Doctoral Degrees (Electrical and Electronic Engineering)

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Browsing Doctoral Degrees (Electrical and Electronic Engineering) by browse.metadata.advisor "Botha, Matthys"

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    Analysis of large disjoint antenna arrays by localised solutions
    (Stellenbosch : Stellenbosch University, 2023-03) Chose, Matthews; Botha, Matthys; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: The method of moments (MoM) is well suited to the full-wave electromagnetic analysis of antenna arrays. This is especially true for perfect electrically conducting (PEC) antennas, when an electric field integral equation (EFIE) formulation with Rao-Wilton-Glisson (RWG) basis functions is the typical approach. This yields fully populated matrices with the solution cost growing rapidly with array size N, as O(N3) and O(N2) for the runtime and storage respectively, when a standard direct solver is employed. This work is concerned with the efficient an d re liable EF IE RWG MoM an alysis of large antenna arrays consisting of identical disjoint PEC elements. Examples of such arrays are encountered within the international Square Kilometre Array (SKA) project, which motivates this work. The new formulations proposed are based on a MoM domain decomposition technique known as the domain Green’s function method (DGFM), which is a perturbation technique developed for analysing large disjoint antenna arrays. It was originally formulated in the context of printed substrate antennas, but has since been applied more broadly. In its existing form, the DGFM is limited to fairly sparse arrays where mutual coupling effects are less pronounced. Three DGFM-based extensions are proposed, in order for the method to be applicable to dense and very large antenna arrays. The first i s t o i ntroduce l arger l ocal solution domains in combination with an iterative scheme, to enable solutions to a pre-specified accuracy. The second is a physics-based row expansion direct-coupling technique, which is a necessary variation on the standard DGFM approach to far couplings, in order to maintain efficiency wh en de aling wi th mu ltiple si ngle-element ex citations fo r embedded element pattern calculations. Thirdly, a hybrid, single-level adaptive cross approximation (ACA) matrix compression scheme is proposed, which is tailored to the acceleration of the DGFM and is applicable to both new formulations. Results for antenna arrays relevant to the SKA low-frequency band show efficient and reliable performance.
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    Enhanced method of moments performance through efficient implementation and error estimation
    (Stellenbosch : Stellenbosch University, 2023-03) Cilliers, Pierre; Botha, Matthys; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: The emergence of increasingly ambitious engineering projects has pushed the limits of traditional computational electromagnetics (CEM) simulation software. This has necessitated the development and implementation of new methods that can effectively utilise the available hardware resources of modern computing systems. Due to the increasing availability of large cluster computing systems, research into increasing the capabilities of electromagnetic (EM) field solvers in terms of performance and scale of the problems they can handle has mainly focused on distributed memory parallelisation schemes. The single-core performance of modern processors has however also continued to improve. New processors are also continually being released with increasingly large core counts. Thus designing implementations of solvers that can effectively utilise the available hardware on shared memory systems is crucial for application to both small and very large problems. To this end, this document presents the development and implementation of a numerical field solver that is designed to push the limits of single central processing unit (CPU) performance for the Method of Moments (MoM). This solver forms the core of a software library, the electromagnetic kernel library (EMK), that aims to provide utilities for performing numerical field simulations as well as for developing methods for large-scale antenna analysis. This solver is compared to the solver in a commercial CEM software suite, to assess its performance and accuracy. As well as efficiently computing numerical solutions, it is also important to verify the validity of such solutions and improve them by locating and eliminating sources of error. This is done through a process of error estimation, which seeks to measure the extent to which a numerical solution deviates from the true solution. To this end, a goal-oriented a posteriori error estimator is formulated for MoM-based EM analysis. Goal-oriented error estimators allow for the solution error to be determined with regard to a particular quantity of interest (QOI). This estimator is used in the computation of multi-port Zparameters by driving a simple mesh refinement algorithm, to assess its effectiveness in generating efficient meshes in terms of degrees of freedom