| With the development of the fifth generation mobile networks technology,the base station is constantly evolving in the direction of broadband and integration,which puts forward higher requirements for the radio frequency transmission link.As an important part of the radio frequency transmission chain,the power amplifier’s performance will directly affect the overall output index of the system.Therefore,the research on broadband and high-efficiency power amplifier has increasing become an urgent social demand.Because the Doherty power amplifier structure has the advantage of maintaining high effiency within the back-off power,it has gradually become a research hotspot.In this thesis,a theoretical study of Doherty power amplifier is carried out based on the active load pull theory,and the design of dual impedance matching is proposed to solve the problem of bandwidth limitation,then the simulation and physical test are carried out,which provides theoretical support for the research of high power and high efficiency Doherty power amplifier.The main contents and contributions of the thesis are as follows:1.Aiming at the limited bandwidth of the traditional Doherty power amplifier,combined with the active load pull theory,the structure of the inverted Doherty power amplifier is analyzed in principle,and its three working states are described in detail.The inverted Doherty power amplifier is simulated,whose working frequency range is 1.805GHz～1.880 GHz.The relationship between the Smith chart and the optimal power point is used to prove the feasibility of the simulation results.2.Aiming at the bandwidth limitation caused by the quarter-wavelength line,the output port of the Doherty power amplifier is matched with dual impedance,and a Doherty power amplifier operating in the 2.11GHz～2.17 GHz frequency band was effectively designed.The measurement results show that the average output power of the power amplifier is 49 d Bm,the gain at the average output power is greater than 15.76 d B,the saturated drain efficiency is between 59.75% and 65.4%,and the drain efficiency at the power backoff is between 54.6% and 55.15%.After DPD optimization,the ACLR is effectively reduced by about 30 d Bc.3.Aiming at the problem of widening the range of back-off power,through theoretical derivation,the adjustment of input power distribution is studied.The relationship between back-off power and drain efficiency is deduced.Combined with the method of dual impedance matching network,an effective design of a Doherty power amplifier working in Band 3 frequency is well designed.The average output power of this power amplifier is 49.3d Bm,the modulation gain at the average output power is greater than 16 d B.The saturation power is 57.5d Bm.The saturated drain efficiency is between 57.3% and 63.9%,and the drain efficiency at the power back-off is between57.0% and 61.4%.After DPD optimization,the ACLR is effectively reduced by about 30 d Bc. |
