Doctor of Philosophy, The Ohio State University, 2022, Electrical and Computer Engineering

The antenna pattern is an essential part of the design of RF systems and affects the performance and capabilities for many applications in communications, radar, and sensing. There are many applications which require specified antenna patterns with specific directivity, beamwidth, and sidelobe level (SLL). Single-element antennas usually have simple and specific patterns which are difficult to be shaped to meet more complicated pattern requirements. For instance, the popular parabolic reflector antenna uses a reflector which can be shaped to produce a desired radiation pattern with high directivity. However, it has a large structure and can only produce single fixed-beam patterns. On the other hand, array antennas consist of multiple antenna elements which together can be used to synthesize antenna patterns with narrower beams and lower sidelobes as compared to single-element antennas. More specifically, many applications which require high directivity, narrow beam patterns with low sidelobes include: (1) radars, which often use a narrow beam to detect targets for achieving a better angular resolution, higher signal-to-noise ratio (SNR), and low sidelobes to avoid ambiguity coming from signal returns from other directions; (2) modern cellular phone base stations which employ specially shaped beam patterns to provide uniform signal strength with the coverage area while minimizing radiation into the sky; (3) newest satellite communications/broadcasting systems which adopt spotlight beams to cover specific zones while reducing interference into neighboring areas for enhanced security and SNR. The first array antennas for producing shaped directive beam patterns were introduced during World War II for early radar systems using an array of dipole elements. The disadvantages of such a dipole array were that the dipole elements were large 3D objects requiring manual labor to produce and the design was difficult to use for higher frequency such as for X band or higher. (open full item for complete abstract)

Committee: Chi-Chih Chen (Advisor); Gabriel Conant (Committee Member); Robert Lee (Committee Member); Emre Ertin (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism; Engineering

Master of Science in Electrical Engineering, University of Dayton, 2020, Electrical and Computer Engineering

Demands for self-sustainable energy sources are rising as we become more and more reliable on electronic devices in our daily lives. Scientists and engineers have been exploring various novel methods to harvest energy from existing resources in order to eliminate or reduce the usage of battery and/or conventional power equipment. Solar, water, tide, wind, and terrestrial heat are renewable and green resources that have been widely adopted and commercialized[1]. With the rapid development of technology, more resources can be used for providing energy and compressing the size of devices. For example, piezoelectricity, vibration, and electromagnetic energy can also be used in the large-scale area[2]. Electromagnetic energy, especially in WIFI frequencies, is recently gaining more and more interest because of the wide signal coverage on campus and residential areas. An unique advantage of harvesting electromagnetic energy is its little dependence from weather related factors, unlike solar, water, tide, wind and terrestrial heat[3]. Given the circumstances, the interest in this work is to design a novel rectenna device to harvest energy from WIFI frequencies and to provide a parametric study in efficiency improvement. Our comfort and fast life in modern society roots in massive volumes of data exchange through wireless transmission. In modern communication systems, different radio spectrum's only use is for single media to prevent interference between users and different devices. International telecommunication Union (ITU) established rules to allocate spectrums for various purposes; the chart [4] shows specific distributions for mobile, broadcast, satellite, and other devices. Since antenna is the only component worked as receiver and transmitter in a device, the main problem in communication systems are the versatility of antenna. So, antenna with reconfigurability is desired in today's multi-band multi-mode communication system front end. The key solution is to wide (open full item for complete abstract)

Committee: Hailing Yue (Advisor) Subjects: Electrical Engineering; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2010, Electrical and Computer Engineering

