Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 99-103).

Thesis (Ph. D.)--City University of Hong Kong, 2005. / "Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves 144-153).

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2006. / Ingram Mary Ann, Committee Chair ; Durgin, Gregory David, Committee Member ; Williams, Douglas B, Committee Member.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Traditional radio astronomy imaging techniques assume that the interferometric array is coplanar, with a small field of view, and that the two-dimensional Fourier relationship between brightness and visibility remains valid, allowing the Fast Fourier Transform to be used. In practice, to acquire more accurate data, the non-coplanar baseline effects need to be incorporated, as small height variations in the array plane introduces the w spatial frequency component. This component adds an additional phase shift to the incoming signals. There are two approaches to account for the non-coplanar baseline effects: either the full three-dimensional brightness and visibility model can be used to reconstruct an image, or the non-coplanar effects can be removed, reducing the three dimensional relationship to that of the two-dimensional one. This thesis describes and implements the w-projection and w-stacking algorithms. The aim of these algorithms is to account for the phase error introduced by non-coplanar synthesis arrays configurations, making the recovered visibilities more true to the actual brightness distribution model. This is done by reducing the 3D visibilities to a 2D visibility model. The algorithms also have the added benefit of wide-field imaging, although w-stacking supports a wider field of view at the cost of more FFT bin support. For w-projection, the w-term is accounted for in the visibility domain by convolving it out of the problem with a convolution kernel, allowing the use of the two-dimensional Fast Fourier Transform. Similarly, the w-Stacking algorithm applies a phase correction in the image domain to image layers to produce an intensity model that accounts for the non-coplanar baseline effects. This project considers the KAT7 array for simulation and analysis of the limitations and advantages of both the algorithms. Additionally, a variant of the Högbom CLEAN algorithm was used which employs contour trimming for extended source emission flagging. The CLEAN algorithm is an iterative two-dimensional deconvolution method that can further improve image fidelity by removing the effects of the point spread function which can obscure source data. / AFRIKAANSE OPSOMMING: Tradisionele beeldvormingstegnieke in radio-astronomie aanvaar dat die interferometriese skikking samevlakkig is. Dit beteken dat die twee-dimensionele Fourier verhouding tussen helderheid en sigbaarheid geldig bly en dat die Vinnige Fourier Transform aangewend kan word. Klein hoogtevariasies in die skikkingsvlak bring die w-ruimtelike frekwensiekomponent mee, wat ’n faseverskuiwing in die inkomende seine tot gevolg het. Dus, in praktyk, moet die bydrae van die nie-samevlakkige basislyneffekte in ag geneem word om sodoende die akkuraatheid van die data te verhoog. Twee benaderings kan gevolg word om die nie-samevlakkige basislyneffekte in ag te neem: Metodes wat die volle drie dimensionele helderheid en sigbaarheidsmodel gebruik kan toegepas word om ’n beeld te herbou, andersins kan die nie-samevlakkige effekte verwyder word om sodoende die drie-dimensionele verhouding te verminder tot ’n twee-dimensionele verhouding. Hierdie tesis beskryf en implementeer die ‘w-projeksie’ en ‘w-stapel’ algoritmes. Die doel van hierdie algoritmes is om die fasefout wat deur nie-samevlakkige sinteseskikkingskonfigurasies veroorsaak word, reg te stel. Hierdie regstelling maak die herwinde sigbaarheid van die beeld meer getrou aan die werklike helderheidsverspreidingsmodel. ’n Bykomende voordeel van die algoritmes is beeldvorming van wye-veld ruimtewaarnemings. In ‘w-projection’ word die w-term in die sigbaarheidsdomein in ag geneem deur die ruimtelike frekwensiekomponent met behulp van ’n konvolusiekern vanuit die probleem te verwyder. Die twee-dimensionele Vinnige Fourier Transform kan gevolglik toegepas word. Soortgelyk hieraan, wend die ‘w-Stacking’ algoritme ’n fasekorreksie aan tot ’n reeks beeldlae, om sodoende ’n beeld te verkry wat die nie-samevlakkige basislyneffekte in ag neem. Die KAT7 teleskoop is gebruik in die simulasie en analiese van die tekortkominge en voordele van beide algoritmes. ’n Hibriede weergawe van die Högbom CLEAN algoritme is bykomend oorweeg. Hierdie algoritme is ’n iteratiewe twee-dimensionele dekonvolusiemetode wat die betroubaarheid van beelde verbeter deur die verskansingseffek van puntverspreidingsfunksies te verwyder. Verder gebruik die Högbom CLEAN algoritme kontoersnoeiing om uitgebreide bron-emisies te identifiseer.

