Abstract
University of Chinese Academy of Sciences, Haidian, Beijing, ChinaAbstract. For synthetic aperture radar (SAR) imaging, a stepped-frequency chirp signal iswidely used to obtain ultrahigh range resolution. There are mainly two challenges in thestepped-frequency SAR imaging. One is the subbands synthesis, and the other is the estimationand compensation of amplitude andphase errors of the subbandscaused by the radar system andthe propagation. An imaging approach for the airborne squinted sliding-spotlight SAR withstepped-frequency chirps is proposed to achieve ultrahigh two-dimensional (2-D) resolution.Due to the squint angle, a Doppler centroid shift is introduced and then a modified space-variantcompensationmethodfortherangedifferencebetweenthesubbandsisrealizedviamultiplyingaphaserampinthe2-Dfrequencydomain.Moreover,arange-dependentphasegradientautofocusalgorithm based on raw data is proposed to estimate and compensate the residual phase errorafter the internal calibration. Afterward, the frequency-domain synthetic bandwidth method isused to complete the bandwidth synthesis. Finally, the extended Omega-K algorithm is appliedto focus the synthesized data. The simulation results and the real data processing results provethe validity of the proposed approach.
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