RF bio-radar system using a compact lumped six-port demodulator and Quadrifilar Helix antenna

This paper presents a bio-radar system using a compact lumped six-port demodulator and a Quadrifilar Helix Antenna (QHA) for remote respiration and heartbeat monitoring. Since bio-radar applications require low power characteristics and six-port structure has an advantage in low power operation, the proposed system is configured with a six-port demodulator replacing active frequency mixers. For the compactness and minimization in size at low frequency applications, the six-port demodulator which consists of three hybrid couplers and a power divider is implemented by lumped elements. Also, the proposed system adopts a QHA module that has high Tx and Rx isolation characteristics. The system performance is verified at 917 MHz by monitoring respiration and heartbeat.