Characteristic Mode Theory is one of the very few numerical methods that provide a great deal of physical insight because it allows us to determine the natural modes of the radiating structure. The key feature of these modes is that the total induced antenna current, input impedance/admittance and radiation pattern can be expressed as a linear weighted combination of individual modes. Using this decomposition method, it is possible to study the behavior of the individual modes, understand them and therefore control the antennas behavior; in other words, control the currents induced on the antenna structure. This dissertation advances the topic of antenna design by carefully controlling the antenna currents over the desired frequency band to achieve the desired performance specifications for a set of constraints. Here, a systematic method based on the Theory of Characteristic Modes (CM) and lumped reactive loading to achieve the goal of current control is developed. The lumped reactive loads are determined based on the desired behavior of the antenna currents. This technique can also be used to impedance match the antenna to the source/generator connected to it. The technique is much more general than the traditional impedance matching. Generally, the reactive loads that properly control the currents exhibit a combination of Foster and non-Foster behavior. The former can be implemented with lumped passive reactive components, while the latter can be implemented with lumped non-Foster circuits (NFC). The concept of current control is applied to design antennas with a wide band (impedance/pattern) behavior using reactive loads. We successfully applied this novel technique to design multi band and wide band antennas for wireless applications. The technique was developed to match the antenna to resistive and/or complex source impedance and control the radiation pattern at these frequency bands, considering size and volume constraints. A wide band pat (open full item for complete abstract)

An ultrawide band (UWB) time domain (TD) radar has been developed for Time Reversal (TR) synthetic inverse scattering. This work describes the fabrication and test of a time domain TR “mirror” (TRM), which is the system that transmits, receives, and processes TR signals. Time reversal electromagnetics is a family of signal processing techniques that exploit the time reversal invariance of Maxwell equations, and allow focusing of waves in space and time with “super resolution”, i.e. beyond the classical resolution limit. In a typical TR experiment, first a pulsed signal is emitted and scattered by a target, which then acts as a weak emitter “source” toward the TRM. Then the TRM senses and records the weak scattered signal. Next, the recorded signals are time-reversed for their subsequent normalization and reradiation into the medium. The result is a signal that focuses in time and space where the target originally was, permitting localization and identification applications. A 12 mW low power short range experimental verification of the above process in the microwave domain is demonstrated in this work. The developed system exhibits a 40 GHz useful bandwidth such as to be able to follow 12 ps transition duration signals without distortion. An antenna system was designed and fabricated to satisfy the above bandwidth specification. The backward propagation in the TR process is executed synthetically on account of the current state of the required technology to recreate ultra-fast signals of arbitrary shape. Owing to its intrinsic TD nature, the finite difference time-domain (FDTD) method was applied as the numerical engine to simulate the electromagnetic fields in the TR process, facilitating the link between acquired data and its interpretation. The system designed showed capable of recreating in TD, with this extended bandwidth, the standard TR experiment as predicted by the theory. Hence, from real measurements the system was able to recreate synthetically space and (open full item for complete abstract)

It is well known that the scope and application of numerically-rigorous techniques for full-wave electromagnetic characterization is limited to problems of moderate electrical size and simplified complexity. These limitations stem from the vast computational resources required by numerical methods such as finite element method (FEM), boundary element method (BEM) or finite difference method (FDM). During the last decade a number of fast and memory efficient numerical algorithms such as Multigrid methods and the Fast Multipole Algorithm (FMA), have been proposed to further reduce storage and computational requirements of full-wave methods. In this dissertation an alternative proposition will be presented, that is a fast and efficient Domain Decomposition (DD) methodology, appropriately tailored for the solution of time-harmonic Maxwell's equations. The DD method proposed here is a non-conforming one, namely it allows for different mesh on either side of domain interface. This not only relaxes and speeds up automatic mesh generation algorithms, but at the same time opens the road of efficient and robust adaptive field computations. The DD technique is based on a divide-and-conquer philosophy. Instead of tackling a large and complex problem directly (as a whole), it divides the computational domain into smaller, possibly repetitive, and easier to solve partitions called domains. Such domains can be solved with a variety of numerical methods, e.g. finite elements, boundary elements, etc. The algorithm proceeds iteratively by appropriately communicating information across domains and ultimately reaching the solution for the original (whole) problem. A detailed presentation of the proposed DD method for electromagnetic problems will be given, along with a novel methodology called "cement" finite elements, for the coupling of domains with non-matching meshes. In addition, a variant of the Finite Element Tearing and Interconnecting (FETI) sub-structuring algorithm will be i (open full item for complete abstract)

This dissertation presents the methodologies used to develop and validate protective zoning requirements for Microwave Landing System (MLS) azimuth and elevation guidance signals. Typically, the aviation community refers to these protective zoning requirements as critical areas. The purpose of defining critical areas about the azimuth and elevation antennas is to protect the radiated guidance signals from multipath errors caused by electromagnetic scattering of these signals by transient vehicles and aircraft. A method for applying the Federal Aviation Administration MLS Mathematical Model to characterize the guidance signal errors caused by interfering aircraft located ahead of the azimuth or elevation antenna is presented. This method was used to generate error-contour plots characterizing the guidance signal errors caused along a standard precision approach profile as a function of interfering aircraft type, location, and orientation. Error budgets were developed, including allocations to the error permitted to be caused by interfering aircraft. Based on these allocations, error-contour plots were analyzed to determine the areas that bound all of the interfering aircraft locations that have the potential to cause guidance-signal error that exceed the allocations. Methods for adapting these criteria to protect non-standard, computed-centerline, and advanced approach procedures are presented. The dissertation provides azimuth and elevation critical-area criteria for basic, computed-centerline, and advanced MLS procedures. Also, it presents the status of critical-area criteria development for Precision Distance Measuring Equipment. The dissertation recommends that validation and refinement of the criteria be performed as indicated by operational experience.