High Resolution Radar Singnal Modeling And Feature Extracting For Micro-motion Targets

Generally, micro-motion is defined as the mechanical vibrations or rotations or other high-order motions of a target or any structure of target in addition to its bulk translation. Micro-motion is widespread in nature and reflects some unique movement and structure character of objects. Therefore, it draws great attentions to the researchers from the areas of target detection and recognition. This dissertation researches the problem of how to deal with the high resolution radar echos from micro-motion targets, and the main studies and contributions can be summarized as follows:In chapterⅡ, the motion model for micro-motion targets and its modulation effect for high-resolution radar is studied systemly. First of all, the three-dimensional motion model of target is established. Then, combined with the two typical wideband waveform, LFM signal and SF signal, the modulation effects caused by micro-motion on Doppler frequency, high resolution range profile, profile sequence and ISAR image are analyzed. Especially, the equivalent instantaneous Doppler frequency is introduced to deal with the coupling between range and Doppler for SF wideband radar.The issue of micro-Doppler signal separation for targets with micro-motion structures is addressed in chapter III. Firstly, the basic principle of signal separation based on chirp rate is introduced. Then, a fast algorithm on parameter estimation of chirplet signlas is proposed. Also, the CRB on Chirplet parameter estimates is deduced and the influence of other parameters on the Chirp rate estimate is analysed. To further reduce computation, a micro-Doppler signal separation method based on AM-LFM decomposition is proposed, which has no constraint on signal envelope and can obtain a better separation results with less computation.The parameter estimation for some typical micro-motion structure is studied in chapter IV. It's pointed out that the vibration and rotation structures will appear as a sinusoid in two-dimensional image (time-range image or time-Doppler image) under the LFM or SF wideband systems. The relationship between the sinusoid parameters and micro-motion parameters is deduced and a time saving approach to extract the sinusoid is proposed. Then, a method based on imaging quality is proposed to estimate the precession parameters for the precessing warhead in middle course. Also, an approach is designed to reduce the searching parameters for the proposed method: searching parameters is reduced to two dimensions after estimating the symmetry axis of echos, and they are further reduced to one dimension by ultilizing the structural and scatter characters of warheads. This algorithm exploits the warheads's structural and scatter characters reasonably, which can estimate the precssion parameters of warheads with unknown size during one period.ChapterⅤstudies how to obtain high-dimensional image for small-angle micro-rotation targets. The Doppler frequency casued by rotation is the foundation for two dimensional imaging, but traditional imaging algorithms only suit for the uniform rotation situation. Taking the oscillating ships in sea as an example, this chapter proposes to use the following AM–FM function to model the radar echoes of complex moving targets: the amplitude of scattering centers are modeled by Q-order polynomial functions, the phase of scattering centers are modeled by cubic polynomial with higher-order error items. Also, a parameter estimation algorithm is proposed for the above model and the phase matrix is formed after the phase history being established for each scattering center. Then, a method based on the singular value decomposition of the phase matrix is proposed to obtain the image for small-angle micro-rotation targets. The image is a focused two-dimensional image for nonuniform rotating targets in plane or a three-dimensional scattering center model for three dimensional rotation targets.In chapterⅥ, the contributions of this dissertation are summarized and the potential problems and difficulties are also pointed out.