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An algorithm of range migration compensation for sidelooking SAR

DOI 10.18127/j15604128-201807-02


A.A. Monakov – Dr.Sc.(Eng.), Professor, Department of Radio Systems, Saint-Petersburg State University of Aerospace Instrumentation

Range cell migration is one of the main reasons for the defocusing of radar images in radars with synthesized antenna aperture (SAR). Nowadays there are two groups of signal processing algorithms for SAR, which compensate for the migrations. The first group includes algorithms that use the recalculation of the signal from the coordinate system «slant range - azimuth» into the system «along-track range – cross-track range» using different mathematical methods of function interpolation. Since the conversion from one coordinate system to another is, especially with large dimensions of the signal array, a fairly costly process, the algorithms of the first group require a significant amount of computing power in the implementation, which is a serious drawback of the algorithms of this class. The second group includes algorithms, the implementation of which does not involve the use of interpolation methods. These algorithms are not only inferior in quality to interpolation methods, but they are also much faster due to the application of fast procedures of the Fourier analysis in calculations. However, the algorithms of this group are also not devoid of shortcomings. These algorithms were developed with the expectation of using chirp-pulses, the time compression of which occurs not in a matched filter, but in the process of realizing the algorithm itself. This disrupts the overall structure of the digital part of the receiver in radar, where aperture synthesis is one of the possible modes of operation. In addition, taking into account that the chirp-pulses used in SAR have a duration that is commensurable with the pulse repetition interval, the signals are processed at large intervals of time, which leads to an increase in computational costs.
The article synthesizes a range migration compensation algorithm that does not use interpolation methods. The synthesized algorithm is a modification of the well-known Chirp Scaling Algorithm (CSA). The main difference lies in the fact that the stage of matched filtering of signals is isolated and implemented outside the migration compensation algorithm. This allows to abandon the assumption that the sounding signal of the SAR is a chirp-pulse with linear frequency modulation, and also reduces the dimensions of the processed signal ar-ray. The basis of the proposed algorithm is the fast procedures of the Fourier analysis. Thus, the proposed algorithm has a high speed and can be used for any sounding wideband signal. Mathematical simulation proved the high efficiency of the algorithm.

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