Grating/side lobes mitigation in sparse UWB MIMO array
With finite aperture size and limited antenna number, sparse ultra-wideband (UWB) multiple-input-multiple-output (MIMO) array based imaging radar suffers from azimuth side/grating lobes. Commonly used aperture-domain mitigation methods such as coherence factor (CF), phase CF (PCF) and their modifications encounter some defects including insufficient data, suppression of weaker targets and heavy computing burden. In this paper, we propose extended CF (ECF) methods based on the sub-band subaperture (SBSA) image data to combat side/grating lobes and simultaneously overcome the above defects. With rational division of sub-bands and sub-apertures, on one hand, sufficient SBSA image data can be achieved in the UWB MIMO array, which guarantees the good side/grating lobe mitigation; on the other hand, SBSA image data have a certain ability of multiple targets discrimination in the range and azimuth directions and the side effects on weaker targets can be relieved. Besides, SBSA image data can be formed efficiently by the inverse fast Fourier transformation (IFFT) assisted back projection. Simulations with an 8-element UWB MIMO array validate the proposed methods.