Until recently, there had been a gap between the output frequencies of electronic and optical sources, which included waves of frequencies around 300 GHz to 3 THz and was known as the Terahertz gap. After the development of sources and detectors that operated at these frequencies, Terahertz radiation began to find its way through a variety of applications such as surveillance, spectroscopy and medical imaging. Terahertz radiation has been used in medical imaging experiments on different in-vitro and some in-vivo biological tissues and has shown promising results in differentiating certain features in those tissues. Moreover, it has demonstrated well in detecting certain polar molecules due to these molecules’ fingerprint in Terahertz range of frequencies. Considering these facts, Terahertz has been proved to have the potential for being a perspective medical imaging method, which can be used as a complement to other imaging techniques such as MRI or X-ray or even as a separate method. Due to the capacity of Terahertz radiation, much research is being done on using Terahertz generation-detection set-ups for medical imaging and improving the imaging parameters of these set-ups to capture more precise and meaningful images. In this thesis, the imaging parameters of two different THz imaging set-ups have been studied and compared. One of these imaging set-ups is a THz pulse set-up with photoconductive dipole antennas as source and detector and the other one is a continuous-wave set-up with a backward wave oscillator as the source and a Golay cell as the detector. To the best of our knowledge, a comparative analysis of the imaging parameters of these two types of THz imaging set-ups has not been performed previously. In this thesis, parameters such as modulation transfer function (MTF), resolution and beam profile have been measured through the experiments, for both the THz pulse and THz CW imaging set-ups. These results are compared to the results obtained by theoretical formulas and the reason for any differences occurred between these two results has been explained. Moreover, the imaging parameters found from the experiments for the two set-ups have been compared together and similarities and differences have been discussed. In this thesis, a set of experiments has also been done to verify the capability of the two imaging set-ups for in-vitro tooth imaging, towards developing THz imaging systems suitable for clinical imaging application. These experiments have been performed on a tooth crown sample with the pulse set-up and on a tooth cross-section sample with the continuous-wave set-up. The capability of our THz pulse imaging system to distinguish thickness variations in a tooth crown sample by time-of-flight imaging has been shown and discussed.

Until recently, there had been a gap between the output frequencies of electronic and optical sources, which included waves of frequencies around 300 GHz to 3 THz and was known as the Terahertz gap. After the development of sources and detectors that operated at these frequencies, Terahertz radiation began to find its way through a variety of applications such as surveillance, spectroscopy and medical imaging. Terahertz radiation has been used in medical imaging experiments on different in-vitro and some in-vivo biological tissues and has shown promising results in differentiating certain features in those tissues. Moreover, it has demonstrated well in detecting certain polar molecules due to these molecules’ fingerprint in Terahertz range of frequencies. Considering these facts, Terahertz has been proved to have the potential for being a perspective medical imaging method, which can be used as a complement to other imaging techniques such as MRI or X-ray or even as a separate method. Due to the capacity of Terahertz radiation, much research is being done on using Terahertz generation-detection set-ups for medical imaging and improving the imaging parameters of these set-ups to capture more precise and meaningful images. In this thesis, the imaging parameters of two different THz imaging set-ups have been studied and compared. One of these imaging set-ups is a THz pulse set-up with photoconductive dipole antennas as source and detector and the other one is a continuous-wave set-up with a backward wave oscillator as the source and a Golay cell as the detector. To the best of our knowledge, a comparative analysis of the imaging parameters of these two types of THz imaging set-ups has not been performed previously. In this thesis, parameters such as modulation transfer function (MTF), resolution and beam profile have been measured through the experiments, for both the THz pulse and THz CW imaging set-ups. These results are compared to the results obtained by theoretical formulas and the reason for any differences occurred between these two results has been explained. Moreover, the imaging parameters found from the experiments for the two set-ups have been compared together and similarities and differences have been discussed. In this thesis, a set of experiments has also been done to verify the capability of the two imaging set-ups for in-vitro tooth imaging, towards developing THz imaging systems suitable for clinical imaging application. These experiments have been performed on a tooth crown sample with the pulse set-up and on a tooth cross-section sample with the continuous-wave set-up. The capability of our THz pulse imaging system to distinguish thickness variations in a tooth crown sample by time-of-flight imaging has been shown and discussed.