Electromagnetic approaches to wall characterization, wall mitigation, and antenna design for through-the-wall radar systems

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Description: Through-the-wall imaging (TWI) is a topic of current interest due to its wide range of public safety, law enforcement, and defense applications. Among the various available technologies such as, acoustic, thermal, and optical imaging, which can be employed to sense and image targets of interest, electromagnetic (EM) imaging, in the microwave frequency bands, is the most widely utilized technology and has been at the forefront of research in recent years. The primary objectives for any Through-the-Wall Radar Imaging (TWRI) system are to obtain a layout of the building and/or inner rooms, detect if there are targets of interest including humans or weapons, determine if there are countermeasures being employed to further obscure the contents of a building or room of interest, and finally to classify the detected targets. Unlike conventional radar scenarios, the presence of walls, made of common construction materials such as brick, drywall, plywood, cinder block, and solid concrete, adversely affects the ability of any conventional imaging technique to properly image targets enclosed within building structures as the propagation through the wall can induce shadowing effects on targets of interest which may result in image degradation, errors in target localization, and even complete target masking. For many applications of TWR systems, the wall ringing signals are strong enough to mask the returns from targets not located a sufficient distance behind the wall, beyond the distance of the wall ringing, and thus without proper wall mitigation, target detection becomes extremely difficult. The results presented in this thesis focus on the development of wall parameter estimation, and intra-wall and wall-type characterization techniques for use in both the time and frequency domains as well as analysis of these techniques under various real world scenarios such as reduced system bandwidth scenarios, various wall backing scenarios, the case of inhomogeneous walls, presence of ground reflections, and situations where they may be applied to the estimation of the parameters associated with an interior wall. It is demonstrated through extensive computer simulations and laboratory experiments that, by proper exploitation of the electromagnetic characteristics of walls, one can efficiently extract the constitutive parameters associated with unknown wall(s) as well as to characterize and image the intra-wall region. Additionally, it is possible, to a large extent, to remove the negative wall effects, such as shadowing and incorrect target localization, as well as to enhance the imaging and classification of targets behind walls. In addition to the discussion of post processing the radar data to account for wall effects, the design of antenna elements used for transmit (Tx) and receive (Rx) operations in TWR radars is also discussed but limited to antennas for mobile, handheld, or UAV TWR systems which impose design requirements such as low profiles, wide operational bands, and in most cases lend themselves to fabrication using surface printing techniques. A new class of wideband antennas, formed though the use of printed metallic paths in the form of Peano and Hilbert space-filling curves (SFC) to provide top-loading properties that miniaturize monopole antenna elements, has been developed for applications in conformal and/or low profile antennas systems, such as mobile platforms for TWRI and communication systems. Additionally, boresight gain enhancements of a stair-like antenna geometry, through the addition of parasitic self-similar patches and gate like ground plane structures, are presented.
Language: English
Format: Degree Work