Made available in DSpace on 2014-12-17T14:55:11Z (GMT). No. of bitstreams: 1 ClarissaLN_TESE.pdf: 4153617 bytes, checksum: 6a9b7ed40b1f66da758afee4efaf74e9 (MD5) Previous issue date: 2013-04-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this thesis, a frequency selective surface (FSS) consists of a two-dimensional periodic structure mounted on a dielectric substrate, which is capable of selecting signals in one or more frequency bands of interest. In search of better performance, more compact dimensions, low cost manufacturing, among other characteristics, these periodic structures have been continually optimized over time. Due to its spectral characteristics, which are similar to band-stop or band-pass filters, the FSSs have been studied and used in several applications for more than four decades. The design of an FSS with a periodic structure composed by pre-fractal elements facilitates the tuning of these spatial filters and the adjustment of its electromagnetic parameters, enabling a compact design which generally has a stable frequency response and superior performance relative to its euclidean counterpart. The unique properties of geometric fractals have shown to be useful, mainly in the production of antennas and frequency selective surfaces, enabling innovative solutions and commercial applications in microwave range. In recent applications, the FSSs modify the indoor propagation environments (emerging concept called wireless building ). In this context, the use of pre-fractal elements has also shown promising results, allowing a more effective filtering of more than one frequency band with a single-layer structure. This thesis approaches the design of FSSs using pre-fractal elements based on Vicsek, Peano and teragons geometries, which act as band-stop spatial filters. The transmission properties of the periodic surfaces are analyzed to design compact and efficient devices with stable frequency responses, applicable to microwave frequency range and suitable for use in indoor communications. The results are discussed in terms of the electromagnetic effect resulting from the variation of parameters such as: fractal iteration number (or fractal level), scale factor, fractal dimension and periodicity of FSS, according the pre-fractal element applied on the surface. The analysis of the fractal dimension s influence on the resonant properties of a FSS is a new contribution in relation to researches about microwave devices that use fractal geometry. Due to its own characteristics and the geometric shape of the Peano pre-fractal elements, the reconfiguration possibility of these structures is also investigated and discussed. This thesis also approaches, the construction of efficient selective filters with new configurations of teragons pre-fractal patches, proposed to control the WLAN coverage in indoor environments by rejecting the signals in the bands of 2.4~2.5 GHz (IEEE 802.11 b) and 5.0~6.0 GHz (IEEE 802.11a). The FSSs are initially analyzed through simulations performed by commercial software s: Ansoft DesignerTM and HFSSTM. The fractal design methodology is validated by experimental characterization of the built prototypes, using alternatively, different measurement setups, with commercial horn antennas and microstrip monopoles fabricated for low cost measurements / Nesta tese, uma superf?cie seletiva de frequ?ncia (FSS) consiste de uma estrutura peri?dica bidimensional montada sobre um substrato diel?trico, que ? capaz de selecionar sinais em uma ou mais faixas de frequ?ncias de interesse. Em busca da obten??o de um melhor desempenho, dimens?es mais compactas, baixo custo de fabrica??o, entre outras caracter?sticas, estas estruturas peri?dicas t?m sido continuamente otimizadas ao longo do tempo. Devido ?s suas caracter?sticas espectrais, que s?o similares as de filtros rejeita-faixa ou passa-faixa, as FSSs t?m sido estudadas e usadas em aplica??es diversas por mais de quatro d?cadas. O projeto de uma FSS com uma estrutura peri?dica composta de elementos pr?fractais facilita a sintonia destes filtros espaciais e o ajuste de seus par?metros eletromagn?ticos, possibilitando uma constru??o compacta, que, em geral, apresenta uma resposta est?vel em frequ?ncia e desempenho superior em rela??o ? sua contrapartida euclidiana. As propriedades ?nicas dos fractais geom?tricos t?m-se mostrado bastante ?teis, principalmente para a constru??o de antenas e superf?cies seletivas de frequ?ncia, permitindo solu??es inovadoras e aplica??es comerciais na faixa de micro-ondas. Em aplica??es mais recentes, as FSSs modificam os ambientes de propaga??o indoor (conceito emergente chamado de wireless building ). Neste contexto, o uso de elementos pr?