Emerging broadband applications with market pressures for miniaturized communication devices have encouraged the use of electrically small antennas (ESA) and highly integrated RF circuitry for high volume low cost mobile devices. This research work focuses on developing a novel scheme to design wideband electrical small antennas that incorporates active and passive loading as well as passive matching networks. Several antennas designed using the proposed design technique and built and measured to assess their performance and to validate the design methodology. Previously, the theory of Characteristic Modes (CM) has been used mostly for antennas analysis. However; in this chapter a design procedure is proposed for designing wide band (both the input impedance bandwidth and the far field pattern bandwidth) electrically small to mid size antennas using the CM in conjunction with the theory of matching networks developed by Carlin. In order to increase the antenna gain, the antenna input impedance mismatch loss needs to be minimized by carefully exciting the antenna either at one port or at multiple ports and/or load the antenna at different ports along the antenna body such that the Q factor in the desired frequency range is suitable for wideband matching network design. The excitation (feeding structure), the loading of the antenna and/or even small modifications to the antenna structure can be modeled and understood by studying the eigenvalues and their corresponding eigencurrents obtained from the CM of the antenna structure. A brief discussion of the theory of Characteristic Modes (CM) will be presented and reviewed before the proposed design scheme is introduced. The design method will be used to demonstrate CM applications to widen the frequency bandwidth of the input impedance of an electrically small Vee shape Antenna and to obtain vertically polarized Omni-directional patterns for such antenna over a wide bandwidth. A loading technique based on the CM to eith (open full item for complete abstract)

Committee: Roberto G. Rojas PhD (Advisor); Garbacz Robert PhD (Committee Member); Teixeira Fernando PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Experiments

Master of Science in Electrical Engineering (MSEE), Wright State University, 2019, Electrical Engineering

This study focuses on the use of microstrip antenna technology for designing an ultra-wideband antenna to meet low size, weight and power requirements. Based on the recent literature for such antennas, a quasi-log periodic microstrip antenna array is designed to operate from 8 to 40 GHz (radar bands X, Ku, K and Ka). The array consists of 33 co-linear, inset-fed, square patches on a Roger's Duroid substrate, and is modeled using the Advanced Design System software from Keysight. The simulated results show the antenna has pass-band gains greater than 5 dB, a half-power beamwidth of 30 degrees, and linear polarization with a broadside radiation pattern. In addition, the fractional voltage standing wave ratio is less than 1.8 for 18 GHz of the pass-band, and the antenna has an efficiency greater than 60 percent over the entire pass band.

Committee: Michael A. Saville Ph.D., P.E. (Advisor); Yan Zhuang Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member); Josh Ash Ph.D. (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Technology

Master of Science, The Ohio State University, 2012, Electrical and Computer Engineering

A novel UHF antenna for a handheld RFID reader is proposed, designed and optimized using ANSYS HFSS simulation software. The optimized design is fabricated and tested, for S ¿¿¿¿¿¿¿¿¿¿¿¿“ parameters and gain, using a network analyzer. The antenna structure designed is low ¿¿¿¿¿¿¿¿¿¿¿¿“ profile, planar, end ¿¿¿¿¿¿¿¿¿¿¿¿“ fire radiating and dual ¿¿¿¿¿¿¿¿¿¿¿¿“ polarized. It is a promising substitute to other existing conventional antennas used such as patch antennas (broadside radiating and linearly/circularly polarized) and helical antennas (end ¿¿¿¿¿¿¿¿¿¿¿¿“ fire radiating and circularly polarized) which are comparatively bulkier to be mounted on a handheld reader. The proposed antenna provides dual ¿¿¿¿¿¿¿¿¿¿¿¿“ polarized gain so that the tags of both orientations (horizontal and vertical) can be read effectively when the reader is pointed at them. Due to its attribute of dual polarization, it forms a vital substitute to the already available planar and end ¿¿¿¿¿¿¿¿¿¿¿¿“ fire radiating antenna designs like Yagi, which are capable of providing only one kind of a polarization. This constraint renders the tags of opposite polarizations to be left unread by the reader, unless the reader itself is twisted to align the polarization direction with the orientation of the tag to be read. The dual polarization of this antenna is provided by combining two different antenna geometries, yielding orthogonal polarizations, onto a single platform and having different excitation ports to feed the two structures when connected to a two ¿¿¿¿¿¿¿¿¿¿¿¿“ port reader.

