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Access Type

WSU Access

Date of Award

January 2025

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

First Advisor

Ivan Avrutsky

Second Advisor

Chung-Tse Michael Wu

Abstract

Metamaterial leaky-wave antennas (MTM-LWAs) represent an innovative class of frequency-scanning antennas that intrinsically support frequency-to-angle radiation mapping. This unique characteristic enables them to perform spatial beam scanning simply by varying the operating frequency, eliminating the need for mechanical rotation or electronic phase shifting. Such properties make MTM-LWAs particularly advantageous for electromagnetic imaging applications where wide field-of-view (FOV), compact hardware, and efficient signal acquisition are required. In this work, I exploit these distinctive features to develop a novel framework for spectrally encoded three-dimensional (3D) microwave tomography and remote sensing, capable of reconstructing the shape and spatial distribution of conductive objects with minimal prior information. The proposed imaging approach is centered around the LSM, a qualitative inverse scattering technique widely recognized for its robustness, computational speed, and non-iterative structure. Traditionally, LSM implementations have relied on single-frequency illuminations and fixed incidence angles, which inherently limit spatial coverage and reconstruction resolution. In contrast, the method introduced here utilizes a frequency-scanning MTM-LWA array that performs natural frequency-to-space mapping across a 3D background domain. This enables the acquisition of diverse angular perspectives using a single-port frequency sweep, thereby enhancing imaging performance without introducing mechanical complexity. To further improve the reliability and accuracy of the reconstructions in challenging environments, we propose a hybrid imaging strategy that combines both frequency and polarization diversity. This dual-domain diversity introduces additional independent measurements, significantly mitigating the effects of noise, measurement uncertainty, and the inherent ill-posedness of inverse scattering problems. The integration of polarization diversity allows the system to access different scattering mechanisms from the same object, enhancing sensitivity to structural features and improving image fidelity, especially in complex or high-contrast scenarios. The effectiveness of the proposed method is demonstrated through a comprehensive series of numerical simulations and experimental validations. The experimental setup, implemented at the Wayne State University Microwave Laboratory, utilizes MTM-LWAs operating over the 1.8–3.0 GHz frequency band to illuminate and reconstruct various unknown targets, including multi-layered and coaxially aligned cylindrical objects with different diameters and material compositions. Results consistently show that the system is capable of accurately reconstructing object shapes and positions with minimal computational overhead and without requiring detailed a priori knowledge of the target or environment.Compared to conventional LSM-based imaging systems, the approach presented in this work offers substantial improvements in spatial resolution, field of view, and computational efficiency. It also demonstrates greater flexibility and adaptability in practical scenarios where complex object geometries and inhomogeneous media are involved. By integrating MTM-LWAs with a hybrid frequency-polarization LSM framework, this work establishes a powerful and scalable solution for advanced 3D microwave imaging and remote sensing applications, with potential relevance in biomedical diagnostics, security screening, and subsurface exploration. KEYWORDS: Inverse Scattering; Leaky Wave Antenna; Linear Sampling Method; Metamaterial; Microwave Tomography; Polarization; Remote Sensing

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