This thesis investigates the variations of electrical properties of linear antennas mounted on certain platforms, depending on the physical properties of that platform. In this respect, related basic antenna simulations, electromagnetic simulations from primitive to complex models of airframes, and scale model measurements were used. Firstly, electrical properties of monopoles at known environment were examined and basic analyses were performed via an electromagnetic simulation tool, named CST Microwave Studio&reg / . In addition, important aspects of simulation tool were investigated. Then, an F-4 aircraft model was used to observe the electrical characteristics of antennas mounted on it. Using 3D model of F-4 aircraft, realistic antenna placement points were assigned and monopoles were attached to those points. Alternatively, a simplified F-4 model was also used and for two different models, identical simulations were done, followed by accuracy and performance analysis between the results obtained from simplified and exact models. As the outcome of these simulations, certain parameters like impedance, antenna-to-antenna coupling and radiation pattern values were examined. Additionally, change in antennas&rsquo / electrical characteristics due to their position over the airframe was investigated. In addition, a 1:10 down-scaled and copper-plated F-4 aircraft model was obtained and equipped with identical antennas. By using the measurements done on this scale model, antenna-to-antenna coupling results of MWS&reg / were verified by measurements. Finally, advantages and disadvantages of using electromagnetic simulation tools and scale model measurements for such antenna studies were discussed.

Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB (A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been confirmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB (A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to confirm the applicability of such protections to efficiently decrease noise exposure in urban areas

Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB(A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been con firmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB(A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to con rm the applicability of such protections to efficiently decrease noise exposure in urban areas.

Le bruit est devenu une nuisance importante en zone urbaine au point que selon l'Organisation Mondiale de la Santé, 40% de la population européenne est exposée à des niveaux de bruit excessifs, principalement dû aux transports terrestres. Il devient donc nécessaire de trouver de nouveaux moyens de lutter contre le bruit en zone urbaine. Dans ce travail, on étudie une solution possible à ce problème: un écran bas antibruit. Il s'agit d'un écran de hauteur inférieure à un mètre placé près d'une source, conçu pour réduire le niveau de bruit pour les piétons et les cyclistes à proximité. Ce type de protection est étudié numériquement et expérimentalement. Nous nous intéressons particulièrement aux écrans adaptés au bruit du tramway puisque dans ce cas les sources sont proches du sol et peuvent être atténuées efficacement. La forme ainsi que le traitement de surface de l'écran sont optimisés par une méthode de gradient couplée à une méthode 2D d'éléments finis de frontière. Les variables à optimiser sont les coordonnées de nœuds de contrôle et les paramètres servant à décrire l'impédance de surface. Les sensibilités sont calculées efficacement par la méthode de l'état adjoint. Les formes générées par l'algorithme d'optimisation sont assez irrégulières mais induisent une nette amélioration par rapport à des formes simples, d'au moins 5 dB (A). Il est également montré que l'utilisation de traitement absorbant du côté source de l'écran peut améliorer la performance sensiblement. Ce dernier point est confirmé par des mesures effectuées sur modèle réduit. De plus, un prototype à l'échelle 1 d'écran bas antibruit a été construit et testé en conditions réelles, le long d'une voie de tramway à Grenoble. Les mesures montrent que la protection réduit le niveau de 10 dB (A) pour un récepteur proche situé à hauteur d'oreilles. Ces résultats semblent confirmer l'applicabilité de ces protections pour réduire efficacement le bruit en zone urbaine / Noise has become a main nuisance in urban areas to the point that according to the World Health Organization 40% of the European population is exposed to excessive noise levels, mainly due to ground transportation. There is therefore a need to find new ways to mitigate noise in urban areas. In this work, a possible device to achieve this goal is studied: a low-height noise barrier. It consists of a barrier typically less than one meter high placed close to a source, designed to decrease the noise level for nearby pedestrians and cyclists. This type of device is studied both numerically and experimentally. Tramway noise barriers are especially studied since the noise sources are in this case very close to the ground and can therefore be attenuated efficiently. The shape and the surface treatment of the barrier are optimized using a gradient-based method coupled to a 2D boundary element method (BEM). The optimization variables are the node coordinates of a control mesh and the parameters describing the surface impedance. Sensitivities are calculated efficiently using the adjoint state approach. Numerical results show that the shapes generated by the optimization algorithm tend to be quite irregular but provide a significant improvement of more than 5 dB (A) compared to simpler shapes. Utilizing an absorbing treatment on the source side of the barrier is shown to be efficient as well. This second point has been confirmed by scale model measurements. In addition, a full scale low height noise barrier prototype has been built and tested in situ close to a tramway track in Grenoble. Measurements show that the device provides more than 10 dB (A) of attenuation for a close receiver located at the typical height of human ears. These results therefore seem to confirm the applicability of such protections to efficiently decrease noise exposure in urban areas