-fractais tamb?m tem apresentado resultados promissores, tornando mais efetiva a filtragem de mais de uma faixa de frequ?ncias com uma estrutura de camada simples. Esta tese aborda o projeto de FSSs com elementos pr?-fractais baseados nas geometrias de Vicsek, Peano e dos ter?gonos, que funcionam como filtros espaciais do tipo rejeita-faixa. As propriedades de transmiss?o das superf?cies peri?dicas s?o analisadas para a concep??o de dispositivos eficientes, compactos e com respostas est?veis em frequ?ncia, aplic?veis na faixa de micro-ondas e adequados para utiliza??es em comunica??es indoor. Os resultados s?o discutidos em termos do efeito eletromagn?tico decorrente da varia??o de par?metros como, n?mero de itera??es fractais (ou n?vel do fractal), fator de escala, dimens?o fractal e periodicidade da FSS, de acordo com o elemento pr?-fractal utilizado. A an?lise da influ?ncia da dimens?o fractal sobre as propriedades de resson?ncia de uma FSS ? uma contribui??o nova no que diz respeito ?s pesquisas com dispositivos de micro-ondas que utilizam geometrias fractais. Devido ?s caracter?sticas pr?prias e a forma geom?trica dos elementos pr?-fractais de Peano, a possibilidade de reconfigura??o destas estruturas tamb?m ? investigada e discutida. Esta tese aborda ainda, a constru??o de filtros seletivos eficientes com novas configura??es de patches pr?-fractais do tipo ter?gonos, propostos para controle de cobertura WLAN em ambientes indoor, rejeitando os sinais nas faixas de 2,4~2,5 GHz (IEEE 802.11b) e 5,0~6,0 GHz (IEEE 802.11a). As FSSs s?o analisadas inicialmente por meio de simula??es executadas pelos programas comerciais Ansoft DesignerTM e HFSSTM. A metodologia de projeto ? validada atrav?s da caracteriza??o experimental dos prot?tipos constru?dos utilizando, alternativamente, diferentes setups de medi??o, com antenas corneta comerciais e monopolos de microfita de fabrica??o pr?pria para medi??es de baixo custo

Made available in DSpace on 2014-12-17T14:55:18Z (GMT). No. of bitstreams: 1 MarceloRS_TESE.pdf: 2113878 bytes, checksum: 1cc62a66f14cc48f2e97f986a4dbbb8d (MD5) Previous issue date: 2014-01-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This thesis describes design methodologies for frequency selective surfaces (FSSs) composed of periodic arrays of pre-fractals metallic patches on single-layer dielectrics (FR4, RT/duroid). Shapes presented by Sierpinski island and T fractal geometries are exploited to the simple design of efficient band-stop spatial filters with applications in the range of microwaves. Initial results are discussed in terms of the electromagnetic effect resulting from the variation of parameters such as, fractal iteration number (or fractal level), fractal iteration factor, and periodicity of FSS, depending on the used pre-fractal element (Sierpinski island or T fractal). The transmission properties of these proposed periodic arrays are investigated through simulations performed by Ansoft DesignerTM and Ansoft HFSSTM commercial softwares that run full-wave methods. To validate the employed methodology, FSS prototypes are selected for fabrication and measurement. The obtained results point to interesting features for FSS spatial filters: compactness, with high values of frequency compression factor; as well as stable frequency responses at oblique incidence of plane waves. This thesis also approaches, as it main focus, the application of an alternative electromagnetic (EM) optimization technique for analysis and synthesis of FSSs with fractal motifs. In application examples of this technique, Vicsek and Sierpinski pre-fractal elements are used in the optimal design of FSS structures. Based on computational intelligence tools, the proposed technique overcomes the high computational cost associated to the full-wave parametric analyzes. To this end, fast and accurate multilayer perceptron (MLP) neural network models are developed using different parameters as design input variables. These neural network models aim to calculate the cost function in the iterations of population-based search algorithms. Continuous genetic algorithm (GA), particle swarm optimization (PSO), and bees algorithm (BA) are used for FSSs optimization with specific resonant frequency and bandwidth. The performance of these algorithms is compared in terms of computational cost and numerical convergence. Consistent results can be verified by the excellent agreement obtained between simulations and measurements related to FSS prototypes built with a given fractal iteration / Esta tese descreve metodologias de projeto para superf?cies seletivas de frequ?ncia (FSSs) compostas por arranjos peri?dicos de patches met?licos pr?