The design and use of metamaterials have shown exciting applications in electrical engineering, physics, optics, and other science fields that are expanding our physical understanding and leading to unprecedented performance of many standard devices such as antennas, microwave circuits, and sensors. The manufacturing of metamaterials, while ingenious, has typically been exotic and depended on the inclusion of sub-wavelength particles in a host medium to tailor the effective characteristics of a material. This work verifies a much more simple approach to realizing a kind of metamaterial, the epsilon-near-zero (ENZ) metamaterial. The intriguing aspect of this metamaterial is that while it is simple to realize, it is a novel approach to many practical applications such as the tunneling energy through highly discontinuous bends and abruptions, cloaking of sensors, miniaturization of microwave components, and design of highly directive antennas. Further, the physics and mathematical formulation of these ENZ materials is both intriguing and counterintuitive. / text

Afin de répondre aux besoins croissants d’équipements de communication pour les applications spatiales, il est important de réduire, le plus possible, la taille et la masse de l’équipement des satellites. Cela conduit à une réduction des coûts de lancement des satellites sur leur orbite ou laisse la possibilité d’ajouter des équipements dans la fusée. Ceci compte aussi pour les composants radioélectriques. L’objectif étant de réduire les dimensions sans pour autant détériorer les performances en rayonnement (directivité, polarisation croisée, bande monomode, etc.). Il est possible de contrôler la propagation des ondes électromagnétiques dans les antennes cornets et les guides d’onde à l’aide de surfaces anisotropes (corrugations, métamatériaux). Ainsi, contrairement à ce que prédisent les lois physiques sur la propagation et le rayonnement d’ondes électromagnétiques dans des structures classiques, les performances des structures à parois anisotropes peuvent être radicalement améliorées : pour le guide d’onde, réduction de la fréquence de coupure ; pour l’antenne cornet, amélioration de la directivité ou réduction du niveau des lobes secondaires. D’après l’état de l’art, même si les résultats de simulations et de mesures obtenus sont très prometteurs, le dimensionnement de la structure des métamatériaux est sujet à optimisation, donc gourmand en ressources informatiques. L’apport principal de cette thèse a été de développer une nouvelle méthodologie de conception s’appuyant sur une Théorie Modale Elargie (TME) analytique pour des guides d’onde à parois anisotropes. Elle permet de dimensionner très rapidement des surfaces à métamatériaux les plus adaptées aux applications requises. Un prototype de guide d’onde et un prototype d’antenne ont été conçus, fabriqués et mesurés grâce à cette méthodologie. Les résultats obtenus démontrent l’intérêt, l'efficacité et le caractère général de la méthode proposée pour la conception de dispositifs hyperfréquences guidés à parois anisotropes. / In space applications, one of the biggest challenges is to reduce the size and mass of equipment, in order to reduce the costs of the rocket launch. For RF components, this has to be done without lowering RF performance (directivity, crosspolarization, single-mode bandwidth, etc.). The challenge is all the more problematic in the case of used horn antennas and waveguides because of their relatively large size. It has been shown that the use of anisotropic surfaces (i.e. corrugations and metamaterials) on the inside walls of guided RF structure makes it possible to influence and control the way electromagnetic waves travel, enabling new devices with radically different and improved performances : for waveguides, reduction of the cuto&# 64256; frequency ; for horn antennas, improvement of the directivity or a reduction of the side lobes. A state of the art of previous work done on metamaterial horn antennas pointed out that, even if the obtained and presented results seem very promising, the procedure to obtain the optimized RF structure is very time-consuming and requires considerable computer resources. The main contribution of this PhD work was to develop a new methodology based on the analytical Modal Expansion Theory (MET) for waveguides with anisotropic walls. This methodology makes it possible to optimize very rapidly the dimensions of the metamaterial surfaces adjusted to the required application. A metamaterial waveguide and antenna prototype have been designed, realized and measured thanks to this methodology. The results obtained demonstrate the usefulness, effectiveness and general applicability of the method developed for the design of RF structures with anisotropic walls.