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Large close range environmental reflections or poor isolation between the transmit and receive paths of an FMCW radar can overload the receiver. The In phase and Quadrature phase (IQ) Reflected Power Canceller (RPC) provides a solution to the problem by cancelling any close range reflections. In this study a procedure to optimise the design of an RPC is developed and the performance limits of a practical RPC is investigated in depth. There are four focus areas in the evaluation and design of the IQ Reflected Power Canceller. First, an analysis was performed on a theoretical IQ Reflected Power Canceller, which provided insight into how the system functioned and made it possible to identify practical application issues that would arise during the design. The next focus area was the IQ Reflected Power Canceller’s dynamic range. Equations, based on the power and noise characteristics of each component in the canceller, were derived. From these equations, a system, with an optimised dynamic range, could be developed. Next, the IQ Reflected Power Canceller’s feedback loop stability was investigated. The canceller is an active negative feedback control system but, in order to obtain the negative feedback, the feedback signal has to be phase shifted by 180 degrees to the phase of the input signal. An analysis of the canceller’s RF phase contribution resulted in an equation that can be used to manage the nett RF phase in the feedback loop. The evaluation model of the IQ Reflected Power Canceller produced favourable results. The tests performed on the system included measuring the level of cancellation that can be achieved, whether the dynamic range corresponds to the predicted values and the amount of RF phase error that can be introduced in the feedback path while maintaining a stable system. The IQ Reflected Power Canceller was found to perform well in the evaluation. It provided a cancellation of more than 45 dB for close range reflections and the canceller remained stable across a wide range of RF centre frequencies (1 GHz). This means that the FMCW radar’s frequency modulation bandwidth will not be limited because of the IQ Reflected Power Canceller. The evaluation clearly showed that the modulator in the feedback loop is the critical element that determines the dynamic range of the radar with an RPC. / AFRIKAANSE OPSOMMING: Onvoldoende isolasie tussen die sender en ontvanger van ’n Frekwensie Gemoduleerde Kontinu Golf radar, sowel as groot weerkaatsings vanaf voorwerpe in die omgewing van die radar, veroorsaak dat die ontvanger versadig. Hierdie beperking veroorsaak dat die radar ’n verminderde dinamiese bereik het, en daarmee ook dat die radar se maksimum teiken-afstand verminder word. Die IQ Gereflekteerde Drywingskanselleerder kan as ’n oplossing gebruik word teen hierdie ongewenste refleksies. Hierdie navorsing poog om ’n kanselleerder te evalueer met die eind doel gestel daarop om ’n praktiese stelsel aanmekaar te sit. Die kanselleerder word geëvalueer deur na vier fokus areas te kyk. Eerstens word ’n ideale model opgestel, wat ’n beter begrip van die kanselleerder bewerkstellig. Uit hierdie ideale model, is daar praktiese oorwegings wat die kanselleerder affekteer, geïdentifiseer. Ten einde die dinamiese bereik van die radar ontvanger te verbeter, word ’n metode afgelei wat gebruik word om die kanselleerder se dinamiese bereik te optimeer. Hierdie metode neem die maksimum drywingsbeperkinge van die komponente in die kanselleerder in ag. Die kanselleerder is ’n aktiewe terugvoer beheerstelsel, en aangesien ’n sommeerder in die terugvoer lus gebruik word, moet die fase deur die lus met 180 grade geskuif word om sodoende ’n kansellerende sein by die ontvangde sein te tel. Die RF fase foute in die kanselleerder word geanaliseer deur ’n nie-ideale model van die kanselleerder op te stel. Hierdie nie-ideale model maak dit moontlik om die effek van ’n RF fase fout op die kanselleerder se stabiliteit te ondersoek. ’n Praktiese kanselleerder is ontwerp uit die inligting wat versamel is gedurende die evaluasie, en ’n werkende stelsel is aanmekaar gesit. Met hierdie praktiese kanselleerder is die hoeveelheid drywing-onderdrukking wat bereik kan word, gemeet. Die dinamiese bereik van die kanselleerder is ook bepaal en vergelyk met die teoreties berekende waardes. Die aannames oor die effek van die RF fase fout in die kanselleerder, is bevestig deur metings te neem. Goeie resultate is met die kanselleerder behaal. ’n Kansellasie van meer as 45 dB is gemeet vir naby-geleë refleksies. Die kanselleerder het ook stabiel gebly oor ’n wye band van senter-frekwensies (1 GHz). Dus sal die Frekwensie Gemoduleerde Kontinu Golf radar se modulasie bandwydte nie beperk word as gevolg van die kanselleerder nie. Uit die evaluasie is daar gevind dat die modulator die kritieke element in the kanselleerder se terugvoer lus is, dus bepaal die modulator die dinamiese bereik van die radar met ’n kanselleerder.

