Linearization Design And Practical Application Of Microwave Power Amplifier

In modern wireless communication system,we use broadband digital transmission and high frequency spectrum utilization rate of the modulation technology,the transmission signal has characteristics of non constant envelope、large capacity、high PAPR. Because the memory effect and nonlinear characteristic of power amplifier, the output signal will produce more serious in band distortion and out band distortion, increasing bit error rate, resulting in the adjacent channel interference. So the broadband wireless communication systems has higher requirements on the linearity of power amplifier, power amplifier linearization technology become one of the key technologies of the next generation wireless communication system. Power amplifier linearization methods are commonly used:powerbackoff、negative feedback、 feedforward、predistortion、LINC and so on. In these techniques, pre distortion technology is considered as the most prospects for the development of the technology, it has stable, flexible and efficient, wideband and adaptive features and it can achieve the moderate degree of linear.This paper first introduces basic technology of microwave power amplifier, the working state of power amplifier has carried on the theoretical analysis, the nonlinear characteristic of power amplifier are introduced in detail, these non linearities contains harmonic distortion, intermodulation distortion, such as AM/am and am/ PM distortion, memory effect、Finally we proposed some measurment of non-linear power amplifier.In order to improve the microwave power amplifier linearity and efficiency, we design a C band microwave power amplifier,using GaN chip,and in the form of Doherty. the amplifier bias circuit, stability, source and load pull/push, output and input matching circuit is designed and simulated using microwave simulation software.We use Protel to make PCB, and carry on the detailed test.Finally, we carry out the design of the linear amplifier. It consists of two parts:RF predistortion and digital predistortion.RF pre distortion using the SC1894 predistortion chip and integrated pre distortion processing algorithms, of input signal and output signal and feedback signal, a delay line were simulation design, the amplifier and frequency modes were pre distortion test; digital pre distortion using FPGA and DSP modern signal processing technology, on the power amplifier pre distortion processing, gives the detailed hardware circuit and software design.The linearized power amplifier applied in a model of point to multipoint microwave communication system, the average output power is 36dBm and ACPR is below the -47dBc, it has about 14 dB improvement and output power increase 4dbm, power amplifier efficiency is higher than 40%. The linear effect is obvious,and it meet s the design goals and overall requirements.