Research On The Technology Of Inverse Synthetic Aperture Radar Imaging For Ballistic Mid-course Targets

For ballistic mid-course targets, in addition to highspeed orbital motion, the target undergoes micro-motion dynamics, such as spin, precession and tumbling. The micro-motions induce modulations on the echoes that generate sidebands about the target’s Doppler frequency shift, which made the ISAR imaging be more complex. With the research background of target imaging and recognition for the wideband radar, this dissertation researches inverse synthesis aperture radar (ISAR) imaging for ballistic mid-course targets based on the mid-course targets micro-motion modulation effects analysis of the wideband radar echoes.Firstly, the research background is introduced, and the development of inverse synthesis aperture radar system for ballistic missile defense system is reviewed. Then technology development of ISAR imaging is summarized, and problems of ISAR imaging for targets with complex motion are analyzed. At last, the main contents of the dissertation are introduced.In chapter2, several typical micro-motion forms for mid-course targets are analyzed to get ISAR imaging model of micro-motion dynamics. According to the complex motion of mid-course targets, the wideband radar echo model of ballistic mid-course targets after dechirping is firstly built. Then, the influence of micro-motion on ISAR imaging based on the established imaging model was presented. Computer simulation to get mid-course target echoes from static darkroom electromagnetic scattering data based on the established target motion model is realized. Finally, the simulated echo is used for ISAR imaging, and the echo model is verified by the imaging result.In chapter3, ISAR imaging for mid-course targets with uniformly accelerative rotation is researched. In ISAR, after rang compression and envelope alignment, the target can be equivalent to turntable imaging target. The motion of ballistic targets is very complex, after translational motion compensation, these targets cannot approximate to uniformly rotating targets, which means that traditional range-Doppler method can hardly achieve the desired ISAR imaging quality. To solve the problem, a new ISAR imaging algorithm based on the GRT and Clean method are proposed. Experiments based on simulation datas show the validity of the algorithm.In chapter4, ISAR imaging for mid-course targets with non-uniform rotation is investigated. Doppler frequency is time-varying due to non-uniform rotation, which results in ISAR images degradation. New ISAR imaging algorithm is proposed for the nonumform rotating target in2-D plane. The basic idea is to reconstruct the uniform sampling wavenumber spectrum of nonuniform rotating targets via the NUFFT transform. It is important to note that the proposed method does not assume any particular target motion model and has no parameter estimation. So it is more adaptable for realistic motion of targets. The result of simulated data shows the effectiveness of the method.In chapter5, an imaging method for mid-course targets within a small aspect sector is presented with the application of sparse signal processing. This method can form. ISAR images with higher resolution from compensated incomplete measured data, improve the clarity of the images and make feature structure much more clear, which are helpful for target recognition. The simulation results indicate that this method can provide clear ISAR images with high contrast under complex motion case.In chapter6, ISAR imaging for mid-course targets based on instantaneous frequency method is investigated. Firstly the performances of HHT transform and Hilbert/Huang time-frequency distributions in instantaneous frequency extraction are analyzed. Then new ISAR imaging algorithm based on EMD and HHT is proposed for time-frequency imaging of mid-course targets, and its performance is discussed afterwards. Experiments based on simulation datas show the validity of the algorithm.Chapter7is the summary of the dissertation. It also discusses the future work to be further researched.