Research On Low Intercept Probability Radar Waveform Design And Detection Method

The research on waveform design and detection method of low probability of intercept radar is one of the key research contents in the field of electronic countermeasures.The radar without low probability of intercept is easy to expose its real position information in the process of task execution,and becomes the key target of the enemy.In the aspect of waveform design,the composite modulation waveform design based on phase coding is a common way to achieve radar low interception,and the coding sequence is an important part of waveform design.Barker code sequences are often used in the design of composite modulation waveform because of their excellent auto-correlation characteristics,but they are few in number and short in length,so the designed waveform have low complexity and have certain limitations in coding length.Therefore,it has important research significance and practical value to design a new coding sequence with auto-correlation performance approaching Barker code under the condition of long code length.At the same time,under the interception factor criterion,the low interception performance analysis index of waveform is relatively single.Therefore,it is necessary to study a new quantitative evaluation standard of low interception performance under the condition of this criterion.In addition,in the aspect of waveform detection,the accuracy of waveform detection results based on machine learning is low when there are few real data sets.Therefore,it is necessary to study the low interception performance of the composite modulation waveform designed in this thesis under the signal processing detection algorithm,and explore the impact of different coding methods on the signal processing process.The main contents of this thesis are as follows:(1)This thesis presents a chaos genetic algorithm to optimize the selection of chaotic discrete coding sequences.Firstly,the three properties of chaotic sequence are simulated,the advantages of chaotic sequence used in radar waveform coding design are analyzed,and a random discrete coding sequence based on chaotic mapping is designed.Compared with Barker code sequence,this sequence solves the problems of small selection range of phase coding sequence and fixed coding length,but it is necessary to further select the sequence whose auto-correlation performance meets the requirements.Then,the genetic algorithm is improved and modeled.Under the criterion of optimizing the ratio of autocorrelation main lobe to peak side lobe of discrete sequences,the improved genetic algorithm is used to optimize the selection of chaotic discrete sequences generated by random initial values.Finally,the chaotic discrete coding sequence with auto-correlation performance approaching Barker code sequence is selected.The algorithm solves the problem of selecting a new coding sequence whose auto-correlation performance is close to Barker code under the condition of long code length.(2)This thesis designs three kinds of low probability of intercept radar waveform with composite modulation.Firstly,according to different radar application scenarios,single pulse composite modulation radar waveform and multi pulse composite modulation radar waveform based on new coding sequence and linear frequency modulation signal are designed.Then,the signal models and ambiguity functions of the three waveform signals are derived respectively,and the ambiguity function diagrams of the three waveform signals are simulated.The characteristics of ambiguity functions of single pulse radar waveform and multi pulse radar waveform are compared and analyzed.Finally,the low interception performance of the three signals is analyzed from three aspects: ambiguity function characteristics,interception factor and interception time cost.From the simulation results,the mono-pulse composite modulated radar waveform not only solves the problem of poor range resolution of single phase modulated mine waveform,but also realizes the encryption of point target range dimension information.On this basis,the two-dimensional coded multi pulse composite modulated radar waveform also realizes the encryption of point target Doppler dimension information.(3)This thesis presents a new quantitative evaluation index to measure the low interception performance of radar waveform,and explores the influence of different coding methods on the signal processing process.Under the condition of low Signal to noise ratio,the interceptor needs to accumulate the intercepted signal in time domain to complete the waveform detection.When the accumulation time reaches that the interceptor can detect the effective information contained in the current intercepted signal,this accumulation time is recorded as the interception time cost of the signal.Under the interception factor criterion,the quantitative index supplements the evaluation index range of radar waveform low interception performance.Then,based on the pseudo-Wigner-Ville distribution detection,the time-frequency analysis of the three composite modulation waveform designed in this thesis is carried out.Finally,the signal processing simulation of the above three kinds of composite modulation radar waveform is carried out to explore the influence of different phase coding methods on signal processing.