A Low-IF Doppler Radar With Asynchronous Bandpass Sampling for Accurate Measurement of Displacement Motions

In this article, a displacement motion sensing technique is proposed for Doppler radar with low-intermediate frequency (IF) architecture, which combines asynchronous bandpass sampling with a phase extraction (PE) technique. Asynchronous bandpass sampling is leveraged to reduce the sampling rate and ease the demands on analog-to-digital converters (ADCs). The PE technique can easily recover the signal phase information without the need for synchronization circuitry or carrier compensation circuitry, compared to the existing low-IF demodulation techniques. Moreover, the proposed technique is able to extract the phase evolution of a moving target from overmodulated IF signals without any distortion, which is superior to the state-of-the-art methods such as the envelope detection (ED) technique. The proposed extended PE technique eliminates the phase drift or jumps present in the PE process by using a multiperiod segmentation method. Experimental results demonstrate that the proposed technique can recover small displacement motions more accurately and has better sidelobe performance than the ED technique. For overmodulated IF signals caused by large displacement motions, the proposed technique can accurately extract the phase trajectory without distortion. Additionally, experiments demonstrate that the proposed technique can successfully capture physiological signals, such as respiration and heartbeat, while reducing the sampling rate to only 100 Hz for an IF of 1050 Hz. Finally, the effect of the extended phase extraction technique in eliminating phase drift or jumps is also verified by theoretical analysis and comparative experiments.