-fractais impressos em camadas diel?tricas simples (FR4, RT/duroid). As formas apresentadas pelas geometrias correspondentes ? ilha de Sierpinski e ao fractal T s?o exploradas para o projeto simples de filtros espaciais rejeita-faixa eficientes com aplica??es na faixa de micro-ondas. Resultados iniciais s?o discutidos em termos do efeito eletromagn?tico decorrente da varia??o de par?metros como, n?mero de itera??es fractais (ou n?vel do fractal), fator de itera??o fractal, e periodicidade da FSS, dependendo do elemento pr?-fractal utilizado (ilha de Sierpinski ou fractal T). As propriedades de transmiss?o destes arranjos peri?dicos propostos s?o investigadas atrav?s de simula??es realizadas pelos programas comerciais Ansoft DesignerTM e Ansoft HFSSTM, que executam m?todos de onda completa. Para validar a metodologia empregada, prot?tipos de FSS s?o selecionados para fabrica??o e medi??o. Os resultados obtidos apontam caracter?sticas interessantes para filtros espaciais de FSS, tais como: estrutura compacta, com maiores fatores de compress?o de frequ?ncia; al?m de respostas est?veis em frequ?ncia com rela??o ? incid?ncia obl?qua de ondas planas. Esta tese aborda ainda, como enfoque principal, a aplica??o de uma t?cnica alternativa de otimiza??o eletromagn?tica (EM) para an?lise e s?ntese de FSSs com motivos fractais. Em exemplos de aplica??o desta t?cnica, elementos pr?-fractais de Vicsek e Sierpinski s?o usados no projeto ?timo das estruturas de FSS. Baseada em ferramentas de intelig?ncia computacional, a t?cnica proposta supera o alto custo computacional proveniente das an?lises param?tricas de onda completa. Para este fim, s?o desenvolvidos modelos r?pidos e precisos de rede neural do tipo perceptron de m?ltiplas camadas (MLP) utilizando diferentes par?metros como vari?veis de entrada do projeto. Estes modelos de rede neural t?m como objetivo calcular a fun??o custo nas itera??es dos algoritmos de busca populacional. O algoritmo gen?tico cont?nuo (GA), a otimiza??o por enxame de part?culas (PSO), e o algoritmo das abelhas (BA), s?o usados para a otimiza??o das FSSs com valores espec?ficos de frequ?ncia de resson?ncia e largura de banda. O desempenho destes algoritmos ? comparado em termos do custo computacional e da 13 converg?ncia num?rica. Resultados consistentes podem ser verificados atrav?s da excelente concord?ncia obtida entre simula??es e medi??es referentes aos prot?tipos de FSS constru?dos com uma dada itera??o fractal

Made available in DSpace on 2014-12-17T14:55:36Z (GMT). No. of bitstreams: 1 IradilsonFC.pdf: 1175734 bytes, checksum: 1b789bd9fa5e1240b46ecdcefd19f939 (MD5) Previous issue date: 2009-08-11 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims to present how the reconfigurable microstrip antennas and frequency selective surfaces can be used to operate at communication systems that require changing their operation frequency according to system requirements or environmental conditions. The main purpose is to present a reconfigurable circular microstrip antenna using a parasitic ring and a reconfigurable dipole frequency selective surface. Thereupon there are shown fundamental topics like microstrip antennas, PIN diodes and the fundamental theory of reconfigurable antennas and frequency selective surfaces. There are shown the simulations and measurements of the fabricated prototypes and it is done an analysis of some parameters like the bandwidth and radiation pattern, for the antennas, and the transmission characteristics, for the frequency selective surface. Copper strips were used in place of the diodes for proof of the reconfigurability concept / Este trabalho tem como objetivo apresentar como as antenas de microfita e as superf?cies seletivas de frequ?ncia reconfigur?veis podem ser alternativas para operar em sistemas de comunica??o sem fio que necessitem alterar sua frequ?ncia de opera??o de acordo com os requisitos impostos a este sistema ou condi??es do meio. O prop?sito central ? apresentar uma antena de microfita com patch circular reconfigur?vel utilizando um anel parasita e uma superf?cie seletiva de frequ?ncia tipo dipolo reconfigur?vel. Para isto s?o apresentados temas fundamentais como as antenas de microfita, diodos PIN e a teoria fundamental de opera??o das antenas e superf?cies seletivas de frequ?ncia reconfigur?veis. S?o apresentadas todas as simula??es e medi??es realizadas dos prot?tipos constru?dos e ? feita uma an?lise de alguns par?metros como largura de banda e diagrama de radia??o, para as antenas, e caracter?sticas de transmiss?o, para as superf?cies seletivas de frequ?ncia. Foram utilizadas fitas de cobre no lugar dos diodos para a prova do conceito de reconfigurabilidade

