Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Electrical and Computer Engineering

The advent of 5G technology has catalyzed a spectrum expansion across various frequency bands, including a low band below 1 GHz, a midband spanning 1-7 GHz, and a high band above 24 GHz. Therefore, researchers and engineers are currently engaged in exploring reconfigurable and tunable devices capable of adapting multi-band front-end modules to accommodate this expanded spectrum range. In this work, there are three types of reconfigurable and tunable filters that have been investigated. Each of them has its unique features and advantages. The surface-mounted technology (SMT) 5th-order elliptic tunable filter is first investigated. It exhibits three consecutive tunable bands within and above the L-band frequency range, specifically at 2.0-2.5 GHz, 2.5-3.0 GHz, and 3.0-3.5 GHz. Utilizing PIN diodes and capacitor banks, tunability is achieved through the DC voltage-controlled capacitance of PIN diodes, with in-band insertion loss maintained below 3 dB. This work already met the design limitation of the pure SMT filter in spite of the limited quality factor of the inductor and capacitor components. This dissertation contributed to two other designs. One is the bulk acoustic wave (BAW) filter, using the piezo effect to realize a filter function with high out-of-band rejection. Another one is the microstrip-coplanar waveguide (MS-CPW) filter, utilizing the coupling effect to guarantee a wide bandwidth and low in-band loss. The BAW resonator and filter, integrating tunable dielectric material barium strontium titanate (BST), offer a solution for sub-10 GHz applications. The BST material grants the BAW device a switchable coupling coefficient (Kt2), resulting in a switchable passband. This dissertation delves into the physical behavior and electrical models of the BAW resonator. In this work, the surface-mounted structure is adopted, and a highly efficient Bragg reflector is designed and fabricated to achieve a better isolation for BAW resonator. Furthermore, the perfo (open full item for complete abstract)

Committee: Guru Subramanyam (Committee Chair); Hailing Yue (Committee Member); Robert Penno (Committee Member); Monish Chatterjee (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering

The unique spectroscopic utility and high spatial resolution of terahertz (THz) waves offer a new and vastly unexplored paradigm for novel sensing, imaging, and communication applications, varying from deep-space spectroscopy to security screening, from biomedical imaging to remote non-destructive inspection, and from material characterization to multi-gigabit wireless indoor and outdoor communication networks. To date, the THz frequency range, lying between microwave and infrared bands, has been the last underexploited part of the electromagnetic (EM) spectrum due to technical and economical limitations of classical electronics- and optics-based system implementations. However, thanks to recent advancements in nano-fabrication and epitaxial growth techniques, sources and sensors with cutoff frequencies reaching the submillimeter-wave (sub-mmW) band are now realizable. Such remarkable improvement in electronic device speeds has been achieved mainly through aggressive scaling of critical device features, such as the junction area for Schottky barrier diodes (SBDs), and the gate length in high electron mobility transistors (HEMTs). Such aggressively-scaled and refined device topologies can significantly enhance the intrinsic device capabilities, however, the overall device performance is still limited by the parasitic couplings associated with device interconnect metallization. Consequently, geometry- and material-dependent parasitic couplings, induced by EM field interactions within the device structure, exacerbate the performance and diminish the gains achieved by the improved intrinsic device behavior. In particular, as the operation frequency approaches the THz barrier, device dimensions become comparable to signal wavelength. The main objective of this dissertation is to develop accurate lumped- and distributed-element equivalent circuits, and full-wave EM simulation-based iterative parameter extraction algorithms, (open full item for complete abstract)

Committee: Kubilay Sertel (Advisor); Fernando Teixeira L. (Committee Member); Patrick Roblin (Committee Member); Gary Kennedy (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Electrical and Computer Engineering

