Sidelobes and Grating Lobes Suppression Method for MIMO Radar Based on 2-D Sign Coherence Factor

Ultra-wideband multiple-input multiple-output （MIMO） radar obtains a large virtual aperture through a combination of different transceiver antennas， which significantly reduces the complexity and cost of the radar system. However， the spacing of transceiver array elements is usually larger than half a wavelength， resulting in sparse spatial sampling. It causes azimuth sidelobes and grating lobes to appear in the imaging results. The limited system bandwidth and sampling points further generate range sidelobes. High energy sidelobes and grating lobes seriously degrade the quality of the radar image and are not conducive to target detection and localization. Therefore， in this paper， a sidelobes and grating lobes suppression method is proposed based on the two dimensional （2-D） sign coherence factor （2-D SCF）. Unlike traditional one-dimensional coherence factor algorithms that calculate signal coherence in the aperture dimension， this method introduces a range coherence factor， which utilizes the sign-bit coherence of signals from different channels and frequencies to suppress the azimuth side/grating lobes and range sidelobes. First， the sign coherence factor （SCF） and range sign coherence factor （RSCF） are calculated. The 2-D SCF is obtained by multiplying the SCF and RSCF. This factor is then applied as a weight to the original back projection （BP） image， to simultaneously suppress the azimuth side/grating lobes and range sidelobes. Moreover， since the calculations are performed based only on the sign-bit of the signal， the computational complexity is lower than that of the 2-D coherence factor （2-D CF） and 2-D phase coherence factor （2-D PCF）， which makes it more conducive to the application of radar in real-time detection scenarios. Simulation and experimental results demonstrate that compared with the traditional one-dimensional coherence factor algorithm， this method increases the peak sidelobe ratio （PSLR） by 11~16 dB and reduces the integrated sidelobe ratio （ISLR） by 8~11 dB， thereby achieving side/grating lobe suppression comparable to 2-D PCF while reducing runtime to one-quarter that of 2-D PCF.