Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Aerospace Engineering (1664)
- Electrical and Computer Engineering (1332)
- Operations Research, Systems Engineering and Industrial Engineering (1238)
- Physical Sciences and Mathematics (1164)
- Operational Research (605)
-
- Signal Processing (455)
- Computer Sciences (443)
- Civil and Environmental Engineering (421)
- Computer Engineering (414)
- Aviation (353)
- Electrical and Electronics (350)
- Physics (350)
- Materials Science and Engineering (329)
- Business (297)
- Navigation, Guidance, Control and Dynamics (250)
- Other Operations Research, Systems Engineering and Industrial Engineering (232)
- Systems Engineering (228)
- Electromagnetics and Photonics (190)
- Aerodynamics and Fluid Mechanics (188)
- Environmental Engineering (185)
- Engineering Science and Materials (176)
- Nuclear Engineering (176)
- Mechanical Engineering (169)
- Digital Communications and Networking (166)
- Space Vehicles (159)
- Optics (147)
- Management and Operations (144)
- Operations and Supply Chain Management (135)
- Semiconductor and Optical Materials (126)
- Keyword
-
- #antcenter (324)
- #csra (125)
- Global Positioning System (63)
- Image processing (61)
- #afcec (60)
-
- Optimization (54)
- Additive manufacturing (51)
- Decision making (51)
- Kalman filtering (51)
- Flight control (48)
- Machine learning (48)
- Target acquisition (47)
- Drone aircraft (46)
- Algorithms (45)
- Microelectromechanical systems (44)
- Composite materials (41)
- Artificial satellites (38)
- Synthetic aperture radar (38)
- Computer vision (37)
- Neural networks (Computer science) (37)
- Computer networks--Security measures (35)
- Signal processing (35)
- Finite element method (33)
- Scheduling (32)
- Simulation (31)
- Decision support systems (30)
- Neural networks (30)
- Remote sensing (28)
- Wireless communication systems (28)
- Silicon carbide (26)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 1411 - 1440 of 5699
Full-Text Articles in Engineering
Tensile Properties And Fatigue Behavior Of Geopolymer Matrix Composites With Carbon Fiber Reinforcement At Elevated Temperature, Steffan M.L. Wilcox
Tensile Properties And Fatigue Behavior Of Geopolymer Matrix Composites With Carbon Fiber Reinforcement At Elevated Temperature, Steffan M.L. Wilcox
Theses and Dissertations
The tensile stress-strain and tension-tension fatigue of geopolymer matrix composites reinforced with 0/90 carbon fibers was investigated at 23 and 300°C in laboratory air. Geopolymers are inorganic polymeric materials composed of alumina, silica, and alkali metal oxides. Because geopolymers are synthesized as a fluid mixture or particles and liquid, they can be cast into a desired shape, and cured at only slightly elevated temperatures. The relative ease of synthesis and low processing temperatures make geopolymers an attractive choice as a matrix material for composite materials. Geopolymers also offer resistance to heat and oxidizing environments. Currently, geopolymer matrix composites are being …
Passive Radiolocation Of Ieee 802.11 Emitters Using Directional Antennae, Bradford E. Law
Passive Radiolocation Of Ieee 802.11 Emitters Using Directional Antennae, Bradford E. Law
Theses and Dissertations
Low-cost commodity hardware and cheaper, more capable consumer-grade drones make the threat of home-made, inexpensive drone-mounted wireless attack platforms (DWAPs) greater than ever. Fences and physical security do little to impede a drone from approaching private, commercial, or government wireless access points (WAPs) and conducting wireless attacks. At the same time, unmanned aerial vehicles (UAVs) present a valuable tool for network defenders conducting site surveys and emulating threats. These platforms present near-term dangers and opportunities for corporations and governments. Despite the vast leaps in technology these capabilities represent, UAVs are noisy and consequently difficult to conceal as they approach a …
Quantifying Permafrost Extent, Condition, And Degradation Rates At Department Of Defense Installations In The Arctic, Christopher A. J. Edlund
Quantifying Permafrost Extent, Condition, And Degradation Rates At Department Of Defense Installations In The Arctic, Christopher A. J. Edlund
Theses and Dissertations
The DoD is planning over $500M in military construction on Eielson Air Force Base (AFB) within the next three years. This construction program will expand the footprint of facilities and change parts of the storm water management scheme, which may have second order effects on the underlying permafrost layer. These changes in permafrost will drive engineering decision making at local and regional levels, and help shape the overall strategy for military readiness in the Arctic. Little site-specific knowledge exists on the human caused effects to permafrost at this location. In 2016, the permafrost degradation rates at Eielson AFB were modeled …
