Frequency-tuning technique for remote detection of heartbeat and respiration using low-power double-sideband transmission in the ka-band

A Ka-band transceiver using low-power double-sideband transmission to detect human heartbeat and respiration signals is demonstrated. The Ka-band electromagnetic wave offers higher detection sensitivity on small movement due to its shorter wavelength. Indirect-conversion receiver architecture is chosen to reduce the dc offset and 1/f noise that can degrade the signal-to-noise ratio and detection accuracy. Furthermore, the double-sideband signals at the transmitter output can be in quadrature by choosing a proper frequency separation to relieve the severe point problem that occurs at high frequency. As a result,the detection accuracy is significantly improved with low transmitted power. This radar sensor system achieves better than 80% detection accuracy at a distance of 2.0 m with a combined transmitted power of only 12.5 μW in both sidebands.