Study On The Imaging And GMTI Algorithms For Distributed Radar

Distributed radars have been paid to extensive attention in recent years and are becoming the hot research field in radar technologies, especially in SAR, because of their broad prospects in realizing high-resolution, wide-swath, three-dimensional imaging and GMTI (Ground Moving Target Indication). The dissertation focuses on the problems of imaging and GMTI by distributed radar with emphases on the imaging algorithms of distributed SAR and GMTI algorithms of STAP (Space Time Adaptive Processing) and SPIR (Scanning Pattern Interferometric Radar). The major contents of each chapter are summarized as follows:Chapter 1 introduces the background and current research status in domestic and abroad, summarizes the major works and contributions.Chapter 2 introduces the works on SAR imaging simulation. Study shows that bright and dark strips appear in simulated SAR images, when point-targets are used to simulate distributed target. In the bright strip areas, both of the resolution and definition are very high, and the phase information is well preserved. In dark strips however, both of the resolution and definition are degraded, as well as the phase information is destroyed. Radiation pattern of sparse array antenna is applied to explain the phenomenon and three methods are proposed to remove this effect.Chapter 3 introduces two processing method for stepped-frequency chirp signals (SFCSs), i.e. the subaperture method based on matched filtering and the de-chirp method, and gives comparison between these two methods. The works in this chapter lay a theoretical foundation for the development of imaging algorithm in chapter 4.Chapter 4 firstly establishes an equivalent relation between the signal models of distributed SAR in both range and azimuthal directions and that of SFCSs. Two preconditions for the existence of equivalent relation should be contented, i.e. the same target point in observed area should be selected to calculate the reference ranges for matched filter of each SAR in range direction, and in azimuthal direction, there should be small squint angle for each SAR and the angle difference between any two neighbor SARs is the same. And then, the algorithms introduced in chapter 3 are applied to process the range and azithumal signals of distributed SAR. This chapter also proposes the idea of general aperture synthesis, i.e. the idea of aperture synthesis across different platforms. The presupposition of general aperture synthesis is that the observed spatial spectrum should be coherent with phase differences between different platforms removed. Studies show that the relative accuracy of range measurement between different SARs and the squint angle measurement accuracy of each SAR dominate the facts of preventing resolution improvement in range direction and azimuthal direction, respectively.Chapter 5 concentrates on the STAP and SPIR algorithms for distributed radar with sparse apertures realizing GMTI functions. In the study of STAP, major facts for affecting the performance of STAP are stressed. In view of the grating lobes, i.e. blind zone problems, inherently existed in sparse array, techniques of using multi-carrier frequencies and non-uniform of array are used to mitigate this problem. In the study of SPIR, the key facts influencing the performance of SPIR investigated, such as the position accuracy of array element, the amplitude and phase accuracy between arrays. Studies show that although the SPIR algorithm solves the blind zone problem well, the performance stability is affected greatly by ground clutter, because the ground clutter results in the increase of condition number of Point Spread Function (PSF) matrix, so clean algorithm must be incorporated to overcome the problem. Simulations show that as the element number of array increases, the ability of putting up with the above errors of SPIR algorithm increases correspondingly. The accurate measurement of real position is much more important than the control of position for a designed distributed architecture in some degree.Chapter 6 gives reviews and concluding remarks for the whole work in the dissertation, and at the same time points out some limitations and proposes four research aspects, which should be aimed to solve in the future.