Fully Polarimetric Calibration of a Near-Field MIMO Imaging Radar Using the QCCLD Reflector

Fully polarimetric multiple input multiple output (MIMO) radars are getting more and more applications for near-field polarimetric scattering matrix (PSM) imagery. A polarimetric MIMO radar consists of a large number of transmitting and receiving channels. The crosstalk and imbalance among the channels severely distort the measured PSM. In this article, a fully polarimetric calibration technique for a near-field MIMO imaging radar is proposed using a single passive calibrator named quarter concave cylinder linked dihedral (QCCLD) reflector which was presented in our previous work. The bistatic PSM of the QCCLD is derived based on physical optics (PO) approximation. For a QCCLD rotating around the line of sight (LOS) between the centers of the MIMO array and the calibrator, higher order scattering components are excited under bistatic transceiver antennas. Besides, a polarimetric calibration procedure for near-field MIMO imaging radar is developed. Utilizing Fourier analysis, three main scattering components (MSCs) of the QCCLD are extracted, while the undesirable scattering components which degrade the calibration accuracy are suppressed. Outdoor experiments are conducted using a polarimetric near-field MIMO imaging radar over 12-18 GHz frequency band. It is shown that after fully polarimetric calibration using the QCCLD, an improvement of more than 12 dB in polarization isolation is obtained, validating the proposed technique. Further analysis using polarimetric decomposition of the calibrated PSM images for both the Sandia laboratories implementation of cylinders (SLICY) benchmark target and a Volvo sport utility vehicle (SUV) demonstrate the usefulness in identifying scattering mechanisms.