| 51. |
- Gustafsson, Mats, et al.
(författare)
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A time-domain approach to the extinction paradox for scattering of electromagnetic waves
- 2008
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Ingår i: ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- The extinction paradox states that a perfectly electric conducting target which is large compared to the wavelength removes from the incident radiation exactly twice the amount of power it can intercept by its geometrical cross section area. In this paper, the extinction paradox is generalized to include temporally dispersive material parameters with finite values of the permittivity and the permeability. From a time-domain approach it is shown that the high-frequency limit of the extinction cross section depends on the material parameters of the target and that a limiting value not necessarily exists. These findings are exemplified by several numerical illustrations with different values of the extinction cross section in the high-frequency limit.
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| 52. |
- Gustafsson, Mats, et al.
(författare)
-
An overview of some recent physical bounds in scattering and antenna theory
- 2009
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Ingår i: ; , s. 1715-1718
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Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to give an overview of some recently developed sum rules and physical bounds in scattering and antenna theory. The sum rules are based on integral identities for Herglotz functions that relate the quantity of interest with its low and high-frequency behavior. The sum rules are transformed to bounds by estimating the integrals and applying variational results to the parameters that appear in the asymptotic expansions. The theoretical findings are exemplified by numerical results for various scattering and antenna configurations.
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| 53. |
- Gustafsson, Mats, et al.
(författare)
-
Forward scattering of loaded and unloaded antennas
- 2012
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 60:12, s. 5663-5668
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Tidskriftsartikel (refereegranskat)abstract
- Forward scattering of antennas is related to antenna performance via the forward scattering sum rule. The forward scattering sum rule is an integral identity that shows that a weighted integral of the extinction cross section over all spectrum is proportional to the static polarizabiliy of the antenna structure. Here, the forward scattering sum rule is experimentally verified for loaded, short circuit, and open circuit cylindrical dipole antennas. It is also shown that the absorption efficiency cannot be greater than 1/2 for reciprocal linearly polarized lossless matched antennas with a symmetric radiation pattern.
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| 54. |
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| 55. |
- Gustafsson, Mats, et al.
(författare)
-
Physical bounds and sum rules in scattering and antenna theory
- 2009
-
Ingår i: Electromagnetics in Advanced Applications, 2009. ICEAA '09. International Conference on. ; , s. 600-603, s. 600-603
-
Konferensbidrag (refereegranskat)abstract
- The objective of this paper is to review some recently developed sum rules and physical bounds in scattering and antenna theory. The sum rules are based on identities for Herglotz functions that relate the quantity of interest integrated over all wavelengths with its static polarizability dyadics. They are transformed to physical bounds by applying variational principles for the polarizability dyadics together with various estimates of the integrals. The theoretical findings are exemplified by numerical results for several configurations.
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| 56. |
- Gustafsson, Mats, et al.
(författare)
-
Physical bounds on the partial realized gain
- 2010
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Ingår i: [Host publication title missing]. ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- An antenna identity, derived from the forward scattering sum rule, shows that the partial realized gain of an antenna is related to the polarizability of the antenna structure. The partial realized gain contains the mismatch, directivity, efficiency, and polarization properties of the antenna. The antenna identity expresses how the performance depends on the electrical size and shape of the antenna structure. It is also the starting point for several antenna bounds. In this paper, the identity, its associated physical bounds, and computational aspects of the polarizability dyadics are discussed.
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| 57. |
- Gustafsson, Mats, et al.
(författare)
-
Physical limitations on antennas of arbitrary shape
- 2007
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Ingår i: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021. ; 463:2086, s. 2589-2607
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, physical limitations on bandwidth, realized gain, Q-factor and directivity are derived for antennas of arbitrary shape. The product of bandwidth and realizable gain is shown to be bounded from above by the eigenvalues of the long-wavelength, high-contrast polarizability dyadics. These dyadics are proportional to the antenna volume and are easily determined for an arbitrary geometry. Ellipsoidal antenna volumes are analysed in detail, and numerical results for some generic geometries are presented. The theory is verified against the classical Chu limitations for spherical geometries and shown to yield sharper bounds for the ratio of the directivity and the Q-factor for non-spherical geometries.
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| 58. |
- Gustafsson, Mats, et al.
(författare)
-
Physical limitations on D/Q for antennas
- 2007
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Ingår i: ; , s. 1-3
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Konferensbidrag (refereegranskat)abstract
- In this paper, physical limitations on the directivity D and Q-factor Q are derived for antennas of arbitrary shape. The quotient D/Q is shown to be bounded from above by the antenna volume and certain shape coefficients in terms of the eigenvalues of the high-contrast polarizability dyadic. The theory is exemplified by numerical results for the half-wave antenna with astonishing agreement.
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| 59. |
- Gustafsson, Mats, et al.
(författare)
-
Physical limitations on scattering and absorption of antennas
- 2007
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Ingår i: ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- In this paper, physical limitations are presented for antennas of arbitrary shape. Antenna properties such as bandwidth and directivity are shown to be bounded from above by the antenna volume and certain shape coefficients given by the eigenvalues of the high-contrast polarizability dyadic. The theoretical results are illustrated by a resonant loop antenna and an ultrawideband (UWB) spiral antenna.
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| 60. |
- Gustafsson, Mats, et al.
(författare)
-
Sum rules and physical bounds in electromagnetic theory
- 2010
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Ingår i: [Host publication title missing]. ; , s. 37-40
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Konferensbidrag (refereegranskat)abstract
- Sum rules are useful in many branches of physics and engineering as they relate all spectrum parameter values with their asymptotic expansions. Properties of the dynamic response can hence be inferred by the, in many cases much simpler, static response. This has e.g., been used for lossless matching networks, radar absorbers, extinction cross section, partial realized gain of antennas, high-impedance surfaces, transmission cross section, transmission coefficients, and temporal dispersion of metamaterials. Here, several sum rules and their associated physical bounds are reviewed and it is shown that integral identities for Herglotz functions offer a unified approach in deriving them.
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