Calibration of Polarimetric Millimeter MIMO Radar for Near-Field Ultrawideband Imaging Measurement

In this article, a polarimetric multiple input multiple output (MIMO) radar with a linear antenna array including eight transmitters and 12 receivers is developed and calibrated for near-field imaging measurement in frequency band spanning from 26.5 to 38 GHz. In the system hardware configuration, the single-polarized antennas are connected to a vector network analyzer (VNA) through a radio frequency (RF) switch matrix as a compromise of performance and expense. A two-step system calibration procedure is proposed in the compensation of signal distortion, where the measured polarimetric data of specified calibrators is compared with the simulation results at each channel to solve the compensation coefficients for frequency response. The measured 2-D radar images are generated by means of back projection (BP), in which the weight coefficient of each channel is calculated to minimize the difference in the simulation counterparts. The full polarimetric data of vehicles is acquired and processed to demonstrate the usefulness of the developed system along with its calibration procedure. The 2-D images generated in different frequency bands show that the dynamic range is about 40 dBsm for horizontal-horizontal (HH) and vertical-vertical (VV) polarizations, while it is around 30 dBsm for vertical-horizontal (VH) and horizontal-vertical (HV) polarizations. Meanwhile, the cross-polarization isolation of the developed system is better than 31 dBsm at the current state.