De nos jours, les mesures sans contact du signal cardiaque du patient en utilisant le radar Doppler a suscité un intérêt considérable chez les chercheurs, surtout que les électrocardiographes traditionnels avec des électrodes fixes ne sont pas pratiques dans certains cas comme les nourrissons ou les victimes de brûlure. En raison de la sensibilité des micro­ondes à de petits mouvements, le radar a été utilisé comme système de surveillance de l'activité cardio-pulmonaire humaine. Selon l'effet Doppler, un signal de fréquence constante est transmis vers la cible ayant un déplacement variable puis réfléchi. Le signal réfléchit possède une variation de phase par rapport au temps. Dans notre cas, la cible est la poitrine du patient; Le signal réfléchi de la poitrine de la personne contient le signal cardiorespiratoire. Le système est basé sur un analyseur de réseau vectoriel et deux antennes cornet. Le S21 est calculé en utilisant un analyseur de réseau. La variation de phase de S21 contient des informations de l'activité cardio-pulmonaire. Des techniques de traitement sont utilisées pour extraire le signal cardiaque de la variation de la phase de S21 . Cette thèse présente une étude comparative dans la détection des signaux de battements cardiaques au niveau de la puissance rayonnée et de la fréquence opérationnelle. Les puissances rayonnées sont comprises entre 3 et -17 dBm et les fréquences opérationnelles utilisées sont 2.4, 5.8, 1 0 et 20 GHz. Cela permet de spécifier la fréquence opérationnelle optimale, qui donne un compromis entre la puissance minimale émise ainsi que la complexité du système de mesure. De plus, une étude comparative entre plusieurs méthodes de traitement de signal est proposée pour extraire la meilleure méthode qui permet de mesurer le signal cardiaque et par suite extraire ses paramètres. Des techniques de traitement basées sur des transformées en ondelettes ou le filtrage classique sont présentées et utilisées afin de faire une comparaison entre elles. Le paramètre extrait dans cette thèse est le taux des battements cardiaques. Les mesures ont été effectuées simultanément avec un électrocardiographe afin de valider les mesures du signal cardiaque. Puisque la personne peut se déplacer d'une pièce à une autre à l'intérieur de son domicile, des mesures des quatre côtés de la personne et derrière un mur sont réalisées. Ajoutons une approche de modélisation fondée sur la mesure cardio-respiratoire pour une personne qui exerce une marche en avant. De plus, une comparaison entre un système à micro-ondes à simple et deux antennes pour une personne qui prend son souffle est effectuée afin de tester la précision du système à antenne unique par rapport au a la deuxième. Par suite, des mesures sont effectuées pour une personne qui respire en utilisant un système à une seule antenne. / Nowadays, contact-less monitoring patient's heartbeat using Doppler radar has attracted considerable interest of researchers, especially when the traditional electrocardiogram (ECG) measurements with fixed electrodes is not practical in some cases like infants at risk or sudden infant syndrome or burn victims. Due to the microwave sensitivity toward tiny movements, radar has been employed as a noninvasive monitoring system of human cardiopulmonary activity. According to Doppler effect, a constant frequency signal reflected off an object having a varying displacement will result in a reflected signal, but with a time varying phase. In our case, the object is the patient's chest; the reflected signal of the person's chest contains information about the heartbeat and respiration. The system is based on a vector network analyzer and 2 horn antennas. The S21 is computed using a vector network analyzer. The phase variation of S21 contains information about cardiopulmonary activity. Processing techniques are used to extract the heartbeat signal from the S21 phase. This thesis presents a comparative study in heartbeat detection, considering different radiated powers and frequencies. The radiated powers used are between 3 and -17 dBm and the operational frequencies used are 2.4, 5.8, 10 and 20 GHz. This helps to make a compromise between the minimum power emitted and the complexity of the measurement system. In addition, a comparative study of several signal processing methods is proposed to extract the best technique for heartbeat measurement and thus to extract its parameters. Processing techniques are based on wavelet transforms and conventional filtering in order to make a comparison between them. The parameter extracted in this thesis is the heartbeat rate HR. Measurements were performed simultaneously with a PC-based electrocardiograph to validate the heartbeat rate measurement. Since the person can move from a room to another inside his home, measurements from the four sides of the person and behind a wall are performed. In addition, a modeling approach based on cardio-respiratory measurement for a person who is walking forward is presented. Furthermore, a comparison between single and two-antenna microwave systems for a non-breathing person is carried out to test the accuracy of the single-antenna system relative to the two ­antenna microwave system. After that, measurements are performed using one antenna microwave system for a person who breathes normally.

