| The ever-increasing demand for high data throughput in modern wireless communication systems leads to the employ of high peak-to-average power ratio(PAPR)signals,which poses a challenge to the radio frequency power amplifier designed for future communication systems.The DPA has been widely adopted in base-station infrastructure due to its excellent ability in maintaining high efficiency over a back-off power range.However,the application of Doherty power amplifier is limited in communication due to its narrow bandwidth.This thesis expounds the theory of wideband continuous mode Doherty power amplifier and analyzes the impedance design space of main power in saturated power level and back-off power level in detail.Based on theoretical analysis,a matching structure is proposed for the design of the main power amplifier output-matching network in order to extend the bandwidth of the output matching of main power amplifier.A broadband continuous mode Doherty power amplifier with a frequency range from 1.7 GHz to 2.7 GHz is designed based on gallium nitride(GaN)high electron mobility transistors.The experimental results show that the 6dB power back-off efficiency and the saturation efficiency of the Doherty power amplifier with a frequency range from 1.6GHz-2.6GHz are greater than 40.7% and 58.4% of the Doherty amplifier,respectively.The output power is higher than 42.9dBm.The paper analyzes the bandwidth limitation of the output impedance of the auxiliary branch to the Doherty power amplifier in the back-off power level.The effect of the output impedance of the auxiliary power amplifier on output matching network of the main power amplifier is simulated by the capacitor and microstrip line series experiment,which explains that the compression of auxiliary branch output impedance is beneficial to the expansion of the bandwidth of the Doherty power amplifier.On this basis,an output impedance adjustment network of auxiliary power amplifier is proposed,which effectively reduces the influence on the main power amplifier in the back-off power level and improves the problem of power leakage.A broadband Doherty power amplifier is designed and fabricated using the proposed Doherty structure.The test results show that the drain efficiency of 6dB back-off power is 44%-51% in the frequency range of 1.4GHz-2.6GHz(relative bandwidth 60%).The saturation efficiency is 54%-74.5%,and the output power is higher than 42.7dBm. |
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