This thesis is focused on a wireless link operating in 60 GHz frequency band. In this band, the attenuation due to resonance of oxygen is high. Thanks to this property, we are able to ensure a proper insulation of communication links working in two close bands. The document compares commercially available modules of offered by different manufacturers for the operation in this band. The design, the simulation and the fabrication of a antenna and its feeder are described in the next part of the thesis. The system is fabricated using a SIW technology.

This master's thesis deals with a design of a planar parabolic reflector antenna. The thesis is divided into several parts. The first section is dedicated to the theory of the parabolic antenna design and a basic introduction of the SIW technology which is used for the realization of an antenna prototype. The second chapter deals with the design of individual parts of the antenna (i. e. a primary and secondary reflector and an antenna feeder excited by a waveguide) for particular assignment. The third part is focused on modeling the designed antenna using ANSYS HFSS. Other parts of the thesis include a conversion of the proposed antenna to the SIW technology and a design of a transition between the antenna and a feeding waveguide WR15. The last part of the thesis deals with measuring of the reflection coefficient and the radiation pattern of the fabricated antenna prototype.

The thesis deals with broadband antennas for measurement purposes. A ridged horn antenna has been selected for this concept, designed for the frequency range 0.9 GHz to 9 GHz. This work contains general theoretical description of antennas and further it focuses on a specific design of the ridged horn antenna, beginning with the calculation of its dimensions, modeling and optimization to obtain desired antenna properties. Finally, the antenna was constructed and measured. The reflection factor s11

The thesis deals with the design and realization of a horn antenna for electromagnetic compatibility measurement. First it focuses on general theory of antennas, than it focuses more on horn antennas and their design. Second part deals with description of antenna realization and comparison of simulated results.

Afin de répondre à la demande croissante de nouveaux services, les objets que nous utilisons au quotidien (les smartphones, les voitures, les avions, etc.) tendent à intégrer de plus en plus de systèmes radio tandis que l’espace disponible pour l’intégration de ces éléments est de plus en plus réduit. Ces systèmes radio nécessitent l’utilisation de plusieurs antennes devant répondre à des critères de compacité, d’isolation, de coût, etc. À titre d’illustration, un smartphone contient plusieurs antennes pour assurer des fonctions telles que la téléphonie, la navigation, la connexion à internet par WiFi, les liaisons Bluetooth, la technologie NFC (Near-Field Communications) et ce nombre tend à s’accroitre considérablement avec l’émergence de nouveaux services. Le même phénomène se retrouve également au niveau des plateformes aéroportées où des fonctions telles que la communication, la navigation, le radar, etc. sont utilisées. Cela conduit donc à la nécessité de réduire le nombre d’antennes en regroupant par exemple plusieurs fonctions au sein d’une même et unique antenne. Dans de précédents travaux de recherches, J. Euzière a démontré la possibilité de combiner une fonction radar et une seconde fonction (ici de communication) en utilisant un réseau de 16 monopoles initialement dédié au seul radar, grâce au Time Modulated Array (TMA). De cette façon, les deux fonctions utilisaient la même fréquence et étaient alimentées par une seule source. L’objectif principal de cette thèse est de proposer une solution d’antenne multifonction pour radar et communication encore plus compacte (constituée d’une seule antenne). L’idée est de partir d’une solution antennaire déjà existante et d’y apporter les modifications nécessaires à l’ajout d’une seconde fonction, sans pour autant augmenter la surface de l’antenne ni la complexité du système. / In order to respond to the increasingly demand of new services, the objects we use on a daily basis (such as mobile phones, cars, airplanes etc.), tend to integrate more and more radio systems while the space available is limited. These radio systems require the use of many antennas that must meet multiple requirements such as compactness, isolation, costs, etc. A smart-phone, for example, contains several antennas for global navigation satellite system (GNSS), WiFi, TV, FM radio, Bluetooth, near-field communications (NFC) and the number is expected to increase as new systems are added. Another example is in airborne platforms where multiple functions such as communication, navigation, radar, electronic warfare are used. This leads to the need of reducing the number of associated antennas by regrouping several radio functions into a single antenna. However, combining the functionality of several antennas into one shared radiating element while maintaining the functionality of the various radio systems presents a great challenge. During its Ph.D, J. Euzière demonstrated the possibility to combine a radar function and a secondary function from a 16-monopole array originally dedicated to radar operation by using Time Modulated Array (TMA) technique. By this way, the two functions were operating at the same frequency and the system was powered by a single source.The main objective of this thesis is to propose a more compact antenna (a single antenna) dedicated to radar and communication operations instead of using antenna array as J. Euzière did it. The idea is to start from an existing antenna solution and make the necessary modifications to add a second function without adding additional surface and complexity. As we are interested in radar applications, we will choose a directive antenna: a horn antenna. The goal is then to study the possibility to modify the radiation pattern of the horn antenna through controllable elements (slots) and to transmit a direct modulated signal at the antenna level for the communication function. Furthermore, polarization diversity is an attractive way to increase the isolation between two applications. Thus, this aspect will be taken into account in the design of the antenna solution.

