Advanced through-the-wall radar imaging using spectral and wall estimation techniques

Abstract

Through-the-wall radar imaging (TWRI) is currently an active and growing area of research and development because the detection and localization of targets in enclosed structures has many civilian and military applications such as rescue operations in case of fire or after earthquakes. However, contrary to free-space imaging, methods needed for TWRI are not a straight-forward process and face many challenges, all imposed by the presence of the building walls [1]. One problem pertains to frequency dependent attenuation and phase dispersion caused by exterior walls. This limits the useful frequency range to the UHF band with its lower frequency limited by the antenna size. Consequently, the bandwidth and image resolution of TWR systems is limited. The second issue is related to the scattering from the building walls and the multipath signals they create. The specular reflection and multiple bounces within the wall create a very strong signal much larger than that of the target behind the wall which normally has a small radar cross section (e.g. human). This leads to two problems: If the target is close to the wall, it's return can be completely covered by the wall return or if the target is further away from the wall, it can still be covered by the strong multiple bounce response or the point spread function sidelobes of the wall return. It is possible to reduce the sidelobe level but at the expense of range resolution by windowing the frequency response of the radar return.