An integrated dual-band transmitter for vital sign detection radar is developed in 0.18-μm CMOS process. The main concept of this system is using frequency diversity to maintain the signal-to-noise ratio (SNR) under various detection environments. The phase-locked loop (PLL) is used for long range detection. By using frequency doubler and frequency divider inherited in the PLL, the transmitter covers two frequency bands, which are 4.27 GHz to 4.98 GHz and 17.06 GHz to 19.93 GHz, respectively. The measured conversion gains (CG) of low band and high band are 13.6-16.3 dB and 13.4-19.3 dB. The maximum output power of low band and high band are -6.2 and 3.4 dBm, respectively. This dual-band transmitter consumes 77-mW dc power within a chip size of 3.52 mm2.