Multi-Phase CW Doppler Radar for Measuring Small Periodic Displacement

A Multi-phase continuous-wave (CW) Doppler Radar is proposed for measuring small periodic displacement. Multi-phase local oscillator (LO) signals are incident to quadrature mixers to simultaneously generate multiple arcs on the complex plane. Multiple arcs obtained from synchronized data at the same time can be provided in the circle fitting method to compensate for DC offset voltages on the radar. A 5.8 GHz CW Doppler radar with four-phased LO signals, which are generated by a passive balun and two hybrid couplers, is implemented on an FR4 PCB for measuring the periodic displacement at the distance of 0.5 m. Compared to the conventional CW Doppler radar based on a single arc, measurement results show a lower root mean square error (RMSE) and that the RMSE is effectively reduced by more than three times at displacements less than 2 mm.