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Articles 211 - 220 of 220
Full-Text Articles in Engineering
Non-Cooperative Detection Of Frequency-Hopped Gmsk Signals, Clint R. Sikes
Non-Cooperative Detection Of Frequency-Hopped Gmsk Signals, Clint R. Sikes
Theses and Dissertations
Many current and emerging communication signals use Gaussian Minimum Shift Keyed (GMSK), Frequency-Hopped (FH) waveforms to reduce adjacent-channel interference while maintaining Low Probability of Intercept (LPI) characteristics. These waveforms appear in both military (Tactical Targeting Networking Technology, or TTNT) and civilian (Bluetooth) applications. This research develops wideband and channelized radiometer intercept receiver models to detect a GMSK-FH signal under a variety of conditions in a tactical communications environment. The signal of interest (SOI) and receivers have both fixed and variable parameters. Jamming is also introduced into the system to serve as an environmental parameter. These parameters are adjusted to examine …
Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann
Characterization And Design Of High-Level Vhdl I/Q Frequency Downconverter Via Special Sampling Scheme, Jesse P. Somann
Theses and Dissertations
This study explores the characterization and implementation of a Special Sampling Scheme (SSS) for In-Phase and Quad-Phase (I/Q) down conversion utilizing top-level, portable design strategies. The SSS is an under-developed signal sampling methodology that can be used with military and industry receiver systems, specifically, United States Air Force (USAF) video receiver systems. The SSS processes a digital input signal-stream sampled at a specified sampling frequency, and down converts it into In-Phase (I) and Quad-Phase (Q) output signal-streams. Using the theory and application of the SSS, there are three main objectives that will be accomplished: characterization of the effects of input, …
Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood
Multi-Dimensional Wave Front Sensing Algorithms For Embedded Tracking And Adaptive Optics Applications, Christopher C. Wood
Theses and Dissertations
Current tracking and adaptive optics techniques cannot compensate for fast-moving extended objects, which is important for ground-based telescopes providing space situational awareness. To fill this need, a vector-projection maximum-likelihood wave-front sensing algorithm development and testing follows for this application. A derivation and simplification of the Cramer-Rao Lower Bound for wavefront sensing using a laser guide star bounds the performance of these systems and guides implementation of a vastly optimized maximum-likelihood search algorithm. A complete analysis of the bias, mean square error, and variance of the algorithm demonstrates exceptional performance of the new sensor. A proof of concept implementation shows feasibility …
An Airborne Radar Model For Non-Uniformly Spaced Antenna Arrays, Matthew V. Young
An Airborne Radar Model For Non-Uniformly Spaced Antenna Arrays, Matthew V. Young
Theses and Dissertations
This thesis presents an airborne radar model for non-uniformly spaced antenna arrays. Non-uniform arrays potentially possess advantages unobtainable by uniformly spaced arrays. An element position matrix is defined to accommodate arbitrary element locations. The new element position matrix affects the time/phase delay to each element, spatial frequencies, steering vectors, space-time snapshots, and covariance matrices. The joint domain localized and factored time-space-time adaptive processing algorithms are also updated so they are compatible with the new model. The non-uniformly spaced array radar model is verified with previous models presented by Jaffer, Ward, and Hale. The model for non-uniform arrays is used to …
Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris
Lqg/Ltr Tilt And Tip Control For The Starfire Optical Range 3.5-Meter Telescope's Adaptive Optics System, Neil D. Paris
Theses and Dissertations
The Air Force Research Laboratory has sponsored research on the tracking control loop portion of the adaptive optics system in the Starfire Optical Range 3.5-meter telescope at Kirtland Air Force Base. The control loop includes two steering mirrors (Coarse Steering Mirror and Fine Steering Mirror) used to remove wavefront tilt and tip phase distortion from light entering the telescope. The objective of this research is to design a single Linear Quadratic Gaussian controller to control both steering mirrors in order to eliminate wavefront tilt and tip distortions induced by the earth's atmosphere, and to evaluate the stability robustness and performance …
Development And Testing Of An Inflatable, Rigidizable Space Structure Experiment, Sarah K. Helms
Development And Testing Of An Inflatable, Rigidizable Space Structure Experiment, Sarah K. Helms
Theses and Dissertations
Many recent space technology concepts require large space structures such as solar arrays and large aperture antennas; however, tight constraints on payload mass and volume often preclude their launch. Employing inflatable, rigidizable structures can reduce mass and volume while providing sufficient packing flexibility and structural stiffness. AFIT has developed RIGEX to flight-test this type of structure. RIGEX will test the deployment and structural characteristics of three thermoplastic composite Sub-Tg tubes. Once launched on the Space Shuttle in 2007, the spaceflight results will be compared to lab data to validate on-orbit reliability and ground test methods. This paper documents three main …
Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee
Evaluation Of Factors Contributing To Damping Of Coated And Uncoated Titanium Plates, Dustin W. Lee
Theses and Dissertations
High Cycle Fatigue (HCF) is the leading cause of component failure in gas turbine engines today, which poses great risk to aircraft, engines, and their crews. Mitigation of HCF effects has become a priority topic, and the damping benefits of hard coatings are being reevaluated for this purpose. Research was conducted to further understanding of damping measurements on these coatings. This study continues work to characterize the damping effects of a magnesium aluminate spinel (mag spinel) coating applied to a titanium plate via vibration testing. Two different plate sizes were evaluated in a clamped-free-free-free condition and a free-free-free-free condition, respectively. …
Investigation Of Frequency-Domain And Time-Domain Free-Space Material Measurements, Kirt J. Cassell
Investigation Of Frequency-Domain And Time-Domain Free-Space Material Measurements, Kirt J. Cassell
Theses and Dissertations
Electromagnetic material characterization is the process of determining the complex permittivity and permeability of a test sample. The primary goal of this thesis is to develop a new two-transmission material measurement method to decrease the error associated with using a reflection measurement. The transmission method uses a sample transmission measurement and an acrylic-backed sample transmission measurement. This technique is first demonstrated in a rectangular waveguide system then extended to frequency-domain and time-domain focus arch free-space systems. The frequency-domain free-space calibration process decreases accuracy at the band edges. The use of a digital oscilloscope with a time-domain reflectometer (TDR) module should …
Forward-Looking Radar Clutter Suppression Using Frequency Diverse Arrays, Piotr Baizert
Forward-Looking Radar Clutter Suppression Using Frequency Diverse Arrays, Piotr Baizert
Theses and Dissertations
This thesis introduces a new array structure, the Frequency Diverse Array (FDA), where each channel transmits and receives at a different frequency. The resulting range-dependent FDA antenna pattern is proposed to improve forward-looking clutter suppression. The planar FDA radar data model is derived and analytically verified to be equivalent to the constant frequency data model when each element frequency is set to the same value. The linear FDA at high platform altitude provides significant benefits? by reducing the range ambiguous clutter contribution, improving target detection by up to 10 dB. At low altitudes without range ambiguous clutter the linear FDA …
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Theses and Dissertations
Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …