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In this paper, we present a fast solution to build a Doppler radar system for noncontact vital sign detection (VSD) using instruments that are generally equipped in radio-frequency and communication laboratories. This paper demonstrates the feasibility of conducting research on VSD in ordinary radio-frequency laboratories. The system is designed with a heterodyne digital quadrature demodulation architecture that helps mitigate quadrature channel imbalance and eliminate the complicated dc offset calibration required for arctangent demodulation. Moreover, its tunable carrier frequency helps select different optimal frequencies for different human objects. Two sets of extensive experiments have been carried out in the laboratory environment with a self-designed 2.4-GHz patch antenna array and a 1-18-GHz broadband antenna. The test results are satisfactory: for a 0-dBm transmit power, the detection range can be extended to 2.5 m with accuracy higher than 80%. The system is also capable of detecting vital signs in the presence of different obstructions between the subject and the antenna.