In this thesis, the properties of the metamaterials are studied. We analyze and discuss the artificial structure called metamaterials. The the effects on the radiation pattern and antenna gain are discussed when the structure is placed above the antenna. First, the propagation of electromagnetic wave in metamaterials is discussed. The metamaterial composed of metal rod array and split-ring is introduced. Next, the effects on permittivity, permeability and refraction index are studied when the structure parameters are changing. Thirdly, according to the above-mentioned summary, we use the structures to achieve an antenna radome. The radome can reduce 3 dB beam-width by about 31.25 percent at 10.75 GHz. The maximum gain achieves 7.25 dBi. In the fourth part, we also discusse the method of reducing the frequency band where negative refraction index occurs. The metamaterial is used to be a radome at the lower frequency band. The maximum gain is about 7.87 dBi. The 3 dB beam-width reduces by about 37.25 percent by the radome structure. Fifthly, the methods of improving the bandwidth are discussed when the antenna radome over the antenna . The enhancement of the antenna performance can be applied to the point-to-point communication. It also can save the cost of the feed network and the numbers of array antenna.

A demanda por qualidade nas aplicações envolvendo radiação laser exigiu melhorias no seu desempenho. Conseqüentemente, equipamentos mais rápidos e precisos nas medidas dos seus parâmetros são indispensáveis. Nas áreas onde o laser é empregado, três parâmetros sobressaem-se nas suas aplicações: (1) potência ou energia, (2) freqüência e (3) comprimento espacial ou largura do feixe. A determinação das bordas, isto é, da largura do feixe, está ligada a um percentual do máximo valor atingido pela energia. O diâmetro do feixe, juntamente com a energia, determina-se a densidade do feixe. Outros parâmetros como: divergência e fator de qualidade (M2), podem ser determinados também. O presente trabalho busca desenvolver um sistema de translação bidimensional que possa ser empregado na caracterização espacial do feixe de lasers. Para determinar o perfil do feixe de lasers utiliza-se o método borda-da-lâmina (knife-edge), relacionando o deslocamento da lâmina posicionada transversalmente ao feixe, com a energia transmitida. Obstruindo o feixe com uma lâmina opaca, obtêm-se a variação da energia do feixe em função da posição da lâmina. Esta variação representa a integral do perfil Gaussiano do feixe. Para a automação do sistema foi empregado o programa Labview (National Instruments). O funcionamento do protótipo mostrou-se eficiente na caracterização de feixes laser e com uma instrumentação de baixo custo para a comercialização nacional. No entanto, apresentou-se lento na aquisição de dados, tornando a tarefa de caracterização do laser mais demorada. Fatores como velocidade do motor de passo e linguagem de programação contribuíram para tornar a aquisição lenta. / The demand for quality in the applications involving laser radiation demanded improvements in its performance. Faster equipments in the measures of its parameters are indispensable. In the areas where the laser is employee, three parameters are important in its applications: (1) power or energy, (2) frequency and (3) beam spatial. The determination of the edges, i. e., the width of the beam, is correlated to a percentage of the maximum reached energy. This parameter, together with the energy, determines beam density; beyond this parameter it also possible to determine the divergence and quality factor (M2). This work searches to develop a system of bi-dimension translation that can be used in the spatial characterization of laser beam. To determine the profile of laser beam it is used the knife-edge method, that it relates the displacement of the blade located transversally to the beam, with the transmitted energy. Blocking the beam with a blade the energy variation of the beam is correlated with blade position; this variation represents the integral of the beam Gaussian profile. For the automation it will be used the Labview program(National Instruments). The prototype had showed to be efficient in the characterization of laser beams and a low cost for national commercialization; however was slow in the data acquisition resulting a longer time to acquire the laser parameters. Instrumental components as step motors or programming language had contributed to slowly acquisition.

