Actes de la Conférence JCMM 2010 03/2010;
Source: OAI

ABSTRACT Les travaux de recherche pour la miniaturisation d'antennes, utilisant de nouveaux matériaux, se sont intensifiés ces dernières années, et notamment avec l'utilisation de matériaux possédant des propriétés magnétiques. La miniaturisation des antennes imprimées est rendue possible en chargeant le volume de l'antenne avec des matériaux à haute permittivité [ ], ferroélectriques [ ], ferromagnétiques [ ], magnéto-diélectriques [ , , ], etc. Plus traditionnellement, les diélectriques présentant une permittivité élevée ont été employés pour diminuer les dimensions physiques de l'élément rayonnant [ ]. Les problèmes souvent rencontrés avec les substrats de haute permittivité sont, par exemple, la dégradation de la bande passante et du gain et donc l'efficacité de l'antenne. L'utilisation de matériaux magnétiques serait une solution intéressante pour la miniaturisation d'antennes sans dégrader les performances grâce à la valeur importante de la perméabilité. Or à ce jour, malgré les progrès technologiques importants réalisés sur les matériaux ferrites doux, ceux-ci sont utilisés principalement en basse fréquence pour la réalisation de dispositifs non réciproques (circulateurs, isolateurs) ou de circuits accordables (filtres, déphaseurs...). Dans la bande UHF, leurs pertes élevées, liées à une contribution des déplacements de parois séparant les domaines magnétiques, excluent leur utilisation comme substrat d'antennes imprimées. Dans ce travail, nous développons un nouveau matériau magnéto-diélectrique pour l'application antennaire. Ses performances sont comparées à celles d'un matériau disponible dans le commerce.

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    ABSTRACT: Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completeness. Good correlation between the computed results and measurements is observed
    IEEE Transactions on Antennas and Propagation 01/2000; · 2.46 Impact Factor
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    ABSTRACT: Biased ferrite materials have been used for electromagnetic applications, particularly those involving printed microwave circuits. Their appeal is that their electrical properties can be easily changed with frequency. By varying the strength of the applied magnetic field, ferrites exhibit interesting characteristics, including non-reciprocal effects, frequency tuning by changing external biasing, polarization diversity using a single element, and various other useful properties
    Antennas and Propagation Society International Symposium, 1997. IEEE., 1997 Digest; 08/1997
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    ABSTRACT: In this paper, the unique features of periodic magneto-dielectric meta-materials in electromagnetics are addressed. These materials, which are arranged in periodic configurations, are applied for the design of novel EM structures with applications in the VHF-UHF bands. The utility of these materials is demonstrated by considering two challenging problems, namely, design of miniaturized electromagnetic band-gap (EBG) structures and antennas in the VHF-UHF bands. A woodpile EBG made up of magneto-dielectric material is proposed. It is shown that the magneto-dielectric woodpile not only exhibits band-gap rejection values much higher than the ordinary dielectric woodpile, but also for the same physical dimensions it shows a rejection band at a much lower frequency. The higher rejection is a result of higher effective impedance contrasts between consecutive layers of the magneto-dielectric woodpile structure. Composite magneto-dielectrics are also shown to provide certain advantages when used as substrates for planar antennas. These substrates are used to miniaturize antennas while maintaining a relatively high bandwidth and efficiency. An artificial anisotropic meta-substrate having μ<sub>r</sub>>ε<sub>r</sub>, made up of layered magneto-dielectric and dielectric materials is designed to maximize the bandwidth of a miniaturized patch antenna. Analytical and numerical approaches, based on the anisotropic effective medium theory (AEMT) and the finite-difference time-domain (FDTD) technique, are applied to carry out the analyzes and fully characterize the performance of finite and infinite periodic magneto-dielectric meta-materials integrated into the EBG and antenna designs.
    IEEE Transactions on Antennas and Propagation 07/2004; · 2.46 Impact Factor

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