Class-X Doherty Power Amplifier With Large Frequency Ratio

This letter presents a bandstop output matching network to design a dual-band class-X Doherty power amplifier (DPA) with large frequency ratio. The introduce of a wide stopband makes the good matching at two far frequencies qualified for both power output saturation and power output back-off (OBO) states possible. First, the limitation of traditional lowpass matching network in DPA design for dual-frequency output matching is stated. Then, the impedance trajectory and achievable frequency ratio of the proposed bandstop structure are quantitatively analyzed. Next, a dual-band matching network with a frequency ratio of 3.18 is designed, and the fundamental impedance of the two bands is located within the design space of class-X at OBO state. Finally, the low-pass postmatching network is designed to control the second harmonic at the combining point. A 1.10-/3.50-GHz DPA is designed with drain efficiencies (DEs) of 70.8% and 71.1% at power saturation state, and at 6-dB power OBO state, the Des are 58.2% and 53.4%, respectively.