Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Equal division microwave power dividers are investigated in this study. A wideband Wilkinson power divider and a wideband directional coupler with a centre frequency of 10 GHz were built. The design of the directional coupler is scaled, such that it can be used between 18 and 40 GHz. The details of the electromagnetic analyses of these structures are discussed and physical implementation issues are investigated. In a complementary study to the design of planar microwave dividers, the FDTD computational method was implemented and used to analyse the Wilkinson divider and the 18 to 40 GHz directional coupler. Results are compared to those obtained from commercial numerical method packages and in the case of the Wilkinson divider, to measured results. Suggestions are made for improvements in the implementation of the directional coupler and methods for a more efficient FDTD implementation are discussed. / AFRIKAANSE OPSOMMING: Mikrogolf drywings verdelers wat gelyk verdeel, word in hierdie studie ondersoek. ’n Wyeband Wilkinson verdeler en wyeband gerigte koppelaar met ’n senter frekwensie van 10 GHz is gebou. Die onwerp van die gerigte koppelaar is ook geskaleer sodat die ontwerp gebruik kan word tussen 18 en 40 GHz. Die details van die elektromagnetiese analise van hierdie strukture word bespreek en kwessies rondom die implementering van die strukture word ondersoek. In ’n komplementere studie, is die Eindige Verskil Tyd Gebied numeriese metode (Engels: FDTD) geimplimenteer en gebruik om die Wilkinson en die 18 tot 40 GHz gerigte koppelaar te analiseer. Resultate word vergelyk met resultate verkry met numeriesie metodes geimplimenteer in kommersiele pakkette, en in die geval van die Wilkinson verdeler, ook met gemete resultate. Aanbevelings word verder gemaak vir verbeterings in die implementering van die gerigte koppelaar asook metodes om ’n meer effektiewe FDTD kode te implementeer.

Thesis (MScEng)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The purpose of this thesis is to implement the Frequency Shift Keying (FSK) modem modules for the Software Defined Radio (SDR), using different Linux sound Application Programming Interfaces (API's). The FSK modulation scheme, uses coherent detection with matched filters. The modules are implemented using the Linux operating system and the programming language used is C/C++. Simulation is performed first and then followed by implementation in real-time, using APIs. The APIs used are Open Sound System (OSS), Advanced Linux Sound Architecture (ALSA), Jack Audio Connection Kit (JACK) and PortAudio (PA). In real-time two computers are used, one acting as the modulator and the other as the demodulator. The two sound cards are connected by an audio cable. Results obtained using OSS, ALSA and JACK are satisfactory. Recommendations are subsequently made for the suitable API(s). Both ALSA and JACK are the best APIs for the implementation. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om modules vir 'n frekwensieskuif-sleuteling (FSK) modem vir 'n Sagteware-gedefinieerde Radio (SDR) te implementeer, deur gebruik te maak van verskillende Linux klankargitekture (API's). Die FSK modulasieskema gebruik koherente deteksie met aangepaste filters. Die modules is geïmplementeer met behulp van die Linux bedryfstelsel en CjC++ is gebruik as programmeringstaal. Simulasies is eers gedoen, gevolg deur 'n reële-tyd implementasie. Die klankargitekture wat gebruik is, is Open Sound System (OSS), Advanced Linux Sound Architecture (ALSA), Jack Audio Connection Kit (JACK) en PortAudio (PA). Twee rekenaars is gebruik vir die reële-tyd stelsel, waar een as die modulator optree en die ander een as die demodulator. Die twee klankkaarte is verbind deur 'n klankkabel. Bevredigende resultate is verkry met behulp van OSS, ALSA en JACK. Aanbevelings is gevolglik gemaak vir toepaslike API's. Beide ALSA en JACK is die geskikste API's vir die implementasie.

