Forward-Looking MIMO-SAR for Enhanced Angular Resolution

Abstract

This paper analyzes the monostatic forward-looking synthetic aperture radar (FL-SAR) imaging problem. A frequency-modulated continuous wave (FMCW) signal model for the FL single input single output (SISO) SAR (FL-SISO-SAR) problem is presented. The FL-SISO-SAR model is then extended to the FL multiple input multiple output (MIMO) SAR (FL-MIMO-SAR). In both cases, the spatial dependence of the Doppler information along the travel path is exploited by means of Doppler beam sharpening (DBS). In addition to enhancing the angular resolution, the proposed method significantly suppresses the grating lobes. Finally, a simple method for reducing the computational complexity of the FL-SISO-SAR and the FL-MIMOSAR, using slow-time decimation with fast-time backprojection, is introduced. Simulation results for four different scenarios are presented. The results show a good angular resolution using the FL-SISO-SAR. Moreover, the FL-MIMO-SAR results in a more refined angular resolution and resolves the targets at zero look-angle, which is a fundamental limitation of DBS. In addition, the FL-MIMO-SAR suppresses the grating lobes, which are due to the large antenna spacing.