Engineering Commons^™

Low Cross-Polarization Vivaldi Arrays, John Logan

Doctoral Dissertations

Ultra-wideband (UWB) electronically scanned arrays (ESA) with high efficiency, excellent polarization agility, and wide-scan matching remain essential for servicing multifunctional RF front-ends and other communications, sensing, and jamming or countermeasure systems. To this day, the most popular antenna array element in modern UWB-ESA systems is the Vivaldi, or flared notch, due to its superior wide-scan wide impedance bandwidth, well-known design guidelines, and practical embodiment versatility. Despite their popularity, these arrays tend to radiate unacceptably high cross-polarization levels, thus encouraging a great research opportunity. This dissertation presents the theory and design of a new class of UWB-ESAs, termed Sliced Notch Antenna …

Trade-Offs In A 1 Tbps Mimo Communication System Between An Airship And An Array Of Ground Receive Antennas, Adam R. Brueggen

Theses and Dissertations

As demand for higher data-rate wireless communications increases, so will the interest in multiple-input and multiple-output (MIMO) systems. In a single transmitter, single receiver communication system, there is a fundamental limit to the data-rate capacity of the system proportional to the systems bandwidth. Since increasing the bandwidth is expensive and limited, another option is increasing the system's capacity by adding multiple antennas at the transmitter and receiver to create a MIMO communication system. With a T transmitter, R receiver MIMO communication system, TR channels are created which allow extremely high data-rates. MIMO systems are attractive because they are extremely robust …

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 …

Trade Space Analysis Of Antenna Array Architecture Using System Modeling Tools, Eugene Johnson

Theses and Dissertations

This trade study has two objectives. The first provides a trade space analysis of differing array architectures and associated radio frequency components using system-modeling tools. The second objective develops system modeling tools aiding similar analysis by other users. These objectives were accomplished by evaluating a selected group of output parameters to include overall system cost, mass, and power consumption, as well as the minimum detectable input level, system spurious free dynamic range, and selected beam spoilage parameters caused by the use of discrete phase shifters. A fixed number of designs were evaluated using simulation. The evaluation process examined input parameter …

An Empirical Prediction Model Of The Performance Impacts Of Material Tolerances In Frequency Selective Surfaces Using The Monte Carlo Method, Matthew D. Craig

Theses and Dissertations

Standard computational tools predicting frequency selective surface (FSS) performance model periodic structures as an infinite-by-infinite array of perfectly placed elements with perfect, identical dimensions, and with dielectric layers of uniform thickness and material composition. These models do not address perturbations caused by manufacturing tolerances of elements and dielectric layers, nor do they address edge effects caused by finite-by-finite dimensional arrays. The Monte Carlo Method was used to determine the effects of random variations in element dimension, placement, dielectric thickness, and dielectric material on FSS performance. A full-factorial experimental design was applied, and eight hundred twenty-five unique finite arrays of elements …

Loop Gain Estimation For Adaptive Control, Jamey P. Sillence

Theses and Dissertations

The identification of a linear discrete-time control system's loop gain is addressed. The classical Kalman filter theory for state estimation in linear control systems is extended, and the control system's loop gain and state are jointly estimated. A rigorous analysis of the measurement situation under consideration yields explicit formulae for the loop gain's unbiased estimate and estimation error's covariance.

Adaptive Beamforming In Frequency-Dispersive Multipath Environments, David A. Murray

Theses and Dissertations

It is well known that an antenna array with N degrees of freedom (DOF) can cancel N - 1 interferers if they approach the array from directions other than that of the desired signal. It has been shown that there are cases in which it is possible for an array with N DOF to effectively cancel more than N - 1 interferers. Specifically, we show how this can be done when there is incident upon an N-element array not only the desired signal and a jammer signal, but more than N - 1 Doppler-shifted multipath copies of the jammer signal …

Interference Cancellation By Time Adjustable Sampling, Josko Zec

Theses

The problem of improving the frequency response of linear arrays is addressed in this thesis. The improvement is measured in the level of rejection of the undesired sources. A new, simple, and practical method is suggested. It is based on adjusting the sampling time in selected channels. Interference cancellation for finite bandwidth signals is accomplished only at, or close to, the carrier frequency. Wideband cancellation requires additional hardware and computational complexity. Conventional way of the wideband interference cancellation utilizes tapped delay line adaptive filters in each channel.

The Time Adjustable Sampling (TAS) method achieves a part of the tapped delay …