Short-Range Millimeter-Wave Imaging in the Presence of Array Element Position Deviation

The focusing performance of an active short-range millimeter-wave imager is vulnerable to phase errors. As two major sources of phase error, delay uncertainty and array deformation are entangled when they are treated by conventional calibration methods, leading to defocusing. First, the defocusing effect caused by the array element position deviation (EPD) is graphically described in the form of ellipse deformation, indicating that the results of imaging a point target can inform on the distribution of EPD. Second, we analyze the phase error coupling problem to show that the EPD-caused phase error is spatially variant, therefore making the imaging performance sensitive to target location to varying extents bounded by the reference target location. Finally, a time-domain calibration method based on a constrained differential delay test is proposed to jointly mitigate the phase errors caused by both delay uncertainty and EPD. Numerical and experimental results demonstrate the efficacy of the proposed method.