Polyphase Coded Signals

With the development of science and technology, radars are required better property in all kinds of fields. To design a radar system with good property, an excellent radar signal plays a key role. At the present stage, the most common radar signals are the linear-frequency modulation signal and the biphase signal. These two kinds of signals have disadvantage in the aspect of sidelobe and Doppler tolerance. To overcome these drawbacks, polyphase pulse compression codes appeared which were derived from the linear-frequency modulation signal.This thesis mainly does a research in P polyphase codes, especially P4 codes. Many simulation results using Matlab are given out to discuss the properties of P4 codes, including frequency spectrum, ambiguity function, pulse compression property and Doppler tolerance. Pulse compression property and Doppler tolerance are mainly talked about. A lot of simulation results prove that P4 codes have a good performance in pulse compression and Doppler tolerance, compared with m sequence and linear-frequency modulation signal. By comparing P4 codes with different length, the thesis summarize the suitable range of length for engineering applications.Because the sidelobe has an effect in radar's detecting ability, this thesis discusses three methods to reduce the peak sidelobe level. They are classic amplitude weighting, post compression 2-sample averager and iterative weighted least square method. The thesis introduces their theory and their performances in sidelobe and Doppler tolerance compared by simulation results, and then it illustrates P4 codes having big Doppler tolerance and good noise immunity by picking P4 codes with hanning window as an example.Besides a new corresponding pulse compression filter concept is developed, which achieves a highly improved sidelobe reduction effect without increasing the system complexity. Simulation results are provided to prove the superior performance of this pulse compression scheme and its robustness.In terms of practical engineering application, this thesis talks about the creation of polyphase codes and realization of its pulse compression. Using AD9858 as an example, the thesis introduces the theory and the configuration of this chip. In addition, the processing of digital pulse compression both in time domain and frequency domain is discussed.