A demanda por qualidade nas aplicações envolvendo radiação laser exigiu melhorias no seu desempenho. Conseqüentemente, equipamentos mais rápidos e precisos nas medidas dos seus parâmetros são indispensáveis. Nas áreas onde o laser é empregado, três parâmetros sobressaem-se nas suas aplicações: (1) potência ou energia, (2) freqüência e (3) comprimento espacial ou largura do feixe. A determinação das bordas, isto é, da largura do feixe, está ligada a um percentual do máximo valor atingido pela energia. O diâmetro do feixe, juntamente com a energia, determina-se a densidade do feixe. Outros parâmetros como: divergência e fator de qualidade (M2), podem ser determinados também. O presente trabalho busca desenvolver um sistema de translação bidimensional que possa ser empregado na caracterização espacial do feixe de lasers. Para determinar o perfil do feixe de lasers utiliza-se o método borda-da-lâmina (knife-edge), relacionando o deslocamento da lâmina posicionada transversalmente ao feixe, com a energia transmitida. Obstruindo o feixe com uma lâmina opaca, obtêm-se a variação da energia do feixe em função da posição da lâmina. Esta variação representa a integral do perfil Gaussiano do feixe. Para a automação do sistema foi empregado o programa Labview (National Instruments). O funcionamento do protótipo mostrou-se eficiente na caracterização de feixes laser e com uma instrumentação de baixo custo para a comercialização nacional. No entanto, apresentou-se lento na aquisição de dados, tornando a tarefa de caracterização do laser mais demorada. Fatores como velocidade do motor de passo e linguagem de programação contribuíram para tornar a aquisição lenta. / The demand for quality in the applications involving laser radiation demanded improvements in its performance. Faster equipments in the measures of its parameters are indispensable. In the areas where the laser is employee, three parameters are important in its applications: (1) power or energy, (2) frequency and (3) beam spatial. The determination of the edges, i. e., the width of the beam, is correlated to a percentage of the maximum reached energy. This parameter, together with the energy, determines beam density; beyond this parameter it also possible to determine the divergence and quality factor (M2). This work searches to develop a system of bi-dimension translation that can be used in the spatial characterization of laser beam. To determine the profile of laser beam it is used the knife-edge method, that it relates the displacement of the blade located transversally to the beam, with the transmitted energy. Blocking the beam with a blade the energy variation of the beam is correlated with blade position; this variation represents the integral of the beam Gaussian profile. For the automation it will be used the Labview program(National Instruments). The prototype had showed to be efficient in the characterization of laser beams and a low cost for national commercialization; however was slow in the data acquisition resulting a longer time to acquire the laser parameters. Instrumental components as step motors or programming language had contributed to slowly acquisition.

International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper details the interaction of a small satellite with a space network and estimates the number of contacts and duration of contacts between the small, spin-stabilized satellite and a TDRS satellite. The simulations were performed using Satellite Tool Kit (STK) version 3.0, an orbital analysis software program. STK was configured for the four vehicles representing the spin-stabilized satellite and three TDRS satellites, TDRS East, West, and TDRS Zone of Exclusion. A set of simulations were run in which the spinstabilized satellite was given orbital elements corresponding to an orbital altitude between 600 km and 1200 km. The orbital inclination angle for the set of simulations was also varied from 20° through 100° along with the antenna cone angle of 10° through 40° to account for the effective beamwidths. In each of the simulations, the access to each TDRS satellite in the SN constellation was examined as a function of orbital altitude, orbital inclination angle, and antenna cone angle.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis describes the second project relating to the development of a SONAR (SOund Navigation And Ranging) object detection and collision avoidance system for use on an AUV (Autonomous Underwater Vehicle) at Stellenbosch University. The main goal is to develop and test techniques that make use of the existing SONAR laboratory platform and wide-beam SONAR transducers to detect and locate objects and their limits/bounds under water in the horizontal plane. The results of the work done show that it is possible to use wide-beam transducers to locate the centroid and edges of a flat target with an error that is significantly smaller than the beam-width. The techniques developed will enable the development of a cost-effective SONAR system that can be implemented on an AUV. / AFRIKAANSE OPSOMMING: Hierdie tesis beskryf the tweede projek rakende die ontwikkeling van ’n SONAR voorwerp opsporings en botsingvermydingstelsel vir gebruik op ’n OOV (Outonome Onderwater Voertuig) aan die Universiteit van Stellenbosch. Die hoofdoel is om tegnieke te ontwikkel en te toets wat gebruik maak van die bestaande SONAR laboratorium opstelling en wye-straal SONAR opnemers om die posisie van voorwerpe onder water te bepaal, sowel as die posisie van die voorwerp se rande in die horisontale vlak. Die resultate van die werk wat gedoen is wys dat dit moontlik is om wye-straal opnemers te gebruik om die posisie van die sentroïde en rande van ’n plat voorwerp te vind met ’n fout wat aansienlik kleiner is as die straal-wydte. Die tegnieke wat ontwikkel is sal ons in staat stel om ’n koste-effektiewe SONAR stelsel te ontwikkel wat op ’n OOV geïmplenteer kan word.

