Noncontact Vital Sensing With a Miniaturized 2.4 GHz Circularly Polarized Doppler Radar

Conventionally, in Doppler radar vital sign detection, two separate linearly polarized TX and RX antennas are used and often placed more than half wavelength away from each other to mitigate mutual coupling. However, the overall footprint of the radar system with separate TX/RX antennas may make it difficult to be integrated into compact consumer devices. In this article, a single dual circularly polarized circular patch antenna was presented to help to achieve a miniature Doppler radar system. The proposed antenna was designed, integrated, and demonstrated with a 2.4 GHz radar transceiver module, but the design method and approach could be extended to higher frequencies to help to reduce the antenna area needed for radar sensing. The designed antenna at 2.4 GHz has the largest dimension of no larger than 5 cm and TX/RX isolation of better than 30 dB, ensuring good detection sensitivity. With a low output power of 0 dBm, both respiration and heartbeat movements of human test subjects can be detected accurately.