In this thesis, a low-profile, high-gain, ultra-wideband (UWB) planar dipole antenna is presented for radar imaging applications. The antenna is loaded with open complementary double concentric split-hexagonal-ring resonators (LC tank) and chip resistors, and backed with a novel double-layer FSS reflector for gain enhancement. A broadband microstrip to parallel-plate transformer is designed as the feeding structure of the antenna to provide impedance matching and balanced-to-unbalanced transition. The measurement results show the proposed antenna operates over the frequency bandwidth of 0.65-3.8 GHz with S11< -10 dB (VSWR) and smooth gains in the range of 6.2-9 dBi.

This thesis describes the development of antennas suitable for mobile coinmunication systems based on a dielectric rod antenna fed from circular waveguide. Pattern control of the antenna is implemented using a combination of Frequency Selective Surface (FSS) elements and metallic endcaps placed on the antenna Both linear and circular polarised feeds have been made for these antennas to ensure they are suitable for a wide range of applications. The suitability of the dominant and next, higher order, waveguide mode were investigated and conclusions drawn as to their suitability for this type of antenna. The antennas were extensively modelled using a commercial TLM based solver and the results of these simulations were compared to the comprehensive set of antenna pattern measurements and S-parameter measurements obtained for the prototype antennas.

Made available in DSpace on 2014-12-17T14:56:20Z (GMT). No. of bitstreams: 1 FranciscoCGSS_Capa_ate_pag41.pdf: 9091246 bytes, checksum: 6f81612f5fd4ab8558666746d9be5489 (MD5) Previous issue date: 2014-06-05 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Frequency selective surfaces (Frequency Selective Surface - FSS) are often used in various applications in telecommunications. Some of these applications may require that these structures have response with multiple resonance bands. Other applications require that the FSS response have large frequency range, to meet the necessary requirements. FSS to design with these features there are numerous techniques cited in the scientific literature. Thus, the purpose of this paper is to examine some common techniques such as: Overlap of FSS; Elements combined; Elements Elements convolucionados and fractals. And designing multiband FSS and / or broadband selecting simple ways in terms of construction and occupy the smallest possible space, aiming at practical applications. Given these requirements, three projects FSS were performed: a technology applied to IEEE 802.11 a/b/g/n and two projects for application in UWB. In project development, commercial software Ansoft DesignerTM and experimental results were satisfactory was used / Superf?cies seletivas em frequ?ncia (Frequency Selective Surface - FSS) s?o usadas frequentemente em diversas aplica??es em telecomunica??es. Algumas dessas aplica??es podem exigir que essas estruturas tenham resposta com m?ltiplas bandas de resson?ncia. Outras aplica??es exigem que as FSS tenham resposta em faixa larga de frequ?ncia, para atender aos requisitos necess?rios. Para projetar uma FSS com essas caracter?sticas existem in?meras t?cnicas citadas na literatura cient?fica. Assim, o prop?sito deste trabalho ? analisar algumas t?cnicas utilizadas tais como: Sobreposi??o de FSS; Elementos combinados; Elementos convolucionados e Elementos fractais. E projetar FSS multibanda e/ou banda larga selecionando maneiras simples em termos de constru??o e que ocupem o menor espa?o poss?vel, visando aplica??es pr?ticas. Tendo em vista estes requisitos, foram realizados tr?s projetos de FSS: um aplicado a tecnologia IEEE 802.11 a/b/g/n e dois projetos para aplica??o em UWB. No desenvolvimento dos projetos, foi utilizado o software comercial Ansoft DesignerTM e os resultados experimentais se mostraram satisfat?rios

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