Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Numerical design optimisation is a powerful tool that can be used by engi- neers during any stage of the design process. Structural design optimisation is a specialised usage of numerical design optimisation that has been adapted to cater speci cally for structural design problems. A speci c application of structural design optimisation that will be discussed in the following report is experimental data matching. Data obtained from tests on a physical structure will be matched with data from a numerical model of that same structure. The data of interest will be the dynamic characteristics of an antenna structure, focusing on the mode shapes and modal frequencies. The structure used was a scaled, simpli ed model of the Karoo Array Telescope-7 (KAT-7) antenna structure. Experimental data matching is traditionally a di cult and time-consuming task. This report illustrates how optimisation can assist an engineer in the process of correlating a nite element model with vibration test data. / AFRIKAANSE OPSOMMING: Numeriese ontwerp-optimisering is 'n kragtige ingenieurshulpmiddel wat ty- dens enige stadium in die ontwerpsproses ingespan kan word. Strukturele ontwerp-optimisering is 'n gespesialiseerde gebruik van numeriese ontwerp- optimisering wat aangepas is om spesi ek van diens te wees by die oplos van strukturele ontwerpsprobleme. 'n Spesi eke toepassing van strukturele ontwerp-optimisering wat in hierdie verslag bespreek sal word, is eksperi- mentele datakorrelasie. Data afkomstig van toetse op 'n siese struktuur sal gekorreleer word met data afkomstig van 'n numeriese model van die selfde struktuur. Die data van belang is die dinamiese eienskappe van 'n anten- nastruktuur, spesi ek die modusvorme en modale frekwensies. Die betrokke struktuur wat gebruik is, is 'n vereenvoudigde skaalmodel van die Karoo Array Telescope-7 (KAT-7) antennastruktuur. Eksperimentele datakorrelasie is, tradisioneel gesproke, 'n moeilike en tydro- wende taak. Hierdie verslag sal illustreer op watter wyse optimisering 'n inge- nieur van hulp kan wees in die proses om 'n eindige elementmodel met vibrasietoetsdata te korreleer.

>Magister Scientiae - MSc / Future radio surveys as the Square Kilometer Array (SKA) and its precursor, the "Meer" Karoo Array Telescope (MeerKAT), will map the Neutral Hydrogen (HI) in large areas of the sky using the intensity mapping (IM). HI IM is currently one of the most promising ways of accessing the Large-Scale Structure of the Universe. The distribution of matter in the Universe not only encodes its composition but also how it evolves and its initial conditions. An effect on the matter distribution that will be detected by the SKA on the post re-ionization Universe are the Baryonic Acoustic Oscillations (BAO). While it has been shown that in single dish mode the SKA can measure the BAO peak in the radial 21cm power spectrum at low redshifts, this possibility has not yet been studied in detail for the MeerKAT. In this thesis we construct a set of full sky simulations to test how well MeerKAT will be able to extract the BAO wiggles along the line of sight. These simulations are done for the frequencies corresponding to MeerKAT L-band. The maps combine the cosmological HI signal, systematic noise, cosmological foregrounds and the instrumental telescope beam. A model-independent estimator is used to extract the BAO wiggles by subtracting a smooth polynomial component from the 21cm radial power spectrum. We test with simulations if this estimator is biased and the signal to noise of the extraction. We conclude that we are able to remove contaminants and recover the cosmological HI signal while not risking the recovery of the BAO signal. We investigate the effects of varying the sky area and the observational hours on the signal to noise ratio for the BAO wiggles. We found that for a HI IM experiment using MeerKAT, the optimal sky area to detect the BAO along the line of sight is 50% of the sky. With a signal-to-noise ratio of 3.37. This can be achieved with 2000 hours of exposure time