Neste trabalho foi desenvolvido um estudo sobre a precessão livre de onda contínua (CWFP-continuous wave free precession), uma condição especial da precessão livre no estado estacionário (SSFP), e algumas aplicações. Os resultados experimentais, e de simulações, mostraram que este sinal é atingido após a passagem por dois estágios iniciais. O primeiro é dependente da não homogeneidade do campo magnético, relacionado a razão Tp/T2*. O segundo, o qual é chamado de estado quasi-estacionáio, é dependente ambos os tempos de relaxação do sistema em estudo, T1 e T2. Este segundo estágio é responsável por levar a magnetização do estado de equilíbrio térmico a um estado verdadeiramente estacionário. Tendo como informação a amplitude da magnetização no estado de equilíbrio térmico e no estado verdadeiramente estacionário, e também do decaimento do sinal durante o estado quasi-estacionário, é possível determinar, rápida e simultaneamente, ambos os tempos de relaxação do sistema, fazendo um único experimento. Esse método oferece aplicações interessantes para o estudo de processos dinâmicos, propostas também neste trabalho. Foi possível verificar que o sinal de CWFP pode ser utilizado para acompanhar cinética de reações, e também variações de viscosidade do meio, por exemplo, em reações de polimerização, associadas à mobilidade molecular em função de mudanças estruturais. Um método para avaliar a condutividade térmica de elastômeros foi proposto, com o fornecimento de resultados quantitativos muito próximos daqueles encontrados na literatura, e que utilizam outros métodos. A dependência do sinal de CWFP com a freqüência de offset também permitiu realizar um estudo, com aplicação em RMN de alta resolução, sobre a supressão de sinal de solvente. Os resultados demonstraram que é necessário fazer alguns ajustes na largura de pulsos, juntamente com o ciclo de fases, para minimizar as anomalias de intensidade e de fase dos sinais no espectro transformado. Essa técnica foi aplicada em espectroscopia ‘in vivo’, a qual permite resolver, por exemplo, problemas como a determinação de açúcares em frutas, onde o sinal é bastante próximo do intenso sinal da água. / In this work a study of the continuous wave free precession (CWFP), a special condition of the steady-state free precession (SSFP), and some applications, was developed. The experimental results, together with simulated ones, have shown that the CWFP signal is attained after two previous stages. The first one is dependent on the non-homogeneity of the magnetic field, related to Tp/T2* ratio. The second, which is called quasi-stationary state, is dependent of both relaxation times, T1 and T2. This second stage allows leading the magnetization in the thermal equilibrium to a truly stationary state. The information of the signal amplitude in the thermal equilibrium and in the steady state, and also the signal decaying during the quasistationary state, allows the fast and simultaneous determination of the relaxation times, performed in a single experiment. This method offers interesting applications for studying dynamical processes, also proposed in this work. It was possible to verify that the CWFP signal can be used to monitor kinetics of reactions, which variations of viscosity are involved, for example, in polymerization reactions, always associated to structural changes. A method for evaluating thermal conductivity in elastomers was proposed, with results in accordance to the literature, which uses other methods. The dependence of the CWFP signal with the offset frequency has permitted to study an application to the High-Resolution NMR, about the solvent suppression. The results demonstrated that it is necessary to perform some adjustments in the pulse width, together the phase cycle, to minimize some phase and intensity anomalies of the frequency-domain signal. This technique was applied in ‘in vivo’ spectroscopy, which can solve, for example, problems with the determination of the sugar content in fresh fruits, where the sugar signal is very close to the intense signal of the water.

