| 41. |
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| 42. |
- Persson, Kristin, et al.
(författare)
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Usage of a surface integral representation to reconstruct equivalent currents - with radome applications
- 2005
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Ingår i: Proceedings of Radiovetenskap och kommunikation. - 9170561230
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Knowledge of the current distribution on a radome can be used to improve radome design, detect manufacturing errors, and to verify numerical simulations. In this paper, the transformation from near-field data to its equivalent current distribution on a surface of arbitrary material, ie the radome, is analyzed. The transformation is based on a full vector surface integral representation that relates the equivalent currents to the near-field data. Measured near-field data originating from a reflector antenna is then examined. The field irradiates a radome whereupon it is measured on a cylindrical surface. The quantity of data is large since the height of the radome corresponds to $29-43unit{wavelengths}$ in the frequency interval $8.0-12.0unit{GHz}$. The presence of axial symmetry enables usage of the fast Fourier transform (FFT) to reduce the computational complexity. Furthermore, the problem is regularized using the singular value decomposition (SVD).
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| 43. |
- Sohl, Christian, et al.
(författare)
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A general approach for deriving bounds in electromagnetic theory
- 2008
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Ingår i: ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- This paper reports on a systematic procedure for deriving physical bounds in electromagnetic theory. The approach is based on the holomorphic properties of certain Herglotz functions and their asymptotic expansions in the low- and high-frequency regimes. A family of integral identities or summation rules is obtained with values governed by the coefficients in the low- and high-frequency expansions. In particular, summation rules for plane-wave scattering by a homogenous and isotropic sphere is derived and verified numerically by computing the extinction cross section and the bistatic radar cross section in the forward direction. It is concluded that summation rules based on Herglotz functions show great potential for deriving new physical bounds in, e.g., scattering and antenna problems.
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| 44. |
- Sohl, Christian, et al.
(författare)
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A scattering and absorption identity for metamaterials: experimental results and comparison with theory
- 2008
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 103:5, s. 1-054906
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Tidskriftsartikel (refereegranskat)abstract
- A dispersion relation for the combined effect of scattering and absorption of electromagnetic waves is presented for a large class of linear and passive material models. By invoking the optical theorem, the result states that the extinction cross section integrated over all frequencies is equal to the static limit of the extinction volume. The present paper focuses on an attempt to experimentally verify this sum rule by measuring the monostatic radar cross section of a fabricated sample of metamaterial. In particular, the paper utilizes the idea that, for a specific class of targets, the scattered fields in the forward and backward directions are identical. It is concluded that the theoretical findings are in good agreement with measurements performed in the frequency range [3.2,19.5] GHz.
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| 45. |
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| 46. |
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| 47. |
- Sohl, Christian, et al.
(författare)
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Bounds on metamaterials in scattering and antenna problems
- 2007
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Ingår i: ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- This paper reports on physical limitations on metamaterials in scattering and antenna problems. A dispersion relation for the extinction cross section is derived from the holomorphic properties of the forward scattering dyadic. The result states that for a given volume, there is only a limited amount of scattering and absorption available in the entire frequency range. The dispersion relation is verified numerically for the perfectly conducting circular disk, and theoretical bounds are illustrated for a plasmonic stratified sphere.
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| 48. |
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| 49. |
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| 50. |
- Sohl, Christian, et al.
(författare)
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Physical limitations on antennas: isoperimetric inequalities and the effect of metamaterials
- 2007
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Ingår i: [Host publication title missing]. - 9789536037506 ; , s. 75-79
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Konferensbidrag (refereegranskat)abstract
- In this paper, physical limitations on antennas are presented based on the holomorphic properties of the forward scattering dyadic. As a direct consequence of causality and energy conservation, a forward dispersion relation for the extinction cross section is established, and isoperimetric inequalities for the partial realized gain and partial directivity are derived for antennas of arbitrary shape. Closed-form expressions for the prolate and oblate spheroids are compared with Chu's classical result for the sphere, and the effect of invoking metamaterials in the antenna design is discussed. The theory is illustrated by numerical simulations of a monopole antenna with a finite ground plane.
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