Continuous wave radar

A continuous wave (CW) radar has been used for the detection and classification of people based on the Doppler signatures they produce when walking . When humans walk, the motion of various components of the body including the torso, arms, and legs produce a very characteristic Doppler signature.

The radar principle used is FMCW (Frequency Modulated Continuous Wave) . The FMCW-radar transmits a high frequency signal whose frequency increases linearly during the measurement phase (called the frequency sweep). The signal is emitted, reflected from the measuring surface and received with a time delay, t.

CW radar can measure the instantaneous rate-of-change in the target’s range. This is accomplished by a direct measurement of the Doppler shift of the returned signal . The Doppler shift is a change in the frequency of the electromagnetic wave caused by motion of the transmitter, target or both.