This masters thesis is focused around the designing and implementation of an anpplication that can extract information on speed of vehicles from radar data. The radar measurements were done by using a continous wave radar. The emphasis is placed on the computation of the angle in which the car approaches the radar and on the speed correction based on this angle. The final design was implemented in Matlab. The evaluation of the implemented solution was done on reference data.

Évaluer la capacité de remplissage des cinq différentes techniques d’obturation canalaire dans l’obturation des canaux ovales. Matériel et méthodes : Un total de 220 molaires mandibulaires, avec 1 canal dans la racine distale, a été sélectionné. Chaque canal a été mise en forme jusqu’à la longueur de travail en utilisant un système mono-instrument le WaveOne Gold Primary Les dents préparées ont été divisées au hasard en cinq groupes égaux (n = 40 par groupe) pour l'obturation: condensation à onde continue (CWC), technique avec tuteur GuttaCore (GC), technique avec tuteur Thermafil (TH), technique utilisant un cône unique (SC), condensation hydraulique à froid (CHC). Les pourcentages de GPFA, SFA et VA ainsi que la présence des matériaux d’obturation à l’intérieur des tubulis dentinaires (tag)à longueur de travail (LT) -4mm et -2 mm a été évalué à par microscopie numérique optique, microscopie électronique à balayage (SEM) et microanalyse par rayons X à dispersion d'énergie (EDX). Analyse statistique : Les données collectées ont été analysées avec la version 11.2 de SigmaPlot (Systat Software, Inc., San José, CA, USA). Les pourcentages de GPFA, SFA, VA correspondant aux différentes groupes ont été comparés en utilisant le test de Kruskal-Wallis avec α=0,05. Résultats: à LT-4 et LT-2 mm, cette étude à montré une différence statistiquement significative en terme de capacité d’obturation pour le cinq techniques. À LT-4, les groupes GC et TH ont montré une différence statistiquement significative par rapport aux trois autres groupes en terme de GPFA et SFA. En terme de VA, il y a une différence statistiquement significative avec les groupes SC et CHC tandis qu’aucune différence n’a été démontrée entre les groupes GC , TH et CWC . À LT-2, les groupes GC et TH ont montré une différence statistiquement significative par rapport aux trois autres groupes en terme de GPFA, SFA, VA. Conclusion : 
Cette étude montre clairement que les obturations par GC et TH sont en mesure de remplir les canaux ovales d’une manière plus appropriée que les autres techniques d’obturation. 
