Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Major de Telecomunicações). Faculdade de Engenharia. Universidade do Porto. 2008

In broadband antenna applications, the antenna's cavity is usually loaded with absorbers to eliminate the backward radiation, but in doing so the radiation efficiency of the antenna is decreased. To enhance the radiation efficiency of the antennas EBG structures are used, but they operate over a narrow band. Uniform electromagnetic band gap (EBG) structures are usually periodic structures consisting of metal patches that are separated by small gaps and vias that connect the patches to the ground plane. The electrical equivalent circuit consists of a resonant tank circuit, whose capacitance is represented by the gap between the patches and inductance represented by the via. EBG structures are equivalent to a magnetic surface at the frequency of resonance and thus have very high surface impedance; this makes the EBG structures useful when mounting an antenna close to conducting ground plane, provided the antenna's currents are parallel to the EBG structure. Because EBG structures are known to operate over a very narrow band, they are not useful when used with a broadband antenna. Mushroom-like uniform EBG structures (that use vias) are compact in size have low loss, can be integrated into an antenna to minimize coupling effects of ground planes and increase radiation efficiency of the antenna. The bandwidth of an EBG structure is defined as the band where the reflection-phase from the structure is between +900 to -900. In this dissertation analysis of EBG structures is established using circuit analysis and transmission line analysis. Methods of increasing the bandwidth of EBG structures are explored, by cascading uniform EBG structures of different sizes progressively and vertically (stacked), and applications with different types of antennas are presented. Analyses in this dissertation are compared with previously published results and with simulated results using 3D electromagnetic tools. Validation of applications with antennas is carried by manufacturing prototypes and comparing measured performance with analysis and 3D electromagnetic simulations. The improvements in performance by using wideband progressive EBG and wideband stacked EBG structures are noted. / Ph. D.

In high-speed digital circuits, in order to utilize the space of printed circuit boards(PCB) efficiently, the signal via is a heavily used interconnection structure to communicate different signal layers. However, because of vias are small and irregular structure in the PCB. When we try to simulate these problems with traditional FDTD method. We must using more fine grid to approximate the structure, so it will take a lot CPU memory and computing times. In this author, we try to combine FDTD and FVTD method. Take FVTD method in these partial small structure and magnify grid in a ratio. Finally, combine the larger FDTD grid to achieve reducing the numbers of grids that will save CPU memory and raise computing speed. In addition, we will present another solution that shifting via to replace using small size via based on a method that is using cascaded EBG structure achieve broadband effects to cost down.

yes / A compact dual U-shaped slot PIFA antenna with Electromagnetic Bandgap (EBG) material on a relatively low dielectric constant substrate is presented. Periodic structures have found to reduce mutual coupling and decrease the separation of antenna and ground plane. A design with EGB material suitable for a small terminal mobile handset operating at 2.4 GHz was studied. Simulated and measured scattering parameters are compared for U-shaped slot PIFA antenna with and without EBG structures. An evaluation of MIMO antennas is presented, with analysis of the mutual coupling, correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss. The proposed antenna meets the requirements for practical application within a mobile handset. / Electronics and Telecommunications

Made available in DSpace on 2014-12-17T14:55:12Z (GMT). No. of bitstreams: 1 HugoMCAM_TESE.pdf: 1103719 bytes, checksum: a172421f313d978128130ee22edd6743 (MD5) Previous issue date: 2013-07-30 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The main objective in this work is the analysis of resonance frequency microstrip structures with glass fiber and electromagnetic band gap (EBG/PBG) substrate and analysis of microstrip antennas with rectangular patch of superconductor of high critical temperature (HTS). In this work was used the superconductors YBCO (critical temperature of 90K), SnBaCaCuOy (critical temperature of 160K), and Sn5InCa2Ba4Cu10Oy (critical temperature of 212K) with results in Gigahertz and Terahertz. Was used microstrip antennas arrays planar and linear phase and linear phase planar with patch with superconductor. It presents a study of the major theories that explain superconductivity. In phase arrays were obtained the factors arrays for such configurations, and the criteria of phase and spacing between the elements compound in the array, which were examined in order to get a main lobe with high directivity and high gain. In the analysis we used the method of Transverse Transmission Line (TTL) used in domain of the Fourier Transform (FTD). The LTT is a full wave method, which obtains the electromagnetic field in terms of the components transverse of the structure. The addition of superconductive patch is made using the boundary condition resistive complex. Results are obtained resonance frequency as a function of the parameters of the antenna, radiation patterns of the E and H Planes, for the phase antenna arrays in linear and planar configurations, for different values of the phase and the spacing between elements / Este trabalho tem como objetivo principal a an?lise da frequ?ncia de resson?ncia em estruturas de microfita, com substrato de banda eletromagn?tica proibida (PBG/EBG) e fibra de vidro, e an?lise de antenas de microfita, com patch retangular supercondutor de alta temperatura cr?tica. Neste trabalho foram utilizados os supercondutores YBCO (temperatura cr?tica de 90K), SnBaCaCuOy (temperatura cr?tica de 160K),e Sn5InCa2Ba4Cu10Oy (temperatura cr?tica de 212K) com resultados das frequ?ncias de resson?ncia em Gigahertz (microondas) e Terahertz (fot?nica/nanotecnologia). S?o realizadas aplica??es em arranjos lineares e planares de antenas de microfita com varia??o de fase, usando o patch supercondutor. ? apresentado um estudo das principais teorias que explicam a supercondutividade. Nos arranjos de fase foram obtidos os fatores de arranjos para tais configura??es, e os crit?rios da fase e do espa?amento entre os elementos compondo o arranjo, ao qual foram examinados com o objetivo de obter um l?bulo principal com alta diretividade e alto ganho. Na an?lise utilizou-se o m?todo da Linha de Transmiss?o Transversa (LTT), aplicado no dom?nio da transformada de Fourier (FTD). O LTT ? um m?todo de onda completa, em que se obt?m os campos eletromagn?ticos em termos dos componentes transversais ? estrutura. A inclus?o do patch supercondutor ? feita utilizando-se a condi??o de contorno complexa resistiva. S?o obtidos resultados da frequ?ncia de resson?ncia em fun??o dos par?metros da antena, diagramas de radia??o dos planos el?tricos e magn?ticos, para os arranjos de fase de antenas nas configura??es lineares e planares para diferentes valores da fase e espa?amento entre os elementos

