Solving Phase Ambiguity in Interferometric Displacement Measurement With Millimeter-Wave FMCW Radar Sensors

The frequency-modulated continuous-wave (FMCW) radar sensor is subject to phase ambiguity in measuring large displacement of over half a wavelength, which is particularly severe in the millimeter-wave FMCW radar sensor due to its short wavelength. The state-of-the-art linear phase demodulation techniques were mostly developed for single tone quadrature continuous-wave (CW) radars such as the Modified differentiate and cross-multiply (MDACM) algorithm. This paper presents a novel linear interferometric displacement measurement technique which can synthesize the quadrature
${I}/{Q}$
signals across slow time from a single-channel FMCW radar. In this way, the linear phase demodulation technique developed for the CW radar can now be leveraged for the FMCW radar. The theoretical analysis and working principles are discussed. Exhaustive experiments are performed to validate the proposed technique. It is demonstrated that the displacement motions as large as 10 times of the wavelength can be precisely extracted from a single channel FMCW radar with micrometer accuracy and without any phase ambiguity.