With rapidly increasing demands for high-speed and data-intensive wireless communications, mm-wave technology has become a promising way to provide unparalleled data rates, ultra-reliable low latency, and a massive increase in device connectivity. However, there are some fundamental challenges in the deployment of mm-wave networks. Considering the same communication distance, the mm-wave suffers from a higher free-space path loss due to its shortened wavelength. The path loss becomes an issue especially when the device is working in rural areas where a longer coverage distance is required. Also, a shorter wavelength can result in extra attenuation brought by random obstacles, for example, the raindrops whose diameter is comparable to the wavelength. For the mm-wave antenna systems with a fixed narrow beam, even light mechanical motions can cause misalignment between the transmitter and receiver leading to intermittent communication. To address these challenges, mm-wave antennas are designed to be highly directional, concentrating energy in narrow beams to combat the high path loss. Besides, beam-steerable antennas, which can dynamically adjust the radiation direction, have been developed to maintain reliable communication links. While the conventional phased array designs have a planar aperture with beam-forming capability, their usage in the mm-wave band is limited by its cost, potentially low efficiency, and high power consumption due to numerous active RF components. The reflector antennas, which have been widely adopted thanks to their decent gain level and high efficiency, face the challenges of a complex reflecting aperture and a large volume due to the separated feeding source. Similar limitations have been observed in other designs using metasurfaces or lenses as well. Therefore, there is an innovation gap for a simple low-cost, low-volume, high-efficiency, high gain, and beam-steerable antenna design for the next-generation mm-wave applications. A low-prof (open full item for complete abstract)

Committee: Chi-Chih Chen (Advisor); Scott Scheer (Committee Member); Fernando Teixeira (Committee Member); Kubilay Sertel (Committee Member) Subjects: Electrical Engineering; Electromagnetics

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

The real-time applications and the IoT promote the need for a newer idle spectrum to support the required high traffic. This pushes toward the emergence of the millimeter-wave (mmWave) and the sub-Terahertz (sub-THz) bands in wireless communication. Albeit these higher frequency bands offer wide spectrum help improving the spectral efficiency, it comes with the challenge of alleviating the severe attenuation. MmWave transceivers use large antenna arrays to form high-directional beams and overcome severe attenuation. A large array size leads to a costly beam alignment process if no prior information about beam directions is available. Beam alignment has two phases: beam discovery, and beam tracking. Beam discovery is finding the beam direction by consuming several pilot symbols to find the optimum direction. Moreover, beam tracking is a common approach to keep the discovered beams tightly coupled without frequent beam discovery to eliminate the overhead associated with realignment. Both phases become more difficult as the beams get narrower since slight mismatches lead to significant degradation in SNR as the beam coherence times are short. As a result, beams may lose alignment before they can be readjusted periodically with the aid of pilot signals. In this thesis, we introduce two complementary proposals. The first proposal is for the issue of beam tracking, and the second proposal is for the issue of beam discovery. In the first part of the thesis, we propose a model where the receiver adjusts beam direction continuously over each physical-layer sample according to a carefully calculated estimate of the continuous variation of the beams. Our approach contrasts the classical methods, which fix the beams in the same direction between pilots. In our approach, the change of direction is configured using the estimate of variation rate via two different methods; a Continuous-Discrete Kalman filter and an MMSE of a first-order approximation of the variation. Our method (open full item for complete abstract)

Committee: C. Emre Koksal (Advisor); Eylem Ekici (Committee Member); Abhishek Gupta (Committee Member) Subjects: Computer Science; Electrical Engineering; Information Science

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

There is a critical need for development of field effect transistors (FETs) operating at high frequencies with a high output power for next generation telecommunication systems. To achieve a high output power density, the device output current and device breakdown voltage should be enhanced. Devices operating with high electron densities are of great interests. High output power density could be achieved with a decent saturation electron velocity for high current drive capability. Unfortunately, for FETs with high channel electron densities, the devices suffer from a low breakdown voltage. The objective of this Ph. D research is to develop new device structures that can improve the device performance including output current, breakdown voltage, and RF output power. Different material and device structures with extremely high two-dimensional electron gas (2DEG) are investigated. The structures include perovskite oxide BaSnO3-based FETs, ScAlN/GaN and AlN/GaN high electron mobility transistors (HEMTs). We implement a high-k dielectric for modulation of the high 2DEG density and the field management for high breakdown. For development of perovskite oxide BaSnO3 channel FETs, we first studied the etching processes of epitaxially grown BaSnO3 and BaTiO3 thin films using an inductively coupled plasma reactive ion etching (ICP-RIE) with BCl3/Ar plasma chemistries. Electron transport mechanisms were then studied as a function of electron concentration. With a BaTiO3/BaSnO3 heterostructure, a BaSnO3 heterostructure field effect transistor (HFET) was fabricated, the device exhibited high current density of Imax = 406.7 mA/mm. The device demonstrated the capability to modulate 5.7×1013 cm-2 electron density in the channel. Using the demonstrated dry etch process to control the electron concentration and channel thickness, a gate-recessed ferroelectric field effect transistor (FeFET) is fabricated with 10 nm HfO2 as gate dielectric. The device exhibited a ferroelectric polariz (open full item for complete abstract)

