Research On Technology And Performance Evaluation Method Of LPI Radar

With the development of the passive detection technology, the electromagnetic jamming and threats from anti-radiation missiles are becoming increasingly severely. As a result, the research of Low Probability of Intercept(LPI) radar has become a hotspot recently, and LPI technique is an effective method for anti-jamming and counter-detection.Firstly, this thesis introduces the principle of LPI radar and the concept of intercept factor. Through the analysis of the intercept factor, this thesis analyzes the factors that affect the LPI performance of radar and discusses a series of LPI technology. This thesis mainly studies two aspects: waveform design and LPI performance evaluation method of radar.The design of radar signal is very important to LPI performance, so this thesis carries on the simulation analysis of characteristics in time domain and frequency domain and ambiguity functions of several typical single modulated radar signals such as LFM signal, symmetrical triangular waveform signal and binary phase-coded signal. The results show that LFM signal has large time-bandwidth product and high resolution in range and speed, and is insensitive to Doppler shift, but its modulation method is too simple and it exists range-Doppler coupling. Symmetrical triangular waveform is a better LPI waveform for it has better resolution in range and speed than LFM signal and it eliminates the range-Doppler coupling. Ambiguity graph of binary phase-coded signal is close to “pushpin” type, so there is no ambiguity in range and velocity and it has good anti-jamming performance. Its shortcomings are mainly the choice of the binary phase sequence is very limited, and it is usually sensitive to Doppler shiftTo make up for the deficiency of single-modulated signal, a mixed modulation signal(LFM-BC) with LFM and 13 bits barker code modulated simultaneously is studied. The ambiguity function expression of LFM-BC is derived and the simulation analysis is carried out. The results show that the LFM-BC signal has a “plate nail” type ambiguity graph, with higher resolution, no range-Doppler coupling and complicate modulation mode, which is difficult to be recognized by scout. The LFM-BC signal makes up for the deficiency of a single-modulated signal and combines their advantages.LPI performance evaluation method is of great significance to the design of radar system. Several methods such as intercept factor, intercept time and Spherical Equivalent Vulnerability Radius are introduced which are not comprehensive. So this thesis proposes the signal intercept probability under a certain detection probability as the indicator to evaluate the LPI performance under the premise that the detection performance of radar is ensured. This method can evaluate the LPI performance quantitatively and comprehensively in terms of space, time domain, frequency domain and energy domain.Finally, the research content is summarized and the future work is prospected.