Study On Space Highspeed Target Detection By Spaceborne Random Noise Radar

With the development of space technology,strategic status of aerospace in political,military and economy is enhancing day by day,technology of space-targets detection gets more and more attention from countries.Space-targets detecting radar can be divided into two forms,ground-based radar and space-based radar.Compared with ground-based radar,space-based radar can work at higher signal frequency,easier to detect small size space-targets,without the influence of atmospheric attenuation and ionospheric scintillation.It also has advantages for observing space-targets in higher orbits.Due to the nonperiodic transmitting signal of noise radar,it has ideal thumbtack ambiguity function,avoiding periodic distance ambiguity,so it is very suitable for detecting highspeed and long-distance targets in orbits.However,superhigh speed of space-targets causes serious deterioration of performance in traditional matched filter algorithm,and the motion compensation research for noise radar needs to combine with the characteristics of noise radar.Research on problems of highspeed space-targets detection by spaceborne noise radar is carried out in this thesis.The main works and innovative points are summarized as follows:1.The position relations and coordinate transformation between space targets and celestial coordinate system(geocentric inertial coordinate system)are firstly studied.Through relationship analysis of radar coordinate system,satellite coordinate system,and celestial coordinate system,the coordinate transformation of position and speed of space-targets from radar coordinate system to celestial coordinate system is deduced.Then highspeed targets echo-models are classified systematically,take Noise Frequency Modulated Continuous Wave(NFMCW)radar as an example,application conditions of echo models are given through concrete analysis.Interpolation method is proposed to construct the echo signals of highspeed targets on account of the characteristics of random noise signal.From the analysis angle of transmit signal of spaceborne radar,the performances of highspeed and long-distance targets detected by Linear Frequency Modulated Continuous Wave(LFMCW)radar and NFMCW radar are simulated and compared,and the results indicate that NFMCW radar has certain advantages in highspeed targets detection in orbits.2.The mathematical expressions of Statistical Mainlobe to Mean Square Sidelobe Ratio(SMMSSR)and Statistical Mainlobe to Peak Sidelobe Ratio(SMPSR)of pulse compression output of Noise Phase Modulated Continuous Wave Radar(NPMCWR)and Noise Frequency Modulated Continuous Wave Radar(NFMCWR)are deduced,by researching on statistical rule of mainlobe and sidelobe of NPMCWR and NFMCWR pulse-compression output.That provide a theoretical basis of quantitative analysis for relation between mainlobe to sidelobe ratio of pulse-compression output with the length of pulse-compression,doppler frequency,bandwith and so on.Monte-Carlo simulation results are close to the calculated results so that verify the correction of the reduction results.3."Time domain correlation method" for space highspeed targets coherent accumulation over range gates by spaceborne noise radar is studied.The method of using single frequency signal to implement velocity measurement,constructing "matched reference signal" according to target velocity,combining conjugate processing of echo signals of NFMCW and single frequency signal,so that to implement coherent accumulation over range gates is proposed.The mainlobe to sidelobe ratio in distance dimension can be improved greatly by this method.This method combined with FFT-IFFT method to "clean" big signal one by one,which could improve dynamic range for multiple targets detection is used.The validity of the above method is proved through simulation results.4."Frequency domain correlation method" for space highspeed targets coherent accumulation over range gates by spaceborne noise radar is studied.Applying a fast discrete time scale transformation method in keystone transform is discussed.According to the feature of aperiodicity of random noise signal,frequency domain correlation based on the equal interval overlapping segmentation is proposed,combining with keystone transform adopting fast algorithm,which can achieve effective long time coherent accumulation for highspeed targets.It can handle multiple targets scene without prior knowledge.Take NFMCWR as an example,processing procedure is presented in detail,and the effectiveness is verified by simulation.5.Short time coherent accumulation for space highspeed targets detection by spaceborne noise radar is studied.The method of using multicarrier techonogy with waveform diversity and frequency diversity,doing statistical processing on the basis of "time domain correlation"and "frequency domain correlation" for NFMCW radar short time coherent accumulation is proposed.The output mainlobe to sidelobe ratio can be improved greatly,meanwhile,the'three crossing' phenomenon can be avoided.The effectiveness is verified by simulation in the end.