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Sökning: LAR1:lu > Sjöberg Daniel > Lunds universitet > Rapport

  • Resultat 1-10 av 37
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  • Bondarik, Alexander, et al. (författare)
  • Gridded Parasitic Patch Stacked Microstrip Antenna With Beam Shift Capability for 60 GHz Band
  • 2014
  • Rapport (övrigt vetenskapligt)abstract
    • A microstrip antenna design is introduced in which a rectangular microstrip patch is coupled electromagnetically with a gridded rectangular patch placed above. The gridded patch consists of nine identical rectangular parts separated by a distance which is much smaller than a free space wavelength for a central frequency. The antenna is designed to operate in the 60 GHz band and is fabricated on a conventional PTFE (polytetrafluoroethylene) thin substrate. The antenna return loss bandwidth is comparable to a single parasitic patch aperture coupled antenna, while the proposed antenna gain is higher. Measurement results are in good agreement with simulation. Measured 10 dB return loss bandwidth is from 54 GHz up to 67 GHz. It fully covers the unlicensed band around 60 GHz. The measured antenna realized gain at 60 GHz is close to 8 dB, while the simulated antenna radiation efficiency is 85%. A simple beam shifting method is possible for this antenna structure by connecting adjacent outside parts in the gridded patch. The designed antenna is suitable for a high speed wireless communication system in particular for a user terminal in a fifth generation (5G) cellular network.
  • Engström, Christian, et al. (författare)
  • A comparison of two numerical methods for homogenization of Maxwell's equations
  • 2004
  • Rapport (övrigt vetenskapligt)abstract
    • When the wavelength is much larger than the typical scale of the microstructure in a material, it is possible to define effective or homogenized material coefficients. The classical way of determination of the homogenized coeffi- cients consists of solving an elliptic problem in a unit cell. This method and the Floquet-Bloch method, where an eigenvalue problem is solved, are numerically compared with respect to accuracy and contrast sensitivity. The Floquet-Bloch method is shown to be a good alternative to the classical homogenization method, when the contrast is modest.
  • Gustafsson, Mats, et al. (författare)
  • Optical theorem and forward scattering sum rule for periodic structures
  • 2011
  • Rapport (övrigt vetenskapligt)abstract
    • Based on energy conservation, an optical theorem is constructed for a slab having an arbitrary periodic microstructure in a plane. A sum rule for low pass structures is derived using analytic properties of Herglotz functions based on causality and passivity. The sum rule relates the extinction cross section to the static polarizability per unit cell, and quantifies the interaction between the slab and electromagnetic fields possible over all wavelengths. The results are illustrated with several numerical and experimental examples.
  • Gustafsson, Mats, et al. (författare)
  • Physical bounds and sum rules for high-impedance surfaces
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • High-impedance surfaces are artificial surfaces synthesized from periodic structures. The high impedance is useful as it does not short circuit electric currents and reflects electric fields without phase shift. Here, a sum rule is presented that relates frequency intervals having high impedance with the thickness of the structure. The sum rule is used to derive physical bounds on the bandwidth for high-impedance surfaces. Numerical examples are used to illustrate the result, and show that the physical bounds are tight.
  • Gustafsson, Mats, et al. (författare)
  • Sum rules and physical bounds on passive metamaterials
  • 2010
  • Rapport (övrigt vetenskapligt)abstract
    • Frequency dependence of the permittivity and permeability is inevitable in metamaterial applications such as cloaking and perfect lenses. In this paper, Herglotz functions are used as a tool to construct sum rules from which we derive physical bounds suited for metamaterial applications, where the material parameters are often designed to be negative or near zero in the frequency band of interest. Several sum rules are presented that relate the temporal dispersion of the material parameters with the difference between the static and instantaneous parameter values, which are used to give upper bounds on the bandwidth of the application. This substantially advances the understanding of the behavior of metamaterials with extraordinary material parameters, and reveals a beautiful connection between properties in the design band (finite frequencies) and the low- and high-frequency limit.
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