Research On Sensing Theory And Method For Low Probability Of Intercept Radar Signal In Air Battlefield

In the modern air battlefield,electronic warfare is the key force for win the war,where the radar signal sensing is a crucial part.On the one hand,radar signal sensing is to obtain electronic intelligence(ELINT)from the radar side.On the other hand,it can guide us to react in time and implement precise jamming.Most current radars have good low intercept characteristics.For this reason,electronic warfare equipment needs to perceive and extract useful information from low probability of intercept(LPI)radar signals in the electromagnetic environment of the air battlefield.LPI radar signals often have characteristics such as wide frequency bands,large dynamics,complex modulation,and parameter agility,making it difficult for passive electronic warfare receivers to detect them.Therefore,research on theories and methods of LPI radar signals sensing for air battlefields has urgent practical needs and broad application prospects.Compared with traditional radar signal sensing,the sensing of LPI radar signals in the air battlefield has increased complexity in many aspects such as time domain,frequency domain,and air domain.In this dissertation,related theoretical derivation and algorithm research is carried out on the sensing architecture,signal detection,intra-pulse inter-pulse modulation recognition,parameter estimation,and signal sorting involved in the air battlefield LPI radar signals sensing,and carried out the semi-physical offline test data verification link.The main body of this dissertation is divided into five parts,and the main contributions are as follows:1.The scheme of the LPI radar signals sensing system for the general air battlefield is investigated.By analyzing the characteristics of the air battlefield LPI radar signals in the time domain,frequency domain,air domain,modulation domain,etc.,the air battlefield LPI radar signals sensing model is constructed.The air battlefield LPI radar signals perception signal processing architecture is proposed.The characteristics of the Nyquist folding receiver(NYFR)and channelized receiver are emphatically analyzed,which provides a schematic model for the development of a similar signal sensing system.2.The LPI radar signals detection technology in the air battlefield is studied.The traditional time-domain energy detection,frequency-domain energy detection,and time-domain autocorrelation detection methods are compared and analyzed.A visibility graphs-based air battlefield LPI radar signals detection algorithm is proposed.The visibility graphs related concepts and signal detection model are introduced,which overcomes the problem of low signal detection probability under the low signal-to-noise ratios(SNRs)of the traditional detection algorithm.On this basis,considering that the signal is multi-component,a multi-component LPI radar signals detection algorithm based on visibility graphs is proposed,which realizes the detection of multi-component radar signals detection under low SNRs.3.The LPI radar signals recognition technology in the air battlefield is investigated.The relationship between the time domain,frequency domain,and time-frequency domain of various LPI radar signals after NYFR folding is studied,and based on the STFT technology,an intelligent LPI radar signals intra-pulse modulation recognition method based on NYFR is proposed.The comparative experiment shows that the recognition effect is very superior under low SNRs.With the help of the visibility graphs algorithm,through the combination of feature extraction and machine learning methods,an automatic radar antenna scan type identification method is proposed,which can effectively distinguish the radar antenna scan type.Based on the two recognition methods,a visibility graphs-based LPI radar signals intra-pulse modulation recognition method is proposed,and the signal modulation type recognition effect is also good.Considering the small number of signal pulses,the method of LPI radar signals sorting based on machine learning is proposed,simulation experiments verify the effectiveness of the proposed algorithm.4.The LPI radar signals parameter estimation technology in the air battlefield is studied.For the combination modulation LPI radar signals,the relevant performance analysis is given,and the LPI radar signals parameter estimation algorithm based on the smoothed pseudo-Wigner-Ville distribution(SPWVD)is proposed.The simulation results verify the effectiveness of the parameter estimation performance.For the multi-component signal model,an improved composite short-time Fourier transform(CSTFT)algorithm is proposed,and on this basis,an LPI radar signals instantaneous frequency(IF)estimation algorithm based on scale-invariant feature transform(SIFT)is proposed.It can realize the estimation of the IF parameters of the multi-component LPI radar signals.The Cramer-Raw Bound(CRB)of multi-component LPI radar signals is derived theoretically.The comparison experiment further illustrates the superiority of IF parameter estimation performance.5.The semi-physical simulation data algorithm verification is implemented.Computer simulation experiments are used to verify the effectiveness and performance of the above-mentioned air battlefield LPI radar signals detection,signal recognition,parameter estimation,etc.,and combined with the research group to build an air battlefield LPI radar signals sensing semi-physical offline platform.Through the analysis and processing of the data intercepted by the LPI radar signals sensing in the experiment,the feasibility and accuracy of some of the LPI radar signals sensing theories and methods proposed in this dissertation are proved.Relevant research results are expected to improve the sensing ability of radar countermeasure systems in the air battlefield environment.