Pragmatic Approach to Phase Self-Calibration for Planar Array Millimeter-Wave MIMO Imaging

To reduce the adverse effects of propagation delay uncertainty caused phase error, a pragmatic self-calibration approach for millimeter-wave multiple-in multiple-out (MIMO) imaging is proposed and demonstrated. Based on the analysis of the contributions of delay uncertainty and the assumption of identical channel design, the direct coupling between array elements is used to estimate the hardware-caused inherent channel delay, requiring no additional reference aid. Of the contributions to the delay, the common part and the part due to the interchannel difference are estimated separately. Combined with the array geometrical configuration, the direct coupling reflections are averaged to find the common channel delay, and the interchannel differences are estimated in a reduced geometric average scheme. The delay uncertainty is compensated by performing a phase shift operation to the received echoes for each channel. In addition, the proposed method also allows the accommodation of the slow change of the channel inherent delay automatically and constantly. Numerical analysis and experimental tests demonstrate the projected performance improvement of the proposed scheme as an alternative approach, which can also serve as a benchmark or booster for reference aided phase calibration methods.