An Analysis Of Major Acquisition Reforms Through Text Mining And Grounded Theory Design, Amanda L. Mcgowin
An Analysis Of Major Acquisition Reforms Through Text Mining And Grounded Theory Design, Amanda L. Mcgowin
Theses and Dissertations
Cost growth is an established phenomenon within Defense Acquisition that the US Government has attempted to abolish for decades through seemingly endless cycles of reform. Dozens of experts and senior leaders within the acquisition community have published their notions on the reasons for cost growth, nevertheless, legislation has yet to eradicate this presumed conundrum. For this reason, this research is aimed at identifying existing trends within past major Defense Acquisition Reform legislation, as well as in a compendium of views from leaders within the Defense Acquisition community on the efficacy of acquisition reform, to determine the possible disconnect. To accomplish …
Segmented Control Of Electrostatically Actuated Bimorph Micromirrors, Kullen W. Waggoner
Segmented Control Of Electrostatically Actuated Bimorph Micromirrors, Kullen W. Waggoner
Theses and Dissertations
Electrostatic actuating bimorph beams are a MEMS device that can be used to control arrays of small micromirrors for optical beam scanning. Previous research has demonstrated that creating high-angle deflection using long repeating arms of bimorph beams is possible. The current devices lack precise control and measurement of the mirror deflection. A solution to improve control and measurement is by using segmented bias channels to control separate portions of the actuation arm. The amount of mirror deflection will vary depending on which segments of the arm are actuated. This thesis discusses the results of FEA modeling and testing.
Human Optimization And Performance Enhancement In Flight Via Real-Time Biofeedback (Project Have Hope), Michael S. Fritts
Human Optimization And Performance Enhancement In Flight Via Real-Time Biofeedback (Project Have Hope), Michael S. Fritts
Theses and Dissertations
A four-phase, chronological, and build-up approach was implemented that commenced with basic hardware testing in a centrifuge and culminated in flights augmented by real-time biofeedback displays. A prototype Portable Electrocardiogram Unit (PECGU) was designed and proven to accurately measure heart rate (HR) and display percent heart rate reserve (%HRR). Results showed that %HRR was not a sole predictor of cognitive state. Cognitive responses indicated some correlation with %HRR, but were influenced by environment (centrifuge vs. flight). Subjective perceived exertion levels did not show statistically significant changes during test with biofeedback. A G-tracking task was evaluated during centrifuge and flight tests. …
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Theses and Dissertations
The direct simulation of turbulent flows is prohibitive at high Reynolds numbers; thus, methods such as RANS and LES are used. However, these methods still require a large number of cells near a solid boundary. To circumvent this issue, a Wall-Modeled Large Eddy Simulation (WM-LES) can be used. Of interest is how these wall models perform in comparison to a Wall-Resolved Large Eddy Simulation (WR-LES) and experimental results of a shock turbulent boundary layer interactions (STBLI) and specifically, whether equilibrium wall models are sufficient to resolve the oscillatory and hence non-equilibrium nature of these flows or whether a non-equilibrium model …
Creep Of Nextel 720/A Ceramic Matrix Composite With Laser Drilled Effusion Holes At 1200°C In Air And In Steam, Savannah N. Minor
Creep Of Nextel 720/A Ceramic Matrix Composite With Laser Drilled Effusion Holes At 1200°C In Air And In Steam, Savannah N. Minor
Theses and Dissertations
Creep behavior of an oxide-oxide ceramic matrix composite (CMC) containing an array of effusion holes was investigated at 1200⁰C in air and in steam. The composite (N720/A) consisted of a porous alumina matrix reinforced with alumina-mullite NextelTM 720 fibers. Test specimens had an array of 17 effusion holes with 0.5-mm diameter. The effusion holes were drilled through the specimen thickness normal to the specimen surface using a CO2 laser. Effect of the effusion holes on tensile properties was evaluated tension tests to failure at 1200°C in air. Creep of specimens with effusion holes at 1200°C was studied for creep stresses …