Committee: Wu Lu (Advisor); Patrick Roblin (Committee Member); Siddharth Rajan (Committee Member) Subjects: Electrical Engineering

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

Over the past few decades, the ubiquity of radio-frequency (RF) devices has improved connectivity and productivity in our lives through wireless communication and sensing technologies. To this end, vehicle-to-everything (V2X) communication and vehicular radar imaging technologies have become the key enablers of Intelligent Transportation Systems (ITS) to promote safety, automation, and coordination in traffic. To enable V2X communication, a limited amount of bandwidth in the 5.9 GHz spectrum is dedicated to vehicles for the exchange of basic safety messages with low latency. However, with the large-scale deployment of connected vehicles, the V2X-dedicated band faces the spectrum scarcity problem that lowers the reliability of vehicular communication. The scarcity of dedicated spectrum also limits the feasibility and capabilities of more advanced vehicular applications that rely on broadband communication. Besides, up to 4 GHz of contiguous bandwidth is allocated as the vehicular radar spectrum that is dedicated solely to vehicles in the 76-81 GHz millimeter-wave (mmWave) bands. To supplement V2X communication, the under-utilized vehicular radar spectrum can be leveraged by joint radar-communication (JRC) systems. The objective of JRC is to perform both data transmission and radar imaging using the same \textit{joint} waveform and transceiver hardware. In this dissertation, we investigate transmission optimization and scheduling approaches to enable vehicular JRC in mmWave bands using adaptive orthogonal frequency-division multiplexing (OFDM). First, we study the joint waveform design problem for wideband vehicular JRC. By exploiting the frequency-selectivity in wideband channels, we adaptively design subcarrier coefficients of OFDM to achieve long-range detection and communication performance. We show that the problem is a non-convex quadratically constrained quadratic programming (QCQP), which is NP-hard. As an alternative to existing approaches, we propose time (open full item for complete abstract)

Committee: Eylem Ekici (Advisor); Ness Shroff (Committee Member); Can Emre Koksal (Committee Member) Subjects: Computer Engineering; Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

With the advantages of high bandwidth and abilities to see through opaque materials, millimeter wave (mmW) band (30 to 300 GHz) has been intensively explored in recent years. Although there are increasing demands for reconfigurable mmW systems for their potential applications in defense, switching, imaging, and sensing, overcoming the limitations such as high losses and large power consumption in mmW systems is still a challenge. Phase change materials (PCM) like vanadium dioxide (VO2), which have novel and tunable physical properties such as electrical resistivity and optical transmittance, are appealing choices for mmW reconfiguration to provide faster operation speed and lower loss microsystems. One aspect of VO2 thin film that is not fully exploited is the metal-insulator transition (MIT) region, where the electrical resistivity changes about four orders of magnitude with external stimuli. In this work, we present a highly sensitive antenna-coupled VO2 microbolometer for mmW imaging. The proposed microbolometer takes advantage of the large thermal coefficient of resistance (TCR) of VO2 at the non-linear region. The thermal resistance of the device is significantly improved by micro-electro-mechanical systems (MEMS) techniques to suspend the device above the substrate, compared with non-suspended microbolometers. The finite element method is employed to analyze the electrothermal and electromagnetic performance of the device. The frequency range of operation is 65 to 85 GHz, and the realized gain at broadside is > 1.0 dB. Simulation results indicate a high responsivity of 1.72x10^3 V/W and a low noise equivalent power (NEP) of 33 pW/√Hz. Targeting for broader applications, it is highly desired to deposit VO2 thin films on silicon (Si) substrate. Here, we employ the annealed alumina (Al2O3) buffer layers to obtain high-contrast VO2 thin films. The fabrication details for the Al2O3 buffer layers using atomic layer deposition (ALD) and VO2 thin films using DC sput (open full item for complete abstract)