Committee: Dr. Robert Burkholder (Advisor); Dr. Prabhakar Pathak (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2012, Electrical and Computer Engineering

There is much interest in developing body-centric wireless communication systems (BWCS) for mobile health care systems. However, the realization of a BWCS is challenging due to the body's interference with the antenna's operation. More specifically, body-worn antennas suffer from impedance detuning, pattern deformation, and gain reduction caused by the body. Therefore, it is important to consider these effects in evaluating body-worn antennas. In this regard, a diversity technique is proposed to improve body-worn antenna performance. More specifically, a channel decomposition method (CDM) is proposed and used to evaluate body-worn antenna systems. The CDM significantly reduces computation time when evaluate body-worn antennas and is applicable to various surrounding environments without recalculation of the more complex interaction. A second contribution of this dissertation is design of a diversity systems which automatically determines the minimum number of antennas while maximizing performance. This approach is employed to design body-worn antenna diversity systems for given communication scenarios. The results obtained via this process demonstrated that this simple method can substantially reduced computation time in designing body-worn antenna diversity system. As a demonstration of the proposed methodology, a vest-mounted UHF body-worn antenna diversity system (BWADS) is developed using 4 light-weight antennas. The proposed BWADS is transparent and unobtrusive to the users but provides performance superior to commercial antennas. A variety of tests were performed to validate the proposed BWADS. It was found that the proposed BWADS provided 7 dB (outdoor) to 16.5 dB (indoor) of higher gain as compared to commercial antennas. The dissertation concludes by proposing other applications of the developed body-worn antennas and design methods.

Committee: John Volakis PhD (Committee Chair); Chi-Chih Chen PhD (Advisor); Fernando Teixeria PhD (Committee Member); Dimitris Psychoudakis PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

This Dissertation presents a new class of broadband, high gain, wearable antennas, namely Bio-Matched Antennas (BMAs) that exceed the state-of-the-art performance of into-body radiation. Motivation for this research began as an attempt to improve the wearable-implantable antenna link, which is quite inefficient. As such, a miniaturized implantable dual-band antenna was designed that has comparable gain to antennas that are 423% larger and was the first implantable antenna to be tested in a post-mortem human subject. Building upon this, we further developed the theoretical modeling and design guidelines for BMAs as an emerging class of wearable, into-body antennas that surpass the state-of-the-art in terms of bandwidth and gain. In brief, BMAs are ultra-wideband, pyramid-shaped antennas that utilize the periodic combination of high and low permittivity materials to enhance performance. This engineered dielectric overcomes the traditional into-body antenna problems of (a) mismatch at the biological tissue and antenna interface, (b) sensitivity to environmental and inter-subject variability, and (c) narrow bandwidth given the frequency-dependent tissue properties. To enable customized performance for diverse applications, we went on to develop a comprehensive design framework. Our studies utilize a comparison of the BMA to a conical antenna to model the low frequency cutoff and employ a Plane Wave Expansion Method analysis to: a) model the high frequency cutoff, and b) predict the permittivity of the Bio-Matched dielectric. We verified our design framework through a novel BMA that operates from 1-12 GHz with 21.4 dB of transmission loss through 3 cm of tissue at 2.4 GHz; a ~15.6 dB improvement over the state-of-the-art. The Dissertation concludes with improvements upon the BMA achieved via: (a) flaring to lower the cutoff frequency without increasing volume, and (b) the first ever artificially anisotropic microwave quarter-wave plate to enable circular polarization. Ov (open full item for complete abstract)

Committee: Asimina Kiourti (Advisor); Kubilay Sertel (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2016, Electrical and Computer Engineering