No description available.

Les études montrent généralement que la partie radio est l'une des plus grandes sources de consommation d'énergie dans un nœud de capteur. Cette source de consommation est directement liée au type d’antenne utilisé sur le module radio du nœud. Or, nombre de nœuds de capteurs sans fil sont généralement équipés d'antennes omnidirectionnelles provoquant ainsi un gaspillage de l'énergie dû à leur rayonnement. Face à un tel constat, ce mémoire présente des systèmes d'antennes directives et reconfigurables dédiés à ces nœuds capteurs en lieu et place des antennes omnidirectionnelles pour pallier à cette perte d’énergie. Il s’agit de petites antennes qui doivent respecter pleinement la gamme de fréquences nécessaire pour fonctionner correctement, mais aussi, dont le rayonnement peut être modifié en utilisant des composants actifs peu gourmands en énergie avec un contrôle actif qui doit également être simple. La première solution proposée est une solution antennaire directive inspirée d'une antenne imprimée Yagi/Uda dans la bande ISM-2,4 GHz. Elle offre, en simulation, un gain élevé avec une valeur de 7,3dB et un angle d’ouverture à -3dB de 57 ° dans le plan azimutal. La deuxième solution proposée est une antenne à plusieurs faisceaux (six) possibles dans le plan azimutal. Celle-ci se compose de six monopôles identiques, ayant chacun un port d’alimentation. De par la sélection du port alimenté, un diagramme directif de gain simulé de 4,6 dB et d’angle d’ouverture à -3dB de 55° est obtenu, permettant ainsi une couverture globale du plan azimutal. De plus, une carte électronique dotée d’un switch de type SP6T dédiée à cette antenne a été conçue pour contrôler ces six diagrammes de rayonnement de manière automatique. Afin de réduire le nombre d'éléments rayonnants tout en améliorant les performances radio électriques obtenues, une troisième solution a été proposée. Elle se compose d'un monopôle alimenté et d'un monopôle parasite chargé par une inductance de 9,6 nH. La nature et la valeur de la charge ont été obtenues en utilisant les équations d'Uzkov qui permettent de calculer les coefficients de pondérations dans le cas de deux antennes monopôles alimentées séparément afin de maximiser le gain et la directivité dans une direction privilégiée. Contrairement à l’usage de la carte électronique pour le contrôle de diagramme de rayonnement dans le cas de la structure antennaire à six monopôles, l’aspect reconfigurable en diagramme est obtenu dans ce cas en utilisant des éléments réflecteurs et directeurs activés par des diodes PIN. Elle procure en simulation un gain maximal de 5,2 dB en azimut pour un angle d’ouverture à -3dB de 52°, dans les directions 90° et 270° selon les diodes sélectionnées. Enfin, une application directe de cette structure est proposée pour couvrir plus de deux directions en azimut. Elle consiste en un ensemble de quatre monopôles dans lequel deux d’entre eux sont alimentés et les deux autres sont chargés par des inductances identiques. Il est capable de diriger son rayonnement dans le plan azimutal couvrant des directions sur 360 ° (0 °, 90 °, 180 ° et 270 °). Le gain total réalisé simulé est de 4 dB pour chaque diagramme de rayonnement dans le plan azimutal avec un angle d’ouverture à 3dB d’environ 60°. Des campagnes de mesures ont été effectuées pour chacune des antennes présentées dans ce mémoire. L’indicateur de la puissance du signal reçu (RSSI) a été la grandeur métrique utilisée pour quantifier les performances des antennes proposées. Suite à ces campagnes, nous avons pu remarquer que l’utilisation d’antennes directives seules, améliorant la portée de communication entre deux nœuds de capteurs s’avère insuffisante dans le cas d’un déploiement aléatoire de nœuds capteurs. / Studies