Thesis (MScEng)--Stellenbosch University, 2005. / ENGLIAH ABSTRACT: Data transmission plays a cardinal role in today's society. The key element of such a system is the antenna which is the interface between the air and the electronics. To operate optimally, many antennas require baluns as an interface between the electronics and the antenna. This thesis presents the problem definition, analysis and performance characterization of baluns. Examples of existing baluns are designed, computed and measured. A comparison is made between the analyzed baluns' results and recommendations are made. / AFRIKAANSE OPSOMMING: Data transmissie is van kardinale belang in vandag se samelewing. Antennas is die voegvlak tussen die lug en die elektronika en vorm dus die basis van die sisteme. Vir baie antennas word 'n balun, wat die elektronika aan die antenna koppel, benodig om optimaal te funktioneer. Die tesis omskryf die probleemstelling, analiese en 'n prestasie maatstaf vir baluns. Prakties word daar gekyk na huidige baluns se ontwerp, simulasie, en metings. Die resultate word krities vergelyk en aanbevelings word gemaak.

Thesis (MScEng)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: Different types of RF and Microwave receiver systems architectures are investigated. The superheterodyne receiver characteristics are studied qualitatively. A three components system (LNA, Mixer and VeO) is selected and the components are first measured individually, and then measured as a single system. A mono filar axial mode helix antenna is designed, simulated using FEKO and constructed. A narrow band interdigital bandpass filter is designed using the capacitance network and its transformation, and it is simulated using two different simulation packages, eST Microwave Studio and AWR Microwave Office. Two filter prototypes are fabricated using cylindrical rods. An open circuited microstrip resonator oscillator is designed and implemented through the negative resistance method. Its performance is verified using the harmonic balance simulator in AWR MWO. A single balanced mixer is designed and implemented using 1800 hybrid junction (rat-race) and it is also fabricated using microstrip transmission line technology. All designed components performed well in comparison to their predicted performance. The LNA and three of the designed components (Filter, Oscillator and a Mixer) are connected together and characterized as a single four block system. The system performed well except for the IF signal which shift to a lower frequency due to oscillator load pulling. / AFRIKAANSE OPSOMMING: Die argitektuur van verskeie RF en Mikrogolf ontvanger stelsels word ondersoek. Die "superheterodyne" ontvanger eienskappe is kwalitatief bestudeer. 'n Stelsel wat uit drie komponente bestaan (LNA, Menger en VeO) is bestudeer. Die individuele komponente is eers gemeet en daarna die stelsel as 'n eenheid. 'n "Mono filar" aksiale modus heliks antenna is ontwerp, gesimuleer met FEKO en gebou. Verder is 'n nouband inter-digitale banddeurlaat filter ontwerp met behulp van die kapasitiewe network metode en sy transformasie. Hierdie ontwerp is gesimuleer deur van twee verskillende sagteware pakette gebruik te maak, naamlik eST Microwave Studio en AWR Microwave Office. Twee filter prototiepes is gebou met silindriese stafies. 'n Oopgeslote mikrostrook ossilator is ontwerp en geimplementeer deur negatiewe weerstand te gebruik. Die stelsel se prestasie is bevestig deur gebruik te maak van 'n harmoniese balans simulator in AWR MWO. Verder is 'n enkelbalans menger ontwerp en geimplimenteer via 'n 1800 hibriede verbinding ("rat-race"). Hierdie menger is gebou met mikrostrook transmisielyn. Al die ontwerpte komponente werk goed in vergelyking met die voorspelde resultate. Die LNA, filter, ossilator en menger word gekoppel en gekarakteriseer as 'n vier blok stelsel. Die stelsel werk goed behalwe vir 'n skuif in die IF-sein by laer frekwensies a.g.v. belasting.

