AC/DC coupling effects on CW and pulse transmission modes in Doppler radar physiological monitoring system

Direct-conversion CW microwave Doppler radar can be used to wirelessly detect cardiopulmonary activity. One of the limitations of homodyne CW Doppler radar systems for physiological monitoring is large DC offset in baseband outputs. The common method to avoid the DC offset is AC coupling. While AC coupling removes the DC offset efficiently, it introduces large settling time and signal distortion in baseband. In this paper we explore the use of direction conversion pulsed Doppler radar to overcome this issue. Performance of CWand pulse radar is compared using mechanical target movement which simulates respiratory motion. The results demonstrate while AC coupling distorts CW radar output, it has a negligible effect on pulse radar output.