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Through the Karoo Array Telescope, and its extension MeerKAT, South Africa is demonstrating its capabilities to host the most powerful radio telescope ever, the Square Kilometre Array (SKA). This new interferometer is intended to assist radio astronomers in unlocking the mysteries concealed in the far regions of the universe. A thorough investigation of Radio Frequency Interference (RFI) sources at each stage of the design becomes relevant for the success of the project. The electromagnetic coupling through coaxial cables is the main focus of this thesis since 90% of the Electromagnetic Compatibility (EMC) problems come from inadequate system layout and grounding, where cabling plays the major role. Interest revolves around better noise immunity, low radiation and cost. Transfer impedance (ZT ) and shielding e ectiveness (SE) are used as the cable selection criteria. Several measurements of coaxial cables identi ed on KAT-7 have been performed for ZT characterisation from 300 kHz up to 1.3 GHz. A current injection method is used to identify the ZT for the low frequency region. We derived the high frequency part of ZT , with a reverberation chamber technique (RC) measuring shielding e ectiveness. At rst, we calibrated the RC according to the relevant IEC 61000-4-21 standard and evaluated the result with an Open Area Test Site (OATS) E- eld estimation. The accuracy of the E- eld within the chamber is also addressed, based on statistical analysis of the chamber's independent samples. The OATS E- eld equivalent determination showed a good correlation with the OATS E- eld data of a standard radiator. A coaxial air-line ZT veri ed the theoretical ZT model within 7 dB and showed the expected 20 dB/decade slope variation. Furthermore, the braiding porpoising e ect has been noticed with some cable samples. Here, a variation less than 20 dB/decade occurs at lower frequency. Then, the slope changes to 20 dB/decade at high frequency. This study illustrates a practical comparison of cable performance and constitutes a rst approach to RFI mitigation of the MeerKAT cabling system. / AFRIKAANSE OPSOMMING: Deur middel van die Karoo Reeks Teleskoop, asook sy uitbreiding MeerKAT, demonstreer Suid-Afrika sy vermo om die mees kragtige radioteleskoop ooit, die Vierkante Kilometer Reeks (SKA), te vestig. Hierdie nuwe interferometer is bedoel om radiosterrekundiges te help in die ontsluiting van die geheimenisse wat versteek is in die verre reike van die heelal. 'n Deeglike ondersoek van Radio Frekwensie Steurings (RFS) bronne by elke stadium van die ontwerp is belangrik vir die sukses van die projek. Die elektromagnetiese koppeling deur koaksiale kabels is die hoo okus van hierdie tesis, aangesien 90% van die elektromagnetiese versoenbaarheid (EMV) probleme ontstaan as gevolg van onvoldoende stelsel-uitleg en beaarding, waar kabels die hoofrol speel. Beter ruis-immuniteit, lae straling en koste vorm die areas van belang. Oordragimpedansie (ZT ) en afskermingsdoeltre endheid (SE) word gebruik as die kabelkeuringskriteria. Verskeie metings van koaksiale kabels wat op KAT-7 gedenti seer is, is uitgevoer vir ZT karakterisering van 300 kHz tot 1,3 GHz. 'n Stroom-induseringsmetode is gebruik om die ZT vir die lae-frekwensiebereik te identi seer. Ons het die ho-frekwensie deel van ZT afgelei met 'n weerkaatsingskamer tegniek (RC) wat afskermingsdoeltre endheid meet. Eerstens het ons die RC gekalibreer volgens die relevante IEC 61000-4-21 standaard en die resultaat met 'n Ope Area Toetsterrein (OAT) E-veld benadering gevalueer. Die akkuraatheid van die E-veld in die kamer is ook aangespreek, gebaseer op 'n statistiese analise van die kamer se onafhanklike monsters. Die OAT E-veld ekwivalente benadering het goed met die OAT E-veld data van 'n standaard uistraler gekorreleer. 'n Koaksiale lugmedium-transmissielyn ZT bevestig die teoretiese ZT model binne 7 dB en het ook die verwagte 20 dB/dekade variasie in helling getoon. Verder is die golwende e ek oor die kabelomvlegting opgemerk met sekere kabels. Hier is 'n variasie van minder as 20 dB/dekade gevind by die laer frekwensie. Dan verander die helling na 20 dB/dekade teen ho frekwensie. Hierdie studie toon 'n praktiese vergelyking van die verrigting van die kabel en 'n eerste benadering tot RFS tempering van die MeerKAT kabelstelsel.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Although mass minimisation is an important application within structural optimisation, other applications include: (1) concept generation, (2) concept evaluation, (3) design for structural feasibility and (4) data matching. These applications, except data matching, are discussed and illustrated on a prototype design of the Karoo Array Telescope (KAT) antenna. The KAT passed through the design process and a full scale prototype was built, but was found to be too expensive. A detailed finite element model of the finalised design was considered as a test bed for reducing costs. Size-, shape- and topology optimisation are applied to three KAT components, while considering wind, temperature and gravity loads. Structural- and nonstructural constraints are introduced. Coupling of the structural optimisation code with an external analysis program to include non-structural responses and the parallelisation of the sensitivity calculations are presented. It is shown that if a finite element model is available, it is generally possible to apply structural optimisation to improve an existing design. A reduction of 2673 kg steel was accomplished for the existing KAT components. The total cost saving for the project will be significant, when considering that a large amount of antennas will be manufactured.