Thesis (MScEng) -- Stellenbosch University, 2002. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: Harmonic mixers are capable of extended frequency operation by mixing with a harmonic of the LO (local oscillator) signal, eliminating the need for a high frequency, high power LO. Their output spectra also have certain characteristics that make them ideal for a variety of applications. The operation of the harmonic mixer is investigated, and the mixer is analyzed using an extension of the classic mixer theory. The synthesis of harmonic mixers is also investigated, and a design procedure is proposed for the design and realization of a variety of harmonic mixers. This design procedure is evaluated with the design and realization of two harmonic mixers, one in X-band and the other in S-band. Measurements suggest that the procedure is successful for the specific applications. / AFRIKAANSE OPSOMMING: Harmoniese mengers kan by hoer frekwensies gebruik word as gewone mengers deurdat hulle gebruik maak van ‘n harmoniek van die LO. ‘n Hoe-frekwensie, hoe-drywing LO word dus nie benodig nie. Die mengers se uittreespektra het ook ‘n aantal karakteristieke wat hulle goeie kandidate maak vir ‘n verskeidenheid van toepassings. Die werking van die harmoniese menger word ondersoek deur uit te brei op die klassieke menger-teorie. Die ontwerp van die harmoniese menger word vervolgens ondersoek, waama ‘n ontwerpsprosedure voorgestel word vir die ontwerp van ‘n verskeidenheid van harmoniese mengers. Hierdie prosedure word getoets met die ontwerp en realisering van twee harmoniese mengers, een in X-band en die ander in S-band. Vanuit die metings is dit duidelik dat die ontwerpsprosedure geslaagd is vir die spesifieke geval.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: One of the most difficult problems in microwave dielectric heating is the generation and control of field and heating patterns. A technique allowing the synthesis of different, pre-determinable heating patterns by interference modulation is proposed. The proposed concept may be described by the term 'interference modulation'. Interference modulation is a technique which enables particular patterns, called features, to be obtained by signals from several sources interfering with each other. The relative phases of the signals are modulated, by which process known features may be selected. Weights are assigned to these features, which may be combined over time to form a new heating pattern. Phase changes may then be used to switch to specific, known features, with weights which will determine the contribution of each feature to the desired overall pattern. In the practical implementation described, magnetron tubes are the sources. Each of these narrow-band high-power sources was injection locked to a low power control signal. The control signals are derived from a reference source and their phase is set to select a corresponding feature. Calculation and measurement showed that reliable locking occurs with a control signal power of at least 3% of the magnetron's emitted power. Measurements of patterns were carried out with materials formed into sheets and blocks. Some were chemically prepared to reveal the overall heating pattern. The observed patters, simulations and field measurements concur, thus validating the concept and operation of the proposed topology. / AFRIKAANSE OPSOMMING: Een van die moeilikste probleme in mikrogolf diëlektriese verhitting is die opwekking en beheer van veld- en verhittingspatrone. 'n Tegniek wat voorsiening maak vir die sintese van verskillende, voorafbepaalde verhittingspatrone deur interferensie word hier voorgestel. Die voorgestelde beginsel kan beskryf word deur die term "interferensie modulasie". Interferensie modulasie is 'n tegniek wat spesifieke patrone, genoem kenmerke, moontlik maak deur seine van verskillende bronne met mekaar te laat interfereer. Bekende kenmerke kan geselekteer word deur die relatiewe fases van die seine te moduleer. Gewigte word aan hierdie kenmerke toegeken wat oor tyd gekombineer kan word om nuwe verhittingspatrone te vorm. Faseveranderings kan dan gebruik word om na 'n spesifieke, bekende kenmerk te skakel met gewigte wat die bydrae van elke kenmerk van die verlangde algehele patroon bepaal. Magnetrons word gebruik as bronne in die praktiese implimentering wat beskryf word. Elkeen van hierdie nouband, hoë drywing bronne is injeksie-gesluit met 'n lae drywing beheersein. Die beheerseine is afgekoppel van 'n verwysingsbron en hul fases is gestelom 'n ooreenstemmende kenmerk te verkry. Berekening en meting toon dat betroubare sluiting voorkom wanneer die beheersein ten minste 3% van die magnetron se uittree-drywing is. Metings van patrone is gemaak met materiale wat in lae en blokke gevorm is. Sommiges is met chemikalië voorberei sodat die algehele verhittingspatroon gesien kan word. Die waargeneemde patrone, simulasies en veldmetings stem goed ooreen en bevestig die beginsel en werking van die voorgestelde topologie.