Committee: Nima Ghalichechian (Advisor); Hanna Cho (Committee Member); Renee Zhao (Committee Member) Subjects: Electrical Engineering; Materials Science; Mechanical Engineering; Nanotechnology

Doctor of Philosophy, The Ohio State University, 2021, Electrical and Computer Engineering

The surge in mobile broadband data demands is expected to surpass the available spectrum capacity below 6 GHz. This expectation has prompted the exploration of millimeter-wave (mmWave) frequency bands as a candidate technology for next-generation wireless networks, like 5G-NR and WiFi ad/ay. However, numerous challenges to deploying mmWave communication systems, including channel estimation, need to be met before practical deployments are possible. The channel estimation problem is particularly complex due to the large antenna arrays, i.e., large-MIMO, used in mmWave transceivers. Large-MIMO antennas offer significant performance gains in terms of improved spectral efficiency, superior spatial multiplexing capabilities, as well as the ability to deliver high transmit signal power, which is crucial for compensating for the severe attenuation of high-frequency signals. However, large-MIMO channel estimation is complex since it entails the discovery of large-sized channel matrices, which is a daunting task and may necessitate a large number of measurements. Channel estimation is especially challenging for ``initial link establishment'', where limited prior knowledge about the channel is available. Reducing the number of necessary measurements thus holds the key to faster link establishment. For sparse MIMO channels, such reduction is possible due to the prior knowledge that the channel can be represented in a domain in which most of its components are negligibly small. The problem of "Fast Link Establishment" is the focus of this dissertation. In particular, we focus on the development and evaluation of sparse channel estimation algorithms that only require a small number of measurements. We divide this dissertation into three research objectives, as follows: First: We seek to develop a reliable channel estimation framework that: (1) requires a limited number of measurements (compared to the channel dimensions), and (2) operates using energy-efficient transcei (open full item for complete abstract)

Committee: Eylem Ekici (Advisor); C. Emre Koksal (Advisor); Ness Shroff (Committee Member) Subjects: Communication; Computer Science; Electrical Engineering

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

In this study, a novel BST varactor design is presented that was originally designed as a way to optimize the Quality Factor, (Q), through an extensive analysis of the physical parameters of a varactor that would perform in the 2 to 20 GHz range. However, through simulations, it was seen to have higher Q past 25 GHz after resonance. The novel design is presented for high tunability and with potential to have high Q in the millimeter wave frequencies. The study goes further to optimize the device through designing variations at different capacitance values from 1 pF to 0.06 pF and varying different physical parameters and seeing their effects on its Q. This study goes through design structure calculations, developing electrical models for the varactor designs and some fabrication results on the wafer tunability.

Committee: Guru Subramanyam Ph.D. (Committee Chair); Robert Penno Ph.D. (Committee Member); Monish Chatterjee Ph.D. (Committee Member) Subjects: Electrical Engineering; Engineering; Materials Science

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

The growing demand for operating bandwidth in modern communication and sensing systems coupled with the shift in cellular networks towards mm-Wave 5G and beyond have demanded a need for voltage-controlled oscillators (VCOs) that can simultaneously achieve wide tuning range (TR) and low phase noise (PN). This demand has created a trend in research that explores new techniques for extending VCO tuning range while not sacrificing PN performance. However, challenges exist for designing mm wave VCOs, such as the low-quality factor associated with passive elements and the significant impact of routing parasitics. These challenges bring about a need to innovate the VCO design methodology. Typically, designing wide tuning range LC-VCOs requires the use of a combination of a fine (analog) tuning varactor and a coarse (discrete) digital tuning switched capacitor bank (CDAC) in order to allow tuning across a wide frequency band. The interconnect transmission lines that link the capacitor bank elements are referred to as feedlines, which are proportional to the capacitor bank size. To achieve a wide tuning range in LC-VCOs, a bigger capacitor bank is employed, which leads to the use of long feedlines. Using long feedlines adds more fixed capacitance to the tank, which is mainly due to the interaction between the routing parasitic inductance and the capacitive elements. To account for the impact of these parasitics, a precise consideration of electromagnetic (EM) effects is required. Unfortunately, careful EM modeling is not a trivial task. This is due to the complexity and time-consuming nature of the EM analysis along with the relative immaturity of the integration of EM design tools in the traditional IC design flow. In this work, a detailed analysis of the CDAC and its routing structure is presented, highlighting a major impact on mm-Wave VCOs performance metrics. A robust technique for extending the TR and reducing the PN in an mm-Wave 5G LC-VCO is proposed, analyz (open full item for complete abstract)

