L'objectif de cette thèse est de trouver la forme optimale d'une antenne planaire ou d'un réseau d'antennes planaires à partir de contraintes imposées (diagramme de rayonnement, gain ou directivité) ou de reconstruire la forme à partir de mesures expérimentales. L'algorithme d'optimisation développé est basé sur une méthode de type gradient et la reconstruction des contours par une méthode d'ensembles de niveaux (Level Sets) ou "contours actifs". Le problème direct est résolu en utilisant une formulation intégrale du problème électromagnétique et une méthode d'éléments finis pour la discrétisation. Le gradient de forme est calculé en utilisant deux méthodes différentes. Tout d'abord, une méthode par différences finies basée sur la dérivée à un nœud du maillage, pour une modification infinitésimale des éléments triangulaires du contour, suivant la direction de la normale extérieure. La deuxième méthode est basée sur le gradient topologique pour le calcul de la déformation des contours. Une méthode d'ensembles de niveaux avec bande étroite a été développée pour faire évoluer le contour des antennes utilisant la vitesse de déformation calculée à partir du gradient de forme. Différentes configurations d'antennes et réseaux d'antennes planaires ont été utilisées pour étudier les performances de l'algorithme d'optimisation. Des techniques de type saut de fréquence et multifréquence ont été utilisées pour optimiser la forme dans une bande de fréquence. L'optimisation de forme pour la miniaturisation d'antennes planaires concerne de nombreuses applications, en particulier, pour les réseaux réflecteurs / The objective of this thesis work is to find the optimal shape of planar antenna elements and arrays from imposed constraints (e.g. desired or imposed radiation patterns, gain or directivity) or to reconstruct the shape from experimental measurements. The optimization algorithm is based on the gradient-type method and an active contour reconstruction by means of the Level Set method. The forward problem is solved using an integral formulation of the EM problem with finite element discretization. The shape gradient is computed using two different methods: one is finite differential method based on nodal point mesh derivation with an infinitesimal modification of the triangular elements on the contour along the outward normal direction, another the topological shape gradient, which is computed based on a topological deformation on a contour. A narrow band level set method has been developed to evolve the contour of antennas and arrays using the deformation velocity computed from the shape gradient. Different configurations of antennas and antenna arrays are studied for investigating the performance of the optimization algorithm. Frequency hopping and multi-frequency techniques have been used for optimizing the shape within a frequency band. Shape optimization for planar antenna miniaturization has a large number of applications, particularly, for reflectarrays

Made available in DSpace on 2014-12-17T14:55:20Z (GMT). No. of bitstreams: 1 ValdezAAF_TESE.pdf: 2001050 bytes, checksum: d0f0b88178102c3f48880303c1c6d765 (MD5) Previous issue date: 2014-03-12 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to show how the application of frequency selective surfaces (FSS) in planar antenna arrays become an alternative to obtain desired radiation characteristics from changes in radiation parameters of the arrays, such as bandwidth, gain and directivity. In addition to analyzing these parameters is also made a study of the mutual coupling between the elements of the array. To accomplish this study, were designed a microstrip antenna array with two patch elements, fed by a network feed. Another change made in the array was the use of the truncated ground plane, with the objective of increasing the bandwidth and miniaturize the elements of the array. In order to study the behavior of frequency selective surfaces applied in antenna arrays, three different layouts were proposed. The first layout uses the FSS as a superstrate (above the array). The second layout uses the FSS as reflector element (below the array). The third layout is placed between two FSS. Numerical and experimental results for each of the proposed configurations are presented in order to validate the research / Este trabalho tem como objetivo apresentar como a aplica??o de superf?cies seletivas em frequ?ncia (FSS) em arranjos de antenas planares se torna uma alternativa interessante para se obter caracter?sticas de radia??o desejadas, a partir de altera??es em par?metros de radia??o dos arranjos, tais como largura de banda, ganho e diretividade. Al?m de analisar esses par?metros, tamb?m ? feito o estudo do acoplamento m?tuo entre os elementos do arranjo. Para realizar tal estudo, foi projetado um arranjo de antenas de microfita, com dois elementos do tipo patch, alimentado por uma rede de alimenta??o. Outra modifica??o feita no arranjo foi a utiliza??o do plano de terra truncado, com o objetivo de aumentar a largura de banda e miniaturizar os elementos do arranjo. Para poder estudar o comportamento das superf?cies seletivas em frequ?ncia aplicadas em arranjos de antenas, foram propostos tr?s layouts diferentes. O primeiro layout consiste em utilizar a FSS como superstrato (acima do arranjo). O segundo consiste em utilizar a FSS como elemento refletor (abaixo do arranjo). O terceiro layout consiste em colocar o arranjo entre duas camadas de FSS, tanto em cima quanto abaixo. Resultados num?ricos e experimentais para cada uma das configura??es propostas s?o apresentados