Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis discusses the design of a dual circularly polarized single element antenna with special emphasis on achieving a wide bandwidth and high polarization isolation. The aim of the study is to produce an antenna for transmission of colour video signals between a ground station and a low earth orbit satellite. Microstrip patch antennas are suitable for satellite applications because they are light weight, conformal and have a thin profile. However, the antennas' inherent naITOW bandwidth is one of their major drawbacks. The aperture coupled microstrip patch antenna boasts of a much-improved bandwidth over the traditional single layer microstrip antenna and the freedom of using separate substrates for the patch and the feeding network. Hence the designed single element antenna is aperture coupled. To achieve dual circular polarization with good polarization purity, the antenna had a crossed slot aperture with a balanced feed. The feed network was designed on a single layer. The design was executed in two steps using IE3D moment of methods simulation software: design of the radiating part, and design of the feed part. Each part was simulated and optimized on its own before the two were combined, simulated and optimized again. Parameters used in the antenna optimization were: the substrates' thicknesses and dielectric constants, patch and aperture dimensions, and the feed line width and offset. The designed antenna was built and measured. Initial measurements of S-parameters yielded unacceptable results, especially for S22 and S21, and so an investigation into the matter was conducted. That led to the sizes of the feed and reflector planes being extended. Absorbing material was used between the parallel feed and reflector planes because some power was, to a lesser extent, still escaping, due to the fact that the planes were fmite. Measurement results demonstrated reasonable agreement with the simulation. The final antenna had a reflection coefficient of less than -10 dB for the entire operating band of 400 MHz centred on 3 GHz, an isolation of approximately -15 dB in the operating band and a gain of 2 dBi and I dBi for Ports 1 and 2, respectively, at 3 GHz. These results, especially the gain, are influenced by the back radiation and the finite sizes of the feed and reflector planes. It is therefore recommended that an enclosed cavity be used at the back of the antenna and a 'dogbone' aperture be used to minimize back radiation. / AFRIKAANSE OPSOMMING: Die tesis omskryf die ontwerp van 'n tweevoudige sikuler gepolariseerde enkel-element antenne met spesiale klem op wye bandwydte en hoe polariserings isolasie. Die doel van hierdie studie is om 'n antenne vir uitsending van kleur video seine tussen 'n grond stasie en 'n omnentelingsatelliet daar te stel. Mikrostrook plakantennes is gepas vir satelliet toepassings weens hulle ligte gewig en dun profiel. Die antenne se gepaardgaande nou bandwydte is egter een van hulle grootste nadele. Die gleufgekoppelde mikrostrook plakantenne gee egter 'n baie beter bandwydte as die tradisionele enkellaag mikrostrook plakantenne asook die vryheid om verskillende substrate vir die plak en die voernetwerkte gebruik. Vir hierdie redes daar besluit om die enkel-element antenne sleufgekoppeld te maak. Om tweevoudige sikuler gepolariseerde met goeie polarisasie suiwerheid te kry, moes 'n kruisvonnige gleuf met 'n gebalanseerde voer ontwerp word. Die voernetwerk was op 'n enkellaag ontwerp. Die ontwerp was in twee fases in IE3D momentmetode simulasie sagteware gedoen: ontwerp van die stralings gedeelte, en ontwerp van die voer gedeelte. Elke gedeelte word afsonderlik gesimuleer en geoptimiseer voordat die twee saam gesimuleer en geoptimiseer word. Parameters wat gebruik word in die antenne optimiseering is: dikte van substraat en dielektriese konstante, plak en gleuf grootes, en voer lynwydte en afwyking. Die ontwerpde antenne is gebou en gemeet. Aanvanklike metings van S-parameters het onaanvaarbare resultate gel ewer, vera I vir S22 en S21,dus is daar besluit om die redes daarvoor te ondersoek. Dit het daartoe gelei dat die voer- en reflector vlakte groter gemmak is. Absorbeer material is tussen die parallel voer- en reflector vlakke gebruik aangesien steeds drywing verloor is weens die eindige vlakke. Meting resultate het taarnlike goed met die simulasies vertoon. Die finale antenne het 'n weerkaatskoeffisient laer as -10 dB getoon vir die volle bandwydte van 400 MHz gesentreerd rondom 3 GHz, 'n isolasie van ongeveer -15 dB in die bandwydte en 'n aanwins van 2 dBi en I dBi vir onderskeidelik Poorte I en 2 by 3 GHz. Hierdie resultate veral die aanwins is deur die straling na agter beinvloed en die eindige grootes van die voer- en reflector vlakke. Dit word om hierdie rede dus voorgestel dat 'n geslote holte aan die rugkant van die antenne gebruik word en dat 'n "dogbone" gleuf gebruik word om straling na agter te minimeer.