have shown that the communication subsystem is one of the greatest sources of energy consumption in wireless sensor networks. This subsystem is directly bounded to the type of antenna used on the radio module. Several sensor nodes are equipped with omnidirectional antennas leading to a waste of energy due to the shape of their beam. Instead of using omnidirectional antennas, directive and reconfigurable antennas system dedicated to wireless sensor networks are presented in this work so as to alleviate the waste of energy. On one hand, such dedicated antennae should be small in size and particularly designed by taking into consideration the frequency bandwidth of the node. On the other hand, their radiation pattern should also be reconfigurable by using powerless active components with a simple active control. To reach these objectives, we have in a first time proposed a directive solution inspired of a Printed-Yagi antenna in the ISM band (2.4-2.485) GHz. It provides high gain with a value of 7.3dB and a half power beam width BW−3dB of 57° in the azimuth plane. Secondly, we have proposed a multiple directional antenna in the ISM band. This antenna consists of six identical monopole antennas arranged in the same structure, having each one feeding port. Due to the selection of each feeding port, the proposed antenna covers the whole azimuthal plane with a simulated beam of 4.6 dB along with a half power beam width BW−3dB of 55°. Moreover, an electronic card equipped with an SP6T switch dedicated to that antenna has been developed to control the radiation pattern of the six identical antennas automatically. Willing to reduce the number of radiating elements while enhancing the radio performance, a third antenna has been proposed. It consists of a fed monopole and a loaded parasitic one having an inductance component of 9.6nH. The nature and the value of this inductance are obtained using the Uzkov equations that calculate the current weighting coefficients in the case of two separately fed antennas to maximize the gain and the directivity in the desired direction. Contrary to the use of electronic card in the control of radiation pattern prior to the conception of the third antenna, the reconfigurable aspect is obtained by using reflectors and director’s elements activated by PIN diodes. It offers a maximum gain of 5.2 dB in simulation at 2.4GHz along with a half power beam width BW−3dB of 52°, in both the 270° and +90° azimuthal directions depending on the selection of the set of PIN diodes. Finally, a straight application of this structure has been proposed in order to cover more than two directions in the azimuth plane. It is an array of four monopole antennas in which two of them are fed and the two others are loaded. Such antenna is capable to steer its radiation pattern in the azimuth plane covering 360° directions (0°, 90°, 180° and 270°). The achieved simulated realized total gain is 4 dB for each radiation pattern in the azimuth plane along with a half power beam width of about 60°. Measurement campaign test has been carried out for each proposed antenna in this work. During these measurements, the received signal strength indicator (RSSI) has been the paramount value to estimate the antenna performance in connection with the sensor node. Following this measurement campaign, we have been able to notice that the use of only directive antennas is not sufficient in a random deployment of sensor nodes. Hence, the reconfigurable aspect of the beam pattern by use of powerless active components should be taken into consideration. Such kind of antennas provide an improvement of the RSSI, which is a key factor in the reduction of collisions drastically on one hand, and on the other hand related to a reduction of power consumption