| The importance of microwave amplifiers linearization has been emphasized with the rapid development of the third generation mobile communication systems and the wide use of linear modulation techniques. Modulated signals with varying envelop will generate intermodulation distortion. The distortion results in errors in the magnitude and the phase of the modulated vector signal, enlarging the spectrum, disturbing the adjacent-channel, worsening the error-code-rate and so on. Besides, the power amplifier is known to be the most power consuming component in a transmitter, hence it is desirable to operate the power amplifier as efficient as possible, i.e., near the saturation region where the signals are most susceptible to nonlinear distortion. The linearization technology has been a hot spot to meet the power amplifier linearity and efficiency requirement.In this thesis, the non-linear characteristics of power amplifiers are analyzed in theory at first. The principle, advantages and disadvantages of various linearization techniques are discussed. Then Considering the demands of power amplifiers such as high-gain, high-power and high-linearity, this thesis has researched the microwave power amplifiers and linearization techniques and it is made of two parts:1. A 2W power amplifier operating in the TD-SCDMA repeater has been developed, and some methods of designing power amplifiers are analyzed. Through theoretical analysis and simulation in the computer, a microwave power amplifier that based on LDMOS FET has been designed. The amplifier has two stages with some main characteristics as below: the work frequency band is 2010MHz~2025MHz, the power gain is more than 48dB, the gain flatness is less than±0.2dB, and the VSWR is less than 1.2. The IM3 is less than -47dBc and the IM5 is less than -54dBc, when the output power is 2W.2. The thesis also studies analog predistortion techniques used in microwave power amplifiers. Compared with various predistortion plans, a novel design scheme which can improve both the IM3 and the IM5 has been proposed. The simulation results show the feasibility of this scheme. Then a real predistortion system has been fabricated and tested whit the designed power amplifier in this thesis. The experiment results shows as below: when the output power of the designed power amplifier is 2W, the IM3 and the IM5 is less than -60dBc, so the predistortion system can improve the IM3 and the IM5 13dB and 8dB; when the output power of the designed power amplifier is less than 10W, the IM3 and the IM5 can be less than -50dBc by the effect of the predistortion system.Both the simulation and test results demonstrate that the predistortion techniques can improve the power amplifier's linearity distinctly. The predistortion techniques can increase the output power of the amplifier with low distortion and advance the efficiency. It is proved to be a very promising linearization technology. |
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