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A new type of wideband lters, with tunability in both the centre frequency and bandwidth, is presented in this thesis. These lters are based on perturbed ring-resonators in cascade, while varactor diodes are used for electronic tuning. The Karoo Array Telescope (KAT-7) requires a front-end lter that has the ability for ne-tuning the response after fabrication, in order to obtain the designed ltering response. Not only are tune-all characteristics required, but also wide bandwidth, at passband, high selectivity and implementation in microstrip technology. In this thesis an extensive investigation of both tunable and wideband lters is done, in order to nd a possible solution for the KAT-7 speci cations. Following this investigation, it is concluded that no suitable design approach for tune-all wideband lters, implemented in microstrip, exists in current literature. Therefore, this thesis proposes a new type of lter along with the development of a complete design procedure. Two lters are designed with this procedure to achieve the required passband from 1.2 to 1.95 GHz (i.e. a fractional bandwidth of 49%). In the rst lter design, with a network consisting of 4 cascaded ltering-sections, the centre frequency is 5% tunable and the bandwidth 17.5%. With the second lter consisting of 6 cascaded ltering-sections, higher selectivity is achieved but with lower return loss. Here the centre frequency is 8.5% tunable and the bandwidth 18.8%. The theoretical results are validated with the fabrication of both lters. This design is very unique in that it achieves wide bandwidth, is realisable in microstrip and most importantly is tunable in both the centre frequency and bandwidth. An advantage of this design procedure is that full wave simulations are minimal, due to the complete circuit models used for optimisation. / AFRIKAANSE OPSOMMING: 'n Nuwe soort van wye-band lters, met verstelbaarheid in beide senter frekwensie en bandwydte, word voorgelê in hierdie tesis. Hierdie lters is gebaseer op versteurde ringresoneerders in kaskade, terwyl varaktordiodes gebruik word vir elektroniese verstelling. Die Karoo Array Telescope (KAT-7) vereis 'n voorkant lter wat die vermoë het vir die instemming van die respons na fabrikasie, sodat die geontwerpde lter respons behaal kan word. Nie net word verstel-als eienskappe vereis nie, maar ook wye bandwydte, plat deurlaatband, hoë selektiwiteit en implimentering in mikrostrook tegnologie. In hierdie tesis is 'n veelomvattende ondersoek gedoen van beide verstelbare en wyeband lters, sodat 'n moontlike oplossing vir die KAT-7 spesi kasies gevind kan word. Na aanleiding van hierdie ondersoek, is die gevolgtrekking dat daar geen gepaste ontwerp benadering vir verstel-als wye-band lters, wat geïmplimenteer is in mikrostrook, in huidige literatuur bestaan nie. Daarom stel hierdie tesis, saam met die ontwikkeling van 'n volledige ontwerp prosedure, 'n nuwe tipe lter voor. Twee lters is ontwerp met hierdie prosedure om die vereiste deurlaatband vanaf 1.2 tot 1.95 GHz (dit is 'n fraksionele bandwydte van 49%) te behaal. In die eerste lter ontwerp, met 'n netwerk wat uit 4 kaskade lter-seksies bestaan, is die senter frekwensie 5% verstelbaar en die bandwydte 17.5%. Met die tweede lter bestaande uit 6 kaskade lter-seksies, word hoër selektiwiteit behaal maar met laer eggoverswakking. Hier is die senter frekwensie 8.5% verstelbaar en die bandwydte 18.8%. Die teoretiese resultate is geldig bewys deur die fabrikasie van albei lters. Hierdie ontwerp is baie uniek in dat dit wye bandwydte behaal, is realiseerbaar in mikrostrook en mees belangrikste dat dit verstelbaar is in beide senter frekwensie en bandwydte. 'n Voordeel van hierdie prosedure is dat heelgolf simulasies minimaal is, a.g.v. die volledige stroombaan modelle wat gebruik word vir optimering.