Researches On Low Probability Of Intercept Signal And Technology Of Low Sidelobe For Pulse Compression

In radar applications, the design of signal waveform not only determines the signal processing method, but also directly affects the performance of the system including resolution, measurement accuracy, low probability of intercept and the ability to suppress clutter. Therefore, signal waveform design has been an important research aspect of modern radar system. In this paper, several signal waveforms of low probability of intercept radar are analyzed, and the techniques of low sidelobe pulse compression for phase shift keying and frequency modulation signals are studied. Main work are listed as follows:Firstly, this paper introduces four signal waveforms of low probability of intercept radar. The emission energy of FMCW is low and widely spread. Moreover, its power spectrum is a rectangle in the modulation bandwidth. The merit of PSK is that its power spectrum is flat and it can-not be distinguished. The advantage of FSK is that the signal energy is allocated in the larger bandwidth, and the frequency of the signal is changed at intervals, so it is difficult to be tracked. The FSK/PSK is a kind of combined signal by adding phase modulation to FSK signal, the energy of the combined signal is more widely dispersed in the whole bandwidth. In addition, it possesses the random character of the Stepped-Frequency signal. Consequently, the low probability of intercept property of the FSK/PSK signal is better.Then, the pulse compression results and doppler sensitivity of 2PSK and QPSK signal is analysed and compared, the sidelobe of QPSK is lower, but its doppler sensitivity is stronger. In order to further suppress the sidelobe of pulse compression of the echo signal, we study three kinds of methods: using the ideal sidelobe character of complementary codes to reduce the sidelobe level; changing codes between every pulses, which can reduce the sidelobe but can not effectively eliminate the clutter; therefore we use another kind of method which changing codes between every two pluses, this method can not only reduce the sidelobe but also remove clutter effectively.Last, we study the low sidelobe pulse compression technique of frequency mudulation signal. the sidelobe is reduced by using the window function, which will be harmful to theSNR and widen the width of the mainlobe. The performance of four kinds of window functions is compared, and the loss caused by low sidelobe is analyzed. Then, it is applied to distinguish the two closed targets, which SNR of the two is largely different, then the best selection of the pulse pressure coefficient when the amplitude is waving according to sin function is analyzed. Finally, for the nonlinear frequency modulation signal, we make use of the Taylor window and S type curve to structure frequency modulation function, which is able to reduce the sidelobe of NLFM signal.