Study Of Imaging Methods Of SAR And Jamming Methods Against SAR

Synthetic aperture radar is a kind of imaging radar with characteristics of all-weather, day/night and long range, which could provide high-resolution image. The advent of SAR expands the original concept of radar. It has the capability of imaging and recognizing the territorial targets, which is of great importance in either military or civilian fields. Since synthetic aperture radar has prominent performances and wide military applications, it is urgent to study jamming methods against SAR, the work is important to technical modernization of national defence.In order to study jamming methods against SAR, we should understand principle and imaging algorithms of synthetic aperture radar, which provide the foundation for study of jamming methods against SAR. Aim of the dissertation is to study imaging and jamming methods of SAR, which include following aspects: imaging principle of SAR in range and azimuth dimension, imaging processing of stripmap SAR and spotlight SAR, imaging algorithms and improved algorithms of SAR, jamming methods against SAR, evaluation of jamming effectiveness of SAR. Primary work of the dissertation is summarized as follows:1. The dissertation studies imaging principle of SAR in range and azimuth dimension, which is basis of two-dimensional SAR imaging methods. The processing methods concerned with range imaging are presented, which include matched filtering and dechirp processing in range dimension. The problem of choosing range sampling rate is studied in order to reduce the range sampling rate. From viewpoint of range point spread function, range resolution is analyzed. The steps of range imaging are given. The processing methods concerned with azimuth imaging are presented in detail, which include matched filtering and dechirp processing in azimuth dimension. Dechirp processing in azimuth dimension is a processing tool which could reduce PRF in spotlight SAR and digital spotlight the desired target area. The dissertation studies the problem of choosing azimuth sampling rate under different conditions in order to reduce the azimuth sampling rate. From viewpoint of azimuth point spread function, azimuth resolution is analyzed. The steps of azimuth imaging are given.2. The dissertation studies difference and relationship between stripmap SAR and spotlight SAR. Spatial frequency interpolation algorithm is discussed, which could adopted to either stripmap SAR or spotlight SAR. The difference on the algorithm between stripmap SAR and spotlight SAR is analyzed, based on which imaging algorithm of both stripmap SAR and spotlight SAR is unified. The dissertation compares stripmap SAR and spotlight SAR in various aspects, which include spectrum structure, bandwidth of echo, resolution, sampling rate, azimuth dechirp processing of spotlight SAR, imaging processing with data of partial beam. The dissertation brings forward a method which adopts spotlight processing of stripmap SAR data under squint condition and analyzes how to choose parameters of the spotlight imaging area. The method could decrease amount of computation and provide flexibility of data processing of SAR.3. The dissertation puts forward an improved imaging algorithm of SAR named as phase alignment algorithm of subaperture reference signal. The algorithm adjusts phases of respective subaperture reference signals in ordre to make them be in phase and adopts the inphase reference signal to demodulate subaperture echo signal of the target area, then constructs a new spotlighting window function for SAR imaging. Theoretical analysis shows that under condition of the same sample data, the improved algorithm could increase SAR scene area in azimuth dimension relative to subaperture digital spotlighting algorithm.4. The dissertation studies serval imaging algorithms of SAR, which include range migration algorithm (RMA) and range stacking algorithm. Key processing methods of the two algorithms are analyzed. Starting from analysis of RMA, the dissertation investigates dechirp processing of SAR imaging thoroughly, which includes range dechirp processing, azimuth dechirp processing, two-dimensional dechirp processing consisting of motion compensation to point and motion compensation to line, range deskew processing plus RVP calibration. The dissertation compares RMA with spatial frequency interpolation algorithm. Based on the theoretical analysis, the dissertation proposes an improved method which modifies spatial frequency interpolation algorithm, with substitution of range dechirp processing plus RVP calibration of RMA for fast-time matched filtering of spatial frequency interpolation algorithm. This method can reduce range sampling rate obviously, which brings great benefit to ultra-bandwidth radar signal processing.5. Since synthetic aperture radar has advantage of high signal processing gain, the dissertation proposes several coherent jamming methods against SAR, key parameters of which are analyzed. Coherent jamming methods could obtain whole or partial processing gain of SAR, which enhances efficiency of jamming power relative to classical incoherent jamming methods. The dissertation proposes a deception jamming method against SAR, which adopts digital image synthesis and obtains the same processing gain as echo of SAR. The quantities of phase and amplitude modulation of the deception jamming method are determined through theoretical analysis. Steps of the deception jamming method are given. The dissertation presents shift-frequency jamming methods against SAR, which include shift-frequency jamming method in range dimension, shift-frequency jamming method in azimuth dimension and two-dimensional shift-frequency jamming method. Model and parameters of the shift-frequency jamming method are developed theoretically. Theoretical analysis shows that the shift-frequency jamming method could obtain partial processing gain of SAR. The dissertation brings forward weighted frequency modulated jamming methods against SAR, which include weighted sine frequency modulated jamming method, weighted sawtooth frequency modulated jamming method and weighted noise frequency modulated jamming method. How to choose key parameters of weighted frequency modulated jamming methods is analyzed. The dissertation puts forward two-dimensional weighted frequency modulated jamming method and a method which combines weighted frequency modulated jamming and shift-frequency jamming in two dimensions in order to jam SAR in two-dimensional domain. Theoretical analysis shows that the weighted frequency modulated jamming against SAR could be regarded as linear combination of multiple shift-frequency jamming and could obtain partial processing gain of SAR.6. The dissertation studies evaluation of jamming effectiveness against SAR. Since SAR is a kind of two-dimensional imaging radar, target of which is extended and result of which is a image, it is necessary to evaluate jamming effectiveness against SAR based on the image. The dissertation discusses mathematical models of different received SAR signals and judging criterion of barrage jamming against SAR. The criterion is established on the basis of variation of ratio of clutter power to noise power and ratio of clutter power to jamming power. From the viewpiont of tactical application, the dissertation discusses a concept called jammed region, which could evaluate barrage jamming effectiveness against SAR. The dissertation proposes a method of distributed jamming system against SAR based on contour curve chart, which could measure jammed scope of SAR in azimuth dimension. From the viewpiont of image qulity evaluation, the dissertation studies evaluation of barrage jamming effectiveness and deception jamming effectiveness against SAR.