1. 
 Derneryd, Anders, et al.
(författare)

Application of gainbandwidth bounds on loaded dipoles
 2009

Ingår i: IET Microwaves, Antennas and Propagation.  17518725. ; 3:6, s. 959966

Tidskriftsartikel (refereegranskat)abstract
 Physical limitations based only on antenna volume, form factor and material parameters are applied to electrically small antennas in the form of single dipoles. The upper bound on the gainbandwidth product is solely determined by the polarisability matrix that characterises the antenna when it is immersed in a uniform applied static field. The polarisability, and hence the bandwidth, is increased by loading the dipole arms close to their ends. The halfpower impedance bandwidth is increased from 5 to 13% by moving the coils from the centre to the ends of the dipole arms. The introduction of a stubmatching further improves the bandwidth but the physical limit is not reached. Finally, a dualresonance dipole antenna is analysed. It is observed that a second resonance hardly reduces the bandwidth of the first resonance if the resonances are separated more than 1.7 times in frequency.


2. 
 Gustafsson, Mats, et al.
(författare)

A timedomain approach to the extinction paradox for scattering of electromagnetic waves
 2008

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 timedomain approach it is shown that the highfrequency 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 highfrequency limit.


3. 
 Gustafsson, Mats, et al.
(författare)

An overview of some recent physical bounds in scattering and antenna theory
 2009

Ingår i: 3rd European Conference on Antennas and Propagation. ; s. 17951798

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 highfrequency 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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5. 
 Gustafsson, Mats, et al.
(författare)

Physical bounds and summation rules in antenna theory
 2008

Konferensbidrag (refereegranskat)abstract
 Although the concept of physical bounds for electrically small antennas was first introduced more than half a century ago by Wheeler and Chu it continuous to receive attention and still there is only a partial knowledge of these bounds. Most of the research effort in this field are based on the ideas of a stored energy in the different partial waves as introduced by Chu and, hence, suffers from the same shortcomings. The objective of this paper is to present three alternative approaches to derive physical bounds on antennas that are solely based on the assumptions of linearity, timetranslational invariance, causality, and reciprocity. These assumptions are utilized in three different scattering settings to construct various Herglotz functions from which summation rules and associated physical bounds are derived.


6. 
 Gustafsson, Mats, et al.
(författare)

Physical bounds on the antenna scattering matrix
 2008

Konferensbidrag (refereegranskat)abstract
 The antenna scattering matrix is based on a spherical vector wave expansion and contains a complete description of the matching, transmission, receiving, and scattering properties of an antenna. It is commonly utilized in nearfield measurements and it can also be used to model MIMO antennas. Here, an approach based on the holomorphic properties of the antenna scattering matrix is used to derive physical bounds on the bandwidth of lossless antennas. The resulting bounds are expressed in the radius of the smallest circumscribing sphere and the polarizability dyadics of the antenna. The derivation and final results resemble both the classical work by Chu (1948) and a recently developed theory based on the forward scattering. However, instead of estimating the Qfactor through the stored energy, the lowfrequency expansion of the scattering matrix is used to obtain a set of summation rules from which bounds on the bandwidth are derived. The use of Cauchy integrals and the lowfrequency expansion in terms of the polarizability dyadics are similar with the approach in (Chu, 1948 and Gustafsson et al., 2007).


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8. 
 Gustafsson, Mats, et al.
(författare)

Physical limitations on antennas of arbitrary shape
 2007

Ingår i: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.  13645021. ; 463:2086, s. 25892607

Tidskriftsartikel (refereegranskat)abstract
 In this paper, physical limitations on bandwidth, realized gain, Qfactor 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 longwavelength, highcontrast 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 Qfactor for nonspherical geometries.


9. 
 Gustafsson, Mats, et al.
(författare)

Physical limitations on D/Q for antennas
 2007

Konferensbidrag (refereegranskat)abstract
 In this paper, physical limitations on the directivity D and Qfactor 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 highcontrast polarizability dyadic. The theory is exemplified by numerical results for the halfwave antenna with astonishing agreement.


10. 
 Gustafsson, Mats, et al.
(författare)

Physical limitations on scattering and absorption of antennas
 2007

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 highcontrast polarizability dyadic. The theoretical results are illustrated by a resonant loop antenna and an ultrawideband (UWB) spiral antenna.

