In this paper, we summarize our efforts of using three different radars (impulse radar, swept frequency radar,
and continuous-wave radar) for through-the-wall sensing. The purpose is to understand the pros and cons of each
of the three radars. Through extensive experiments, it was found that the radars are complementary and multiple
radars are needed for different scenarios of through-the-wall target detection and tracking.
In this paper, human motion model and RCS (radar cross section) simulation of radar returns from human are investigated.
Micro-Doppler signatures [1-6] induced by human motions are studied. It shows that the time-frequency representation
of micro-Doppler signature provides distinctive time-varying features for human motions. Motion of different body part
has different micro-Doppler signature. Thus, micro-Doppler can be a promising method for classifying human activities.
Measurement data using an experimental X-band micro-Doppler radar were collected and the results are compared with
the corresponding simulation results. The classification of human motions based on micro-Doppler signatures is also discussed.