BDTD - Biblioteca Digital de Teses e Dissertações
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Master Thesis Arranjos Log-Periódicos Compactos em Microfita com Elementos Fractais de Koch(Universidade Federal do Rio Grande do Norte, 2010-06-14) Almeida Filho, Valdez Aragão de; D'assunção, Adaildo Gomes; ; ; http://lattes.cnpq.br/2356160324946863; Silva, Paulo Henrique da Fonseca; ; http://lattes.cnpq.br/0656625630248917; Souza, Rui Fragassi; ; http://lattes.cnpq.br/5359107500377040; Gomes Neto, Alfrêdo; ; http://lattes.cnpq.br/1403715441701958; Martins, Ronaldo de Andrade; ; http://lattes.cnpq.br/0978273656336966; Fontgalland, Glauco; ; http://lattes.cnpq.br/4256595317953538This work aims to present how the application of fractal geometry to the elements of a log-periodic array can become a good alternative when one wants to reduce the size of the array. Two types of log-periodic arrays were proposed: one with fed by microstrip line and other fed by electromagnetic coupling. To the elements of these arrays were applied fractal Koch contours, at two levels. In order to validate the results obtained some prototypes were built, which were measured on a vector network analyzer and simulated in a software, for comparison. The results presented reductions of 60% in the total area of the arrays, for both types. By analyzing the graphs of return loss, it was observed that the application of fractal contours made different resonant frequencies appear in the arrays. Furthermore, a good agreement was observed between simulated and measured results. The array with feeding by electromagnetic coupling presented, after application of fractal contours, radiation pattern with more smooth forms than the array with feeding by microstrip lineDoctoral Thesis Aplicação de superfícies seletivas em frequência para melhoria de resposta de arranjos de antenas planares(Universidade Federal do Rio Grande do Norte, 2014-03-12) Almeida Filho, Valdez Aragão de; Campos, Antônio Luiz Pereira de Siqueira; ; http://lattes.cnpq.br/1982228057731254; ; http://lattes.cnpq.br/2356160324946863; Mendonça, Laércio Martins de; ; http://lattes.cnpq.br/1853488415531363; Gomes Neto, Alfrêdo; ; http://lattes.cnpq.br/1403715441701958; Maniçoba, Robson Hebraico Cipriano; ; http://lattes.cnpq.br/4396628695466189This 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