A Fundamental-and-Harmonic Dual-Frequency Doppler Radar System for Vital Signs Detection Enabling Radar Movement Self-Cancellation

This paper proposes and presents a cost-effective fundamental-and-harmonic dual-frequency (FHDF) Doppler radar system for vital signs detection from a mobile radar platform. The proposed FHDF radar architecture concurrently transmits the fundamental signal component (FSC) and its inherent second harmonic signal component (SHSC) of the voltage-controlled oscillator toward opposite directions. The FSC is transmitted toward a target in motion, while the SHSC is transmitted toward a stationary low-cost reflector. For the receiver, a coherent dual-band dual-low-IF architecture is derived and proposed for the first time. This architecture can concurrently receive the reflected FSC that is phase modulated by both motions of the target and the radar platform, and the reflected SHSC that is phase modulated only by the motion of the radar platform, without aliasing, thus enabling the reduction of the overall radar size, power consumption, and system cost. Through the subtraction of a pertinent information contained in the received SHSC from the information embedded in the received FSC using an adaptive noise cancellation technique, the resulting signal contains the desired information that is free of motion artifacts from a moving radar platform. Experimental results show that the proposed radar system is capable of extracting human vital signs, including respiration and heartbeat, even in the presence of a large radar platform movement. By using the proposed FHDF radar system, a see-through-wall vital signs detection from a mobile radar platform can also be successfully conducted without using any additional sensors.