A 5 GHz double-sideband radar sensor chip for non-contact vital sign detection was designed and fabricated in UMC 0.18 mum mixed-mode/radio frequency CMOS process. The transceiver was designed with a differential architecture. Measurements show that it has over 1 GHz tuning range, and can successfully detect both the respiration and the heartbeat signals of a human subject. It is also shown that the differential architecture has the advantage of reducing local oscillation leakage. The 5 GHz double-sideband system can avoid null detection point by frequency tuning.