| P3, P4 polyphase pulse compression codes, which were derived from linear-frequency modulation pulse compression waveforms and brought out by Lewis B.L. in early 1980s, are a kind of common pulse compression codes. Compared to linear-frequency modulation signals, they have low range-time-sidelobes without weighting in receiver; Compared to biphase signals, they have large Doppler tolerance. Additionally, these codes have low cross-correlation, ease of implementation, compatibility with digital implementation and compatibility with bandpass limited receivers. So these codes are valued very much all the time. But, their utilization have been limited because of their complex compression procedure compared to biphase codes. These years, with the rapid development of digital technology and integrated circuit technology especially the implementation of DDS technology and Very Large Digital Signal Processor, it is possible to create and deal with these codes.This essay did some research in P3, P4 polyphase's properties and their realization technologies, discussed their spectrum, ambiguity functions, Doppler tolerance and other properties thoroughly and systematically, and also researched their realization based on DDS, including performance evaluation board. In real utilization, we need more lower sidelodes to detect small targets beside large targets, because large targets' sidelobe will submerge small targets. So it is very valuable to reduce the peak sidelobes. This thesis discussed three Weighting methodsto reduce the peak sidelobes-Classic Amplitude Weighting, Post Compression 2-SampleAverager and Iterative Least Squares Techniques. Many computer simulation results and conclusions are given out. These conclusions provide a basis for their implementation. |
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