A heterodyne receiver for Harmonic Doppler radar cardiopulmonary monitoring with body-worn passive RF tags

Harmonic Doppler radar can be used to isolate a subject's respiratory motion from environmental clutter. In this paper, a heterodyne receiver is used to detect tag motion and human cardiopulmonary activity, with the results compared with a that using a homodyne receiver. The heterodyne system is shown to work at a greater distance from the subject (more than 160 cm) with greater sensitivity to tag motion (more than 10 dB), using the same transmitted power (10 dBm). Both homodyne and heterodyne receivers are also used to successfully detect a human heartbeat by attaching a passive harmonic tag over a subject's chest.