Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Common mode currents are a major source of interference in electrical and electronic systems. A universal solution to counteract common mode interference is to introduce an electromagnetic shield with known characteristics. Cable trays are often used to shield cables from unwanted electromagnetic interference (EM!) and its shielding characteristics are defined in terms of its transfer impedance. This thesis pursues the modelling and measurement of the transfer impedance and mutual inductance of non-magnetic cable trays. Theoretical analysis is firstly employed by means of Maxwell's equations after which method of moments (MoM) simulations are performed in order to determine the transfer impedance and mutual inductance within the interior region of a cable tray. The results obtained through simulation are then validated with measurements conducted with an automatic network analyser (ANA). The computational and measured data are in good agreement and the developed model can be used to predict the transfer impedance in the cross-section of non-magnetic cable trays. / AFRIKAANSE OPSOMMING: Gemenernodus strome is 'n bron van interferensie in elektriese en elektroniese stelsels. 'n Universele oplossing om hierdie gemenernodus interferensie teen werk is om 'n elektromagnetiese skerm met bekende eienskappe te implementeer. Geleier leikanale word dikwels gebruik om kabels teen elektromagnetiese interferensie te beskerm en die afskermings eienskappe word in terme van die kanaal se oordragsimpedansie gedefinieer. Hierdie tesis ondersoek die modelering en meting van die wedersydse induktansie en oordragsimpedansie van nie-magnetiese geleier leikanale. 'n Teoretiese analise word eers uitgevoer deur middel van Maxwell se vergelykings waarna metode van momente (MvM) simulasies uitgevoer word om die oordragsimpedansie en wedersydse induktansie in die interne gebied van 'n leikanaal te bepaal. Die resultate verkry deur simulasie word dan bevestig deur meting wat uitgevoer word met behulp van 'n automatiese netwerk analiseerder (ANA). Die numeriese en gemete data stem goed ooreen en die ontwikkelde model kan deurgaans gebruik word om die oordragsimpedansie in die deursnit area van nie-magnetiese geleier leikanale te voorspel.

Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The development of a radar system is a complex process, requiring a substantial amount of testing. In general, these tests are performed using field trials. Such trials are expensive, and their exact conditions can never be repeated. A radar environment simulator allows for repeatable testing of the majority of a radar's functionality; however, most commercial products are not cost effective. In this thesis we investigate the various approaches to modelling targets and the littoral environment, and then develop a low-cost, largely software defined simulator. This simulator is capable of generating real-time video signals for a monopulse doppler tracking radar. The core simulation routines reside in an extensible software framework which is populated with simple target and clutter models for a prototype simulator. Closed loop tracking tests verify the operation of the prototype simulator. / AFRIKAANSE OPSOMMING: Die ontwikkeling van 'n radarstelsel is a ingewikkelde proses wat verskeie stelseltoetse benodig. Veldtoetse, wat gewoonlik gebruik word, is 'n duur proses, en die toestande is nooit presies dieselfde nie. 'n Radar-omgewingsimulator kan 'n groot deel van 'n radar se funksionaliteit herhaaldelik toets. Daar is egter weinig koste-effektiewe kommersile produkte vir hierdie doel beskikbaar. Hierdie tesis ondersoek verskeie teiken- en omgewingsmodelle, waarna 'n lae-koste, meestal sagteware-gedefinieerde simulator ontwikkel word. Hierdie simulator genereer intydse videoseine vir 'n enkelpuls-dopplervolgingsradar. Die kernfunksionaliteit van die simulator is in sagteware gesetel, en basiese teiken- en omgewingsmodelle is geïmplementeer. Die prototipe-simulator word getoets deur dit aan die radar self te koppel, en dan die teiken-opsporing en -volging te verifieer.

