Exploitation and Mitigation of Multipath in Complex Wave Propagation Environments for Target Detection, Tracking, and Communication.

Abstract

This thesis introduces novel wave propagation models and RF based techniques for detection, tracking, and communication in highly cluttered environments. The applications of interest include localization of deeply submerged targets such as UXO and clandestine tunnels, real-time positioning and tracking of small robotic platforms for search and rescue missions, and enhanced situational awareness in urban warfare.

First, an accurate near-ground wave propagation model for indoor and urban scenarios that is based on a hybrid physical optics and asymptotic expansion of dyadic Green's function for a half-space dielectric medium is presented. This model and other full-wave solvers are then used to: 1) investigate direction finding in highly cluttered environments, and 2) analyze the performance of compact antenna diversity systems. Second, a novel sub-wavelength RF source tracking system for applications in GPS-denied environments is realized and measured. The system utilizes a highly miniaturized transmit antenna and a biomimetic circuit that mimics the hearing mechanism of a fly to achieve a compact system. It is shown that tracking with absolute positioning of better than 70cm in complex buildings through multiple layers of walls is achievable from outside in a standoff distance. The third part of the work focuses on a physics-based analysis technique for compact and co-located antenna diversity systems that takes into account the complex radiation pattern of the diversity antennas in conjunction with an accurate near-ground propagation model. A co-located, co-polarized radiation pattern diversity system prototype is realized and characterized. Based on the above analysis technique and measurement results, a diversity gain of 8dB is achieved. In the last part of the work, a subsurface imaging radar system based on distributed near-ground sensor networks that utilize ultra-wideband waveforms in the VHF range is described. Numerical models and laboratory scale model measurements are used to demonstrate high resolution synthetic aperture imaging of deeply submerged targets under a layered medium using an ad hoc network of mobile transceivers.