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)--Stellenbosch University, 2008. / This thesis presents the design of a control system for the autonomous precision landing of an unmanned aerial vehicle aided by an infra red camera for precision position measurements. An optimal kinematics state estimator was designed using two Kalman filters. A Monocular vision algorithm that uses markers on the runway was developed to supply accurate position measurements on the final approach of the landing. Inner-loop controllers as proposed by [14] and implemented in [5] are used to reduce the aircraft dynamics to a point mass with steerable acceleration vector. Outer-loop controllers as proposed by [13] were modified and expanded to guide the aircraft on the circuit and final approach. The hardware in the loop simulator that was designed in [6] was expanded for optical measurements and used to verify the system. An infra red camera node was designed and built to supply the optical measurements. The system was installed on a model aircraft and partially tested with practical test flights.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / There is currently a disparity in the amount of research done in underwater communication when compared to terrestrial communication. Therefore, it was the goal of this work to try and make an initial step towards bridging that gap. To start with, an introductory analysis was made of the ocean as a communications medium, focusing on any areas where the ocean characteristics could negatively affect communication. Furthermore, an overview was conducted of current communication schemes, to determine where ocean communication would differ from terrestrial communication, with the idea of determining the limiting parameters of such communication, specifically in terms of protocol design for swarms and sensor networks. Using this research, a n-ary tree-based routing algorithm was designed and incorporated into an overall protocol in line with current ISO convention. The strategy was simulated using the Erlang platform and it was found that underwater communication can be achieved with favourable results. It was however also found that using Erlang as a communications tool is currently not the best option and has various shortcomings, although with further work it could be more usable. The implemented strategy appears eminently feasible and should provide a basis for further research and practical implementation

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. / SumbandilaSat is the second South African satellite, and is scheduled to be launched in April/May 2007. A software defined radio (SDR) automatic identification system (AIS) receiver is proposed as a possible experimental payload for this satellite. The AIS receiver can be used to track and store movement of ships at sea, and then forward this information to the ground station upon request. This thesis demonstrates the design of a SDR AIS receiver for Sumbandila satellite. The design of a GMSK/FMmodem as used in AIS is presented. Models are developed and simulated in Matlab. Digital signal processing algorithms developed for the AIS receiver are highlighted. Algorithms are developed to decode and translate the AIS encapsulated binary messages. The models are transferred to C++ and the AIS receiver is implemented on the SDR architecture. Finally the real time performance of the AIS receiver is presented along with some test results and performance analysis.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / Nanoelectromechanical systems (NEMS) are the integration of nanotechnology and microelectromechanical systems (MEMS). The idea of this thesis is to give a basic preparation to approach NEMS, a subcategory of nanotechnology. This is performed by gaining knowledge of the two separate fields NEMS consist of, namely MEMS and nanotechnology. This document will discuss the basic theory and fabrication tools for microelectromechanical systems, as well as its limits as MEMS feature sizes decrease, reaching toward nanotechnology. It starts with an introduction that includes the history, giving a basic background. The essence is captured with theory of the equipment, the main material, some concepts of design and the creation of structures. To stimulate further interest, this thesis also illustrates practical design and fabrication methods. With the knowledge and skills that were discussed, one should be ready to get started with NEMS.

Thesis (MScEng (Electrical and Electronic Engineering))--Stellenbosch University, 2008. / This thesis relates to the analysis and design of a SQUID microscope. Superconductor theory is discussed in depth to provide a thorough understanding of Josephson junctions and of dc SQUID magnetometers. The behaviour and suitability of different types of single-layer dc SQUIDs are looked at. The quality of the superconducting material patterned onto a substrate and the Josephson junction design used affect the behaviour of a practical dc SQUID. Noise and cooling play an integral part in the design and operation of a dc SQUID. The source of noise is looked at in an effort to minimize its effect. Cryocooling is essential to real world operation so different cooling strategies and their consequences are analyzed. This thesis focuses on modeling the behaviour of the dc SQUID to creating a practical system for use inside a SQUID microscope. Operating the dc SQUID with the appropriate electronics will linearize the device, reduce the effect of noise, and create a device with wide bandwidth. Each step in creating a practical system is discussed in detail. Simulations are used to create models predicting the behaviour of the dc SQUID and the electronics. They are then used to design and create practical electronic systems. Measurements are performed on Josephson junctions and dc SQUID magnetometers using the designed electronics. The Josephson junctions behave as predicted and were successfully tested. The dc SQUIDs did not behave as predicted and were not successfully tested. The SQUIDs were damaged, either by a malfunction in the cryocooler or through age related deterioration. A full test of the flux-locked loop was not possible and the dc SQUID was not linearized.

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))--University of Stellenbosch, 2006. / The African Speech Technology (AST) project ran from 2000 to 2004 and involved collecting speech data for five South African languages, transcribing the data and building automatic speech recognition systems in these languages. The work described here form part of this project and involved implementing methods for automatic boundary placement in manually labelled files and for determining errors made by transcribers during the labelling process.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2005. / In an ideal software defined radio (SDR), all parameters are defined in software, which means the radio can be reconfigured to handle any communications standard. A major technical challenge that needs to be overcome before this SDR can be realised, is the design of an RF front end that can convert any digital signal to an analogue signal at any carrier frequency and vice versa. Quadrature mixing (QM) can be used to implement and analogue front end, that performs up and down conversion between the complex baseband centred around 0 Hz and the carrier frequency. By separating the tasks of frequency conversion and digital-to-analogue conversion, the latter can be performed at a much lower sample rate, greatly reducing the demands on the hardware. Furthermore, as QM can handle variable carrier frequency and signal bandwidth, this can be done without sacrificing reconfigurability. Using QM as an analogue front end may therefore be the solution to implementing SDR handsets.

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.