Un des enjeux majeurs dans l'intégration de nouveaux systèmes de guerre électronique (GE) dans les avions d'armes est notamment la réduction de l'encombrement des antennes. En GE, La bande passante des antennes peut être de l'ordre de la décade et la fréquence basse peut être voisine de la centaine de MHz, ce qui rend l'intégration des antennes difficile voire impossible selon les cas. Les antennes de GE font habituellement appel à des antennes dites "indépendantes de la fréquence" placées au-dessus d'une cavité absorbante. La fabrication des matériaux absorbants est à ce jour encore "artisanale" et donc onéreuse. De plus, ces matériaux sont lourds et ils ne présentent pas les mêmes caractéristiques électriques d'une fabrication à l'autre. Les travaux présentés dans ce manuscrit sont dédiés à la réalisation d'antennes à très large bande passante de très faible épaisseur et sans absorbant. Nous avons proposé et validé une nouvelle structure basée sur les matériaux à bandes interdites électromagnétiques (BIE). Le nouveau dispositif permet de remplacer les matériaux absorbants, de réduire l'épaisseur des antennes large bande et de réduire les coûts de fabrication grâce à un procédé industriel de fabrication. La nouvelle structure présente contrairement à toutes les autres structures BIE l'avantage d'être ultra large bande et compacte (de l'ordre de 1/100ième de longueur d'onde d'épaisseur). Nous avons montré l'intérêt d'utiliser un tel dispositif pour réduire l'épaisseur et améliorer les performances des antennes planaires de forme et de polarisation quelconque.

Genetic algorithms (GAs) are global optimization methods that can be applied to almost all problems, requiring only proper fitness function to evaluate. However, one problem of general GA is slow convergence. An improved GA is presented to speed up the efficiency of searching for global optimum in this author. The concept of this proposed method uses a few cost to obtain better individuals in initial population, and the evolution of GA is divided into two-stage with the concept of the genetic evolution process, which uses to improve efficiency. An improved GA with finite-difference time-domain (FDTD) will be applied to optimize mushroom-type EBG structures, which can obtain a wide range stop-band by adjusting the position of via with different patch size cascaded without changing via size, then the simulation and measurement results are also compared. In addition, the novel steps will be presented to design broadband mushroom-type EBG structures with smaller size systematically.

