Programa de Pós-Graduação em Engenharia Elétrica e de Computação
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Doctoral Thesis Análise e projeto de antenas patch de microfita com substrato inspirado em arranjo EBG(2019-07-26) Andrade, Betoven Oliveira de; Mendonça, Laercio Martins de; ; ; D'Assunção, Adaildo Gomes; ; Campos, Antonio Luiz Pereira de Siqueira; ; Silva, José Patrocinio da; ; Andrade, Humberto Dionisio de; ; Araújo, Wellington Candeia de;After decades of the first publications on microstrip antennas, research and applications continue to expand. This is the consequence of several of its attractive features, especially the possibility of mounting in the same plane of the transceiver circuits. It turns out that this advantage causes some problems, for example, the waves produced by the circuits reflect and refract inside the substrate, since it has different refractive indexes, which causes surface currents in the earth plane, leading to a bandwidth narrower and also at lower radiation efficiency and low gain, since some of the energy is wasted. To solve such undesirable characteristics, several techniques have been investigated and employed, one of the most promising being the use of Electromagnetic Band-Gap (EBG) substrates. The EBG materials are periodic structures in a dielectric or conductive material. They propagate the electromagnetic waves at a frequency specific to all states of polarization and angles of incidence, offering pass-band and stop-band characteristics. Studies of new structures, techniques and equations for EBG materials in the form of periodic holes in the substrate are presented in this thesis. The objectives of this work consist of the following topics: (i) proposition of new antennas, including antennas with 3D printed substrates; (ii) proposal of antenna design, by means of adequate techniques of holes that result in the non-displacement of frequency, usually caused by change in the permittivity after insertion of the holes; (iii) proof that different geometric shapes of holes are not related to the variation of the resonance frequency; (iv) verifying that a nonconventional (non-cylindrical) geometry can promote efficiency improvements in design time; (v) application of an artificial neural network capable of improving the time to obtain return losses; (vi) proposition of low-cost techniques for the development of antennas with EBG substrate. The methodology of the research, theoretical reference and the analyze cited are presented throughout the work. The validations of the study proposals are presented through simulation results and prototype measurements.Master Thesis Estudo de arranjos de antenas de microfita com Patch quase-fractal para comunicações sem fio(Universidade Federal do Rio Grande do Norte, 2014-12-11) Andrade, Betoven Oliveira de; Mendonça, Laércio Martins de; ; http://lattes.cnpq.br/1853488415531363; ; http://lattes.cnpq.br/0826736246513218; D'Assunção, Adaildo Gomes; ; http://lattes.cnpq.br/4159638862269940; Silva, José Patrocinio da; ; http://lattes.cnpq.br/5753289728835624; Araújo, Wellington Candeia de; ; http://lattes.cnpq.br/7101691755497961In this dissertation, are presented two microstrip antennas and two arrays for applications in wireless communication systems multiband. Initially, we studied an antenna and a linear array consisting of two elements identical to the patch antenna isolated. The shape of the patch used in both structures is based on fractal geometry and has multiband behavior. Next a new antenna is analyzed and a new array such as initial structure, but with the truncated ground plane, in order to obtain better bandwidths and return loss. For feeding the structures, we used microstrip transmission line. In the design of planar structures, was used HFSS software for the simulation. Next were built and measures electromagnetic parameters such as input impedance and return loss, using vector network analyzer in the telecommunications laboratory of Federal University of Rio Grande do Norte. The experimental results were compared with the simulated and showed improved return loss for the first array and also appeared a fourth band and increased directivity compared with the isolated antenna. The first two benefits are not commonly found in the literature. For structures with a truncated ground planes, the technique improved impedance matching, bandwidth and return loss when compared to the initial structure with filled ground planes. Moreover, these structures exhibited a better distribution of frequency, facilitating the adjustment of frequencies. Thus, it is expected that the planar structures presented in this study, particularly arrays may be suitable for specific applications in wireless communication systems when frequency multiband and wideband transmission signals are required.