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Sökning: LAR1:lu > Sjöberg Daniel > Lunds universitet > Kungliga Tekniska Högskolan

  • Resultat 1-4 av 4
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1.
  • Helander, Jakob, et al. (författare)
  • Performance Analysis of Millimeter-Wave Phased Array Antennas in Cellular Handsets
  • 2016
  • Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1536-1225. ; 15, s. 504-507
  • Tidskriftsartikel (refereegranskat)abstract
    • This letter discusses the usage of high-gain steerable antenna arrays operating at millimeter-wave (mmWave) frequencies for future cellular networks (5G). Based on the probable outline of the 5G networks, a method for characterizing phased array antennas in cellular handsets has been introduced. For analyzing the performance, the total scan pattern of the array configuration together with its respective coverage efficiency are essential to consider in order to compare different antenna designs and topology approaches with each other. Two design approaches and subarray schemes of these have been considered in order to illustrate the relevance of such a characterization method. The results show the importance of evaluating potential array antennas in such manners. The method can be applied to much more complex system models, where polarization diversity, hand and body effect, and statistical modeling of the channel may be included.
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2.
  • Ramprecht, Jörgen, et al. (författare)
  • Biased magnetic materials in RAM applications
  • 2007
  • Ingår i: Progress in Electromagnetics Research. - 1559-8985. ; 75, s. 85-117
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetization of a ferro- or ferri-magnetic material has been modeled with the Landau-Lifshitz-Gilbert (LLG) equation. In this model demagnetization effects are included. By applying a linearized small signal model of the LLG equation, it was found that the material can be described by an effective permeability and with the aid of a static external biasing field, the material can be switched between a Lorentz-like material and a material that exhibits a magnetic conductivity. Furthermore, the reflection coefficient for normally impinging waves on a PEC covered with a ferro/ferri-magnetic material, biased in the normal direction, is calculated. When the material is switched into the resonance mode, two distinct resonance frequencies in the reflection coefficient were found, one associated with the precession frequency of the magnetization and the other associated with the thickness of the layer. The former of these resonance frequencies can be controlled by the bias field and for a bias field strength close to the saturation magnetization, where the material starts to exhibit a magnetic conductivity, low reflection ( around - 20 dB) for a quite large bandwidth ( more than two decades) can be achieved.
3.
  • Ramprecht, Jörgen, et al. (författare)
  • Magnetic Losses in Composite Materials
  • 2008
  • Ingår i: Journal of Physics D : Applied Physics. - 0022-3727. ; 41:13, s. 135005
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss some of the problems involved in homogenization of a composite material built from ferromagnetic inclusions in a nonmagnetic background material. The small signal permeability for a ferromagnetic spherical particle is combined with a homogenization formula to give an effective permeability for the composite material. The composite material inherits the gyrotropic structure and resonant behaviour of the single particle. The resonance frequency of the composite material is found to be independent of the volume fraction, unlike dielectric composite materials. The magnetic losses are described by a magnetic conductivity which can be made independent of frequency and proportional to the volume fraction by choosing a certain bias. Finally, some concerns regarding particles of small size, i.e. nanoparticles, are treated and the possibility of exciting exchange modes are discussed. These exchange modes may be an interesting way to increase losses in composite materials.
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4.
  • Ramprecht, Jörgen, et al. (författare)
  • Scattering from a thin magnetic layer with a periodic lateral magnetization application to electromagnetic absorbers
  • 2008
  • Ingår i: Progress in Electromagnetics Research. - 1559-8985. ; 83, s. 199-224
  • Tidskriftsartikel (refereegranskat)abstract
    • A magnetized thin layer mounted on a PEC surface is considered as an alternative for an absorbing layer. The magnetic material is modeled with the Landau-Lifshitz-Gilbert equation, with a lateral static magnetization having a periodic variation along one lateral direction. The scattering problem is solved by means of an expansion into Floquet-modes, a propagator formalism and wave-splitting. Numerical results are presented, and for parameter values close to the typical values for ferro- or ferrimagnetic media, reflection coefficients below -20 dB can be achieved for the fundamental mode over the frequency range 1-4 GHz, for both polarizations. It is found that the periodicity of the medium makes the reflection properties for the fundamental mode almost independent of the azimuthal direction of incidence, for both normally and obliquely incident waves.
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  • Resultat 1-4 av 4
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fritt online (2)
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tidskriftsartikel (4)
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refereegranskat (4)
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Ramprecht, Jörgen (3)
Ying, Zhinong (1)
Norgren, Martin, (1)
Helander, Jakob, (1)
Zhao, Kun (1)
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Engelska (4)
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