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.

The Thesis can be broadly classified into 2 sections. Initially it attempts to solve an existing long-term problem in the spark plug manufacturing industry, namely reliability and criteria for spark plug production testing. The second section of the Thesis develops the preliminary work and explores the fundamental theory of ignition sparks in preparation for the main study of ignition system and ignition spark mathematical modelling. Section 1 of the Thesis begins by introducing spark plug faults and existing production faults detection equipment and methods. An evaluation of potential new fault detection and classification systems follows, in two phases: detection and analysis. A suitable electrical test and neural network based production test system is then derived from the preceding work. This first section of the Thesis culminates in a factory evaluation of the prototype system at the sponsoring company. Section 2 of the Thesis uses experience gained from Section 1 to effect an investigation into the fundamentals of ignition spark development, leading to the mathematical modelling of Kettering-type ignition systems and associated spark profiles. Finally, the practical benefits of the modelling are discussed with respect to potential real automotive applications. There are two main novel aspects of the work. (1) The use of a neural network to analyse and classify ignition spark waveforms is believed to be a novel idea which can be further extended in many areas beyond the spark plug testing application discussed here. (2) Ignition system and spark modelling is a relatively unexplored research area. This work has resulted in an increase in the level of complexity of model and therefore a potential increase in precision.

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2003. / The imaging of platiniferous reefs in the Bushveld Igneous Complex (BIC) is of great economical and sociological importance. Borehole radar technology has been identified as a viable mapping tool to be used in day-to-day mining operations, but a critical assessment has to be made on the feasibility of this postulation. The system analysis made of the borehole radar deployed in the BIC is presented in this dissertation. The analysis is done using a specific example - the GeoMole borehole radar system. A novel procedure, based on the basic theory of electromagnetic radiation and propagation, is proposed by which the entire physical radar system can be characterized. The power transmitted by an unconventional borehole-deployed transmitter is estimated by a sequence of free space measurements, numerical simulations and theoretic derivations and approximations. Antenna transfer functions (magnitude and phase) are numerically simulated for a variety of deployment configurations. The total system transfer function of the receiver analogue and digital chain is determined. This enables the calculation of the radar's performance figures necessary to determine the applicability of the radar in a specific geological setting. A radar system is only complete when considered in its environment. The BIC is a stratified system of numerous rock layers. An in-depth study is done on the propagation of radiowaves in stratified lossy media. Only the case for non-magnetic media is discussed in this dissertation. The developed theory is used to predict the system response to a typical transmitted radar pulse in the UG1 - UG2 stratigraphy of the BIC, determine the maximum detection range of reef horizons and estimate the reflectivity of the reefs. Resolution is one of the key parameters that determine the performance and accuracy of imaging. An algorithm is proposed, developed and tested by which the resolution of the system is increased and overlapping echoes become resolvable. Even though some of the techniques are developed with a specific system in mind, the applicability of the concepts and algorithms is universal.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / This thesis examines three reduced complexity algorithms for subspace tracking in the context of radio direction finding. Projection Approximation Subspace Tracking (Yang), the Fast Data Projection Method (Doukopoulos and Moustakides) and OPERA (MacInnes) are presented and compared in terms of performance and efficiency. The algorithms’ performances are contrasted using step changes in direction of arrival, sensitivity to noise and minimum angular discrimination. Their relative efficiencies are examined by comparing their theoretical complexities and by assessing benchmark results. The construction of a PC based signal simulator and direction finding client using the MUSIC algorithm are described. The results of a field assessment of the algorithms are presented, and finally, conclusions regarding the relative merits of the algorithms are drawn.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates the compensation of voltage flicker in an industrial environment. Industrial loads draw progressively less sinusoidal currents. These currents cause non-sinusoidal voltage drop over the line impedance, causing a distorted line voltage. The light output of incandescent electric lighting systems is quadratically proportional to the line voltage, and thus variations in the line voltage cause irritating variations in the output of such systems. Two tools to analyse flicker problems are developed: A USB data logger is built to log measured waveforms to computer hard disk. These data are analysed using a MATLAB implementation of the IEC-specified flicker meter. A converter-based flicker compensator is found to be the only compensator capable of compensating general flicker loads. Such a compensator is developed using the synchronous reference frame filtering technique. Several aspects of the compensator are dealt with in detail including selection of a current control strategy, calculation and implementation of the converter duty cycles and compensation of the various non-idealities in such a controller. Full compensation is contrasted to reactive compensation – the second option being less expensive but also less effective in the compensation of certain loads. The effectiveness of reactive compensation is found to be dependent not only on the type of load, but also on the type of line feeding the flicker load. Three industrial flicker loads are measured and analysed: a three-phase welder, a sawmill and a rock crusher. These loads are simulated, and the compensation proposed confirmed via these simulations. The compensation of the three-phase welder is tested using a hardware scale model. This verified the operation of the proposed flicker compensator in practice.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / A radar system observes an aircraft once during each scan of the airspace, and uses these observations to construct a track representing a possible route of the aircraft. However when aircraft interact closely there is the possiblility of confusing the identities of the tracks. In this thesis multiple hypothesis techniques are applied to extract an identity confidence from a track, given a set of possible tracks and observations. The system utilises numerous estimation filters internally and these are investigated and compared in detail. The Identity Confidence algorithm is tested using a developed radar simulation system, and evaluated sucessfully against a series of benchmark tests.

