Programa de Pós-Graduação em Engenharia Elétrica e de Computação
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Doctoral Thesis Caracterização de superfícies seletivas de frequência de periódicas e não-periódicas(Universidade Federal do Rio Grande do Norte, 2014-12-15) Araújo, Lincoln Machado de; D'Assunção , Adaildo Gomes; ; http://lattes.cnpq.br/4159638862269940; ; http://lattes.cnpq.br/2266045393321248; Gomes Neto, Alfredo; ; http://lattes.cnpq.br/1403715441701958; Cavalcante, Gervasio Protásio dos Santos; ; http://lattes.cnpq.br/2265948982068382; Lins, Hertz Wilton de Castro; ; http://lattes.cnpq.br/7712686175574736; Mendonça, Laércio Martins de; ; http://lattes.cnpq.br/1853488415531363The past years have seen a great interest in the use of frequency selective surfaces (FSS), as spatial filters, in many microwave applications. Among these, we highlight applications in telecommunication systems (such as satellite communications and radar), high gain antennas (combined with planar antennas) and (home and industrial) microwave ovens. The FSS is usually composed of two-dimensional periodic arrays, with equally spaced elements, which may be metallic patches (printed on dielectric substrates) or aperture (holes in thin metal surfaces). Using periodic arrays, the FSS have been able to meet the demands of the telecommunications industry. However, new demands are finding technological limitations. In this context, adverse filtering requirements have forced designers to use FSS optimization methods to find specific formats of FSS elements. Another alternative that has been used to increase the selectivity of the FSS is the cascaded FSS, a simple technique that has as main drawback the increased dimensions of the structure, as well as its weight. This work proposes the development of a new class of selective surfaces frequency (FSS) composed of quasi-periodic (or non-periodic) arrangements. The proposed FSS have no array periodicity, in relation with the spatial position of their elements. The frequency responses of these structures were simulated using commercial softwares that implement full-wave methods. For the purpose of validation of this study, FSS prototypes were built and measured, being possible to observe a good agreement between simulated and measured results. The main conclusions of this work are presented, as well as suggestions for future works.Master Thesis Análise teórica e experimental de superfícies seletivas de freqüência e suas aplicações em antenas planares(Universidade Federal do Rio Grande do Norte, 2009-08-13) Araújo, Lincoln Machado de; Campos, Antônio Luiz Pereira de Siqueira; ; http://lattes.cnpq.br/1982228057731254; ; http://lattes.cnpq.br/2266045393321248; Martins, Ronaldo de Andrade; ; http://lattes.cnpq.br/0978273656336966; Silva, Jefferson Costa e; ; http://lattes.cnpq.br/7399512856151138; Silva, Paulo Henrique da Fonseca; ; http://lattes.cnpq.br/0656625630248917This work presents a theoretical and numerical analysis of structures using frequency selective surfaces applied on patch antennas. The FDTD method is used to determine the time domain reflected fields. Applications of frequency selective surfaces and patch antennas cover a wide area of telecommunications, especially mobile communications, filters and WB antennas. scattering parameters are obteained from Fourier Transformer of transmited and reflected fields in time domain. The PML are used as absorbing boundary condition, allowing the determination of the fields with a small interference of reflections from discretized limit space. Rectangular patches are considered on dielectric layer and fed by microstrip line. Frequency selective surfaces with periodic and quasi-periodic structures are analyzed on both sides of antenna. A literature review of the use of frequency selective surfaces in patch antennas are also performed. Numerical results are also compared with measured results for return loss of analyzed structures. It is also presented suggestions of continuity to this work