The focus of this thesis is on the design and selection of systolic architectures for ASIC implementation of the real-time digital signal processing task of Modi- fied Covariance spectral estimation. When used with pulsed Doppler ultrasound blood flow detectors, the Modified Covariance spectral estimator offers increased sensitivity in the detection of arterial disease over conventional Fourier transform based methods. The systolic model of computation is considered because through pipelining and parallel processing high levels of concurrency can be achieved to attain the nec- essary throughput for real-time operation. Systolic arrays of simple processing units are also well suited for implementation on VLSI. The versatility of the de- sign of systolic arrays using the rigorous data dependence graph methodology is demonstrated throughout the thesis by application to all sections of the spectral estimator design at both word and bit levels. Systolic array design for the model order 4 Modified Covariance spectral estima- tor, known to offer accurate estimation of blood flow mean velocity and d1stur- bance at an acceptable computational burden, is initially discussed. A variety of problem size dependent systolic arrays for real-time implementation of the fixed model order spectral estimator are designed using data dependence graph mapping methods. Optimal designs are chosen by comparison of hardware, com- munication and control costs, as well as efficiency, timing, data flow and accuracy considerations. A cost/benefit analysis, based on results from structural simula- tion of the arrays, allows the most suitable word-lengths to be chosen. Problem size independent systolic arrays are then discussed as means of coping with the huge increases in computational burden for a Modified Covariance spec- tral estimator which is programmable up to high model orders. This type of array can be used to reduce the number of PEs and increase efficiency when compared to the problem size dependent arrays and the research culminates in the proposal of a novel spiral systolic array for Cholesky decomposition.

This thesis presents the development of MUSIC algorithm based novel approaches for the estimation of Direction of Arrival (DOA) of electromagnetic sources. For the 2D-DOA estimation, this thesis proposes orthogonally polarized linear array configuration rather than the conventionally invoked two dimensional array. An elegant one dimensional search technique to compute 2D-DOA estimation for a single source scenario has been proposed. To facilitate one dimensional search for 2D-DOA estimation, a closed form relationship between the azimuth and elevation angles of the 2D-DOA is derived using the analytical expressions of radiation patterns of Rectangular Waveguide (RWG) and Circular Waveguide (CWG). The computation time for the proposed one dimensional search technique is reduced by a factor of 50 and 150 for 1 and 0:5 search interval respectively. To improve the accuracy and the resolution of 2D-DOA estimation in case of closely spaced sources, this thesis proposes novel array configurations such as orthogonally polarized planar array, orthogonally mounted linear array and orthogonally polarized linear array. Through numerous simulation studies, a relative performance comparison of 2D-DOA estimation realized through various proposed novel array configurations has been carried out to highlight the accuracy and resolution under wide range of SNR conditions. The thesis presents a discussion on the analysis of effect of spatial de correlation in lieu of the employed orthogonally polarized elements in the array configuration on the improved accuracy and resolution of the 2D-DOA estimation. This thesis also deals with the utility of the proposed orthogonally polarized array configurations for tracking of 2D-DOA angles of non-stationary signal sources. The weighting factor and forgetting factor approaches for smoothing the time-varying covariance matrix of the non-stationary sources are studied. The simulation studies on 2D-DOA tracking by invoking proposed array configurations along with the proposed smoothing techniques prove that orthogonal polarized array configuration track the DOA source angle with minimum estimation errors. The thesis proposes the replacement of computationally intensive numerical schemes in Multiple Signal Classification (MUSIC) algorithm such as eigen decomposition and singular value decomposition with the subspace tracking techniques such as Bi-Iterative Singular Value Decomposition (Bi-SVD) algorithm. Invoking the concept of sub-band processing, the thesis addresses the validity of the extension of the presented 2D-DOA estimation analysis to wide band signal. A two subband filter approach is proposed for the estimation 2D-DOA of single and two wideband sources. The simulation study of the two subband filter approach along with the orthogonal polarized array configurations confirms the better estimation accuracy as well as the lesser computation time.

M.Ing. / Please refer to full text to view abstract

In this study a new approach to active-element pattern analysis, for large phased array antennas, was created using Floquet's theorem. The classic approach to finding active-element patterns uses a full array simulation that can become slow and produce patterns that are specific to certain elements in the array, though basically identical away from the array edge. Instead of producing specific active-element patterns an average active-element pattern could be created and then applied that to the array. The average active-element pattern can be used for every element in the array with a small margin of error. Using Floquet's theorem reduces any differences between elements in the array and gives the most accurate active-element pattern within a reasonable time constraint. Floquet average active-element patterns are computed by using an infinite array and a summation is done for the far-field radiation values of a finite array based on the number of elements using typical pattern multiplication techniques. Therefore, accuracy of the Floquet element approach is excellent for arrays on the size of hundreds to thousands of elements. An active-element pattern is determined by scanning the array and taking the far-field radiation value at each beam scan-angle. Each beam scan-angle value is a summation of the element radiation patterns in that specific direction. These beam scan-angle values are then reduced by the number of elements in the array to form a radiation pattern. This radiation pattern is the average active-element pattern. / Master of Science

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