Research On Technology For Radar Accurate Polarimetry On Moving Targets

In modern information war,radar has been one of the important keys to the success of the warfare.With the development of radar technology,some researchers gradually realized that the target's polarimetric scattering characteristics contain a wealth of physical attribute of the target.The use of these polarimetric scattering characteristics can promote the intelligence level of a radar.In general,the polarimetric scattering characteristics of the target can be described by the target polarization scattering matrix(PSM).The measurement of the target's PSM indicates the beginning era of the vector measurement.Under the static condition,the target's PSM can be accurately measured in a microwave anechoic chamber.However,in fact,the target measured by a radar is usually in motion and non-cooperative."How to obtain the moving target's real PSM in a non-cooperative condition",this is the major issue of the polarimetric radar detection and recognition.The measurement of the target's PSM is closely related to the scheme and signal processing flows of the radar.In this paper,we first discussed the polarimetric calibration and the corresponding PSM measurement using different schemes.And then,according to the characteristics of moving target's echo,we designed some special measurement schemes for the moving target.In addition,considering the application environment,the detection and PSM estimation of the moving target in a low signal to noise ratio(SNR)circumstance were also discussed.The main innovations of this dissertation are listed as follows:1.A method of internal calibration is proposed for the simultaneous polarization measurement scheme(SPMS).The internal calibration mainly concentrates on the effect of imperfection of some electron devices such as band-pass filter,power amplifier,and others.The proposed calibration method is a collection of the digital predistortion(DP)and the frequency error compensation.This method is the continuation and extension of the traditional calibration method.On the other hand,the proposed method is also taken the coupling effect between the orthogonal waveform and system frequency error into consideration.Based on the error model of the system intermediate frequency and sampling frequency,the influence of the frequency error can be compensated.After DP and frequency error compensation,the mean amplitude errors of the Ke Da-Accurate Polarization Measurement System(KD-APMS)is about 0.5d B,and the mean phase error is about 1°.2.A special measurement scheme and a pair of orthogonal waveform is designed for the moving target.For the traditional timesharing polarization measurement scheme(TPMS),the target motion introduces additional phase error into the measured target's PSM.To overcome this shortcoming,a special measurement scheme using three polarizations(3-Pol)was proposed.It has been proven that the 3-Pol is robust for the structure of the target's PSM,and its measurements are immune to the estimations of the target's radial velocity.When signal to noise ratio(SNR)is greater than 10d B,the mean of the polarized correlation coefficient(PCC)can be above 0.9.For the SPMS,instead of employing the LFM waveform with opposite slopes,the new SPMS uses the amplitude modulated LFM(AMLFM)waveform with a unitary slop.Then,the coupling between waveform and system frequency error can be avoided.When SNR>12d B,the PCC means of the measurement results can be greater than 0.9.3.Methods of the small target detection and its PSM estimation are proposed.For the target detection and tracking,an algorithm of track-before-detection(TBD)is designed for the dual-polarization radar.When SNR>5d B,and false alarm probability is10^-3,the target detection probability can be 0.8.For the velocity estimation and the PSM compensation,a method using the particle filter is proposed.Under the same accuracy of the PSM compensation,the time consumption of the proposed method is only 30%of that in traditional method.Besides,the essence of motion compensation is a compensation process of the target echoes.After the motion compensation and pulse integration,the SNR of the radar data is improved.By this way,a method of measurement selection(MS)is proposed to improve the SNR of the radar data.Then,the MS is also used for the PSM estimation.When SNR>5d B,the PCC means of the estimation results can be above 0.9.Compared with the traditional motion compensation method,the MS method can effectively reduce the impact of the velocity estimation errors on PSM estimation.