It is well known that quad-ridged horn antennas in general have impedance and radiation characteristics that are significantly worse than that of their double-ridged counterparts. Normally a voltage standing wave ratio (VSWR) of 3 over the operational bandwidth is used for the design specification of quad-ridged horn antennas. The bandwidth of operation is severely restricted due to the excitation of higher order modes in the co-axial to waveguide transition of the antenna. The higher order modes cause a break-up in the radiation pattern of the antenna and large dips in the boresight gain. The performance of the quad-ridged horn antenna with pyramidal sidewalls is improved by separating the antenna into the transition and flared horn sections, and optimizing these sections individually. It is shown that a transition section with a pyramidal cavity and steps, and a flared horn section with an exponential profile with a circular segment for the ridges deliver the best performance. These configurations for the transition and flared horn sections are combined in the complete antenna. The optimized antenna has a 12.5:1 operational bandwidth with improved performance in terms of the VSWR, the coupling between the ports and the boresight gain. A prototype of this antenna is manufactured. Good agreement between the measured and simulated performance is achieved. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / unrestricted

With global warming on the rise and the urge for conserving our natural resources, it becomes very important that proper steps are taken to protect our natural resources and utilize them efficiently. Forest fires are one of the many issues on the charts towards protection of natural resources. The catastrophic aftermaths caused by forest fires are known to all. The causes for these fires could be known/unknown natural causes or human intervention. Remote sensing techniques use the electromagnetic radiation in the RF/Microwave region, emitted from an object. The amount of energy emitted from an object depends on its present conditions, primarily its temperature and its emissivity. The sensing devices used in such measurements are classified into active and passive sensors. Herein, passive radiometry is used to investigate a model for the propagation of subsurface radiation from underground forest fires through upper ground layers of soil till the land-air interface. Passive radiometry involves capturing the radiation incident on a radiometer antenna aperture directly or deflected from several objects. The energy emitted from sources above 0K is collected and is compared with the calibration standards to estimate the physical quantity under test. Detecting forest fires is one of the potential applications of passive radiometry investigated here.

Yes / In this paper, a pyramidal horn antenna loaded with unit cell of metamaterial is proposed, designed and realized for L-band that including terrestrial digital audio broadcasting TDAB, GPS and GSM. The proposed antenna operates in the frequency range from 1.722 GHz to 1.931 GHz. The metamaterial is fabricated on a printed circuit board as Capacitive Loaded Loop (CLL). The work aims to exhibit the advantage of metamaterial loaded inside the horn antenna in terms of the gain enhancement of the radiation pattern and the resonant frequency shift towards lower frequency. The retrieval technique used show that the constitutive parameters of the unit cell as CLL have a zero index metamaterial (ZIM) from 1.34 GHz to 1.49 GHz and a near zero index of refraction from 1.495 GHz to 2 GHz, which is within the operating frequency of the horn antenna. The achieved results show that the total gain is improved over the frequency range. The simulation and the measurement are in good agreement.