Committee: Waleed Khalil (Advisor); Niru Nahar (Committee Member); Tawfiq Musah (Committee Member) Subjects: Electrical Engineering

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

With an increasing demand for high-speed wireless communication, current wire- less infrastructure cannot provide the bandwidth required for high-speed data transfer for multiple users. The next generation of millimeter-wave (mmW) communication systems operate in the frequency range of 30–300 GHz and can provide orders of magnitude greater bandwidth. In addition, these systems rely on adaptive strategies to achieve high data-rate communication which requires reconfigurable elements. In our research, we introduce a new class of reconfigurable radio frequency (RF) microsystems using paraffin phase-change material (PCM) that enables low-loss recon- figuration for mmW components. Paraffin (alkane) is a low-loss nonpolar dielectric that undergoes a 15% reversible volume change through its solid to liquid phase transition. Using this unique combination of loss characteristics and mechanical properties, we have developed continuously variable capacitors. These electro-thermally actuated variable capacitors are low loss with series resistance of less than 0.7 Ω at the mmW band and can be monolithically integrated with antennas and RF components to introduce reconfiguration. In this work, we present a frequency reconfigurable slot antenna which covers the 94 GHz–102 GHz band. In order to achieve reconfiguration, the slot antenna is loaded with two paraffin PCM capacitors. The capacitors are actuated using joule heaters and with the increase in temperature, paraffin goes through a solid to liquid transition. As the volume of the paraffin increases, the capacitance decreases continuously by approximately 15%, which results in increasing the resonance frequency. The realized gain of the antenna at 100 GHz is 3 dBi and it is approximately constant over the reconfiguration range. The Efficiency of the antenna is >72% for the entire reconfiguration range thanks to the low dielectric loss of the paraffin. To evaluate the performance gains of the reconfigurable antennas, new p (open full item for complete abstract)

Committee: Nima Ghalichechian Professor (Advisor); Khalil Waleed Professor (Committee Member); Kubilay Sertel Professor (Committee Member); Kisha Radliff Professor (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

Utility of wireless connectivity has been steadily increasing as broadband internet becomes widely available and having low-cost technology leads to more devices built with Wi-Fi capabilities and sensors. As the traditional radio-frequency (RF) bands (sub 3 GHz) become congested, the mmW band offering vast amount of spectrum, is poised to be the backbone of 5G wireless networks. Particularly, thanks to much smaller wavelengths, antenna-integrated transceivers are viable solutions for the future 5G wireless networks. However, key challenges still remain for on-chip implementation of efficient radiators at such high frequencies. Namely, poor antenna bandwidths, severely low radiation efficiencies, as well as laborious and expensive antenna-transceiver integration (wire bonds, flip-chip, ball grid arrays, etc.) limit the utility of truly-integrated on-chip antennas. To overcome these prevailing obstacles we present an ultra-wideband (UWB), low-profile, high efficiency, tightly-coupled array topology which is adopted from RF-frequency realizations and modified as a multilayered structure suitable for standard micro-fabrication process. Through this work, we show that on-chip radiation efficiency is well above 60% over the entire impedance bandwidth. The proposed array exhibits wideband performance, covering 35-75 GHz, achieving an unprecedented coverage that spans most of the bands allocated for mobile communications. Utilization of low-loss materials in such designs can address the substrate coupling issues and improve the radiation efficiency. Moreover, the structural support and packaging materials that exhibit low loss are indispensable for cost-effective realization of integrated high frequency systems. To effectively address these requirements, polymers are a natural, low-cost choice for structural support and packaging of microchips due to their favorable chemical, thermal, and mechanical properties. However, many polymers have not been studied for mmW and TH (open full item for complete abstract)

Committee: Kubilay Sertel (Advisor); Niru Nahar (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Electromagnetism

Doctor of Philosophy, The Ohio State University, 2018, Electrical and Computer Engineering