Made available in DSpace on 2014-12-17T14:55:47Z (GMT). No. of bitstreams: 1 EmanueleSRM_DISSERT.pdf: 2423953 bytes, checksum: 516a98f7f1136b2e57265165c2a43b20 (MD5) Previous issue date: 2010-12-21 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Frequency Selective Surfaces (FSS) are periodic structures in one or two dimensions that act as spatial filters, can be formed by elements of type conductors patches or apertures, functioning as filters band-stop or band-pass respectively. The interest in the study of FSS has grown through the years, because such structures meet specific requirements as low-cost, reduced dimensions and weighs, beyond the possibility to integrate with other microwave circuits. The most varied applications for such structures have been investigated, as for example, radomes, antennas systems for airplanes, electromagnetic filters for reflective antennas, absorbers structures, etc. Several methods have been used for the analysis of FSS, among them, the Wave Method (WCIP). Are various shapes of elements that can be used in FSS, as for example, fractal type, which presents a relative geometric complexity. This work has as main objective to propose a simplification geometric procedure a fractal FSS, from the analysis of influence of details (gaps) of geometry of the same in behavior of the resonance frequency. Complementarily is shown a simple method to adjust the frequency resonance through analysis of a FSS, which uses a square basic cell, in which are inserted two reentrance and dimensions these reentrance are varied, making it possible to adjust the frequency. For this, the structures are analyzed numerically, using WCIP, and later are characterized experimentally comparing the results obtained. For the two cases is evaluated, the influence of electric and magnetic fields, the latter through the electric current density vector. Is realized a bibliographic study about the theme and are presented suggestions for the continuation of this work / As Superf?cies Seletivas de Frequ?ncia (FSS) s?o estruturas peri?dicas em uma ou duas dimens?es que atuam como filtros espaciais, podendo ser formadas por elementos do tipo patches condutores ou aberturas, funcionando como filtros rejeita-faixa ou passa-faixa, respectivamente. O interesse no estudo das FSS tem crescido atrav?s dos anos, pois tais estruturas atendem a requisitos espec?ficos como baixo custo, dimens?es e pesos reduzidos, al?m da possibilidade de se integrar com outros circuitos de micro-ondas. As mais variadas aplica??es para tais estruturas t?m sido investigadas, como por exemplo, radomes, sistemas de antenas para avi?es, filtros eletromagn?ticos para antenas refletoras, estruturas absorvedoras, etc. V?rios m?todos t?m sido utilizados para a an?lise de FSS, dentre eles, o M?todo das Ondas (WCIP). S?o diversas as formas de elementos que podem ser utilizados em FSS, como por exemplo, os do tipo fractal, que apresenta uma relativa complexidade geom?trica. Este trabalho tem como objetivo principal propor um procedimento de simplifica??o geom?trica de uma FSS fractal, a partir da an?lise da influ?ncia dos detalhes (fendas) da geometria da mesma no comportamento da frequ?ncia de resson?ncia. De forma complementar ? mostrado um m?todo simples de ajustar a frequ?ncia de resson?ncia atrav?s da an?lise de uma FSS, que utiliza uma c?lula b?sica retangular, na qual s?o inseridas duas reentr?ncias e as dimens?es dessas reentr?ncias s?o variadas, tornando poss?vel o ajuste da frequ?ncia. Para isso, as estruturas s?o analisadas numericamente, utilizando o WCIP, e posteriormente s?o caracterizadas experimentalmente, comparando-se os resultados obtidos. Para os dois casos ? avaliada, a influ?ncia dos campos el?trico e magn?tico, este ?ltimo atrav?s do vetor densidade de corrente el?trica. ? realizado um estudo bibliogr?fico a cerca do tema e s?o apresentadas sugest?es para a continuidade deste trabalho

