Quadrature Radar Demodulation Techniques for Accurate Displacement Detection

Abstract

Microwave Doppler radar systems can be used to measure human vital signs by tracking torso displacement. Technical requirements for such systems depend on detection object and objective, resolution and sensitivity, as well as practical constraints such as cost, size and power consumption. Due to its simple structure and validity, direct conversion systems are commonly used for vital signs detection applications. One problem with such systems is that motion or displacement detection accuracy is often compromised by the presence of dc offset that limits the overall signal to noise ratio (SNR) and the system resolution. While the portion of dc offset caused by system imperfections and the external environment is problematic, the dc offset contributed from the subject is critical for accurate displacement measurement. In this research, dc offset optimization methods for direct conversion systems are studied. A method is proposed to make possible accurate measurements of a moving subject, through a system which preserves useful dc contributions while eliminating non-essential dc components which would otherwise undermine the use of appropriate gain and resolution. The performance is contrasted with an ac coupling method using high-pass or band-pass filters and other established dc management approaches.