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: South Africa and Australia are now the two remaining countries bidding for the Square Kilometre Array (SKA), the biggest and most sensitive project ever undertaken in radio astronomy. The South African SKA is demonstrating its technology capabilities through the Karoo Array Telescope (KAT or MeerKAT). The development of KAT is taking place in stages to optimise design and minimise risks at each stage. An array of seven 12 m antennas will be complete by the end of 2009, called KAT-7. The following phase will see the construction of MeerKAT, which will lead to eighty arrayed dishes. Lightning and RFI studies for KAT-7 are the focus of this dissertation. Due to the extent and complexity of the South African demonstrator project, these studies have largely been conducted on a single structure. Parameters for the dish antenna and pedestal design changed throughout their development. To be effective, the doctoral research had to track these changes appropriately. A Method of Moments frequency domain computational electromagnetic code, FEKO, is used throughout the study. The consequences of direct and indirect lightning strikes are examined for the KAT-7 structure. Important FEKO model verification is achieved through measurement of physical scale models in an anechoic chamber. The microwave simulation code, CST, gives direct comparison of FEKO results by using a finite volume time domain method of calculation. Using frequency domain analysis on these models, the lightning down conductor design over the dish antenna bearings is optimised with cost-effectiveness as one driving parameter. RFI coupling levels for different designs are compared to each other to identify areas requiring RFI mitigation. Analysis of resonances enables evaluation of the mitigation at frequencies sensitive to radio astronomy. A Sommerfeld integral ground plane is used together with the computational model to investigate the use of the concrete foundation steel reinforcing as part of the lightning earthing electrode system. Different interconnections of the steel reinforcing elements are critically evaluated. The KAT-7 design incorporated clear lightning protection and RFI mitigation policies derived from recommendations contained within this dissertation. / AFRIKAANSE OPSOMMING: Suid-Afrika en Australie is nou die oorblywende twee lande wat bie vir die Vierkante Kilometer Reeks (SKA), die grootste en mees sensitiewe projek nog ooit in radio astronomie onderneem. Die Suid Afrikaanse SKA demonstreer sy tegnologiese bekwaamheid met die Karoo Reeks Teleskoop (KAT of MeerKAT). Die ontwikkeling van KAT vind plaas in fases om die ontwerp te optimaliseer en risikos te minimaliseer met elke fase. ’n Reeks van sewe 12 m antennas, genaamd KAT-7, sal teen die einde van 2009 klaar wees. Die volgende fase behels die konstruksie van MeerKAT, wat sal lei tot ’n tagtig-skottel reeks. Die fokus van hierdie proefskrif hanteer weerlig en radiofrekwensie steurings (RFS) vir KAT-7. As gevolg van die omvang en kompleksiteit van die Suid-Afrikaanse demonstreerder projek, is die studies hoofsaaklik op een struktuur gedoen. Parameters vir die antenna-skottel en -voetstuk ontwerp het met hul ontwikkeling deurgaans verander. Om effektief te wees, moes die doktorale navorsing hierdie veranderinge toepaslik volg. ’n Metode-van-Momente frekwensiedomein rekenaar elektromagnetiese kode, FEKO, is deurgaans met die studie gebruik. Die gevolge van direkte en indirekte weerligslae vir die KAT-7 struktuur is ondersoek. Belangrike FEKO model bevestiging is bereik met metings van skaalmodelle in ’n anego¨ıse kamer. Die mikrogolf-simulasie kode, CST, gee ’n direkte vergelyking met die FEKO resultate deur ’n eindige-volume-tyd-domein metode van berekening te gebruik. Met behulp van frekwensiedomein analise van hierdie modelle, is die weerligafleierontwerp oor die antenna-skottel laers ge-optimaliseer, met koste-effektiwiteit as een van die drywingsparameters. RFS koppelingsvlakke vir onderskeie ontwerpe is teen mekaar opgeweeg om areas te identifiseer wat RFS tempering benodig. Analise van resonansies stel die evaluering van die tempering in staat teen frekwensies wat sensitief is vir radio astronomie. ’n Sommerfeld integrale grondvlak word saam met die rekenaarmodel gebruik om die insluiting van die beton se staalversterking as deel van die aardingselektrodestelsel te ondersoek. Verskillende bindmetodes van die onderlinge staalversterkingselemente word krities ge¨evalueer. Die KAT-7 ontwerp inkorporeer duidelike weerligbeveiligings- en RFS temperingstrategie ¨e, komende van aanbevelings in hierdie proefskrif omskryf