Over the past few years, the rapid advances in silicon technology have made multi-Gbps wireless digital communication become attractive due to the low-cost and high integration levels. The 57 to 66 GHz ISM band with 9-GHz available bandwidth is believed to be a great candidate for high-speed short-range wireless communications. 60-GHz wireless link systems in silicon integrated circuits have recently attracted widespread research interest and commercial development. This research focuses on developing a fully-integrated 60-GHz coupled oscillator antenna array system using IBM 0.13-µm SiGe BiCMOS technology for short-range wireless communications. This work is different from previous related works because all the 60 GHz components, including the antenna, are fully integrated. The smaller size, lower cost, lower power, and higher compatibility make VLSI implementation more attractive in high-speed communication systems. The content includes three main topics, which are on-chip electrically small antenna design, self-oscillating active-integrated antenna (AIA) design, and coupled-oscillator antenna array (COAA) design. A novel on-chip antenna design technique is presented to isolate the antenna from the lossy silicon substrate thus increasing the antenna gain and radiation efficiency at mm-wave frequencies. The active-integrated antenna, which includes an on-chip dipole antenna, a voltage controlled oscillator (VCO), and injection-locking networks, is designed as a basic element of the coupled-oscillator array system. Finally, a two-element COAA with non-reciprocal coupling is presented for beam scanning applications. The COAA consists of two AIAs and a non-reciprocal coupling network (NRCN). The NRCN provides adjustable coupling gain and coupling phase between adjacent AIAs. This new topology overcomes several of the problems with this class of beam scanning arrays discussed in the literature.

Committee: Roberto Rojas (Advisor); Fernando Teixeira (Committee Member); Steven Bibyk (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2012, Electrical and Computer Engineering

In the past few decades, GPS has revolutionized navigation positioning and timing with numerous civilian and military applications. Recently, there is increased interest in GPS navigation for small cylindrical platforms which can have a potentially high rotation rate (up to 350 Hz). The purpose of this work is to extend the state-of-the-art of GPS receiver and antenna technology for this specific application of small cylindrical platforms. This presents a set of design challenges for engineers, and this work will make contributions to three aspects of the problem: antenna design, satellite coverage, and receiver design. First, a novel dual-band antenna that provides right-hand circular polarization (RHCP) coverage at the GPS L1/L2 bands for reception of C/A-, P(Y)-, and M-coded GPS signals is designed. The availability of GPS measurements at two bands allows one to remove the biases due to the ionsphere and reception of P(Y) and M-coded signals improves navigation accuracy. Importantly, the antenna size is only 4cm × 4cm × 5.08mm (λ/6 × λ/6 × λ/50). Second, this antenna is specifically designed to have a robust tuning such that it can be mounted on metal cylinders of various diameters (60-160mm) and still function properly. For these cylinders, the antenna has broad RHCP coverage and good gain bandwidth performance. Third, the satellite coverage provided by the antenna is investigated. As expected, a single element cannot provide the full spherical coverage which is needed for continuous satellite tracking as the platform rotates. It is shown that the maximum gain method (i.e. choosing the element with the highest gain) is able to obtain full spherical coverage even with only two elements. However, it is a challenge to implement this method because the time-varying platform attitude is unknown. Therefore, a novel receiver tracking algorithm that implements the maximum gain method is designed by modifying the receiver itself, specifically the delay lock loop. Example (open full item for complete abstract)

Committee: Inder Gupta PhD (Advisor); Chi-Chih Chen PhD (Committee Member); Joel Johnson PhD (Committee Member); Hesham El-Gamal PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

There is strong interest to combine many antenna functionalities within a single, wideband aperture. However, size restrictions and conformal installation requirements are major obstacles to this goal (in terms of gain and bandwidth). Of particular importance is bandwidth; which, as is well known, decreases when the antenna is placed closer to the ground plane. Hence, recent efforts on EBG and AMC ground planes were aimed at mitigating this deterioration for low-profile antennas. In this dissertation, we propose a new class of tightly coupled arrays (TCAs) which exhibit substantially broader bandwidth than a single patch antenna of the same size. The enhancement is due to the cancellation of the ground plane inductance by the capacitance of the TCA aperture. This concept of reactive impedance cancellation was motivated by the ultrawideband (UWB) current sheet array (CSA) introduced by Munk in 2003. We demonstrate that as broad as 7:1 UWB operation can be achieved for an aperture as thin as λ/17 at the lowest frequency. This is a 40% larger wideband performance and 35% thinner profile as compared to the CSA. Much of the dissertation's focus is on adapting the conformal TCA concept to small and very low-profile finite arrays. Three particular designs are presented. One is a 6x6 patch array occupying a λ/3 x λ/3 small aperture (mid-frequency is at 2.1 GHz). Remarkably, it is only λ/42 thick yet delivers 5.6% impedance bandwidth (|S11| < -10dB), 4.4dB realized gain (87% efficiency) and 23% gain bandwidth (3dB drop). The second finite TCA consists of 4x2 patches and occupies a λ/3.2 x λ/3.2 aperture on a λ/26 thick substrate (mid-frequency is at 2 GHz). This antenna delivers 17.3% impedance bandwidth, 4.8dB realized gain (95% efficiency) and 30% gain bandwidth. That is, more than twofold impedance bandwidth is delivered as compared to a single patch antenna of the same size on conventional or EBG substrate. The third array being considered consists of 3x2 patches occu (open full item for complete abstract)