Submitted by Lara Oliveira (lara@ufersa.edu.br) on 2017-05-24T22:06:39Z No. of bitstreams: 1 AnamariaSM_DISSERT.pdf: 10659120 bytes, checksum: 007308f84bbdb900c2823d1a72b2f4a4 (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2017-05-26T11:53:10Z (GMT) No. of bitstreams: 1 AnamariaSM_DISSERT.pdf: 10659120 bytes, checksum: 007308f84bbdb900c2823d1a72b2f4a4 (MD5) / Approved for entry into archive by Vanessa Christiane (referencia@ufersa.edu.br) on 2017-05-26T11:54:09Z (GMT) No. of bitstreams: 1 AnamariaSM_DISSERT.pdf: 10659120 bytes, checksum: 007308f84bbdb900c2823d1a72b2f4a4 (MD5) / Made available in DSpace on 2017-05-26T11:54:39Z (GMT). No. of bitstreams: 1 AnamariaSM_DISSERT.pdf: 10659120 bytes, checksum: 007308f84bbdb900c2823d1a72b2f4a4 (MD5) Previous issue date: 2016-05-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Communication systems it has excelled in the development, social, economic and cultural society. Every time there are new technologies seeking to offer the fastest, easy and reliable access to various communications services. In this context, the microstrip antennas stand out by having compact size and reduced cost. However, it presents some limitations related to narrow bandwidth and low gain. A significant advance to minimize these losses came to the use of structures EBG (Electromagnetic Band Gap) and PBG (Photonic Band Gap) in the components of the antennas. This paper proposes the study and analysis of the behavior of microstrip antennas properties designed with EBG/PBG structures in the substrate and the ground plane. So that the structures are arranged just under the patch and are developed with variations in radius, cylinder height and positioning in the ground plane. For the resonance frequency 5.85 GHz, and substrates of different permittivity. In computer modeling was used ANSYS HFFS® software. After analyzing the simulated results seven devices were built, through a vector network analyzer, the measurements of the main parameters were performed. Ultimately simulation are compared and measured values, so that the results presented in most configurations a concord in the pattern of graphics, although the frequency displacement. Also noted that antennas with the EBG/PBG structures presented multiband, enabling the application specific frequency bands as well as, an increase in the value of total gain, bandwidth and reduction of surface currents / Os sistemas de comunicação assumiram papéis fundamentais para o desenvolvimento, social, econômico e cultural na sociedade. A cada momento, surgem novas tecnologias procurando oferecer o acesso mais rápido, fácil e confiável aos diversos serviços de comunicações. Nesse contexto, as antenas de microfita se destacam por possuírem características como, tamanho compacto e custo reduzido. No entanto, apresentam algumas limitações relacionadas a largura de banda estreita e ganho reduzido. Um avanço significativo para minimizar essas perdas, proveio com a utilização de estruturas de bandas proibidas (EBG – Eletromagnetic Band Gap e PBG – Photonic Band Gap) nos componentes das antenas. Este trabalho propõe o estudo e análise do comportamento das propriedades de antenas de microfita projetadas com configurações de estruturas EBG/PBG no substrato e no plano de terra. De modo que as estruturas estão arranjadas apenas sob o patch e, são desenvolvidas com variações no raio, altura do cilindro e posicionamento no plano de terra. Para a frequência de ressonância de 5,85 GHz, e substratos de diferentes permissividades. Na modelagem computacional foi utilizado o software ANSYS HFFS®, e com a análise dos resultados simulados foram fabricados sete dispositivos, onde através de um analisador de redes vetoriais, foram realizadas as medições dos principais parâmetros. Por fim são comparados os valores simulados e medidos, de modo que que os resultados apresentaram na maioria das configurações uma concordância no padrão de seus gráficos, apesar dos deslocamentos de frequência. Também foi observado que as antenas com as estruturas EBG/PBG apresentaram comportamento de multibandas, possibilitando a aplicação em faixas de frequências específicas, assim como, ocorreu um aumento nos valores de ganho total, largura de banda e a redução das correntes de superfície / 2017-05-24

The thesis deals with linearly polarized dielectric rectangular resonator antenna (DRA) operating in the basic mode TEy11 and higher order mode TEy131 at f0 = 10GHz surrounded by an electromagnetic band gap structure (EBG). The dielectric resonator antennas, the EBG structure were designed and a method of integration of both components was developed. The simulated results show a significant improvement of the radiation pattern in the E-plane radiation pattern (narrower main beam, lower level of side lobes, higher directivity) in comparison to a conventional DRA. This was verified by the TEy11 measurement.

Made available in DSpace on 2014-12-17T14:55:39Z (GMT). No. of bitstreams: 1 LincolnMA.pdf: 1667449 bytes, checksum: b8113389f31903ba22cf94dbc22192c1 (MD5) Previous issue date: 2009-08-13 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / This 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 / Este trabalho apresenta uma an?lise te?rica e num?rica de estruturas que utilizam superf?cies seletivas de frequ?ncia aplicadas a antenas do tipo patch. Para isso, ? utilizado o m?todo das diferen?as finitas no dom?nio do tempo (FDTD) visando determinar os campos refletidos a partir de uma onda plana incidente no dom?nio do tempo. As aplica??es das superf?cies seletivas de freq??ncia e antenas patch abrangem uma grande ?rea das Telecomunica??es, principalmente em comunica??es m?veis e v?o desde filtros at? as antenas banda larga. Especificamente, a an?lise usa os campos transmitidos e refletidos obtidos no dom?nio do tempo, em conjunto com transformada de Fourier permitindo a obten??o dos par?metros de transmiss?o da antena. A condi??o de contorno absorvedora utilizada foi a de camada perfeitamente casada (PML), permitindo a determina??o num?rica dos campos com uma quantidade menor de interfer?ncias provenientes de reflex?es nos limites do espa?o discretizado. S?o considerados patches retangulares condutores sobre uma camada diel?trica e alimentados por linha de microfita. Foram analisadas superf?cies seletivas de frequ?ncia peri?dicas e quase peri?dicas tanto no plano de terra quanto no plano do pr?prio patch. ? realizada uma revis?o bibliogr?fica a respeito da utiliza??o de superf?cies seletivas de frequ?ncia em antenas patch. Tamb?m s?o comparados resultados num?ricos e medidos para a perda de retorno das estruturas analisadas. S?o apresentadas, ainda, sugest?es de continuidade para este trabalho