Study On Polarization Radar Characteristics Of Chaff Clouds And Anti-jamming Techniques

In modern information warfare,as a typical representative of precision guided weapons,anti-ship missiles are the main offensive weapon in maritime warfare.They have played a very important role in many naval wars,including the Middle East War,the UK-Argentina Falklands War,and the Gulf War and so on.They have become one of the main defensive targets of naval vessels in naval warfare.As one of the main means of the terminal guidance of the anti-ship missiles,radar guidance mode has many important advantages,such as long detecting distance,weatherproof and so on,which has been widely used.To further improve the detection,recognition and tracking ability of radar seekers to adapt to complex and changeable battlefield environment,many countries are actively developing new anti-ship radar seekers,such as synthetic aperture radar(SAR)technology is applied to guidance(SAR seeker),polarization technology is applied to radar seeker and so on.Polarization imaging radar seeker is an important development direction of current anti-ship radar seeker.However,radar seekers are also vulnerable to the electromagnetic environment in the battlefield,because active guidance of radar needs to transmit electromagnetic waves to complete the detection,location and tracking of targets,etc.As a typical passive jamming means,chaff has many advantages,such as low cost,simple manufacture,easy use and ability to jam various radar seekers,and it has been widely used in maritime electronic warfare.Especially,considering the complex and changeable movement,diffusion and distribution orientation of chaff clouds in the air,and the uncertainty factor,as well as the reasonable tactical application,chaff clouds are clustered and complex,and their radar characteristics are quite complex,even advanced radio frequency radar seekers are difficult to deal with.Therefore,chaff jamming is still one of the main threats to the new anti-ship radar seeker.To this end,how to improve the anti-chaff jamming ability of the new anti-ship radar seeker is an urgent military frontier problem.Based on the above background and military requirements,in this dissertation,the new polarized anti-ship radar seeker is taken as the object of study,and the new countermeasure technologies and methods against chaff jamming faced by the seeker in the terminal guidance stage were studied.The main research work includes the following aspects.1.Characteristic of chaff motion diffusion and its radar polarization scattering.The characteristics of chaff movement and diffusion were expounded.Based on the existing research results in open literature,the distribution functions of three kinds of typical chaff clouds were summarized,and the motion diffusion simulation experiments of the typical chaff clouds were carried out.Begin with the polarization scattering matrix(PSM)of the chaff fiber,the radar polarization scattering characteristics of the chaff fiber under different orientations were analyzed.On this basis,the PSM of three kinds typical distributed of chaff clouds were given.The probability density distribution functions(PDF)of chaff clouds,including amplitude,phase and radar cross-section(RCS)in each polarization channel were analyzed.The correlation between chaff clouds' echoes in the co-and cross-polarization channels was studied.Based on this,the unified expression of the coherence matrix of chaff clouds was summarized.2.Anti-chaff dilution jamming method of full-polarization forward-squint radar seeker.The anti-ship missile SAR seeker was taken as the object of study,and three anti-chaff dilution jamming methods were proposed on the basis of studying the imaging characteristics of chaff clouds in full-polarization forward-squint SAR.1)A chaff jamming recognition method based on target's average scattering mechanism was proposed.This method introduces the A decomposition theory in polarimetric SAR,and the polarization scattering characteristics of parameters ? of chaff clouds under three kinds typical distributed were analyzed in detail.The parameters ? and the correlation between the co-and cross-polarization channels were taken as the identification characteristic parameters,and the validity and feasibility of this method are verified by numerical simulation and the support vector machine(SVM)classification method.2)A chaff jamming recognition method based on the four-component model-based decomposition were proposed.In order to further improve the recognition rate of chaff jamming,an improved generalized polarimetric model-based decomposition method(IC4G)was proposed.The scattering mechanism of ship target and chaff jamming was analyzed.According to the volume scattering component in the four-component model-based decomposition method,a characteristic parameter for identifying chaff interference was proposed.The flow chart of chaff jamming recognition was given and the simulation experiments of measured SAR data were carried out.3)A chaff jamming recognition method based on layered polarization characteristics was presented.This method combines aerodynamics characteristics with polarization characteristics of chaff clouds.The elevation information of ship target and chaff clouds were retrieved by using interference principle.The chaff jamming was discriminated by the difference of the layered polarization characteristics between ship target and chaff clouds,and the feasibility of this method was verified by simulation experiments.3.Anti-chaff centroid jamming method for polarization mono-pulse radar seeker.Taking polarized mono-pulse radar seeker of anti-ship missile as an object,three anti-chaff centroid jamming methods were proposed.The proposed method in this paper abandons the traditional anti-jamming idea,i.e.,based on "chaff jamming suppression".In the circumstance of chaff centroid jamming,the jamming is usually in the same range and angle resolution cells as the target.Under these circumstances,the essence of anti-chaff centroid jamming is to estimate two unresolved targets' angles in the main beam of the radar seeker.Under this new idea,firstly,based on maximum likelihood criterion,a point target angle estimation method based on maximum likelihood(ML)function was proposed.Considering this method needs to estimate the prior information of the relative RCS ratio of chaff jamming and target,a point target angle estimation method based on polarization mono-pulse radar was presented.This method utilizes the polarization information dimensionality of mono-pulse radar,and effectively solves the shortcomings of the point target angle estimation method based on maximum likelihood function,which has low computational complexity and high angular measurement accuracy.Finally,for the broadband mono-pulse radar system,an angle estimation of extended target method based on polarization mono-pulse radar was proposed.The theoretical analysis and simulation results show that,the angle estimation accuracy of the target can be effectively improved by using the extended information of multi-scattering centers of extended target on radar range unit.