Committee: John L. Volakis PhD (Advisor); Kubilay Sertel PhD (Advisor); Robert J. Burkholder PhD (Committee Member); Fernando L. Teixeira PhD (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Master of Science in Engineering, Youngstown State University, 2024, Department of Electrical and Computer Engineering

As part of this project, a complex terahertz (THz) antenna was fabricated using two-photon polymerization (2PP), a highly precise additive manufacturing method. The design and rigorous simulation testing were conducted using Ansys HFSS, with a focus on achieving minimal losses. Special emphasis was placed on impedance matching, confirmed by the S11 parameter showing minimal power reflection over a large part of the THz band. The antenna was fabricated using OrmoComp, a hybrid polymer. A significant portion of the thesis is dedicated to fine-tuning the intricate fabrication steps necessary for producing complex designs, demonstrating the capability to also fabricate simpler structures. The most significant outcomes of this work on the highly directional THz antenna are the optimized process parameters such as slicing direction, way of printing, power and speed settings of laser for 2PP and finally development time of post processing, which enabled the production of the complex structure. The fidelity of the final fabricated design was verified using electron and light microscopy.

Committee: Vamsi Borra PhD (Advisor); Frank X. Li PhD (Committee Member); Srikanth Itapu PhD (Committee Member); Pedro Cortes PhD (Committee Member) Subjects: Design; Electrical Engineering; Electromagnetics; Nanotechnology

Master of Science in Electrical Engineering (MSEE), Wright State University, 2021, Electrical Engineering

A dual-band array of reconfigurable elements is modeled and simulated. The array consists of four single square spiral microstrip antennas that are corporately fed and are used as a unit cell. The single square spiral uses two PIN diodes as switching elements to achieve reconfiguration. The array has four switch states that can operate over four discrete frequencies in the S and C bands. The unit cell radiation pattern is used with the pattern multiplication model to quickly simulate the array pattern of larger arrays. A 3 x 3 array of the unit cells is modeled with only the center element active and designated as the embedded unit cell. The embedded unit cell is used to capture the effects of mutual coupling and to see how significantly the coupling affects the radiation patterns. The effects of mutual coupling are found to be negligible for a 2 x 2 and larger sized arrays.

Committee: Michael A. Saville Ph.D., P.E. (Advisor); Joshua Ash Ph.D. (Committee Member); Yan Zhuang Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 0, Electrical and Computer Engineering