Pseudo Linear Hall Effect Thruster Characterization Through Potential, Magnetic, And Optical Measurements, Braeden A. Sheets
Pseudo Linear Hall Effect Thruster Characterization Through Potential, Magnetic, And Optical Measurements, Braeden A. Sheets
Theses and Dissertations
Electric propulsion systems are a more mass efficient method for providing a change in velocity, ΔV, to on-orbit spacecraft, than their chemical counterparts. In comparison, electric systems generally have a much higher specific impulse, Isp, than chemical systems. One option within the realm of electric propulsion is Hall Effect Thrusters, which have moderately high specific impulse values. From their advent in the 1960s, Hall Effect Thrusters have been used for orbit station keeping, attitude control, and orbit transfer. Although the discharge cavity is conventionally circular, pseudo-linear or racetrack shaped cavities have been developed. Even though Hall thrusters have decades of …
Investigation Of Geometric And Thermal Scaling Effects On Simulated Turbine Vane Leading Edge Model, James G. Tewaheftewa
Investigation Of Geometric And Thermal Scaling Effects On Simulated Turbine Vane Leading Edge Model, James G. Tewaheftewa
Theses and Dissertations
Film cooling is still a bustling research topic, especially with burgeoning manufacturing techniques on the horizon that will open the design space. However, despite the number of years that have gone into gas turbine design and research, evaluating cooling performance on components still presents challenges. This task becomes especially difficult and dangerous if trying to do so in realistic engine conditions. Therefore, the majority of film cooling research is performed at conditions far from realistic engine conditions, often using materials that would never hold up to turbine inlet temperature, and scaled to predict results at engine conditions. Previous film cooling …
Characterization And Analysis Of Plasma Instabilities In A 600 W Permanent Magnet Hall Thruster, Samuel D. Wright
Characterization And Analysis Of Plasma Instabilities In A 600 W Permanent Magnet Hall Thruster, Samuel D. Wright
Theses and Dissertations
Electric propulsion is an important technology for the future of space operations and exploration. Within the range of electric propulsion devices, Hall Effect Thrusters provide a balance of thrust and specific impulse well-suited for many Earth-centric missions. Hall Effect Thrusters have been studied since their development in the 1960s and have been flown on hundreds of spacecraft, but the intimate details of the plasma behavior within the thruster exhaust plume are still not well understood. Furthering this knowledge may be key to improving thruster design to yield better performance and longer lifetimes. To this end, experiments were conducted to measure …
Estimating Defensive Cyber Operator Decision Confidence, Markus M. Borneman
Estimating Defensive Cyber Operator Decision Confidence, Markus M. Borneman
Theses and Dissertations
As technology continues to advance the domain of cyber defense, signature and heuristic detection mechanisms continue to require human operators to make judgements about the correctness of machine decisions. Human cyber defense operators rely on their experience, expertise, and understanding of network security, when conducting cyber-based investigations, in order to detect and respond to cyber alerts. Ever growing quantities of cyber alerts and network traffic, coupled with systemic manpower issues, mean no one has the time to review or change decisions made by operators. Since these cyber alert decisions ultimately do not get reviewed again, an inaccurate decision could cause …
Progressive Network Deployment, Performance, And Control With Software-Defined Networking, Daniel J. Casey
Progressive Network Deployment, Performance, And Control With Software-Defined Networking, Daniel J. Casey
Theses and Dissertations
The inflexible nature of traditional computer networks has led to tightly-integrated systems that are inherently difficult to manage and secure. New designs move low-level network control into software creating software-defined networks (SDN). Augmenting an existing network with these enhancements can be expensive and complex. This research investigates solutions to these problems. It is hypothesized that an add-on device, or "shim" could be used to make a traditional switch behave as an OpenFlow SDN switch while maintaining reasonable performance. A design prototype is found to cause approximately 1.5% reduction in throughput for one ow and less than double increase in latency, …
