Wearable Vital Sign Sensing Radar Antenna with Moving Clutter Immunity

This work adopts a self-injection locked (SIL) bistatic radar capable of achieving the properties of high-sensitivity, small form factor, and low power consumption. This architecture is ideal for wearable vital sign sensor, the primary circuits are an SIL tag consisting of an omnidirectional monopole antenna and a frequency selective surface (FSS), and a mobile receiver consisting of a left-hand circularly polarized (LHCP) antenna and a delay discriminator. Worn on the subject's chest, the mobile tag can sense the fluctuations on skins caused by cardiopulmonary activities, and the polarization of the radiating electric field is then converted by the FSS to send an LHCP wave to the remote handheld receiver. Benefiting from polarization diversity, the SIL tag can reject moving clutter in the environment. In the experiments, the 2.4 GHz prototype was not affected by the movement of the handheld receiver or a walking person in the environment. The cardiopulmonary information is still reliable.