Characteristics Of Micro-Doppler And Feature Extraction Of Midcourse Ballistic Target In Bistatic Radar

The bistatic/multistatic radar is recognized for the potential of counterretrodirective jammers, counter-ARM, counter-zero feet penetrate and counter-stealth. The ballistic missile defense system includes several of the same type radar and several different types of radar which have common frequency range. These radars have the ability to construct several bistatic/multistatic radar systems. Because the several receiver of the bistatic/multistatic radar can acquire more information, more comprehensive target information can be extracted by information fusion. So the bistatic/multistatic radar which may be realised in the ballistic missile defense system has remarkable advantage and potential of detecting, tracking and recognizing ballistic missiles. And the feature of micro-motion is academically acknowledged as one of the most important features which used for radar target recognition in the middle section of the ballistic curve. In this thesis, based on the background of radar target recognition, we systematically study the micro-Doppler models, characteristics analysis and feature extraction of ballistic target in bistatic radar by combining the theoretical analysis, the electromagnetic computing and the dynamic simulation. In summary, the work is composed with three parts according the study sequence: establishing micro-Doppler model, detecting the micro-motion curves and parameter estimation of the micro-motion targets. The main contents of this dissertation include:In the aspect of the bistatic electromagnetic scattering characteristics and the bistatic micro-motion models of midcourse target: At First, the bistatic scattering centers of the cone-shaped warhead and the blunt-nosed bipyramid are analyzed. For the cone-cylinder warhead with fins, the bistatic scattering centers which related to the fins are confirmed by analogy. Then the bistatic micro-Doppler models of the cone-shaped warhead and the blunt-nosed bipyramid are derived, and the bistatic micro-Doppler models of the scattering centers which related to the fins are derived when the warhead with fins is spinning or precessing. These bistatic micro-Doppler models are validated by dynamic simulations using the bistatic scattering coefficients of these warhead models.1. For the cone-shaped warhead, the bistatic scattering centers are analyzed by the geometrical theory of diffraction(GTD). The two scattering centers in the conical bottom are the points where the projection of the bistatic bisector on the conical bottom intersects the edge of the conical bottom. They coincide with the monostatic scattering centers when the radar locates on the bistatic bisector. The bistatic scattering centers of the blunt-nosed bipyramid and the blunt-nosed multipyramid are confirmed by analogy. For the cone-cylinder warhead with fins, the monostatic scattering centers which related to the fins are the tips of fins and the conjunction of the fins and the body, so the bistatic scattering centers which related to the fins are also confirmed by analogy.2. It’s found that the bistatic scattering centers slip on the warhead when the cone-shaped warhead is precessing. Then the bistatic micro-motion trajectory models of the scattering center at the conical point and two slip-type scattering centers on the edge are derived. The bistatic micro-Doppler models are the bistatic micro-motion trajectory models’ differential. The bistatic models are similar with the monostatic models, and the ratio of the bistatic models to the monostatic models is the cosine of the half of the bistatic angle. The bistatic micro-Doppler models of the blunt-nosed bipyramid are confirmed by analogy. The bistatic models of the scattering centers which related to the fins are derived when the warhead with fins is spinning or precessing. They are also similar with the monostatic models.3.The bistatic scattering coefficients of the blunt-nosed cone, the blunt-nosed bipyramid and the blunt-nosed multipyramid are calculated by the electromagnetic computational software. When the warhead without fins is precessing, the azimuth angle and elevation angle of the incident and scattering directions are stationary, but if we suppose that the warhead is stationary, the azimuth angle and elevation angle of the incident and scattering directions will change regularly. The formulas which calculate the changing azimuth angle and elevation angle are derived. Then the flow chart of analyzing the characteristics of the precessing warhead’s micro-motion in bistatic radar is proposed. And the bistatic models of the precessing warhead without fins are validated by dynamic simulations. For the warhead with fins, the different formulas which calculate the changing azimuth angle and elevation angle are derived when the warhead with fins is spinning or precessing. The flow charts of analyzing the characteristics of the spinning or precessing warhead with fins in bistatic radar are proposed. The bistatic models of the spinning or precessing warhead with fins are also validated by dynamic simulations.In the aspect of the method of detecting the micro-motion curves: At First, the advantages and disadvantages of the parameter estimation method based on Hough transform are listed. Because the scattering center’s intensity obeys an unkown distribution, the detection threshold in parameter domain can’t be determined. To solve the problem of detecting the scattering centers, the method of detecting the micro-motion curves based on the particle filter based track-before-detect(PF-TBD) algorithm is proposed for the first time.1. The micro-Doppler curves in the Time-Frequency graph are regarded as the target’s moving trace, and then the target motion model and the energy diffusion model are established. The method of detecting the micro-Doppler curves based on the PF-TBD algorithm is proposed. Then several time frequency graphs are obtained via the time-frequency analysis on the calculated bistatic scattering coefficients of the blunt-nosed cone and the blunt-nosed biconical warhead model. The method is validated by detecting the micro-Doppler curves correctly and extracting them from the time frequency graphs.2. Bistatic HRRPs containing both the bistatic micro-motion trajectory and micro-Doppler information are validated by bistatic scattering coefficients of the blunt-nosed cone. After the bistatic micro-motion trajectories in bistatic HRRPs are regarded as different targets’ s moving traces, the method of detecting the micro-motion trajectories and micro-Doppler curves based on the PF-TBD algorithm is proposed. The detection probabilities of the method are analyzed by Monte Carlo simulation. The method is validated by detecting the micro-motion trajectories and the micro-Doppler curves correctly.In the aspect of characteristc analysis of the micro-motion models of the warheads without fins and feature extraction in bistatic radar: To estimate all parameters of the precessing warhead without fins by the micro-motion trajectories and the micro-Doppler curves, the feasibility of estimating the bistatic micro-motion models’ parameters are studied. After the characteristcs of the micro-motion models are analyzed, the parameter estimation method are proposed1. It’s proved that when we use Hough transform to estimate the bistatic models’ parameters, all parameters but only precession period and initial angle can not be estimated accurately. It’s found that the unkown parameters in the micro-motion trajectory models and micro-Doppler models can be reduced by using the symmetric scattering centers. After reducing the micro-motion trajectory models and micro-Doppler models’ parameters, we can estimate the left parameters accurately. When structure/angle parameters are known, angle/structure parameters can be estimated accurately based on the micro-motion trajectories and micro-Doppler curves.2. Based on the needs of using the symmetric scattering centers to reduce the unkown parameters in the micro-motion trajectory models and micro-Doppler models, the characteristics of the micro-motion trajectory models and micro-Doppler models are analyzed, the method of distinguishing the symmetric scattering centers are propsed. Then the condition and the approach to estmate parameters of the precessing warheads without fins are summarized.3.It’s proved that because of the size of the warhead, range resolution,precessing angle,the radar aspect angle and SNR, using Hough transform can not confirm the type of bistatic micro-motion trajectory correctly in some situations, but the type of bistatic scattering center can be confirmed by analyzing its micro-Doppler curve’s characteristcs. And the parameter estimation method for the precessing warhead without fins in wideband bistatic radar is propsed for the first time. At last, the parameter estimation errors are analyzed by Monte Carlo simulations, the feasibility of the parameter estimation method is validated by two dynamic simulations.The micro-motion models, the methods of detecting the micro-motion trajectories and the micro-Doppler curves and the parameter estimation method for the precessing warhead without fins in wideband bistatic radar, which are proposed in the thesis,will improve the theoretical architecture of radar information processing of micro-motion targets and furthermore support the target recognition application of ballistic missile defense system.