A Multifrequency Radar System for Detecting Humans and Characterizing Human Activities for Short-Range Through-Wall and Long-Range Foliage Penetration Applications
A multifrequency radar system for detecting humans and classifying their activities at short and long ranges is described. The short-range radar system operates within the S-Band frequency range for through-wall applications at distances of up to 3？m. It utilizes two separate waveforms which are selected via switching: a wide-band noise waveform or a continuous single tone. The long-range radar system operating in the W-Band millimeter-wave frequency range performs at distances of up to about 100？m in free space and up to about 30？m through light foliage. It employs a composite multimodal signal consisting of two waveforms, a wide-band noise waveform and an embedded single tone, which are summed and transmitted simultaneously. Matched filtering of the received and transmitted noise signals is performed to detect targets with high-range resolution, whereas the received single tone signal is used for the Doppler analysis. Doppler measurements are used to distinguish between different human movements and gestures using the characteristic micro-Doppler signals. Our measurements establish the ability of this system to detect and range humans and distinguish between different human movements at different ranges. 1. Introduction The ability to detect human targets and identify their movements through building walls and behind light foliage is increasingly important in military and security applications. Expeditionary warfighters and law enforcement personnel are commonly faced with unknown enemy threats from behind different types of walls as well as those concealed behind shrubs and trees. Technology that can be used to unobtrusively detect and monitor the presence of human subjects from stand-off distances and through walls and foliage can be a powerful tool to meet such challenges. Although optical systems achieve excellent angular resolution, optical signals are unable to penetrate solid barriers and foliage cover and therefore are totally ineffective in detecting humans in defilade. However, signals in the microwave frequency range can penetrate barriers to an acceptable degree and are therefore the sensors of choice in detection of targets through optically opaque walls. In this case, the choice of the frequency of operation depends on the application, specifically on the barrier type, target position behind the wall, stand-off requirement, and resolution requirements, all of which are somewhat interrelated. Furthermore, since signals in the millimeter-wave frequency range are able to penetrate light foliage cover to an acceptable degree and can be
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