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Data volumes produced by the next generation of earth observation sensors have increased greatly in recent years. Sensors are generating more data than can be easily stored onboard satellites and transmitted to the ground-stations. There are two strategies for solving this problem. The first is to process all images onboard the satellite, and only extract the useful or valuable information. The second is to use a compression algorithm to reduce the data volume. This thesis looks at both strategies and then focusses on an evaluation of the Embedded Zerotree Wavelet (EZW) algorithm, a wavelet-based lossy image compression algorithm, as a solution to reduce the data volumes. Possible hardware implementation strategies for this algorithm are also explored. Finally, a suggested implementation of the EZW algorithm is compared with the FlexWave-II system and with JPEG2000. / AFRIKAANSE OPSOMMING: Die data volumes wat deur die nuwe generasie van aardobservasiesensore geproduseer word, het dramaties vergroot in die laaste paar jaar. Daar word nou meer data geproduseer as wat aanboord van die satelliet gestoor kan word en meer as wat in die beperkte kommunikasietyd aan die grondstasie gestuur kan word. Daar is twee strategiee om hierdie probleem aan te spreek. Eerstens kan beelde aanboord die satelliet verwerk word om die belangrikste of waardevolste inligting uit te haal en die res van die data word dan geskrap. Die alternatief is om 'n beeldkompressie-algoritme te gebruik om die data te verminder. Hierdie tesis ondersoek hierdie strategieë en fokus dan op 'n evaluasie van die "Embedded Zerotree Wavelet" -algoritme. Die EZW-algoritme is 'n verlieserige, golfie-gebaseerde beeldkompressie-algoritme. Moontlike hardeware-implementeringsopsies word ondersoek en die resultate van een voorgestelde opsie word vergelyk met die FlexWave-II stelsel asook die nuwe JPEG2000-standaard.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: We investigate object detection against cluttered backgrounds, based on the MINACE (Minimum Noise and Correlation Energy) filter. Application of the filter is followed by a suitable segmentation algorithm, and the standard techniques of global and local thresholding are compared to watershed-based segmentation. The aim of this approach is to provide a custom region-based object detection algorithm with a concise set of regions of interest. Two industrial case studies are examined: diamond detection in X-ray images, and the reading of a dynamic, and ink stamped, 2D barcode on packaging clutter. We demonstrate the robustness of our approach on these two diverse applications, and develop a complete algorithmic prototype for an automatic stamped code reader. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die herkenning van voorwerpe teen onduidelike agtergronde. Ons benadering maak staat op die MINACE (" Minimum Noise and Correlation Energy") korrelasiefilter. Die filter word aangewend saam met 'n gepaste segmenteringsalgoritme, en die standaard tegnieke van globale en lokale drumpelingsalgoritmes word vergelyk met 'n waterskeidingsgebaseerde segmenteringsalgoritme. Die doel van hierdie deteksiebenadering is om 'n klein stel moontlike voorwerpe te kan verskaf aan enige klassifikasie-algoritme wat fokus op die voorwerpe self. Twee industriële toepassings word ondersoek: die opsporing van diamante in X-straal beelde, en die lees van 'n dinamiese, inkgedrukte, 2D balkieskode op verpakkingsmateriaal. Ons demonstreer die robuustheid van ons benadering met hierdie twee uiteenlopende voorbeelde, en ontwikkel 'n volledige algoritmiese prototipe vir 'n outomatiese stempelkode leser.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: This study investigates the theory of precision satellite orbit propagation and satellite lifetime prediction and lead to the development of two necessary software tools for analysis in these fields. Precision propagation was achieved through the implementation of Cowell's method of special perturbations, considering perturbations due to a 70x70 asymmetrical gravity field, atmospheric drag, Luni-Solar attraction and Solar radiation pressure. The satellite's perturbed equations of motion were integrated utilizing a seveneighth order Runge-Kutta-Fehlberg numerical integration procedure, limiting error propagation by employing adaptive step size control. The MSlS-90 atmospheric density model, providing for diurnal and semi-annual variations, was employed to determine atmospheric density. Care was taken in the precision modelling of the motion of the 12000 equator and equinox. Propagation