Made available in DSpace on 2014-12-17T14:56:15Z (GMT). No. of bitstreams: 1 ValdemirPSN_DISSERT.pdf: 1834625 bytes, checksum: 95e248e92979a128a6b21a87f73fdd48 (MD5) Previous issue date: 2013-07-26 / The planar circuits are structures that increasingly attracting the attention of researchers, due the good performance and capacity to integrate with other devices, in the prototyping of systems for transmitting and receiving signals in the microwave range. In this context, the study and development of new techniques for analysis of these devices have significantly contributed in the design of structures with excellent performance and high reliability. In this work, the full-wave method based on the concept of electromagnetic waves and the principle of reflection and transmission of waves at an interface, Wave Concept Iterative Procedure (WCIP), or iterative method of waves is described as a tool with high precision study microwave planar circuits. The proposed method is applied to the characterization of planar filters, microstrip antennas and frequency selective surfaces. Prototype devices were built and the experimental results confirmed the proposed mathematical model. The results were also compared with simulated results by Ansoft HFSS, observing a good agreement between them. / Os circuitos planares s?o estruturas que atraem cada vez mais a aten??o dos pesquisadores, pelo bom desempenho e pela capacidade de integra??o com outros dispositivos, na prototipagem de sistemas de transmiss?o e recep??o de sinais na faixa de micro-ondas. Neste contexto, o estudo e o desenvolvimento de novas t?cnicas de an?lise desses dispositivos t?m contribu?do de forma significativa na concep??o de estruturas com desempenhos excelentes e alto grau de confiabilidade. Neste trabalho, o m?todo de onda completa baseado no conceito de ondas eletromagn?ticas e no princ?pio da reflex?o e transmiss?o de ondas em uma interface, Wave Concept Iterative Procedure (WCIP), ou m?todo iterativo das ondas ? descrito como uma ferramenta com alto grau de precis?o no estudo de circuitos planares de micro-ondas. O m?todo proposto ? aplicado na caracteriza??o de filtros planares, antenas de microfita e superf?cies seletivas de frequ?ncia. Prot?tipos dos dispositivos foram constru?dos e os resultados experimentais comprovaram o modelo matem?tico proposto. Os resultados obtidos tamb?m foram comparados com os resultados simulados pelo Ansoft HFSS, tendo sido observada uma boa concord?ncia entre eles

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.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-02-17T19:02:33Z No. of bitstreams: 1 JannaynaDominguesBarrosFilgueira_TESE.pdf: 2533006 bytes, checksum: da08862481c89d6eac3b9988828ee15f (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-02-17T21:41:02Z (GMT) No. of bitstreams: 1 JannaynaDominguesBarrosFilgueira_TESE.pdf: 2533006 bytes, checksum: da08862481c89d6eac3b9988828ee15f (MD5) / Made available in DSpace on 2017-02-17T21:41:02Z (GMT). No. of bitstreams: 1 JannaynaDominguesBarrosFilgueira_TESE.pdf: 2533006 bytes, checksum: da08862481c89d6eac3b9988828ee15f (MD5) Previous issue date: 2016-07-18 / As superf?cies seletivas em frequ?ncia (FSS) pertencem a uma subclasse dos metamateriais composto por patchs met?licos bidimensionais. Por apresentar um comportamento seletivo de frequ?ncia, essas estruturas t?m sido aplicadas nas ?reas de micro-ondas e sistemas de comunica??o, al?m de ser tema de pesquisa por parte de estudiosos. A literatura define basicamente uma superf?cie seletiva de frequ?ncia como um arranjo peri?dico de patches que exibe um determinado comportamento de filtragem de frequ?ncia podendo apresentar caracter?sticas de filtro rejeita-faixa ou passa-faixa que permite a reflex?o ou a transmiss?o de sinais em uma determinada faixa de frequ?ncia. As FSS s?o utilizadas em diversas aplica??es que v?o desde sistemas de micro-ondas e antenas at? aplica??es em radomes e comunica??es via sat?lite. Estruturas de FSS com comportamento Eletromagn?tico adequado t?m sido estudadas por pesquisadores da ?rea. Por?m, a an?lise das caracter?sticas espectrais dessas estruturas requer t?cnica com elevada complexidade computacional. Para reduzir o esfor?o computacional relacionado ao tempo de processamento, podem ser utilizadas t?cnicas de otimiza??o. Neste aspecto, esta pesquisa prop?e a utiliza??o de um