Les groupes GC et TH, à LT -4 et -2mm, présentaient des tags de gutta-percha à l’intérieur des tubulis dentinaires. La présence de tags de gutta-percha à l’intérieur des tubulis dentinaires (à la place de tags de ciment beaucoup plus vulnérables) pourrait se comporter comme une barrière physique, capable de sceller les bactéries à l’intérieur des tubulis et surtout non résorbable dans le temps. / Assess the filling ability in oval-shaped canals using five different filling techniques. Materials and Methods : 220 human mandibular first molars with one distal oval canal were selected. Distal Canals were shaped using WaveOne Gold Primary. The prepared teeth were randomly divided in four equal groups (n = 40) for obturation : Continuous Wave Condensation (CWC), GuttaCore carrier based technique (GC), Thermafil (TH) carrier based technique, Single Cone technique (SC), Cold hydraulic Condensation (CHC). The proportions of gutta-percha filled areas (GPFA), sealer filled areas (SFA), void areas (VA) and the tags into dentinal tubules at 4 mm and 2 mm were analyzed by Optical numeric microscope, SEM and EDX. Statistical analysis : they were compared by Kruskal-Wallis one-way ANOVA on ranks, with statistical significance set at α = 0.05. Results : At 4 and 2 mm from the apex, this study discloses statistically different filling ability for the five techniques. At 4 mm from the apex, the GC et TH groups showed significantly higher PGFAs than lateral condensation and System B techniques. The GC et TH groups showed a statistically significance difference compared with the others three groups in terms of higher PGFA, lower SFA. It showed a statistically significance difference with SC and CHC groups in term of VA. At 2 mm level from the apex, the GC et TH groups showed a statistically significance differece compared with the others three groups in terms of higher PGFA, lower SFA and VA. Conclusions : GC obturation is able to fill oval-shaped canals in a more appropriate way than the other filling techniques. GC was the only group which showed the presence of gutta-tags at 4 and 2 mm from the apex. The gutta- percha tags could behave as a physical barrier able to entomb bacteria.

Additive manufacturing has the power to redefine how we create components. In order to minimize removal of printed material, deformation must be kept a minimum. When deposition rate is increased during directed energy deposition so is the power requirement for melting the feedstock. This increases the residual stresses in the material and leads to more deformation. The deposition rate must be increased without introducing large deformation, if additive manufacturing is ever to be economical in many engineering fields. This study aims to explore if pulsing the laser can decrease deformation using a design of experiments approach. Other types of defects and microstructural changes are also evaluated. A total of 17 sets of parameters were used varying laser power, pulse frequency and the time fraction when the laser was powered on. The amount of powder added to a substrate was constant and the build geometry as similar as possible for all tests. Ultimately no conclusion could be drawn regarding pulsing parameters effect on deformation. It was found pulsing the laser lowered the powder efficiency drastically, which may have had a bigger effect on the experimental set up than anticipated. In a similar manner, no relation between pulsing parameters, defects and microstructure could be observed. / Additiv tillverkning ger oss möjligheten att tillverka komponenter på ett sätt som tidigare inte har varit möjligt. För att minimera efterföljande svarvning och fräsning av additivt tillverkade delar måste deformationen kontrolleras. När deponeringshastigheten ökar måste även sträckenergin ökas i direktenergideponeringsprocesser. Detta leder till höjda restspänningsnivåer i materialet och medför en större efterföljande deformation. Om additiv tillverkning i framtiden ska ha en chans att mäta sig ekonomiskt med konventionella metoder måste deponeringshastigheten öka för många applikationsområden. Denna studie använder Design of Experiments för att undersöka om en pulserande laser kan utnyttjas för att minska deformationen när metallpulver används som tillsats. Även andra typer av defekter och förändringar i mikrostruktur har utvärderats. Totalt undersöktes 17 olika parameteruppsättningar med varierande lasereffekt, pulsfrekvens och aktiv lasertid. Pulverdeponeringshastigheten hölls konstant mellan försöken och byggeometrierna var så lika som möjligt för alla tester. I slutändan kunde ingen slutsats dras när det gäller hur pulserande parametrar påverkar deformationen. Det visade sig att en pulserande parameter sänker pulvereffektiviteten drastiskt, vilket kan ha haft en större effekt på experimentets uppsättning än förutspått. På liknande sätt kunde inget säkert samband mellan pulserande parametrar, defekter och mikrostruktur observeras.

