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Sökning: WFRF:(Kristensson Gerhard)

  • Resultat 1-10 av 252
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1.
  • Karlsson, Anders, et al. (författare)
  • Transient wave propagation in gyrotropic media
  • 1992
  • Ingår i: Invariant inbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 77-89
  • Bokkapitel (övrigt vetenskapligt)abstract
    • In this paper transient electromagnetic wave propagation in an inhomogeneous,<br /> cold plasma is considered. It is assumed that a constant magnetic<br /> induction is present and that the plasma is spatially inhomogeneous in the<br /> direction of the magnetic induction. Losses in the plasma are modeled with a<br /> collision frequency ν. The direct problem, which is to calculate the reflected<br /> and transmitted responses of the plasma, is considered in this paper. Special<br /> attention is paid to the precursor effects in the plasma and several examples<br /> of precursor effects in an inhomogeneous plasma are showed.
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2.
  • Karlsson, Anders, et al. (författare)
  • Wave splitting and imbedding equations for a spherically symmetric dispersive medium
  • 1992
  • Ingår i: Invariant inbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 103-113
  • Bokkapitel (övrigt vetenskapligt)abstract
    • The direct problem of time dependent electromagnetic scattering in the dispersive<br /> sphere is solved by a wave splitting technique. The electric field is<br /> expanded in a series involving vector spherical harmonics, leading to a system<br /> of wave equations for each term. These systems are reduced to scalar<br /> wave equations for each term, which are solved via reflection operators. Some<br /> preliminary numerical results are presented.
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3.
  • Kristensson, Gerhard, et al. (författare)
  • Time domain inversion techniques for electromagnetic scattering problems
  • 1992
  • Ingår i: Invariant imbedding and inverse problems. - SIAM. - 0-89871-305-6 ; s. 1-29
  • Bokkapitel (övrigt vetenskapligt)abstract
    • This paper presents a review of and a comparison between two different methods<br /> to solve an inverse scattering problem in the time domain. The problem<br /> is that of propagation of transient electromagnetic waves in spatially inhomogeneous<br /> slabs of finite length. The permittivity and conductivity profiles<br /> are assumed to vary only with depth and the scattering problem is thus onedimensional.<br /> Several algorithms to solve the direct and inverse scattering<br /> problems for continuous and discontinuous permittivity profiles are suggested.<br /> Some of these algorithms have not been published before. The aim of this paper<br /> is to compare and review these methods. More specifically, the numerical<br /> performance of the invariant imbedding approach (layer-stripping)and the<br /> Green functions formulation (downward continuation)is compared. Some<br /> new results based upon time reversal techniques for a lossless slab are presented<br /> in an appendix.
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4.
5.
  • Alayon Glazunov, Andres, et al. (författare)
  • Branch cross-correlation in presence of spatially selective interference Expressed in Terms of the spherical vector wave expansion of the electromagnetic field
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • In this paper we present an analysis of the cross-correlation coe±cient between signals at two antennabranches (ports) in the presence of spatially selective interference and additive white gaussian noise. Morespeci¯cally, we look at a §45± slanted polarization diversity arrangement, which is rotated around the axisperpendicular to the plane containing the antennas. Results are provided as a function of the rotation angle.The analysis is based on the spherical vector wave multi-pole expansion of both the ¯eld impinging on theantennas and the antenna radiation properties.
6.
  • Alayon Glazunov, Andres, et al. (författare)
  • On the mean effective gain expressed in terms of the spherical vector wave expansion of the electromagnetic field
  • 2008
  • Konferensbidrag (refereegranskat)abstract
    • The mode expansion o®ers a general framework for the analysis of the interaction between antennas andpropagation channels. In this paper, the Mean E®ective Gain (MEG) of an antenna is expressed in termsof the spherical vector wave expansion of the electromagnetic ¯eld. An explicit expression of the MEG isprovided as a function of the normalized average power of modes excited in the propagation channel andthe correlation between the channel modes due to the polarization and spatial selectivity of plane wavesimpinging at the antenna.
7.
  • Alayon Glazunov, Andres, et al. (författare)
  • Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis
  • 2008
  • Rapport (övrigt vetenskapligt)abstract
    • In this paper we introduce an approach to analyze the interaction between<br /> antennas and the propagation channel. We study both the antennas and the<br /> propagation channel by means of the spherical vector wave mode expansion of<br /> the electromagnetic field. Then we use the expansion coefficients to study<br /> some properties of general antennas in those fields by means of the antenna<br /> scattering matrix. The focus is on the spatio-polar characterization of<br /> antennas, channels and their interactions. We provide closed form<br /> expressions for the covariance of the field multi-modes as function of the<br /> Power Angle Spectrum (PAS) and the channel cross-polarization ratio (XPR). A<br /> new interpretation of the Mean Effective Gains (MEG) of antennas is also<br /> provided. The maximum MEG is obtained by conjugate mode matching between the<br /> antennas and the channel; we also prove the (intuitive) results that the<br /> optimum decorrelation of the antenna signals is obtained by the excitation<br /> of orthogonal spherical vector modes.
8.
  • Alayon Glazunov, Andres, et al. (författare)
  • Spherical Vector Wave Expansion of Gaussian Electromagnetic Fields for Antenna-Channel Interaction Analysis
  • 2009
  • Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 57:7, s. 2055-2067
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we introduce an approach to analyze the interaction between antennas and the propagation channel. We study both the antennas and the propagation channel by means of the spherical vector wave mode expansion of the electromagnetic field. Then we use the expansion coefficients to study some properties of general antennas in thosefields by means of the antenna scattering matrix. The focus is on the spatio-polar characterization of antennas, channels and their interactions. We provide closed form expressions for the covariance of the field multimodes as function of the power angle spectrum (PAS) and the channel cross-polarization ratio (XPR). A new interpretation of the mean effective gains (MEG) of antennas is also provided. The maximum MEG is obtained by conjugate mode matching between the antennas and the channel; we also prove the (intuitive) results that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector modes.
9.
  • Bernekorn, Peter, et al. (författare)
  • Propagation of transient electromagnetic waves in inhomogeneous and dispersive waveguides
  • 1995
  • Rapport (övrigt vetenskapligt)abstract
    • Transient wave propagation in a waveguide filled with an inhomogeneous dispersive<br /> medium is analyzed. The waveguide is inhomogeneous in the longitudinal<br /> direction, but is homogeneously filled in the transverse directions. The<br /> analysis is performed in the time domain and is based upon a wave splitting<br /> technique and the method of propagators. The propagator maps the exciting<br /> field from one position in the waveguide to the field at another position. This<br /> mapping is represented as time convolution integrals. The theory is exemplified<br /> by numerical examples where it is shown how wave trains of different<br /> shapes are propagating in a waveguide filled with a homogeneous dispersive<br /> medium.
10.
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