Research On Broadband Doherty Amplifier With High Efficiency At S Band

Doherty amplifier(DPA)is a commonly used power amplifier structure.DPA characterizes high drain efficiency and can amplify the signal of high peak-to-peak power ratio(PAPR),thus has an important application in modern wireless communications.However,DPA generally operates in a narrow band,which limits its ability in broadband and multi-standard communication applications.This thesis analyzes the basic theory and actual bandwidth of DPA,explains the effect of quarter-wavelength impedance transform line on DPA,and explains theoretically how to design wide-band DPA with high performance.Firstly,a matching network based on impedance compensation at secondary path and two-point matching technology at the master path is proposed.Its structure is simple.It utilizes two-point matching technology and broadband network synthesis technology for wideband optimization,and can operate from 1.8GHz to 2.8GHz based on gallium nitride(GaN)HEMT transistors.The design of broadband high-efficiency DPA shows that the efficiency at the retreat point is greater than 50%,the saturation point efficiency is greater than 58%,and the maximum output power is greater than 43 dBm.The measured results show that in the range of 1.6-2.2GHz,the efficiency of the retreat point is greater than 40%,the saturation point efficiency is greater than 50%,and the output power is similar with the one from simulations.The paper further analyzes the working principle of the J-type continuous-mode amplifier.The results show that the harmonics generated by the nonlinear capacitor help to extend the bandwidth of the matching network,thereby increasing the wide-band capability under high-efficiency operation conditions.This feature is used in conjunction with the Doherty amplifier.Theoretical analysis of the continuous mode DPA design is conducted.Finally,a continuous-mode Doherty amplifier based on harmonic control at the junction node of the master and slave paths is designed.The efficiency at the retreat point is 52% and the saturation point efficiency is greater than 63% in the range of 1.7-2.8 GHz,thus illustrates the effectiveness of such a scheme.