Thesis (MScEng (Electical and Electronic Engineering))--University of Stellenbosch, 2007. / Software defined radios (SDRs) implement in software those parts of a radio which have traditionally been implemented in analogue hardware. We explain the importance of this definition and introduce reconfigurability and portability as two further goals. Reconfigurabilty is a property of the SDR platform, which may be a microprocessor, configurable hardware device, or combination of the two. We demonstrate that the field-programmable gate array is suficient for the implementation of practical SDR systems. Portability, on the other hand, is a property of the modulation and demodulation software, also known as waveform specification software. We evaluate techniques for achieving portability and show that waveforms can be specified in a generic form suitable for the autogeneration of implementations targetting both microprocessor- and FPGA-based architectures. The generated code is in C++ and VHDL respectively, and the tools used include formal models of computation and the XSLT language.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / This thesis presents the analysis, design, simulation and practical implementation of a novel control system for a variable stability blended-wing-body unmanned aerial vehicle. The aircraft has a moveable centre of mass that allows it to operate in an aerodynamically optimised minimum drag configuration during cruise flight. The primary purpose of the control system is thus to regain nominal static stability for all centre of mass positions, and then to further regulate motion variables for autonomous way point navigation. A thorough analysis of the parameters affected by the varying centre of mass position leads to the identification of the main control problem. It is shown that a recently published acceleration based control methodology can be used with minor modification to elegantly solve the variable stability control problem. After providing the details of the control system design, the customised avionics used for their practical implementation are presented. The results of extensive hardware in the loop simulations verify the functionality of the controllers. Finally, flight test results illustrate the practical success of the autopilot and clearly show how the control system is capable of controlling the variable stability aircraft at centre of mass locations where a human pilot could not.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / This thesis discusses the design, development and measured results of a phase-locked loop based frequency synthesiser for X-band Doppler radar. The objective is to obtain phase noise comparable or lower than that typically achieved with direct analogue frequency synthesis techniques. To meet this objective, a theoretical study of the noise contributions of individual components of the synthesiser and their effect on the total phase noise within and outside the loop bandwidth of the PLL is performed. The effect of different phase margins on the closed-loop frequency response of the PLL, and hence the total phase noise, is investigated. Based on the results, an optimal phase-frequency detector reference frequency, loop bandwidth, adequate phase margin, and suitable components are chosen for optimal phase noise performance. The total phase noise at the output of the synthesiser is calculated and it is shown that the phase noise specification can be met. A significant part of this thesis is devoted to the design, modelling and characterisation of a frequency multiplier, as well as to a combline and interdigital bandpass filter required for the frequency synthesiser. In the first case, a piecewise linear circuit model is used to model the behaviour of the nonlinear multiplier circuit. Fourier theory is used to calculate the large-signal driving point input and output impedances of the nonlinear circuit, enabling the computation of the circuit elements for the input and output matching networks. The measured response of the frequency multiplier under various different operating conditions is presented and discussed. The design of the microwave bandpass filters is based on the theory of coupling and external quality factors. To aid in the verification and optimisation of the design, a software simulation tool is used. The presented S-parameter measurements of the filters show how well the theory matches with what is obtained in practice. The measured spectral and phase noise response of various components comprising the synthesiser, are discussed. These measurements provide insight into the response of individual components under different operating conditions and show the behaviour of important subsystems of the synthesiser. The thesis culminates in the presentation of the measured phase noise of the complete synthesiser. It is shown how well the measured phase noise correlates with the calculated phase noise. In addition, the measured spectral content and transient behaviour of the synthesiser are investigated and discussed. High power spurious components at some output frequencies are indentified and reduced. The feasibility of using the developed prototype phase-locked loop based frequency synthesiser for coherent X-band Doppler radar is discussed and demonstrated.