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A unified method is proposed to treat saturation in both Multi-Input-Multi-Output MIMO and Single-Input-Single-Output controllers. This method offers superior performance over existing MIM 0 anti-saturation schemes. The anti-saturation problem is posed as a linear programming problem. A practical and efficient implementation of the algorithm is developed by transforming the problem into its dual linear programming form. The problem, in dual form, is then solved using the dual simplex method rather than the primal simplex method. The nature of the problem when expressed in dual form and the properties of the dual simplex method are harmonised to guarantee an initial basic feasible solution and an optimal bounded final solution in a finite, predictable and minimal number of iterations. The resultant controller never saturates, hence cannot windup. Furthermore the resultant controller always applies the optimal control effort to the plant to minimise the error signal input as follows: • The controller is governed such that while the future free response combined with the present forced response of the controller results in no saturation limits being exceeded, now or at some time in the future, the normal linear response of the controller prevails. • When the future free response combined with the present forced response of the controller will result in a saturation limit being reached, now or at some time in the future, the present time input signal into the controller is optimally governed to prevent the saturation limit from being exceeded at any future time. / AFRIKAANSE OPSOMMING: 'n Metode word voorgestel waarmee versadiging in enkel-inset enkel-uitset en meer-inset meeruitset (MIMU) stelsels beheer kan word. Die metode presteer beter as ander huidige teenversadiging- maatreels vir (MIMU) beheerders. Die teen-versadigings-probleem word as 'n lineere programmeringsprobleem herformuleer. 'n Praktiese en effektiewe implementering van die algoritme word verkry deur die probleem na die duale vorm te transformeer. Die probleem, in duale vorm, word opgelos met die duale simplex metode, in plaas van die direkte metode. Die eienskappe van hierdie formulering is 'n gewaarborgde, aanvanklike, bereikbare oplossing en 'n optimale, begrensde, finale oplossing in 'n eindige, voorspelbare en minimum aantal stappe. Die uiteindelike beheerder versadig nooit nie, en wen gevolglik nie op nie. Die beheerder wend altyd die optimale aanleg-inset aan om die foutsein te minimeer soos volg: • Wanneer die nul-inset gedrag saam met die huidige inset-gedrag geen beperkings nou of in die toekoms saloorskry nie, word geen beperkende aksie geneem nie, en tree die beheerder dus lineer op. • Sodra die toekomstige nul-inset gedrag saam met die huidige inset-gedrag, nou of later versadiging sou veroorsaak, word die huidige inset tot die beheerder optimaal begrens om latere versadiging te voorkom.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This document describes the breadboard design and practical evaluation of a mobile field station, capable of communicating with the SUNSAT micro satellite. A study of existing satellite communication systems employing LEO satellites, as well as the physical phenomena, influencing the VHF communication link between earth and such satellites was done and used to determine the specifications needed for a functional field station. The design entailed work on different building blocks like a receiver, transmitter and modem unit as well as the writing and testing of the necessary software on a controlling personal computer. The measurements done showed that the field station satisfies most of the specifications, and that it is capable of communicating with a satellite. The document is concluded by suggesting improvements and possible further work before a commercial version of the field station may be build. / AFRIKAANSE OPSOMMING: In hierdie dokument word die ontwerp en praktiese evaluasie van 'n mobiele veldstasie beskryf wat met die SUNSAT mikrosatelliet kan kommunikeer. 'n Ondersoek na bestaande satellietstelsels in lae-aard wentelbane en die fisiese faktore wat die radioskakel tussen die grond en sulke satelliete beïnvloed is gebruik om spesifikasies vir 'n werkende veldstasie daar te stel. Die ontwerpstaak het werk aan 'n ontvanger, sender, modem en beheerproggramatuur ingesluit. Die voltooide veldstasie is gekarakteriseer deur 'n meetproses wat aangetoon het dat dit met 'n satelliet kan kommunikeer. Die dokument word afgesluit met voorgestelde verbeterings en verdere werk aan die veldstasie voordat 'n kommersiële weergawe daarvan voltooi kan word.

