Desenvolvimento teórico e experimental de FSS com elementos fractais de Gosper em estruturas de multicamadas

The fractal self-similarity property is studied to develop frequency selective surfaces (FSS) with several rejection bands. Particularly, Gosper fractal curves are used to define the shapes of the FSS elements. Due to the difficulty of making the FSS element details, the analysis is developed for elements with up to three fractal levels. The simulation was carried out using Ansoft Designer software. For results validation, several FSS prototypes with fractal elements were fabricated. In the fabrication process, fractals elements were designed using computer aided design (CAD) tools. The prototypes were measured using a network analyzer (N3250A model, Agilent Technologies). Matlab software was used to generate compare measured and simulated results. The use of fractal elements in the FSS structures showed that the use of high fractal levels can reduce the size of the elements, at the same time as decreases the bandwidth. We also investigated the effect produced by cascading FSS structures. The considered cascaded structures are composed of two FSSs separated by a dielectric layer, which distance is varied to determine the effect produced on the bandwidth of the coupled geometry. Particularly, two FSS structures were coupled through dielectric layers of air and fiberglass. For comparison of results, we designed, fabricated and measured several prototypes of FSS on isolated and coupled structures. Agreement was observed between simulated and measured results. It was also observed that the use of cascaded FSS structures increases the FSSs bandwidths and, in particular cases, the number of resonant frequencies, in the considered frequency range. In future works, we will investigate the effects of using different types of fractal elements, in isolated, multilayer and coupled FSS structures for applications on planar filters, high-gain microstrip antennas and microwave absorbersNeste trabalho, as propriedades de auto-similaridade dos fractais são exploradas para o desenvolvimento de superfícies seletivas de frequência (Frequency Selectives Surfaces - FSS) com várias bandas de rejeição. Em particular, são considerados fractais de Gosper, na definição dos formatos dos elementos das FSS. Por conta da dificuldade de impressão de detalhes dos elementos das FSS, são considerados apenas elementos pré-fractais, com até três iterações fractais. As simulações foram realizadas com o uso do programa comercial Ansoft Designer. Para fins de validação de resultados, foram construídos vários protótipos de FSS com elementos pré-fractais. No processo de fabricação, os formatos dos elementos pré-fractais foram desenhados com auxílio do programa Corel Draw. Os protótipos construídos foram medidos através de um analisador de redes vetorial (modelo N3250A, da Agilent Technologies). A utilização de elementos pré-fractais nas estruturas de FSS consideradas, permitiu verificar que o aumento do nível fractal possibilita a redução do tamanho dos elementos, porém reduz a largura de banda das mesmas. Neste sentido, é também investigado o efeito produzido pelo cascateamento de estruturas de FSS na largura de banda. Foi observado que o uso de estruturas cascateadas, além de aumentar a largura de banda, permitiu, em alguns casos, a obtenção de até respostas em frequência com três bandas de operação entre 6 GHz e 15 GHz