The Research Of Microwave GaAs Power Amplifier And FET Predistortion

Microwave power amplifier design bases on the accurate devices'model. However, not all the devices'models are given by the manufacturers. So this paper starts from small-signal model, then large-signal model and finally to input and output impendence which are used to input and output match network. For power amplifiers always work at 1dB compression point nearby, even higher than it. The non-linear is very seriously at this situation that are the third harmonic wave and the fifth harmonic wave. So it is of great importance for designers to improve the non-linear. This paper uses FET as pre-distortion device to improve the non-linear of the power amplifiers.There are several power amplifier linearization methods available which can be classified mainly as power back off, feedback, feed forward and predistortion. This paper researches on analog predistortion.First part. This paper start with the traditional GaAs FET modeling methods, establish small-signal model of the microwave power GaAs FET, and then test GaAs FET DC characteristic curve, fitted to its large-signal model, at last, we use harmonic balance method to analysis nonlinear model. The harmonic balance algorithm is different from the past, where we have put forward the concept of transformation matrix, using the whole frequency domain harmonic balance algorithm, makes the efficiency of calculation greatly enhanced.Second part. Several linearization methods are firstly analyzed and compared in simple way. Meanwhile, the advantages of analog predistortion are presented compared with other methods. Then, the analog predistortion are specially discussed for the system. The FET-based predistortion are analyzed and compared for system scheme. Meanwhile, the loop structures of analog predistortion are analyzed, including single-loop and dual-loop. Through the analysis, simulation and comparison, the FET-based analog predistortion with dual-loop is adopted for this design.