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: This product is designed as an educational tooL It was developed to make a classroom more organised. Better and easier communication between the teacher and the students can be established, as well as improved communication between different classrooms. The stand alone unit can be used anywhere because there is no wiring between this and the computer. It can be a big addition to the educational system, especially in places where books are not readily available for the students. The system consists of various components. These components are a computer, a stand alone unit and an interconnection for these two. The interconnection was incorporated with the use of radio links. At the computer side of the design, a windows interface was developed to enable the computer user to communicate with the stand alone unit user. The radio link was inserted to make the communication between the computer and the stand alone unit wireless. The stand alone unit consists of a keypad, liquid crystal display, serial port and a floppy drive. The serial port is used as connection between the stand alone unit and the radio links. It is possible to expand the system. The keypad can be replaced by a keyboard to enable the stand alone user to type and save data on the stand alone unit itself, and a hard drive might be added to increase the storage space. The inclusion of the floppy drive makes the system more compact and creates the possibility of transferring data by use of the floppy, which in tum does not limit a person to working only in one place. / AFRIKAANSE OPSOMMING: Hierdieproduk is ontwerp as 'n hulpmiddel vir die onderwys stelsel. Dit is ontwerp om 'n klaskamer meer georganiseerd te maak. Beter en makliker kommunikasie tussen onderwysers en studente word op hierdie manier verseker, asook verbeterde kommunikasie tussen verskillende klaskamers. Die alleenstaande eenheid kan enige plek gebruik word, aangesien daar geen bedrading is tussen die eenheid en die rekenaar nie. Dit kan 'n groot bydrae wees tot die onderwysstelsel, veral in plekke waar boeke nie so alledaags beskikbaar is nie. Die stelsel bestaan uit verskeie komponente. Hierdie komponente is 'n rekenaar, 'n alleenstaande eenheid en 'n verbinding tussen hierdie twee. Die verbinding tussen hierdie twee is met behulp van radio skakels gedoen. By die rekenaar kant van die ontwerp, is 'n rekenaar program geskryf wat die kommunikasie tussen die rekenaar en die alleenstaande eenheid beheer. Die radio skakel is ingesluit in die ontwerp om die kommunikasie tussen die rekenaar en die alleenstaande eenheid draadloos te hou. Die alleenstaande eenheid bestaan uit 'n miniatuur sleutelbord, vloeibare kristal vertoon, 'n serie poort en 'n slapskyf dryf. Die serie poort word gebruik as verbinding tussen die alleenstaande eenheid en die radio skakels. Dit is moontlik om die stelsel te vergroot. Die miniatuur sleutelbord kan vervang word deur 'n standaard sleutelbord om die alleenstaande eenheid gebruiker in staat te stelom data op die eenheid self te tik en te stoor. 'n Hardeskyf kan ook ingevoeg word om die stoor spasie van die stelsel te vergroot. Die insluiting van die slapskyf veroorsaak dat die stelsel meer kompak is en ontwikkel die moontlikheid om die data oor te dra met behulp van die skyf, wat weer 'n persoon in staat stelom op meer as slegs een plek te werk.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The co-existence of electronic devices and their attached transmission cables requires a careful planning regarding the energy leakage across cable shields. This leakage poses potential serious problems and impedes system functioning. This thesis pursues an investigation into the EMC cabling protocols for microsatellite systems. Network analysis techniques are applied in calibrating current probes and to recover the cable transfer impedance, Zr. The calibration approach provides accurate results for frequencies up to 600MHz. The methods used to determine Zr are based on injecting a disturbance current onto the outside of the cable-under-test (CUT) and measuring the corresponding voltage induced on the centre conductor. Useful results are obtained up to 80MHz with the use of a O.5m length of cable. It is thus proposed that Zr is a practical concept for shielding performance evaluation and for the testing of cable philosophy. The results are usable in classifying cables for verification and signal usage. Further research involves a prediction tool called an EMC ITS that simulates the hardware of a microsatellite system to allow studies on design trade-offs, transmission cable criteria and placement of devices. / AFRIKAANSE OPSOMMING: Die gelyktydige bestaan van elektroniese toestelle en hul aangehegte transmissielynkabels benodig deeglike beplanning met betrekking tot die lek van energie deur die kabels se afskerming. Hierdie lekkassie kan ernstige probleme tot gevolg hê en die stelsel se funksionering belemmer. Hierdie tesis