Defense Date
2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Electrical & Computer Engineering
First Advisor
Erdem Topsakal
Abstract
The modern world is replete with reasons for employing reconfigurable electromagnetic (EM) structures, but some of the most pressing needs require advancements in power consumption, speed, and footprint [1]. Next generation air defense (NGAD) fighters could benefit from new electronic warfare (EW) countermeasures [2], as well as adaptive stealth technology [3], while doctors could benefit from reconfigurable microwave ablation antennas that can modify radiation pattern and input impedance to match changes in tissue during ablation and account for variations in tumor shapes [4]. The future of antennas, filters, and lenses is reconfigurable as real-world matters of life and death may be impacted by advancements in the field. To compound the issue, data usage rates of modern devices have resulted in a need for real time spectrum management in order to fulfill usage demand [5]. This requires equipment capable of switching frequencies on demand to continue transmitting and receiving data [6]. This work aims to aid in advancing reconfigurable EM structures through investigation of hybrid approaches to reconfiguration of antennas, and lenses by employing combinations of mechanical, magnetic, liquid, and solid-state approaches. The goal of this dissertation is to use hybrid reconfiguration approaches to produce more optimal outcomes for the desired output metrics and resources used, or that serve a particular purpose or use case. With regards to this work, the primary resources used in reconfigurable antenna design are defined as physical space (footprint), materials, time for reconfiguration, and power, while the primary outputs are defined as changes in various antenna parameters, including but not limited to frequency, gain, bandwidth, beam width, radiation efficiency, directivity etc. The input and output metrics will vary for other EM structures such as frequency selective surfaces (FSS), and lenses, but predominant approaches to reconfiguration are similar, and the inputs and outputs will be classified in an equivalent manner and are all targets for optimization. Furthermore, in most cases filters and lenses are used with antennas as part of a larger reconfigurable system, and therefore antennas systems are the focus of this research. A significant amount of research has been conducted on the topic of individual reconfiguration methods for antennas [7], filters [8], and lenses [9] and reviews of these methods abound [10- 11], but there are not comprehensive studies on using combinations of reconfiguration approaches to achieve optimal outcomes prior to this work. The work presented here use multiple reconfiguration approaches to achieve smaller wavelength normalized footprints for mobile communications and pattern reconfigurable waveguide antennas with respect to the gain. For the tunable mobile communications antenna, the largest dimension was 94 mm and the maximum gain was 3.9 dBi in the 2.4 GHz industrial scientific and medical (ISM) band and 0.7 dBi in the 900 MHz ISM band, with a tunable range of 0.65 GHz - 0.68 GHz, 0.79 GHz - 0.93 GHz, 1.17 GHz - 1.27 GHz, and 1.44 GHz - 3.30 GHz using the 3:1 voltage standing wave ratio (VSWR) standard. The pattern reconfigurable waveguide achieved competitive performance with comparable antennas while maintaining only a 2.05λ length. The work here also used multiple reconfiguration methods to solve challenging niche problems, such as implementation of microwave ablation waveguides, with impedance matching for all possible values of human tissues throughout the ablation process and tunable MIMO antennas, with minimal variation in gain (0.77 dB). This work shows that hybrid reconfiguration approaches are suitable for improving the footprints of EM structures, which is important for reconfigurable antennas in general, and for solving challenging niche problems.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
9-16-2024