Hard-Wall Radar Imaging: Localization of Objects Shadowed by Metallic Walls With MIMO Radar

Abstract

The technology of “through-the-wall radar imaging” enables seeing through walls by reconstructing the image based on backscattered waves passing through an optically opaque dielectric wall. However, when the electromagnetic waves cannot penetrate the shielding walls (such as metallic walls), a problem called “hard-wall radar imaging” (HWRI) must be investigated. As the objects are located in the shadow region, where only the diffracted field can be reflected back via edges, conventional imaging techniques are not applicable. The HWRI problem is an imaging scenario with an intrinsic multipath of signal propagation. Therefore, it has been studied using a model-based time-reversal (TR) decomposition of TR operator imaging method. In this paper, an imaging technique with a distributed transmitting and receiving array is proposed as a robust way resolving the problem with a low signal-to-clutter ratio in TR imaging. In this method, the interelement response matrix is collected for the construction of the covariance matrix, from which the geometry of the hard wall is determined from the direction of arrival by the multiple signal classification techniques. Next, the adaptive interference cancellation technique is applied to suppress the interference terms in the image function due to the multipath effects. The experimental results were obtained from a distributed multiple-input multiple-output radar system and show that this method is useful not only for the detection of a weak object echo but also for the localization of multiple targets hidden behind the wall.