results for this test case proved to be superior to the SGP4 propagator and a commercial package. The long-term effects of Earth oblateness and atmospheric drag on a satellite's orbital elements were investigated and applied to the orbit decay prediction problem. Orbit decay was predicted by integrating the rates of change of the orbital elements due to Earth oblateness and atmospheric drag. A semi-analytical technique involving Runge-Kutta and Gauss-Legendre quadrature was employed in the solution process. Relevant software was developed to implement the decay theory. Optimum drag coefficients, estimated from drag analysis using precision propagation, were used in decay prediction. Two test cases of observed decayed satellites were used to evaluate the theory. Results for both test cases indicated that the theory fitted observational data well within acceptable limits. / AFRIKAANSE OPSOMMING: 'n Ondersoek is gedoen oor die teorie van presiesie satelliet-wentelbaan vooruitskatting en satelliet-wentelbaanleeftyd afskatting en het gelei tot die ontwikkeling van twee analiseprogramme vir gebruik in hierdie vakgebiede. Presiesie vooruitskatting is bereik deur die gebruik van Cowell se metode van spesiale perturbasies, wat die invloed van 'n nie-simmetriese 70x070 gravitasieveld, atmosferiese sleur, Son-Maan aantrekkingskragte en druk van sonradiasie, in ag neem. Die satelliet se versteurde bewegingsvergelykings is numeries ge-ïntegreer deur gebruik te maak van die sewe-agste orde Runge-Kutta- Fehlberg metode wat fout-voortplanting inhibeer deur gebruik te maak van 'n aanpasbare integrasiestaplengte. Die MSIS-90 atmosferies model, wat voorsiening maak vir dag-nag en half-jaarlikse atmosferiese variasies, is gebruik vir die berekening van atmosferiese digtheid. Sorg is gedra by die presiesie modellering van die beweging van die J2000 ekwator en ekwinokse. Resultate vir hierdie toetsgeval toon meer voortreflik te wees as die SPG4 - en 'n kommersieël-beskikbare vooruitskatter. Die langtermyn effekte van aard-afplatting en atmosferiese sleur op wentelbaanleeftyd is ondersoek en toegepas op die wentelbaanverval-afskattingsprobleem. Wentelbaanverval is bereken deur die integrasie van die tydsafgeleides van die wentelbaanelement onder invloed van aard-afplatting en atmosferiese sleur. Vir die doel is 'n semi-analitiese tegniek, wat gebruik maak van Gauss-Legendre kwadratuur en Runge-Kutta numeriese integrasie, gebruik gemaak. Nodige rekenaar programmatuur is ontwi kkeI om die vervalteorie te implimenteer. Optimale sleur-koëffisiënte is afgeskat deur van presiesie wentelbaananalise gebruik te maak. Twee gevallestudies van bekende vervalde satelliete is gebruik om die vervalteorie te evalueer. Resultate vir beide gevallestudies toon aan dat eksperimentele resultate werklike vervaltye binne aanvaarbare limiete navolg.

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The quadrifilar helix antenna has frequently been employed to provide the wide angle, circularly polarized radiation pattern which is preferable for mobile satellite communications. A detailed study of this antenna and its varieties is presented. When used as an element in wide angle scanning arrays for aeronautical satellite tracking applications, the additional requirement of a low profile with light weight applies. This further complicates the realization of good circular polarization close to the horizon. A top disk is incorporated into various antenna structures in an effort to improve the radiation performance when used within a closely spaced array while reducing the height of the radiating element. The array performance of these elements are investigated which hints at a supported traveling mode aiding the ability to accomplish the wide angle beam steering. Subsequent study of leakywave antennas initiated the study and implementation of leaky-wave structures in phased arrays of quadrifilar helix elements. / AFRIKAANSE OPSOMMING: Die vierledige heliksantenna word dikwels gebruik vir toepassings wat ’n wye, sirkulêr gepolariseerde stralingspatroon benodig. ’n Verskeidenheid van hierdie antennas is noukeurig bestudeer en hul toepaslikheid vir mobiele sattelietkommunikasie ondersoek. Wanneer hierdie antennas in fase gestuurde skikkings gebruik word, word dit ook vereis dat die eenhede liggewig is met ’n lae profiel. Dit bemoeilik die verkryging van goeie sirkulêre polarisasie naby die horison aansienlik. In ’n poging om die wyehoek straling met kort antennas te verbeter, is ’n oorhoofse skyf tot verskillende heliksstrukture toegevoeg. In nou gespasieerde skikkings maak hierdie skywe ’n positiewe bydrae to wyehoekstralingeienskappe. Die invloed van lekmodusse wat binne die struktuur voortplant is ondersoek en gebruik in skikkings waarvan die bundel naby aan die horison gestuur word.