Reflectarrays combine the favorable aspects of both reflectors and phased array antennas, including high aperture efficiency, high gain, low profile, low weight, and simplicity of the design. These electrical and mechanical characteristics make them an excellent candidate for satellite communication and direct broadcasting services. This dissertation makes three original contributions to the topic of reflectarrays. First, a novel circular polarized metal-only reflectarray capable of producing 360° of phase shift was designed. Second, reflectarrays with rectangular and triangular lattices are compared in terms of their ability to form a cosecant-squared beam pattern. Finally, a novel high power mechanical reconfigurable reflectarray capable of producing over 300° of phase shift was designed. Traditionally microstrip technology is used to create passive reflectarrays, with the patch antenna array printed onto a low loss dielectric substrate. As the aperture of a reflectarray can be quite large, the substrate can make the design prohibitively expensive. Additionally, the introduction of dielectric material into a harsh environment can lead to a decrease in antenna performance. To circumvent these problems, a metal-only reflectarray is a superior alternative for applications that require a fixed beam. Current metal-only designs have limited phase coverage or only work for linear polarization. In this work, a circularly-polarized multi-slot element that has 360° of phase coverage, over a 30% bandwidth spanning 18-24 GHz is presented. The fabricated reflectarray achieves a 3-dB axial ratio bandwidth of 32.5%, and a bandwidth of 10.1% for each polarization within which the gain remains within 3 dB of the peak value. Little attention is paid to an aperture's topology in reflectarrays as most focus is on the radiating elements. Reflectarrays are traditionally designed with a rectangular lattice having 0.5λ0 by 0.5λ0 spacing as it is a standard spacing to compromises betw (open full item for complete abstract)

Committee: Nima Ghalichechian (Advisor); Chi-Chih Chen (Committee Member); Joel Johnson (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2020, Electrical and Computer Engineering

The Frequency Diverse Array (FDA) antenna provides range - angle - time dependent beampattern, potentially generating highly directional beams with high gain that may be steered directly and continuously to the desired position. This research explores using FDA antenna for tracking a Low Earth Orbit (LEO) satellite. Although FDA array antenna has been growing in use for radar communication systems with advantages of it is electronically beam steering, it is still not truly used in integrate with LEO systems. The mathematical model of FDA antennas with dierent geometries for tracking LEO satellite is presented. Then, the radiation characteristics of linear and Planar-FDA under dierent situations are investigated. Further, the planar FDA array owns greater superiority over the linear FDA array, and it can cover the observation space indicating great potential in LEO tracking and communication applications. A ground receiving antenna system based on planar FDA array antenna is presented for tracking and communicating with (LEO) satellite at ground station. This is required to minimize a complexity and the cost of ground station. To meet the system gure of merit (G/T) requirement, the radiation characteristics, the gain requirements, the array size, the minimum number of elements and their distribution for several FDA array antenna architectures are calculated and analyzed. Moreover, a general overview of system temperature is presented including a noise model for FDA array antenna, and the link budget analysis and evaluation are introduced.

Committee: Michael Wicks Phd (Advisor) Subjects: Engineering

Master of Science, The Ohio State University, 2020, Electrical and Computer Engineering

The characterization of antenna radiation patterns in millimeter-wave (mmW) bands can be particularly challenging. There are several reasons for this, but one of the most significant is that the misplacement of just a few millimeters of the probe antenna can generate substantial errors in the pattern measurement result. To overcome this, a highly precise measurement system that incorporates a FANUC 6-axis small robotic arm is implemented. System testing shows a positional accuracy and repeatability of approximately 20 μm. After the system is implemented, programmed, and tested, pattern measurements are done on three different millimeter-wave antennas. By characterizing the radiation pattern of a V-band horn antenna, it is demonstrated that far-field measurements can be performed accurately with the robotically controlled system. Furthermore, the characterization of the center element pattern of a 60 GHz phased array has shown that the measurements with the system are repeatable as well. Additionally, it is demonstrated that the system can perform near-field measurements by successfully characterizing a U-band horn antenna with a planar scan. The instrumentation, testing methodology, results and challenges are reported.

Committee: Nima Ghalichechian (Advisor); Asimina Kiourti (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2020, Electrical and Computer Engineering