Assessing The Competing Characteristics Of Privacy And Safety Within Vehicular Ad Hoc Networks, Jacob W. Connors
Assessing The Competing Characteristics Of Privacy And Safety Within Vehicular Ad Hoc Networks, Jacob W. Connors
Theses and Dissertations
The introduction of Vehicle-to-Vehicle (V2V) communication has the promise of decreasing vehicle collisions, congestion, and emissions. However, this technology places safety and privacy at odds; an increase of safety applications will likely result in the decrease of consumer privacy. The National Highway Traffic Safety Administration (NHTSA) has proposed the Security Credential Management System (SCMS) as the back end infrastructure for maintaining, distributing, and revoking vehicle certificates attached to every Basic Safety Message (BSM). This Public Key Infrastructure (PKI) scheme is designed around the philosophy of maintaining user privacy through the separation of functions to prevent any one subcomponent from identifying …
Modeling A Space-Based Quantum Link, Alexander W. Duchane
Modeling A Space-Based Quantum Link, Alexander W. Duchane
Theses and Dissertations
Quantum sources and single photon detectors have improved, allowing quantum algorithms for communication, encryption, computing, and sensing to transition from theory and small-scale laboratory experiments to field experiments. One such quantum algorithm, Quantum Key Distribution, uses optical pulses to generate shared random bit strings between two locations. These shared bit strings can be turned into encryption keys to be used as a one-time-pad or integrated with symmetric encryption techniques such as the Advanced Encryption Standard. This method of key generation and encryption is resistant to future advances in quantum computing which significantly degrade the effectiveness of current asymmetric key sharing …
Assured Android Execution Environments, Brandon P. Froberg
Assured Android Execution Environments, Brandon P. Froberg
Theses and Dissertations
Current cybersecurity best practices, techniques, tactics and procedures are insufficient to ensure the protection of Android systems. Software tools leveraging formal methods use mathematical means to assure both a design and implementation for a system and these methods can be used to provide security assurances. The goal of this research is to determine methods of assuring isolation when executing Android software in a contained environment. Specifically, this research demonstrates security properties relevant to Android software containers can be formally captured and validated, and that an implementation can be formally verified to satisfy a corresponding specification. A three-stage methodology called "The …
Mitigating The Effects Of Boom Occlusion On Automated Aerial Refueling Through Shadow Volumes, Zachary C. Paulson
Mitigating The Effects Of Boom Occlusion On Automated Aerial Refueling Through Shadow Volumes, Zachary C. Paulson
Theses and Dissertations
In flight refueling of Unmanned Aerial Vehicles (UAVs) is critical to the United States Air Force (USAF). However, the large communication latency between a ground-based operator and his/her remote UAV makes docking with a refueling tanker unsafe. This latency may be mitigated by leveraging a tanker-centric stereo vision system. The vision system observes and computes an approaching receiver's relative position and orientation offering a low-latency, high frequency docking solution. Unfortunately, the boom -- an articulated refueling arm responsible for physically pumping fuel into the receiver -- occludes large portions of the receiver especially as the receiver approaches and docks with …
Stereo Vision: A Comparison Of Synthetic Imagery Vs. Real World Imagery For The Automated Aerial Refueling Problem, Nicholas J. Seydel
Stereo Vision: A Comparison Of Synthetic Imagery Vs. Real World Imagery For The Automated Aerial Refueling Problem, Nicholas J. Seydel
Theses and Dissertations
Missions using unmanned aerial vehicles have increased in the past decade. Currently, there is no way to refuel these aircraft. Accomplishing automated aerial refueling can be made possible using the stereo vision system on a tanker. Real world experiments for the automated aerial refueling problem are expensive and time consuming. Currently, simulations performed in a virtual world have shown promising results using computer vision. It is possible to use the virtual world as a substitute environment for the real world. This research compares the performance of stereo vision algorithms on synthetic and real world imagery.