loods 'n ondersoek na die EMV bekabelingprotokolle vir mikrosatellietstelsels. Netwerk analise tegnieke word gebruik in die kalibrasie van stroom-probes en die verkryging van die kabel se oordragsimpedansie, Zr. Die benadering wat gevolg is in die kalibrasie verskaf akkurate resultate tot en met frekwensies van 600MHz. Die metode wat gebruik word om Zr te bepaal is gebaseer op die injeksie van 'n versteuringstroom op die buitekant van die toetskabel en die meting van die ooreenstemmende spanning wat opgewek word op die binne-geleier. Bruikbare resultate is tot en met 80MHz verkry met die gebruik van 'n kabel met 'n lengte van O.Sm. Daar word dus voorgestel dat Zr 'n praktiese wyse is om afskermingsprestasie mee te evalueer, asook vir die toetsing van kabel-filosofie. Die resultate is bruikbaar in die klassifikasie van kabels vir verifikasie en seingebruik. Verdere navorsing sluit in 'n voorspellingswyse wat 'n EMV GTS genoem word, wat die hardewaarde van 'n mikrosatellietstelsel simuleer om studie aangaande ontwerpkompromieë, transmissielyn kriteria en die plasing van toestelle binne die gebruiksomgewing moontlik te maak.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: In the past few years, a need for consulting on microwave heating has surfaced. Since most specialised microwave components are imported, this adds a hefty price tag in developing the infrastructure for such consultation. This thesis looks at the design oflow cost alternatives for use in the laboratory. A microwave source output with variable output power is often required for consultation. The calculation of product costs may also be simplified if the available microwave power is constant despite load changes. The magnetron as a load was first investigated and a high voltage SMPS was then designed to control the output of the magnetron according to operator / consulting requirements. To ensure adequate feedback of system output and load matching, a dual directional coupler has been designed and implemented. Since the amount of microwave power required has a direct impact on the initial capital expenditure, costs need to be kept low by optimising the system. An impedance matching unit was designed to match the magnetron with the load, saving energy and reducing system costs. Through automation, the system will strive for the optimum load condition without operator intervention. / AFRIKAANSE OPSOMMING: Die afgelope paar jaar het 'n behoefte ontstaan aan konsultasiewerk op die gebied van mikrogolfverhitting. Aangesien gespesialiseerde komponente meestal ingevoer word, bemoeilik die koste daarvan die ontwikkeling van die nodige infrastruktuur vir konsultasie. Hierdie tesis kyk na die ontwerp van goedkoper alternatiewe vir laboratoriumgebruik. 'n Mikrogolf bron met 'n verstelbare kraglewering is dikwels nodig tydens konsultasiewerk. Produk kosteberekinge kan ook vereenvoudig word indien die mikrogolf kraglewering konstant bly, ongeag produk veranderinge. Die magnetron as GS las is eers ondersoek waarna 'n hoogspanning geskakeldekragbron ontwerp is om die uittree van die magnetron te verstel volgens operateur- / konsultasievereistes. 'n Dubbele direksionele koppelaar is ontwerp en by die laboratorium opstelling gevoeg om voldoende terugvoer van die kraglewering en impedansie aanpassing te verseker. Die hoeveelheid mikrogolf drywing wat benodig word, het 'n direkte impak op die aanvanklike kapitale uitgawe vir die stelsel. 'n Optimale stelsel is dus noodsaaklik om kostes te bespaar. 'n Impedansie-aanpassingsnetwerk is ontwerp om die magnetron en las by mekaar aan te pas om sodoende energie en kostes te bespaar. Deur outomatisering streef die stelsel na optimale werkverrigting sonder enige ingryping deur die operateur.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Keywords: Dielectric Resonators, Radial Mode Matching, Whispering Gallery Modes The aim of this investigation was to develop accurate modelling techniques to determine the resonant frequencies of dielectric resonators. These resonators could be simple dielectric posts, rings or combinations of these two. To do this, a radial mode matching technique was implemented and applied to a post resonator, a ring resonator and finally a combination of the two. The resulting method was used to develop a model of a high-Q whispering gallery mode resonator consisting of a post and a ring resonator combination with an spurious free region region. / AFRIKAANSE OPSOMMING: Sleutelwoorde Dielektriese Resoneerders, Radiale Modale-Pas Tegniek, 'Whispering Gallery' Modus Die doel van hierdie navorsing was om 'n akkurate tegniek te ontwikkelom die resonante frekwensie van 'n dielektriese resoneerder vas te stel. Hierdie resoneerders kon eenvoudige resoneerders, ring resoneerders of kombinasies van die twee wees. 'n Radiale Modale-Pas tegniek is vir hierdie doel geïmplementeer en is op 'n eenvoudige resoneerder, 'n ring-resoneerder en kombinasies van die twee toegepas. Hierdie tegniek is dan gebruik om 'n hoë-Q resoneerder te ontwerp wat gebruik maak van 'n 'whispering gallery' modus. In hierdie geval is die resoneerder 'n kombinasie van 'n pil en 'n ring-resoneerder.