m?todo de otimiza??o no projeto de FSS. Os m?todos de otimiza??o t?m como objetivo obter os resultados de um sistema por meio do ajuste dos par?metros de entrada, ou seja, ao ajustar estes par?metros os m?todos de otimiza??o procuram um melhor resultado de sa?da de modo que o desempenho do sistema, em termos de qualidade, custo e efici?ncia, possam ser otimizados. Esses m?todos podem ser aplicados em diversas ?reas. Atualmente, na ?rea do Eletromagnetismo, os circuitos de micro-ondas e antenas t?m aplicado diversas t?cnicas de otimiza??o como Algoritmos Gen?ticos (AG), Redes Neurais Artificiais (RNA) e Otimiza??o com Enxame de Part?culas (PSO). O m?todo de otimiza??o descrito nesta pesquisa foi desenvolvido com base no conceito do arranjo ortogonal, o M?todo Taguchi. Este m?todo fornece uma maneira eficiente para escolher os par?metros do projeto em um processo de Resumo otimiza??o e reduz efetivamente o n?mero de experimentos requerido na aplica??o. O M?todo Taguchi ? aplicado com sucesso nas ?reas de Engenharia Qu?mica e Engenharia Mec?nica e mais recentemente t?m-se aplica??es na ?rea de Eletromagnetismo, por?m, sua aplica??o em FSS ? in?dita. Neste estudo aplicamos o M?todo Taguchi em tr?s estruturas de FSS: FSS quadrada, FSS quadrada com grade e dipolo cruzado. O objetivo do m?todo ? obter os melhores valores para par?metros f?sicos da FSS, de modo que esta opere de forma satisfat?ria, de acordo com especifica??es determinadas no projeto. Utilizamos tamb?m nesta pesquisa o M?todo do Circuito Equivalente. A precis?o do m?todo Taguchi ? verificada experimentalmente e comparada com as simula??es realizadas no ANSYS Designer. Em seguida os prot?tipos s?o constru?dos e caracterizados experimentalmente. / Frequency Selective Surfaces (FSS) belong to a subclass of metamaterial consisting of two-dimensional metallic patches. By presenting a selective frequency behavior, these structures have been applied in the microwave and communication systems fields, in addition it is a research topic by scholars. The literature defines basically the Frequency Selective Surface as a periodic arrangement of patches that displays a certain frequency filtering and it may present characteristics of a band-stop or band-pass filter, which allows the reflection or the transmission of signals in a given frequency range. The FSS are used in diverse applications ranging from microwave and antennas systems to applications in radomes and satellite communications. Researchers have studied FSS structures with appropriate electromagnetic behavior. However, the analysis of spectral characteristics of these structures requires technique with high computational complexity. In order to reduce the computational effort related to the time of processing, it may be used optimization techniques. Concerning to it, this study proposes the use of an optimization method in the FSS design. Optimization methods are intended to get the best results of a system by tuning of the input parameters, that is, when these parameters are adjusted, the optimization methods seek a better output result so that the system performance, in terms of quality, cost and efficiency can be improved. These methods can be applied in various areas. Currently, in the Electromagnetism area, the microwave circuits and antennas have applied various optimization techniques like genetic algorithms (GA), Artificial Neural Networks (ANN) and Particle Swarm Optimization (PSO). The optimization method described in this research was developed based on the concept of the Orthogonal Arrangement, Taguchi Method. This method provides an efficient way to choose the project parameters in a process of optimization and it effectively reduces the number of experiments required in the application. Taguchi method is successfully applied in the chemical engineering and mechanical engineering fields and recently, there have been applications in the Abstract Electromagnetism area, however, its application in FSS is unprecedented. In this study, it was applied the Taguchi Method in three structures of FSS: Square FSS, Square with grid FSS and Cross Dipole. The purpose of the method is to obtain the best values for physical parameters of the FSS, so that is operating in a satisfactory manner, in accordance with certain specifications in the project. It was also used in this research the Equivalent Circuit Method. The accuracy of Taguchi Method is verified experimentally and it is compared to the simulations performed in the ANSYS Designer ?. Then, the prototypes are built and measured in order to validate the experimental results.

