Study On Radar Signal Models Of Wideband Low Probability Of Interception And Random Polarization

Along with the rapid development of radar technology,radar countermeasure and electronic warfare technology have also made great progress.On the one hand,the traditional radar system cannot meet the growing application needs.Radar needs to satisfy the application requirements of battlefield reconnaissance under harsh electromagnetic environment,not only to search and track targets,but also need to obtain more accurate information of the target,such as high resolution imaging,micromotion feature extraction and so on.On the other hand,radar needs to improve its survivability,reduce the probability of being intercepted and jammed by hostiles,and achieve RF stealth and good anti-jamming performance.This dissertation mainly studies on radar signal models of wideband low probability of interception(LPI)and random polarization.The main contributions and innovations are as follows:(1)Dechirp compression method for nonlinear frequency modulation waveform is proposed.NLFM signal is regarded as the compound signal of inverted S-type FM signal and linear-FM signal.The pulse compression of wideband NLFM signal under low-rate sampling is realized by using the dechirp compression method,so as to avoid use of high speed analog to digital convertor(ADC).Both numerical simulation and high resolution one-dimensional range imaging experiment prove that the proposed dechirp compression method can work with low speed ADC,and at the same time ensure the low sidelobe performance.(2)A novel low sidelobe random radar signal model is proposed,which is obtained by modulating the signal's spectrum in frequency domain.The phase spectrum and amplitude spectrum of the signal are modulated by random sequence and Gaussian window function respectively and thus it is of Gaussian power spectral density,and in this way low sidelobe performance is achieved,which is validated by both numerical simulation and real pulse compression experiments.(3)A novel linear-FM random radar signal model and its dechirp compression method are proposed.The designed waveform combines the advantages of random radar signal and linear frequency modulation signal.It not only has approximate thumbtack-typed ambiguity function,good orthogonality and Doppler tolerance,but also achieves pulse compression at low sampling rate by dechirp compression method,which greatly reduces the sampling rate of radar hardware.The numerical simulation and one-dimensional range profile simulation experiments validate the excellent performance of the designed linear-FM random radar signal and the effectiveness of dechirp compression method.Real experiment of high resolution circular SAR imaging is further conducted to show the good performance of the designed random signal and the compression method.(4)Randomly polarized radar signal(RPRS)model is proposed.The theoretical mechanism of random polarization radar signal is analyzed.It is shown that when two incoherent random radar signals are transmitted by an antenna with orthogonal polarizations,the randomly polarized radar signal can be generated.The research field of LPI radar signal is extended from time and frequency domains to polarization domain.According to the scattering mechanism RPRS from a target,an active repeater jamming identification method based on the degree of polarization(DoP)is proposed.The jamming identification is carried out by comparing DoPs of target echo signal and the repeater jamming signal.The effectiveness of the proposed method is verified by numerical simulation.