Wireless communication networks have become ubiquitous in recent years. Current wireless applications are possible thanks to small WiFi cells that provide high-speed indoor coverage and outdoor macro-cells that support user mobility. Next generation wireless networks will use similar architectures to enable new applications such as augmented and virtual reality, the internet of things, ultra-high definition video streaming, and massive data transmission and storage. However, these applications require unprecedented high-speed data transfer capabilities enabled by large frequency bandwidths. Motivated by spectrum scarcity in bands below 6 GHz, previously unused millimeter-wave (mmWave) bands, where large bandwidths are available, are now considered for future wireless networks. The necessity for efficient communication techniques for such large bandwidths and mmWave frequencies is the main motivation for this dissertation, with a focus on the complex radiowave propagation conditions found in indoor environments. Propagation mechanisms such as multiple reflections, diffractions, and transmissions through walls are commonly found in indoor wireless communications, which cause variations in the received signal along its bandwidth (wideband or frequency-selective channels). Traditionally, antenna arrays have been used together with beamforming (linear processing) techniques to improve the system's performance. However, those techniques were designed for narrowband systems (e.g., zero-forcing or matched filtering) and their application to wideband systems requires additional processing that increases system's complexity. In the first part of this dissertation, we tackle the problem of beamforming in frequency-selective channels with two approaches: \emph{i}) we use the electromagnetic time-reversal (TR) effect to directly design novel wideband beamformers, and \emph{ii}) we generalize the block-diagonalization (BD) procedure used in narrowband channels to the freque (open full item for complete abstract)

Committee: Fernando Teixeira (Advisor) Subjects: Electrical Engineering

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

Automotive radar is an emerging field of research and development. Technological advancements in this field will improve safety for vehicles, pedestrians, and bicyclists, and enable the development of autonomous vehicles. Many automotive companies have already begun to develop autonomous emergency braking (AEB) to avoid or mitigate pedestrian and bicyclist crashes. However, the effectiveness of such systems needs to be accurately tested using standardized test procedures, which have yet to be agreed upon by the international automobile industry and associated government agencies. European testing standards, such as the Euro New Car Assessment Program (NCAP) AEB and AEB-VRU (vulnerable road user), are currently among the first of these standards, and are used for vehicle and pedestrian targets; with plans to include bicyclist targets in the near future. Such standards allow consumers and government regulatory agencies to assess the effectiveness of a vehicle equipped with an AEB system. Obviously, it is neither practical nor safe to use real targets such as pedestrians, bicyclists, or vehicles to conduct such tests. Therefore, a key element of standardized AEB test protocols is standardized surrogate targets that can produce similar sensor responses as real-life cars, pedestrians, and bicycles. In addition, such standard targets need to withstand repeated impacts from the vehicle under test (VUT), prevent damage to the VUT, and be easily reassembled after impacts. This dissertation establishes the steps for characterization of various targets through measurements, the design of a surrogate bicyclist target, and demonstrates successful hardware-in-the-loop (HIL) emulation of targets for AEB scenarios. To design a surrogate target means that the original target must be accurately characterized. This can be done by first studying the far-field radar cross section (RCS) of the target. Since most AEB test scenarios range from 0 m to 100 m, the RCS measurement in t (open full item for complete abstract)

Committee: Chi-Chih Chen (Advisor); Joel Johnson (Committee Member); Graeme Smith (Committee Member); Ahmet Selamet (Committee Member) Subjects: Automotive Engineering; Electrical Engineering; Electromagnetics

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

Master of Science (M.S.), University of Dayton, 2017, Electrical and Computer Engineering

As radar technology development advances and more devices are employed in traditional frequency allocation bands, such as the microwave portion of the frequency spectrum, users are increasingly struggling to operate amidst this spectrum congestion. With spectrum congestion on the rise, application performance degradation is progressively being realized due to scarce available bandwidth. Therefore, users, such as the 5G wireless community and the automotive industry, are exploring applications at higher portions of the frequency spectrum with such efforts being focused in the millimeter wave (MMW) frequency bands. A number of novel applications, such as full-body imaging and automotive collision avoidance systems, have been improved on or realized with the aid of MMW frequencies and their associated phenomenology. However, this portion of the spectrum lags, in some cases by orders of magnitude, far behind in research and development in comparison to other bands such as those found in the microwave region. Therefore, a clear need to aid the knowledge base and investigate MMW radar phenomenology has been undertaken in this thesis. The research this thesis documents concerns designing, building and, fielding a distributed aperture array W-band (MMW) radar system. This thesis details incrementing the current fielded radar system capability from mono-static to bi-static imaging configurations. An improved method for calibrating the radar system resulting in higher quality imagery is also documented. The defined radar system was designed with the goal of performing multi-static Tomographic imaging. The research covered in this thesis is the first step toward incrementing the fielded system to full maturity.

