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Multiple-channel ISAR Imaging

Posted on:2012-12-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y T ZhuFull Text:PDF
GTID:1118330362460314Subject:Information and Communication Engineering
Abstract/Summary:PDF Full Text Request
Imaging to the flying target is very useful for both military and civil use. Inverse synthetic aperture radar (ISAR) is the typical imaging technique to flying target. But the unexpectable target motion trail and parameters will lower down the ISAR imaging quality. This problem will become more serious when imaging to the high motion target. Compared with ISAR imaging technique, array imaging technique can realize single snap imaging to the flying target, and will nearly be not affected by the target motions when pulse width of the transmitting signals is narrow. But to realize array imaging needs lots of physical antenna elements, the hardware is complex and the cost is high. If ISAR imaging technique and array imaging technique can be combined, the combined imaging technique will use less antenna elements and shorter coherent processing interval (CPI), and can realize high resolution imaging to most of flying targets. The multi-channel ISAR imaging technique researched in this paper is this kind of combined imaging technique.There are four sections researched in this paper, i.e. multi-channel ISAR imaging theory, MIMO-ISAR 2-D imaging technique based on the MIMO (multi-input multi-output) radar linear array, MIMO-ISAR 3-D imaging technique based on the MIMO radar plane array and imaging performance improving methods.Conventional ISAR imaging technique is based on the turntable imaging model, which considers that the target motion is smooth. However, only single radar is used in conventional ISAR to detect target, and the coherent processing interval (CPI) is quite long. In fact, many targets can not always keep smooth motion in the long CPI, and do not completely fit the conventional ISAR imaging model. Multi-channel ISAR imaging technique uses multiple radar channels to detect target, its CPI is very short, so the target motion during the CPI can be regarded as continuously smooth and fits the imaging model well. Additionally, multi-channel ISAR imaging technique can estimate target motion parameters based on the spatial positions of all radar channels, so the imaging algorithms can be modified and the imaging qualities will be improved. There are mainly three modes in multi-channel ISAR imaging technique, i.e. single-transmitter multi-receiver ISAR imaging technique, multi-radar ISAR imaging technique and MIMO-ISAR imaging technique. The MIMO-ISAR imaging technique is proposed by the same author of this paper in Sept. 2009, which is the first time it appears in the world. The MIMO-ISAR imaging technique uses MIMO (multiple input multiple output) radar array to realize ISAR imaging. Compared with other multi-channel ISAR imaging modes, when using the same number of antenna elements it can obtain more target information, and has obvious advantages in many aspects such as imaging performances, hardware cost and application ranges and so on. This paper mainly focuses on MIMO-ISAR imaging technique.Firstly, some basic techniques of MIMO radar are researched. The orthogonal signal modes and design methods are summarized. And an important MIMO radar array design theory, spatial convolution theory, is analyzed and expressed by mathematic equations. Based on it a MIMO radar array design method by using self-convolution operation is proposed. Then, another important MIMO radar array design theory, phase center approximation (PCA) theory is introduced and the relationship between it and spatial convolution theory is analyzed. Finally the equivalent relationship between MIMO radar array space sampling and ISAR time sampling is discussed, and MIMO-ISAR imaging theory is expounded.In the second section, MIMO-ISAR imaging technique based on MIMO radar linear array is proposed. It includes MIMO radar linear array design, orthogonal signal design, target motion parameter estimation, data fusing, motion compensation and imaging algorithm and so on. To research this technique, a kind of MIMO radar linear array design scheme is introduced at first. Then two data rearrange methods are proposed which are based on minimum entropy principle and based on correlation operation respectively. According as characteristics of the range image in MIMO-ISAR 2-D imaging, the multi-subsection correlation motion compensation algorithm is proposed. And a migration through range cell (MTRC) correction method is introduced. Finally, MIMO-ISAR 2-D imaging model is built and corresponding realizing procedure is given also.The key techniques to expend MIMO-ISAR system from 2-D imaging to 3-D imaging are MIMO radar plane array design, 3-D data rearranging and fulfilling technique and 3-D imaging algorithms. Focus on these key techniques, two kinds of MIMO radar array designs are proposed at first, i.e. the orthogonal cross MIMO radar plane array and double-rectangle MIMO radar plane array. The MIMO-ISAR 3-D imaging model is built and two typical imaging procedures, i.e. imaging in turns and imaging as a whole, are analyzed. Then 3-D data rearranging and fulfilling techniques are researched, and two algorithms i.e. a correlation operation 3-D data rearranging algorithm and a dimension reduction 3-D data fulfilling algorithm are proposed respectively.For reason that multi-channel ISAR imaging technique combines the space sampling of multi-channel and the time sampling of ISAR, its point spread function (PSF) and corresponding spectrum support are obviously different from conventional radar imaging. So in the last section of this paper, some methods which can improve the quality of multi-channel ISAR imaging are researched. Firstly, some important characters about PSF and spectrum support are given and the definition of sidelobe direction is proposed, they are propitious to discuses the particularity of MIMO-ISAR imaging. Then based on the characters of 2-D Fourier transform, the sidelobe direction properties are summarized and three typical applications are given. At last, ellipse window 2-D sidelobe reduction algorithm and spectrum reshaping sidelobe reduction algorithm are proposed.
Keywords/Search Tags:multi-channel, MIMO radar, inverse synthetic radar, radar imaging, array design, spatial converlution, phase center approximation, sidelobe reduction
PDF Full Text Request
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