Diese Diplomarbeit stellt den Entwurf eines frequenzmodulierten Dauerstrichradars (FMCW) mit ultrabreitbandigem Frequenzbereich von 50 MHz bis 3 GHz unter Verwendung kommerziell verfügbarer Komponenten (COTS) für die Anwendung als Bodenradar in einer Mondlandeeinheit dar. Dazu werden dem Stand der Technik entsprechende Topologien zur Erzeugung ultrabreitbandiger Signale aufgezeigt und analysiert. Die theoretischen Hintergründe einer Aufteilung des Frequenzsweeps und der späteren Zusammensetzung des Beatsignals werden behandelt. Die Entwürfe der Schaltung, des Layouts und der Software werden erläutert. Bei der Charakterisierung des Radarsystems stellt sich heraus, dass die geforderten Eigenschaften unter dem Einfluss eines Temperaturbereichs von −40 °C bis 75 °C bzw. bei Bestrahlung mit einer Gesamtdosis bis 168 Gy erreicht werden können und die Verwendung von modernen COTS Komponenten die Performance nicht einschränkt. Abschließend werden Verbesserungsvorschläge für Hard- und Software gegeben, welche sich während der Arbeit mit dem System ergeben haben. / This thesis presents the design of a miniature frequency modulated continuous wave (FMCW) radar with a frequency range of 50 MHz to 3 GHz using only commercial off the shelf (COTS) components. The system is intended for use as ground penetrating radar (GPR) as part of a lunar lander. State of the art topologies for ultra wideband signal synthesis are presented and compared. The theoretical background of split frequency ramps and the thus required stitching of baseband signals is discussed. The schematic design, layout and software development is described. The characterization of the radar system shows that the specification is met within a temperature range of −40 °C to 75 °C and while exposition to radiation with an accumulated dose of up to 168 Gy. The use of COTS components does not impair the performance. Finally suggestions for hard- and software improvements are given, that resulted from working with the radar system.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A well-known problem with FM-CW radar systems is the leakage of transmitter power into the receiver which leads to the making of close-in targets, and can severely limit the system dynamic range performance. This thesis considers two solutions to this radar system problem for a low frequency radar operating in the VHF band. The first method to suppress coupling is using separate transmit and receive antennas designed in such a way as to reduce coupling between them. The second is to design a negative feedback loop as part of the radar receiver where the feedback loop adaptively reduces the amount of transmitter leakage through to the receiver. This project details the realisation of these two solutions. A number of antenna designs are modelled in software and simulated to determine their characteristics of which the transmit-to-receive coupling is the key parameter. As no low coupling configuration could be found a simple configuration is chosen and practical measurements are taken. These antennas are then used in the radar system that is to be built. An FM-CW radar system is designed and simulated using software with a negative feedback loop being designed and implemented into the radar simulation. A practical radar system is then made inclusive of the feedback loop. Measurements are then taken to determine the efficacy of the feedback loop. / AFRIKAANSE OPSOMMING: ʼn Bekende probleem met FM-CW radar stelsels is die lekkasie van versender krag tot in die ontvanger wat lei tot die maak van nabye teikens en kan die stelsel se dinamiese sendbereik steng beperk. Hierdie tesis oorweeg twee oplossings tot hierdie probleem vir ʼn lae frekwensie radar wat in die VHF band werk. Die eerste metode wat na gekyk word om die koppeling te onderdruk is om die twee antennas van die radar stelsel so te ontwerp sodat die hoeveelheid koppeling tussen hulle verminder is. Die tweede is om ʼn negatiewe terugvoerlus as deel van die ontvanger te ontwerp. Hierdie terugvoerlus sal die versender lekkasie sein aanpassend in die ontvanger verminder. In hierdie projek word die realisering van bogenoemde oplossings uiteengeset. ʼn Paar verskillende antenna ontwerpe word gemodelleer in sagteware en word gesimuleer om hul karakteristieke te bepaal. Die belangrikste van hierdie faktore is die versender na ontvanger koppeling. Sienend dat geen ontwerp met ʼn lae genoeg koppeling gevind kon word nie, is ʼn eenvoudige ontwerp gekies en praktiese metings daarvan geneem. Hierdie antennas word dan gebruik in die radar stelsel wat gebou sal word. ʼn FM-CW radar stelsel word ontwerp en gesimuleer in sagteware. Die negatiewe terugvoerlus word ook ontwerp en geïmplementeer in die radar simulasie. ʼn Praktiese radar stelsel word dan gemaak insluitend die terugvoerlus. Metings word dan geneem om die effektiwiteit daarvan te bepaal.