A UWB impulse Doppler radar has been developed recently to detect the micro-Doppler signatures of human motions. The system RF front-end, wideband antenna array and high speed data acquisition module are introduced in details. The developed radar is used to detect the Doppler features of arms swing, which has unique characteristics compared to movements of other body components, for intelligent human gait recognition. Several experiments, including human marching and walking, with either one-arm or two-arm swings, have been performed. Promising experimental results have been achieved from both high resolution range profiles and Doppler spectrogram. The developed radar is also capable of detecting vibrations of respiration and heartbeat for stationary human targets buried in collapse for search and rescue operations.