In this paper we present the design, implementation and characterization of a radar front-end module for the detection of human vital signs. It utilizes a constant wave (CW) concept and can operate with a programmable 868–870 MHz carrier frequency in the industrial, scientific and medical (ISM) radio band of the short range devices in Europe. The printed circuit board integrates connectors for interfacing of the receive (RX) and transmit (TX) antennas and the in- and quadratur-phase outputs of the I/Q demodulator for further digital signal processing. A direct-conversion and a quadratur operation mode are possible. In direct-conversion mode the vital signs are easily detectable from the modulated common mode voltage.
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