| In the radar system, in order to maximize the efficiency of the power amplifier to increase the radar's detection range, the emission signal is generally constant envelope modulation signal. With the development of radar technology, non-constant envelope modulation method is gradually applied to the radar systems. Same as other wireless communication systems, non-constant envelope modulation is very sensitive for the nonlinear characteristics of power amplifier. Once the power amplifier fell into the nonlinear region, the output signal will have a serious adjacent channel interference and band distortion. Therefore, the study of power amplifier's linearization technology is of great value in theory and its application.In this dissertation, author did widely research on RF power amplifier linearization. Firstly the principles of power amplifier's non-linear characteristic was introduced .Then the techniques of RF power amplifier linearization was discussed in detail, including feed-forward, feedback, and digital base-band pre-distortion technology. The author mainly studied the digital base-band pre-distortion techniques and did various simulations about base-band pre-distortion adaptive algorithm and improved the original algorithm. In the studying of the memoryless power amplifier model, according to the principle of finding roots of nonlinear equations, a new adaptive algorithm– dichotomy was proposed. MATLAB simulation showed that compared with classical RASCAL algorithm,dichotomy had faster convergence speed and better accuracy. Because there is some delay between the launch signal and feedback signal in the T.R loop, the adaptive process needed delay estimation. This dissertation proposed a improved algorithm of loop-delay estimation to estimate a multiple loop delay but not use any multiplier. In order to get the accurate phase and amplitude of a signal in the FPGA, this dissertation simulated the CORDIC algorithm in MATLAB and improved the original algorithm make it finally reached better accuracy during the square root computation.Author designed the hardware platform for verification of the pre-distortion algorithm. Based on system research of the power amplifier pre-distortion and simulate of various pre-distortion algorithm, finally, auther realized the base-band digital pre-distortion algorithm in FPGA by verilog hardware description language. Experiments showed that the pre-distortion algorithm improved the narrow-band signal's quality significantly. The power amplifier's third-order inter-modulation signal power spectrum was reduced by 10db and the fifth-order inter-modulation signal power spectrum lower over 7db through the pre-distortion system. |