Antennas mounted on aircraft, UAVs, and other platforms are used in a number of critical applications, such as navigation, communication, and situational awareness. Since the platform can heavily affect the antenna pattern, one should carry out in situ characterization of the antenna to evaluate the performance of the RF systems. It is often too expensive or impractical to measure the antenna on the intended platform, so instead, the antenna under test (AUT) is measured on a simple ground plane. The measurements are then imported into computational electromagnetics (CEM) codes to simulate platform scattering from the platform of interest. However, current approaches struggle to isolate the antenna radiation from the measurement ground plane interactions, leading to inaccuracies in the AUT representation. Furthermore, many approaches rely on near-field measurements for accuracy and use many current elements to represent the AUT leading to long simulation run-times. This dissertation presents a novel approach for in situ manifold estimation which represents measured data via a weighted sum of simple basis element far-fields. The approach, the Sparse-Constrained Equivalent Element Distribution Method (SC-EEDM), provides a more accurate representation of the AUT compared to existing techniques. The SC-EEDM accurately represents the AUT using measured far-field data only, and represents the AUT using a small number of current elements. In addition, the SC-EEDM isolates antenna radiation from antenna-ground plane interactions, leading to more accurate in situ manifold estimations. Using high-fidelity simulations, the method is shown to accurately estimate antenna far-fields on complex platforms from antenna measurements on simple structures.

Committee: Inder Gupta (Advisor); Robert Burkholder (Committee Member); Teixeira Fernando (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Doctor of Philosophy, Case Western Reserve University, 2019, Physics

Magnetic Resonance Imaging (MRI) has become an important imaging method in the field of medical diagnostics and therapy due to its soft tissue contrast and use of non-ionizing radiations (unlike CT and X-ray). However, MRI also presents a number of safety issues including RF induced heating created by the interaction of the RF electromagnetic fields with human tissue and possible medical implants. A particular and important concern arises in the presence of any electrically conducting implant within the imaging specimen. The coupling between the conducting implants and RF electromagnetic fields produces relatively strong electrical currents within the implant and surrounding tissue which lead to ohmic heating and possibly unsafe temperature rises that damage tissue. One type of implant, and the focus of this thesis, are Stereo-electroencephalography (SEEG) electrodes. The SEEG electrodes are partially inserted into the brain of epilepsy patients for the localization and monitoring of focal epileptic zones. The electrical contacts on the SEEG electrode within the brain are connected via signal wires to external instrumentation to monitor the electrical activity in the brain. In this work, we study the RF induced heating due to the SEEG electrodes using both experimental measurements and numerical simulations. As a means for improved understanding of RF heating with implants containing both internal and external conductors, and to help validate the agreement between simulations and experiment, studies were first performed with a single insulated conducting copper wire using an MRI phantom. The benchmark for characterizing the level of RF heating was the temperature rise within the phantom and near the implants. These studies were then extended to include an 8 contact SEEG electrode, and then configurations with multiple wires and multiple SEEG electrodes. The results of the study demonstrate the importance of the length of the SEEG electrode and the signal wire (open full item for complete abstract)

Committee: Michael Martens Prof. (Advisor) Subjects: Biomedical Engineering; Biomedical Research; Physics

Master of Science, University of Akron, 2018, Electrical Engineering

This thesis studies the optimal inputs and capacities of non-coherent correlated multiple-input single-output (MISO) channels in fast Rayleigh fading. We consider two scenarios: channels under per-antenna power constraints and channels under joint per-antenna and sum power constraints. For per-antenna power constraints, we establish the convexity and compactness of the feasible sets, and demonstrate the existence of optimal input distribution. By exploiting the solutions of a quadratic optimization problem, we show that the Kuhn-Tucker condition (KTC) on the optimal inputs can be simplified to a single dimension and prove the discreteness and finiteness of the optimal effective magnitude distribution. Then, we are able to construct a finite and discrete optimal input vector and determine the capacity gain of MISO over SISO. We also extend the results to MISO channels subject to the joint per-antenna and sum power constraints. For this case, the optimal phases and the optimal power allocation among the transmit antennas need to be determined simultaneously via a quadratic optimization subject to inequality constraints. Based on our results, the capacity of considered channels can be obtained and exploited as an upper bound for the operational transmission rate. Further researches can also rely on our analysis of the optimal inputs to construct reliable coding schemes for MISO fading channels.

