A New Linearizer For Microwave Power Amplifier

With the rapid development of communication system, the channels become more and more crowded in the frequency band. In order to make the limited spectrum range accommodate more communication channels, some linear modulation techniques are proposed, such as QAM (Quadrature Amplitude Modulation), QPSK (Quadrature Phase Shift Keying), etc. These changes demand a higher spectrum and power efficiency to the communication system, with a stress on the spectrum efficiency. To solve these problems, a high linearity is demanded for the power amplifier system, and it is necessary to take some measures against the non-linear distortion of power amplifier. In many linear techniques (feedback, feedforward, predistortion), we have chosed the predistortion method, mainly because its features are suitable for this project. The main contents of this dissertation is as follows.1, It introduces the commonly used linear techniques for microwave power amplifier at present which include feedback, feedforward, predistortion, LINC and CALLUM, analyzed their principles, application, advantages and disadvantages. Followed, it gives the data and feature analysis of the TWTA (Taveling Wave Tube Amplifier) producted by THALES. In view of the small size and high reliability for the satellite use equipment, predistortion is the best choise.2, It lists and analyzes the operating principle and application of the single diode, double diode and single GaAs FET linearer and finds that they are all inconvenient to be adjusted. In order to solve this problem, a new predistorter is presented on the basis of single GaAs FET structure. The new structure includes a FET and a diode(or two), and they are connected in a series form. Then, the dissertation give analysis to the structure. The predistorter is easy to be adjusted and has not been touched upon in the present papers.3, After simulated by the ADS2004A of Agilent, the simulation result is give, fix on the microstrip circuit and product the testing circuit.4, Through measurement and adjustment, we can obtain 0~3.0dB gain composition and 0～29°phase shifting generated from this new structure. We also can obtain variour gain and phase characteristics through adjusting the bias voltage of the predistorter.