Utilizing moving object's Doppler frequency-shifting effect, its moving speed and direction can be measured. Further introducing FMCW technology, one can measure targets' distance. Trigiant mmW's Doppler radar head is indeed a mmW T/R front end which is composed of a microstrip patch array antenna and a K-band Doppler transceiver module consisting of a Gunn diode oscillator and two Schottky diode mixers assembled into a die-cast waveguide package. By processing the mixing IF-I and IF-Q outputs, targets' speed, direction and even distance can be calculated.