Research On Radar Imaging Technique Bassed On The Space-spectrum Analysis

A high resolution radar images moving targets. Target structure information can be obtained, which is beneficial to target characteristic analysis and target recognition. The imaging radar must obtain the space-spectrum samples in an interested region to achieve high resolution and reconstruct target reflectivity-functions. According to the method of obtaining space-spectrum samples, the moving target imaging technique can be divided into two kinds: inverse synthetic aperture radar (ISAR) imaging technique and real aperture radar imaging technique. The sufficient space-spectrum samples of ISAR imaging are formed by target motion with respect to the imaging radar, whereas a real aperture imaging radar obtains the space-spectrum samples along different directions by a large antenna array.By analyzing the space-spectrum measurement of radar imaging, the applicable scope of different imaging methods can be examined, furthermore it is more convenient to find a way for investigating suitable imaging methods. The target motion of ISAR imaging induces phase errors and changes the distribution of the space-spectrum samples, whereas the sensor arrangement of a real aperture radar determines the data-support region in space-spectrum space.In this dissertation, we analyze ISAR imaging technique from space-spectrum measurement, and present the ISAR imaging methods under the conditions of different space-spectrum measurements firstly. Considering the difficulty of real aperture imaging, we propose the imaging method based on distributed multi-channels radars secondly. The research results of the dissertation are given as follows:(1) Target motion effect on ISAR imaging is investigated. We detail the range-compressed phase history induced by different target motions firstly. Moreover, we investigate the space-spectrum measurement under the conditions that imaging targets have two-dimensional rotation and three-dimensional rotation respectively, in order to illuminate target motion effect more clearly.(2) The ISAR imaging methods based on the space-spectrum samples on a plane are proposed. When the direction of a target rotation vector is constant, the space-spectrum samples on a plane can be divided three kinds: In the first situation, the target uniformly rotates through a small angle, therefore the space-spectrum measurement can be approximated to the uniform samples in a rectangle; in the second situation, the space-spectrum samples are non-uniform in cross directions because of the non-uniform rotation of the imaging target; in the third situation, the space-spectrum measurement are the non-uniform samples in a pan, since the target rotates through a large angle-interval. For the three kind of the space-spectrum measurement, we propose the autofocusing algorithm based on the maximum likelihood estimation, the imaging method based on the discrete chirp-Fourier transform and the approximately polar formatting algorithm respectively. (3) The ISAR imaging methods based on the space-spectrum samples in a curve are proposed. Firstly we present the echo-signal model of the targets with three-dimensional rotation, which causes space-spectrum samples to be on a curve. Moreover, we propose the imaging algorithm of complex motion targets, under the condition that the space-spectrum measurement curve is approximate to a plane. Finally, we propose the algorithm to select imaging time for the great maneuver targets.(4) The imaging method of a distributed multi-channel radar is proposed. After investigating the difficulty of real aperture radar imaging, we propose the imaging method of a distributed multi-channel radar by analyzing space-spectrum measurement firstly. Moreover, we present the imaging principle of this radar. Finally, we examine the distribution characteristic of space-spectrum samples, investigate the image performance and discuss the phase errors induced by the location errors of the transmitters and receivers.(5) The target imaging implement of a distributed multi-channel radar is proposed. We propose the rules about transmitter/receiver distribution through analyzing the sensor-distribution effect on imaging performance firstly. Then after investigating the phase errors characteristic of distributed multi-channel radars, we propose the algorithms for phase error correction. Finally, we present the polar-format imaging method based on the characteristic of space-spectrum samples.