A Surprising Symbiosis: Examining The Mutualism In Department Of Defense Conservation Partnerships, Andrew J. Lankow
A Surprising Symbiosis: Examining The Mutualism In Department Of Defense Conservation Partnerships, Andrew J. Lankow
Theses and Dissertations
Because of the DoD’s unique and significant role in the conservation of natural resources, military leaders and natural resource managers need a trail guide to frame interagency collaboration in a way that shapes productive partnerships. The purpose of this research was to examine successful DoD conservation partnerships in order to identify key success factors (KSFs) and the most prominent challenges faced, and how those characteristics enable the accomplishment of each partner’s objectives. The research questions were answered through a comprehensive literature review and the use of the multiple-case study method. 19 key informants from three installations participated in semi-structured interviews, …
Managing Supply Discrepancies: The Effect Of Performance Measurement And Feedback On Order Fulfillment Quality, Michael J. Weber
Managing Supply Discrepancies: The Effect Of Performance Measurement And Feedback On Order Fulfillment Quality, Michael J. Weber
Theses and Dissertations
Extensive research on the impact of shipping and packaging errors in the private sector finds numerous negative outcomes, including reduced customer satisfaction, reduced customer loyalty, and lower profitability. However, little research has been done examining the impact of order fulfillment errors on military operations. The purpose of this research is to quantify the impact of supply discrepancy reports (SDRs) on military aircraft readiness metrics, including cannibalizations, not mission capable supply (NMCS) hours, aircraft availability and MICAP hours. Results show SDRs significantly impact aircraft readiness metrics in seven of the fifteen analyses conducted. Additionally, a quasi-experimental study is implemented at DLA …
Design And Test Of A Uav Swarm Architecture Over A Mesh Ad-Hoc Network, Timothy J. Allen
Design And Test Of A Uav Swarm Architecture Over A Mesh Ad-Hoc Network, Timothy J. Allen
Theses and Dissertations
The purpose of this research was to develop a testable swarm architecture such that the swarm of UAVs collaborate as a team rather than acting as several independent vehicles. Commercial-off-the-shelf (COTS) components were used as they were low-cost, readily available, and previously proven to work with at least two networked UAVs. Initial testing was performed via software-in-the-loop (SITL) demonstrating swarming of three simulated multirotor aircraft, then transitioned to real hardware. The architecture was then tested in an outdoor nylon netting enclosure. Command and control (C2) was provided by software implementing an enhanced version of Reynolds’ flocking rules via an onboard …
United States Air Force Applications Of Unmanned Aerial Systems: Modernizing Airfield Damage Assessment, Samuel M. Clark
United States Air Force Applications Of Unmanned Aerial Systems: Modernizing Airfield Damage Assessment, Samuel M. Clark
Theses and Dissertations
Modernizing airfield damage assessment has long been a priority mission at the Air Force Civil Engineer Center (AFCEC). Previously, AFCEC has made advances to expedite unexploded ordnance (UXO) neutralization and pavement repair. Missing from these initiatives is the initial assessment component. This thesis expands the idea of using Small Unmanned Aerial Systems (SUAS), applies it to the Air Force mission, and provides SUAS vehicle configuration and sensor recommendations. In this study, 25 civil engineer officers reviewed airfield imagery gathered using two small air vehicles. For the first review, participants attempted to identify UXOs and foreign object debris (FOD) in a …
Control, Characterization, And Cooling Of An Ultra-Compact Combustor, Kevin J. Demarco
Control, Characterization, And Cooling Of An Ultra-Compact Combustor, Kevin J. Demarco
Theses and Dissertations
An Ultra-Compact Combustor (UCC) is novel alternative to axial flow combustors commonly used in gas turbine engines. The UCC offers multiple benefits to engine design. First, the UCC aims to increase the thrust-to-weight ratio of an aircraft gas turbine engine by decreasing the size, and thus weight, of the engine's combustor. This is done by utilizing a Circumferential Cavity (CC) wrapped around the main core flow which hosts the combustion event, allowing a shortened combustor length. Second, within the CC, the combusting mixture is subjected to a high centrifugal loading which aids combustion by improving both flame propagation and residence …
Analytical Determination Of A Helicopter Height Velocity Diagram, Michael J. Harris
Analytical Determination Of A Helicopter Height Velocity Diagram, Michael J. Harris
Theses and Dissertations
A helicopter height velocity (HV) diagram was analytically constructed using optimal control techniques. A three degree of freedom, point-mass, dynamic model was developed and validated with flight test data. An induced velocity calculation was incorporated which addressed the effects of vortex ring state. The problem was posed as an open final time, constrained initial state, constrained final state problem, with the objective function as a weighted sum of the initial altitude and quadratic controls. This formulation was solved using direct pseudo-spectral collocation and adaptive mesh refinement as implemented by the GPOPS-II® software suite. Proper adjustment of path constraints was crucial …
