A Cost-Effective Single-Channel Displacement Measurement Technique Without Down-Conversion Using Low-IF Doppler Radar

A novel cost-effective displacement measurement technique based on low-IF Doppler radar is introduced in this paper. This technique only requires the acquisition of the single-channel IF signal, avoiding the
$\boldsymbol{I}/\boldsymbol{Q}$
mismatch issue and reducing circuit complexity. The
$\boldsymbol{I}/\boldsymbol{Q}$
signals are obtained by splitting and solving the single-channel IF signal with a transformation matrix, eliminating the need for the digital down-conversion and thus avoiding low-pass filtering-induced group delay issues. Moreover, this technology allows asynchronous bandpass sampling of the IF signal, reducing the demand for analog-to-digital converter sampling rate. An experiment involving mechanical vibration also demonstrates the superiority of the proposed technique, with a calculated root mean square error (RMSE) of only 2.9% of the displacement and without group delay issues faced by the digital down-conversion method, while the intermediate frequency is 10.4 kHz, and the sampling rate is 1 kHz.