A Dual-Phase-Locked-Loop Single-Sideband Low-IF Radar With Asynchronous Bandpass Sampling for Precise Displacement Motion Detection

In this article, a novel technique combining asynchronous bandpass sampling and an optimized phase extraction technique (PET) is proposed to demodulate single-channel intermediate frequency (IF) signals for displacement motion detection in a dual-phase-locked-loop (PLL) single-sideband (SSB) low-IF radar. The proposed technique leverages the SSB low-IF radar to enable single-channel demodulation of IF signal, thereby preventing any demodulation performance degradation resulting from I/Q channel imbalances. Additionally, asynchronous bandpass sampling is employed to achieve spectral shifting of the IF signal based on a suitable sampling rate interval, consequently reducing the sampling rate and the volume of data. An optimized PET utilizing a sliding window and Fourier transform is introduced to demodulate single-channel IF signals, which offers a higher theoretical maximum unambiguous velocity compared to the conventional PET. Furthermore, compared to the commonly used digital downconversion (DDC) technique, the proposed technique has higher accuracy of the recovered motion trajectory, whose signal-to-noise ratio (SNR) is proven to be approximately 7 dB higher in both theory and experiments under a certain window length. Finally, comprehensive experiments on detecting low and high-speed actuator motion, as well as physiological monitoring, were implemented to demonstrate the advantages of the proposed technique in terms of detection accuracy, SNR, maximum unambiguous velocity, and effectiveness of vital signs detection.