Les surfaces sélectives en fréquence (FSS) pour la furtivité radar ou l’optique ont été largement étudiées. Depuis plus de vingt ans, des matériaux artificiels ont été conçus, permettant d’obtenir des propriétés particulières, notamment l’existence de bandes permises ou interdites, réfraction négative, ultra-réfraction. Par ailleurs, des antennes basées sur la mise en réseau d’un élément rayonnant sont plus compactes et plus facilement intégrables. Le problème de la diffraction d’une onde plane par des réseaux tridimensionnels bipériodiques peut être résolu par éléments finis ou par équations intégrales bipériodiques ; il l’est souvent par une méthode hybride combinant la méthode des éléments finis et la méthode aux équations intégrales. Nous avons choisi de développer une méthode hybride utilisant deux variantes de la méthode aux équations intégrales. Les domaines semi-infinis (l’extérieur du réseau) sont traités par des équations intégrales bipériodiques (EI3D2D), et les domaines bornés (l’intérieur du réseau) sont traités par des équations intégrales tridimensionnelles (EI3D), auxquelles on impose des conditions aux limites de pseudopériodicité. Ce code numérique est développé dans le cadre du code SPECTRE de Dassault-Aviation, qui est un code généraliste 3D, afin de bénéficier de la richesse des modèles qui y ont déjà été développés (modèle composé d’un nombre quelconque de sous-domaines de formes et de matériaux quelconques, traitement des différents cas de jonctions entre sous-domaines, matériaux de faible épaisseur). L’efficacité en termes de précision et en temps de calcul de la méthode numérique est validée par comparaison des résultats avec d’autres simulations numériques et également avec des résultats de mesures. Les cas testés sont représentatifs de plusieurs des principaux phénomènes liés aux métamatériaux : surfaces sélectives en fréquence, transmission « extraordinaire », surfaces à haute impédance. Enfin, nous étudions un radôme passe-bande indépendant à l’angle d’incidence, à l’aide de la méthode numérique que nous proposons. La structure retenue se base sur un réseau de cavités coaxiales dans une couche métallique. Nous expliquons l’origine physique des résonances qui apparaissent et nous suggérons une évolution géométrique du profil des cavités, afin d’augmenter la largeur de bande passante. / Frequency selective surfaces (FSS) for radar stealth or in optics have been widely studied. For more than two decades, articial materials have been designed to highlight specific behaviour, like the existence of allowed or forbidden bands, negative refraction, ultra-refraction... Moreover, antennas based upon an array of radiating elements improve the compactness and integration of these features. The problem of the diffraction of a plane wave by 3D biperiodic scatterers can be solved by finite-elements methods (FEM) or biperiodic boundary integral equations (BIE). It is often done by hybrid methods, that combine FEM and BIE. We choose to develop a hybrid method that uses two variants of the BIE method. Semiinfinite outer domains are treated by biperiodic integral equations (3D2D IE) and inner bounded domains are treated by 3D free-space integral equations (3D IE). Pseudoperiodic boundary conditions are enforced in the scattering biperiodic structure. The numerical code is developed in the framework of Dassault Aviation’s SPECTRE code, which is a general 3D code, in order to take advantage of the various models that have already been developed : arbitrary number of sub-domains of various shapes or materials, treatment of the different types of junctions between sub-domains, thin slabs. The efficiency in terms of accuracy and computation time of the numerical code is validated by comparison of the results from other numerical simulations or measurements. All the test cases are representative of several of the main phenomena that can be observed in metamaterials : FSS, “extraordinary” transmission, high-impedance surfaces. Finally, a bandpass radome which is independent to the angle of incidence is studied. The proposed numerical method is used. The chosen structure is based upon an array of coaxial cavities in a metallic slab. We explain the physical origin of resonances that appear and we suggest a geometrical evolution of the profile of the cavities, to favor a wideband behavior.

