The Research On Broadband Doherty Microwave Power Amplifier

With the rapid development of wireless communication network,in order to achieve higher data transfer rate,the bandwidth of the modulated signal increases from 5MHZ of W-CDMA signal to 100 MHz signal bandwidth of LTE-Advance.With the increase of modulation bandwidth,high efficiency spectrum modulation technology has been applied to mobile communication,and the modulated signal often has a large peak to average ratio(PAR).In this case,the traditional power amplifier has not been able to guarantee the high efficiency of the communication system.The Doherty power amplifier(DPA)based on active load-pull theory,has high saturation efficiency and the drain efficiency of 6dB back-off point has 78.5% in theory.Because of these advantages,Doherty has become a hot topic in the field of communication.In this thesis,the basic principle of Doherty power amplifier and its application in microwave circuit are deeply analyzed.In this thesis,firstly,the output matching circuit of Doherty power amplifier is analyzed theoretically,and the sufficient conditions,which Doherty power amplifier output load network should meet,are proposed.In the following chapters,we designed and fabricated the Doherty power amplifiers with 180 degree and 0 degree transmission phase,respectively.By testing the designed Doherty circuit,conclusions are as follows:1.Doherty power amplifier with 180 degrees transmission phase has high peak and 6dB back-off efficiency.In the working frequency band 1.75-1.95 GHz,the variation range of saturation output power is 43.54-44.15 dBm,and the variation range of saturation gain is 8.5-10.3dB.Within the operating frequency range,the range of saturation and 6dB back-off drain efficiency is 58.7%-71.7% and 50.9%-61.4%,respectively.The Doherty's average peak efficiency and the average 6dB back-off efficiency is 66.3% and 57.5%,respectively.2.Doherty power amplifier with 0 degrees transmission phase has high 6dB backoff efficiency,high peak efficiency and wide bandwidth.In the working frequency band 1.3-2.3 GHz,the variation range of saturation output power is 42.71-44.67 dBm,and the variation range of saturation gain is 7.01-8.71 dB.Within the operating frequency range,the range of saturation and 6dB back-off drain efficiency is 59.15%-71.4% and 50.1%-61.6%,respectively.The Doherty's average peak efficiency and the average 6dB back-off efficiency is 65.2% and 54.7%,respectively.