Algorithms For Small Satellite Formation Flying, Robert B. Larue
Algorithms For Small Satellite Formation Flying, Robert B. Larue
Theses and Dissertations
This thesis presents algorithms for spacecraft formation flying using impulsive thrust and low-thrust methods. The general circular orbit formation initial conditions are derived in terms of equinoctial elements. Physical significance of the bounded relative motion parameters is presented for the case of general circular orbits. The developed algorithms are posed in terms of equinoctial elements for a singularity-free approach. The algorithms are assessed by numerical propagation of the inertial equations of motion with J2 and drag perturbations. Methods are presented for minimizing the ΔV required for formation initialization. An examination of the performance of open-loop and closed-loop control is provided …
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 1000°C In Air And In Silicic Acid-Saturated Steam, Brian G. Kroeger
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 1000°C In Air And In Silicic Acid-Saturated Steam, Brian G. Kroeger
Theses and Dissertations
Advanced SiC/SiC ceramic matrix composites (CMCs) are being considered for a variety of applications. Of interest is their ability to withstand exposure to high temperature in an aggressive oxidizing environment. The presence of steam creates such an environment. As steam traverses across a SiC/SiC composite and through cracks in the SiC matrix, it becomes saturated with silicic acid, Si(OH)4. It is essential to understand the long-term impacts and durability of SiC/SiC CMCs that have been exposed to such a demanding environment. The present research investigated creep of Hi-Nicalon™ S SiC fibers at 1000°C in air and in silicic …
Variable Speed Simulation For Accelerated Industrial Control System Cyber Training, Luke M. Bradford
Variable Speed Simulation For Accelerated Industrial Control System Cyber Training, Luke M. Bradford
Theses and Dissertations
It is important for industrial control system operators to receive quality training to defend against cyber attacks. Hands-on training exercises with real-world control systems allow operators to learn various defensive techniques and see the real-world impact of changes made to a control system. Cyber attacks and operator actions can have unforeseen effects that take a significant amount of time to manifest and potentially cause physical harm to the system, making high-fidelity training exercises time-consuming and costly. This thesis presents a method for accelerating training exercises by simulating and predicting the effects of a cyber event on a partially-simulated control system. …
Evaluation Of Resiliency In A Wide-Area Backup Protection System Via Model Checking, Kolby H. Elliot
Evaluation Of Resiliency In A Wide-Area Backup Protection System Via Model Checking, Kolby H. Elliot
Theses and Dissertations
Modern civilization relies heavily on having access to reliable power sources. Recent history has shown that present day protection systems are not adequate. Numerous backup protection (BP) systems have been proposed to mitigate the impact of primary protection system failures. Many of these novel BP systems rely on autonomous agents communicating via wide-area networks. These systems are highly complex and their control logic is based on distributed computing. Model checking has been shown to be a powerful tool in analyzing the behavior of distributed systems. In this research the model checker SPIN is used to evaluate the resiliency of an …
Securing Critical Infrastructure: A Ransomware Study, Blaine M. Jeffries
Securing Critical Infrastructure: A Ransomware Study, Blaine M. Jeffries
Theses and Dissertations
This thesis reviews traditional ransomware attack trends in order to present a taxonomy for ransomware targeting industrial control systems. After reviewing a critical infrastructure ransomware attack methodology, a corresponding response and recovery plan is described. The plan emphasizes security through redundancy, specifically the incorporation of standby programmable logic controllers. This thesis goes on to describe a set of experiments conducted to test the viability of defending against a specialized ransomware attack with a redundant controller network. Results support that specific redundancy schemes are effective in recovering from a successful attack. Further experimentation is conducted to test the feasibility of industrial …
Bandwidth Analysis Of A Tightly-Packed Crossed-Dipole Array For Satellite Communications, Lawrence J. Lee
Bandwidth Analysis Of A Tightly-Packed Crossed-Dipole Array For Satellite Communications, Lawrence J. Lee
Theses and Dissertations
A bandwidth analysis of a tightly-packed crossed-dipole array antenna is presented in this thesis. A parametric study is described which varies the element spacing in the array and the resulting change in the terminal impedances is reported. The increased mutual coupling seen by the elements as a result of smaller element spacings is shown to minimize the variation in the value of the elements terminal currents across a 0.3 GHz to 3.0 GHz frequency range. This small variation in current translates into a minimal variation in the terminal impedances for a fixed excitation voltage. This is shown to be an …