[pt] Neste trabalho é desenvolvido um modelo matemático para descrever o comportamento estatístico da interferência produzida por redes VSAT/MFTDMA. O modelo proposto é utilizado para avaliar a interferência produzida pelos lances de subida de enlaces VSAT/MF-TDMA em enlaces de uma outra rede que utiliza um satélite vizinho. No modelo proposto, expressões analíticas foram desenvolvidas para levar em conta os efeitos de variações nas potências transmitidas, nos tamanhos das antenas e nos erros de apontamento das antenas transmissoras. As posições geográficas das estações terrenas são modeladas por processos pontuais de Poisson, bi-dimensionais. O modelo proposto é suficientemente geral para acomodar outros tipos de processos pontuais, além de situações envolvendo áreas de serviço contendo múltiplos tipos de distribuição geográfica das estações terrenas. Resultados numéricos obtidos com o modelo proposto são comparados àqueles baseados em valores reais de parâmetros (e.g. localização das estações terrenas, tamanhos de antenas e potências de transmissão) que foram fornecidos por um operador brasileiro de satélites. / [en] In this work a mathematical model to describe the statistical behavior of the interference produced by VSAT/MF-TDMA networks is developed. The model is used to assess the interference produced by the uplinks of a VSAT/MF-TDMA network into links of a network that uses a neighboring satellite. In the proposed model, analytical expressions were developed to account for the effects of the varying transmitting powers, antenna sizes, and transmitting antenna pointing errors. The earth station locations are modeled by a two dimensional Poisson point process. The model is general enough to accommodate other types of point processes and can be applied to situations involving service areas containing multiple types of earth station geographical distribution. Numerical results obtained with the proposed model are compared to those based on the actual parameters values (e.g. earth station locations, antenna sizes and transmitting powers) which were provided by a Brazilian satellite operator.

The majority of wheat research in the world and in Canada is conducted by the public sector. The government of Canada has introduced legislation to update its plant breeder’s rights (PBR) legislation, making Canada compliant with the International Union for the Protection of New Varieties of Plants (UPOV) 91 convention, with the goal to stimulate private investment in wheat variety research. International experience with UPOV 91 reveals a wide range of outcomes depending on the specific royalty setting mechanisms allowed within their domestic legislation. This thesis compares Canada’s existing policy to three very different international examples (France, United Kingdom, and Australia) of UPOV 91 compliant royalty collection systems for wheat. The model presented is one of a monopolistic competitive wheat-breeding industry with the introduction of a new certified seed variety. Farmers have the option to use farm saved seed (FSS) or certified seed on their farm. The additional economic benefit created from the innovation and its distribution is analyzed and interpreted for both, farmers (social benefit) and breeders (private benefit). The results of the analysis show that while each UPOV 91 compliant model generates more revenue for farmers and breeders than Canada’s current policy, they tend to generate less than expected revenue in the short-run. If a country has strong intellectual property rights (IPRs), it will attract some domestic and foreign investment and possibly a beneficial collaboration between the public, private, and producer sector, also known as P4 (public-private-producer-partnerships).