No description available.

Yes / The present work investigates the operation performance of 2-element configuration multiple input Multiple Output (MIMO) antennas system using Cylindrical Dielectric Resonator (CDR). The MIMO antenna arrays achieve 22.2% impedance bandwidth at S11 ≤ -10 covering the bandwidth from 10GHz to 12.5GHz that meets the essential requirements of wide band communications applications. The first array gives a maximum isolation of 27dB at an element spacing of 22mm, whereas the second array presents a maximum isolation of 42.55dB at element spacing of 12.25mm.

University, Diss., 2003--Bonn.

Universiẗat, Diss., 2005--Bonn.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Temos como objetivo neste trabalho estudar as propriedades dielÃtricas em rÃdio frequÃncia (RF) e micro-ondas do composto Sr2CoNbO6 (SCNO) adicionando com o Ãxido de titÃnio (TiO2) em porcentagens variando de 15% a 22% em massa. O SCNO à uma perovskita dupla, que foi preparado atravÃs do mÃtodo de reaÃÃo do estado sÃlido. As amostras foram caracterizadas estruturalmente atravÃs da difraÃÃo de raio â X (DRX). O mÃtodo utilizado para obtenÃÃo da fase desejada foi realizada atravÃs do refinamento de Rietveld, que mostrou estrutura de simetria cÃbica do tipo pm3m. As propriedades dielÃtricas: constante dielÃtrica (εâ) e fator de perda dielÃtrica (tgδ) foram medidas à temperatura ambiente na faixa de frequÃncia de 100KHz a 2GHz e mostraram que a permissividade diminui com a frequÃncia. Abaixo de 50MHz a constante dielÃtrica se apresenta alta e acima de 1GHz se apresenta baixa. A picnometria realizada mostrou que as densidades relativas ficaram todas acima de 80%. Para que o estudo de micro-ondas ficasse completo aplicamos o mÃtodo de Hakki Coleman, que mostrou crescimento da permissividade dielÃtrica com o aumento da concentraÃÃo de TiO2 (14 â 52)e perdas dielÃtricas variando de 10-2 - 10-4 . O coeficiente de temperatura da frequÃncia de ressonÃncia (τf) mostrou que o SCNO apresenta τf negativo (-634ppm/oC). Com a adiÃÃo do TiO2 o τf passou a apresentar valores positivos. A simulaÃÃo numÃrica de uma antena ressoadora dielÃtrica (DRA) baseada no SCNO e adicionada com TiO2 foi realizada atravÃs do software HFSS e os resultados se apresentaram bastante concordantes com os experimentos. O baixo ganho e uma pequena eficiÃncia apresentada para o SCNO puro foi melhorado substancialmente com a adiÃÃo do TiO2. Estas propriedades podem ser melhoradas com uma proposta de uma nova geometria para a (DRA) e com adiÃÃo do TiO2 em novas porcentagens para anÃlises de propriedades dielÃtricas e parÃmetros de antenas.

Antennas are an important component of wireless ("without wires") communications, regardless of their use. As these systems have become increasingly complex, antenna design requirements have become more demanding. Conventional antenna design consists of selecting some canonical radiator structure described by a handful of key dimensions, and then adjusting these using an optimization algorithm that improves some performance-related objective function that is (during optimization) repeatedly evaluated via a full-wave computational electromagnetics model of the structure. This approach has been employed to great effect in the enormously successful development of wireless communications antenna technology thus far, but is limiting in the sense that the "design space" is restricted to a library of canonical (or regular near-canonical) shapes. As increased design constraints and more complicated placement requirements arise such an approach to antenna design could eventually become a bottleneck. The use of antenna shape synthesis, a process also referred to as inverse design, can widen the "design space", and include such aspects as occupancy and fabrication constraints, the presence of a platform, even weight constraints, and much more. Dielectric resonator antennas (DRAs) hold the promise of lower losses at higher frequencies. This thesis uses a three-dimensional shape optimization algorithm along with a characteristic mode analysis and a genetic algorithm to shape synthesize DRAs. Until now, a limited amount of work on such shape synthesis has been performed for single-feed fixed-beam DRAs. In this thesis we extend this approach by devising and implementing a new shaping methodology for significantly more complex problems, namely directivity-maximized multi-port fixed-beam DRAs, and multi-port DRAs capable of the beam-steering required to satisfy certain spherical coverage constraints, where the location, type and number of feed-ports need not be specified prior to shaping. The approach enables even low-profile enhanced-directivity DRAs to be shape synthesized.

Yes / A compact dielectric resonator antenna for ultra-wideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed.

No / A small dielectric resonator antenna has been designed for ultra wideband (UWB) communication system applications. The antenna element is a rectangular low permittivity ceramic block, with a dielectric constant of 9.4, and the modified T-shaped feed network includes a 50 ohm microstrip line to achieve strong coupling, and some bandwidth enhancement. The antenna performance is simulated and measured over a frequency band extending from 3100 MHz to 5500 MHz; the impedance bandwidth over this interval is 55.8% with VSWR <; 2, making the antenna suitable for UWB applications.

Yes / A compact dielectric resonator antenna (DRA) for wideband applications is proposed. Two cylindrical dielectric resonators which are asymmetrically located with respect to the center of a rectangular coupling aperture are fed through this aperture. By optimizing the design parameters, an impedance bandwidth of about 29%, covering the frequency range from 9.62 GHz to 12.9 GHz, and a gain of 8 dBi are obtained. Design details of the proposed antenna and the results of both simulation and experiment are presented and discussed.

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.