Committee: Michael Wicks (Committee Chair); Lorenzo Lo Monte (Committee Member); Howard Evans (Committee Member); Robert Penno (Committee Member); Andrew Bogle (Committee Member) Subjects: Electrical Engineering; Engineering

Doctor of Philosophy, The Ohio State University, 2014, Physics

Millimeter wave imagers provide a unique way to see through obscurations with enough angular resolution to identify hidden objects. However, current millimeter wave imaging applications require a cooperative subject at close proximity to provide accurate target identification. In this dissertation, I develop a multi-angle illumination method that overcomes these limitations and demonstrate its target identification accuracy at a range of 50 meters. Specular, or mirror-like, surfaces that are not in optimal alignment reflect power away from the receiver. Optimal alignment of specular targets becomes more difficult as the distance from the receiver increases. Consequently, direct illumination millimeter wave imaging applications that rely on optimal alignment of specular targets become increasingly less accurate with distance. For randomly rough surfaces, coherent illumination causes speckle. Speckle is a granularity in an image that is caused by coherent interference from scattering elements within a pixel. The speckle granularity severely decreases target recognition of randomly rough objects. To address these limitations, I develop a method that illuminates the target from many modes using an indirect illumination technique that increases target detection probability regardless of orientation. Additionally, illumination of the target from many angles results in many independent speckle patterns. Averaging the independent speckle patterns decreases speckle effects and results in a significant increase in accurate target detection. This research shows that indirect illumination techniques, combined with range resolved radar cross section (RCS) techniques, produce millimeter wave images with range information that significantly reduces speckle. The elimination of the requirement for special target orientation and the ability to produce an image with depth information at long range with minimized speckle represents a significant adva (open full item for complete abstract)

Committee: Frank C. De Lucia (Advisor); Richard Furnstahl (Committee Member); Klaus Honscheid (Committee Member); Douglass Schumacher (Committee Member) Subjects: Physics

Master of Science in Engineering (MSEgr), Wright State University, 2011, Electrical Engineering

Room temperature direct detectors operating in the so-called Terahertz (THz) region of the electromagnetic spectrum, and representing the most common detection technologies currently available, were characterized at 104, 280 GHz or 600 GHz within their intended range of operating frequencies. These detectors included commercial Schottky-diode rectifiers (Virginia Diodes and Spacek Labs), commercial pyroelectric detectors (Spectrum Detector), and a commercial Golay cell (QMCI). The characterization included antenna patterns, responsivity, electrical noise, noise equivalent temperature difference (NEΔT ), and noise equivalent power (NEP). Since all the characterization measurements were made the same way, quantitative comparisons can be made between the performances of the individual detectors and conclusions are drawn about their relative merits for particular applications. The noise characteristics of the amplifiers used in the experiments were also measured and taken into account in the characterization of the detectors.

Committee: Elliott Brown PhD (Advisor); Douglas T. Petkie PhD (Committee Member); Yan Zhuang PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Physics

Master of Science (MS), Wright State University, 2006, Physics

With sub-millimeter wave or terahertz devices becoming more readily available, there is interest in developing sensors in this region of the spectra. To support this interest, we have developed a Fourier Transform Far InfraRed (FTFIR) spectrometer to characterize broadband transmission and reflectance coefficients of materials. The spectrometer utilizes a broadband blackbody source, a Michelson interferometer, and silicon bolometer. The path difference in the Michelson is obtained using a linear stage and data acquisition and stage control were both implemented in a Labview programming environment. The details of the experimental setup and experimental results are presented in this thesis. The instrument demonstrated capability to measure the broadband transmission spectra of cloth and cardboard samples and we found that these spectra, which showed transmission < ~0.5 THz and increased in attenuation at higher frequencies, agreed with accepted general trends.

Committee: Doug Petkie (Advisor) Subjects: Physics, Optics