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This thesis pursues the establishment of a new Electromagnetic Compatibility (EMC) framework for South Africa. The aim of this framework is to ensure that the user is protected from sub-standard products as well as to ensure that products such as medical devices operate safely within the electromagnetic environment. The thesis presents a basic introduction into EMC and then overviews current worldwide legislation. After this information is studied a new framework is proposed for South Africa. This framework covers all areas of industry and the standards with which one has to comply as well as the procedure for demonstrating the compliance of the product. In order to establish the basis whereby smaller manufacturers can show compliance by means of in-house testing, a method for establishing measurement accuracy is also presented. In conclusion some standard measurements and an overview of some alternative measurement techniques are presented. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek en stel 'n nuwe Elektromagnetiese Versoenbaarheids (EMV) raamwerk voor vir Suid Africa. Die doel van die raamwerk is om 'n eenvormige stelsel daar te stel waarteen produkte getoets kan word om die publiek teen onder standaard produkte te beskerm. In sekere gevalle help die raamwerk ook om te verseker dat produkte soos mediese toerusting veilig werk in die Elektromagnetiese omgewing. Die tesis lê 'n basiese inleiding oor EMV voor en gee 'n opsomming van huidige wêreldwye wetgewing as inleiding tot 'n raamwerk vir Suid Afrika. Nadat die inligting bestudeer is, word 'n nuwe raamwerk vir Suid Afrika voorgestel. Die raamwerk dek die hele elektroniese industrie, spesifiseer die toepaslike standaarde en voorsien die metodes hoe voldoenning aan die vereistes bewys moet word. Die tesis verskaf ook riglyne hoe kleiner vervaardigers kan bewys dat hulle voldoen aan die vereistes, deur in-huis toetsing. Tesame met 'n oorsig oor basiese meet tegnieke en alternatiewe tegnieke word 'n metode daar gestel vir sulke vervaardigers om hul metings se akuraatheid te bewys.

Thesis (MScEng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The three-level neutral-point-clamped(NPC) converter, being a widely used multilevel inverter, received a lot of attention recently due to problems associated with de-link capacitor voltage balancing. There are mainly two problems associated with the neutralpoint voltage of the NPC inverter: 1. At high modulation indices a low frequency ripple occurs on the neutral-point voltage. 2. Steady-state unbalance in the neutral-point voltage may arise due to a variety of factors including component imperfections, transients and other non-idealities and imbalances. In this thesis we study the balancing problem with focus on the steady-state imbalance. This is achieved by a systematic and mathematically rigorous study of the natural balancing mechanisms of the three-level three-phase NPC inverter. Orthogonality of two sets of switching spectra in the frequency domain would imply that the DC-bus voltages balance in the steady state. This is done through mathematical analysis using Carrara's PWM strategy of alternative phase opposition disposition(APOD), phase opposition disposition( POD) and phase disposition(PD); and Bennet's geometric model for double Fourier series adapted for use with power converter systems by Bowes. The theory is verified through simulation. / AFRIKAANSE OPSOMMING: Aangesien die drie-vlak, geklemde, neutrale-punt omsetter(NPC) 'n algemene omsetter konfigurasie is, is daar onlangs baie aandag gegee aan die probleme wat geassosieer word met die balansering van die omsetter se gelykstroombuskapasitorspanning. Die twee hoof probleme wat gepaart gaan met die neutraalpuntspanning van die NPC omsetter is: 1. Met 'n ho modulasie-indeks ontstaan daar 'n lae frekwensie rippel op die neutralepuntspanning. 2. 'n Bestendige toestand wanbalans van die neutrale-puntspanning kan ontstaan as gevolg van 'n verskeidenheid faktore, onder andere komponent nie-idealiteite, oorgangs- en ander wanbalanse. In hierdie tesis word op die bestendige-toestandwanbalans gefokus. Dit word gedoen deur middel van die neutraalbalanseeringsmeganisme van die drie-vlak, drie-fase NPC omsetter, sistematies en gedetaileerd wiskundig te bestudeer. In die bestendige toestand sal orgonaliteit van twee stelle skakel spektras in die frekwensie gebied, GS-bus spanning balans impliseer. Dit word wiskundig geanaliseer deur gebruik te maak van Carrara se alternatiewe fase opposiesie disposisie (APOD), fase oposisie disposisie (POD) en fase disposisie(PD), puls-wydte modulasie strategie, asook Bennet se geometriese modelle vir die dubbel Fourier reeks wat aangepas is vir drywingsomsetters deur Bowes. Ten slotte is die teorie geverifieer deur simulasies.