Research On Clutter Modeling And Localization For Airborne Passive Radar

Passive bistatic radar(PBR)uses the existing radiation source as the transmitters.The radar itself does not transmit signals,then it has the advantages of strong concealment,low cost,anti-jamming and anti stealth.In recent years,with the rapid development of Unmanned Aerial Vehicle(UAV)technology,airborne passive bistatic radar has become a new hot issue hotspot.On the other hand,with the establishment of Beidou system in China,a large number of satellite signals that can be used as illuminators of opportunity have not been effectively utilized,so the research on airborne passive bistatic radar with different types of illuminators deserves attention.An important problem of airborne radar is clutter suppression,and space-time adaptive processing is the main method to solve this problem.However,clutter heterogeneity and nonstationarity lead to the deterioration of algorithm performance in complicated practical environment,so the research on clutter properties before algorithm design is particularly important.In addition,due to the high cost of real experiment,reasonable clutter modeling is conducive to the verification of the algorithm.The main work of this thesis concludes:1.The structural characteristics of digital terrestrial multimedia broadcasting(DTMB),Beidou and global positioning system(GPS)signals are studied.According to the signal characteristics,two radar equations suitable for DTMB and satellite navigation signals are designed respectively,and the detection performance of PBR system is also analyzed combined with monostatic / bistatic radar ambiguity function.2.The geometric model of aircraft transmitte-aircraft receiver scene is established,the two cases of the ground projection point of the receiver inside and outside the clutter ring are analyzed,and the azimuth value range centered on the receiver is deduced,Finally,the Doppler analytical solution of clutter unit at a range gate with different azimuth angles centered on the receiver is derived.Compared with the existing geometric model,the model can be used for fast clutter multi range gate modeling.Using this model,the clutter angle Doppler trajectory characteristics of DTMB airborne PBR under several flight modes are analyzed,and the causes of clutter doppler range dependence are analyzed from the perspective of beam traces and Doppler isoline.3.The geometric model of satellite transmitte-aircraft receiver scene is established,and the longitude and latitude equations of equal distance and clutter ring are derived in spherical coordinate system.In this model,the curvature and rotation of the earth are considered,and the three-dimensional velocity vector of the satellite can be obtained by using the parameters such as satellite orbit height,orbit inclination and sub satellite point position;The velocity vector of the satellite is obtained by using the operating speed,direction and altitude of the aircraft relative to the ground,and finally the angle Doppler relationship of the clutter is obtained.The same results as the previous model are obtained in the scene where the bistatic is an aircraft,which verifies the correctness of the model.Then,the relationship of clutter angle with one-way receiving Doppler trajectory under different satellite elevation,different orbital altitude,different receiving direction and different range gate is analyzed.This model is also suitable for the analysis of air-based or space-based bistatic radar.4.The received clutter data model at the receiving end is constructed.The relevant models include:(1)three-dimensional beam model of receiving uniform linear array(2)clutter scattering coefficient model(3)clutter scattering unit area division model.For the calculation of clutter scattering unit area,based on the two geometric models designed,this thesis constructs a division method based on clutter angle doppler center,which is not affected by the grazing angle.The space-time power distribution and range dependence of clutter dopple in various scenarios are analyzed by using airborne front and side array and space-time two-dimensional spectrum and characteristic spectrum.Considering only the small clutter broadening,GEO satellite is more suitable as a transmitting station than other satellites.Several dimensionality reduction space-time adaptive processing algorithms are studied:(1)Time-Space Adaptive method(2)Combined Space-time Main Channel Adaptive Processing method(3)Generalized Adjacent Multiple-Beam Generalized method.5.Aiming at the three-dimensional positioning problem of PBR target,the direct and indirect solution methods based on bistatic range difference are studied.On this basis,the one-dimensional angle parameter is introduced,and the direct and indirect solution methods based on bistatic range difference-angle of arrival are proposed.The Geometric Dilution Of Precision(GDOP)based on bistatic range difference and bistatic range difference-angle of arrival are derived.The root mean square error of four positioning methods in different multistatic scenarios is calculated by Monte Carlo method,which proves the effectiveness of the algorithm.The sensitivity of positioning accuracy to observation parameter error is further analyzed.When the number of transmitters is more than three,the positioning accuracy of the system is hardly affected by the angle of arrival error.Finally,the positioning performance of PBR system in ultra long baseline scenario with satellite as transmitter is studied,which shows that satellite can be used as an auxiliary transmitting station of airborne PBR.