Committee: Nghi Tran (Advisor); Hamid Bahrami (Committee Member); Shivakumar Sastry (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

Many high performance wireless applications continue to be integrated onto increasingly small platforms, such as satellites, UAVs, and handheld devices. Lowprofile and ultra-wideband antenna arrays have emerged as a potential solution, by allowing many disparate functions to be consolidated into a shared, multi-functional aperture. Simultaneously, the demand for high data rate communications has driven these applications to higher frequencies, with many now exploring the use of the millimeter-wave spectrum. However, existing UWB arrays often utilize complex feed structures which cannot scale to these frequencies. The development of wideband millimeter-wave arrays compatible with low-cost commercial fabrication processes is critical to enabling these small and highly connected platforms. Tightly Coupled Arrays are one family of low-profile and wideband arrays which have demonstrated superior bandwidth and wide scanning capability. However, the feed design of these arrays is limited to operation below 5 GHz, and suffers from reduced efficiency when scanning. In this work, the feed is modified to improve efficiency by eliminating a Wilkinson power divider, and mitigating the resultant cavity resonances with the application of shorting pins. Likewise, strenuous fabrication requirements are relaxed, allowing fabrication at higher frequencies. This effort is approached initially through the intermediate frequencies in the X-, Ku- and Ka-bands, and is demonstrated to allow the new design to scale up 49 GHz. An 8x8 prototype operating over 3.5–18.5 GHz is fabricated and measured to validate the design. Infinite array simulations show VSWR < 2 across this band at broadside, with scanning to ±45deg in the H-plane (VSWR < 2.6) and as far 70deg in E-plane (VSWR < 2). At millimeter-wave frequencies, planar co-fabrication of the entire array is critical to achieving repeatable fabrication, by eliminating the need for complex assembly at such small scales. Simultaneously, (open full item for complete abstract)

Committee: John Volakis (Advisor); Robert Burkholder (Committee Member); Kubilay Sertel (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2016, Electrical and Computer Engineering

This work advances state-of-the-art Radio Frequency (RF) emitter geolocation from an airborne or spaceborne antenna array. With an antenna array, geolocation is based on Direction of Arrival (DOA) estimation algorithms such as MUSIC. The MUSIC algorithm applies to arbitrary arrays of polarization sensitive antennas and yields high resolution. However, MUSIC fails to obtain its theoretical resolution for simultaneous, closely spaced, co-frequency signals. We propose the novel Nullspace MUSIC algorithm, which outperforms MUSIC and its existing modifications while maintaining MUSIC's fundamental orthogonality test. Nullspace MUSIC applies a divide-and-conquer approach and estimates a single DOA at a time. Additionally, an antenna array on an aircraft cannot be perfectly calibrated. RF waves are blocked, reflected, and scattered in a time-varying fashion by the platform around the antenna array. Consequently, full-wave electromagnetics simulations or demanding measurements of the entire platform cannot eliminate the mismatch between the true, in-situ antenna patterns and the antenna patterns that are available for DOA estimation (the antenna array manifold). Platform-induced manifold mismatch severely degrades MUSIC's resolution and accuracy. We show that Nullspace MUSIC improves DOA accuracy for well separated signals that are incident on an airborne antenna array. Conventionally, geolocation from a mobile platform draws Lines of Bearing (LOB) from the antenna array along the DOAs to find the locations where the DOAs intersect with the ground. However, averaging the LOBs in the global coordinate system yields large errors due to geometric dilution of precision. Since averaging positions fails, a single emitter is typically located by finding the position on the ground that yields the Minimum Apparent Angular Error (MAAE) for the DOA estimates over a flight. We extend the MAAE approach to cluster LOBs from multiple emitters. MAAE clustering geolocates multiple sim (open full item for complete abstract)

Committee: Inder Gupta (Advisor); Joel Johnson (Committee Member); Fernando Teixeira (Committee Member); Can Koksal (Committee Member) Subjects: Aerospace Engineering; Applied Mathematics; Computer Engineering; Computer Science; Electrical Engineering; Electromagnetics; Electromagnetism; Engineering; Experiments; Mathematics; Music; Remote Sensing; Scientific Imaging; Systems Design