Miniaturized Circularly Polarized Doppler Radar for Human Vital Sign Detection

In this paper, a compact circularly-polarized (CP) continuous wave doppler radar system at 2.4 GHz is presented. The radar front end is a single dual CP antenna, which consists of a dual linearly polarized patch connected to a modified ring shaped quadrature hybrid coupler. This results to a very small overall footprint of the CP antenna (50mm × 50mm × 3mm). Despite its compact size, the high isolation (better than 30 dB) between the two ports of the CP antenna is achieved. With such a good isolation, the CP radar system with 0 dBm output power is sensitive enough to reliably detect both the heartbeat and respiration movements of a human test subject beyond 60 cm.