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Antenna Q and stored energy expressed in the fields, currents, and input impedance

Gustafsson, Mats LU and Jonsson, B.L.G (2015) In IEEE Transactions on Antennas and Propagation 63(1). p.240-249
Abstract
Although the stored energy of an antenna is instrumental in the evaluation of antenna Q and the associated physical bounds, it is difficult to strictly define stored energy. Classically, the stored energy is either determined from the input impedance of the antenna or the electromagnetic fields around the antenna. The new energy expressions proposed by Vandenbosch express the stored energy in the current densities in the antenna structure. These expressions are equal to the stored energy defined from the difference between the energy density and the far field energy for many but not all cases. Here, the different approaches to determine the stored energy are compared for dipole, loop, inverted L-antennas, and bow-tie antennas. We use Brune... (More)
Although the stored energy of an antenna is instrumental in the evaluation of antenna Q and the associated physical bounds, it is difficult to strictly define stored energy. Classically, the stored energy is either determined from the input impedance of the antenna or the electromagnetic fields around the antenna. The new energy expressions proposed by Vandenbosch express the stored energy in the current densities in the antenna structure. These expressions are equal to the stored energy defined from the difference between the energy density and the far field energy for many but not all cases. Here, the different approaches to determine the stored energy are compared for dipole, loop, inverted L-antennas, and bow-tie antennas. We use Brune synthesized circuit models to determine the stored energy from the input impedance. We also compare the results with differentiation of the input impedance and the obtained bandwidth. The results indicate that the stored energy in the fields, currents, and circuit models agree well for small antennas. For higher frequencies, the stored energy expressed in the currents agrees with the stored energy determined from Brune synthesized circuit models whereas the stored energy approximated by differentiation of input impedance gives a lower value for some cases. The corresponding results for the bandwidth suggest that the inverse proportionality between the fractional bandwidth and Q-factor depends on the threshold level of the reflection coefficient. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
antenna Q, stored energy, antennas
in
IEEE Transactions on Antennas and Propagation
volume
63
issue
1
pages
240 - 249
publisher
IEEE--Institute of Electrical and Electronics Engineers Inc.
external identifiers
  • wos:000347383500025
  • scopus:85016354053
ISSN
0018-926X
DOI
10.1109/TAP.2014.2368111
project
EIT_CACO-EMD Complex analysis and convex optimization for EM design
language
English
LU publication?
yes
id
64f8eb89-f196-4fff-a9fd-61440771cf14 (old id 4731124)
date added to LUP
2014-10-28 10:41:03
date last changed
2017-11-12 03:41:09
@article{64f8eb89-f196-4fff-a9fd-61440771cf14,
  abstract     = {Although the stored energy of an antenna is instrumental in the evaluation of antenna Q and the associated physical bounds, it is difficult to strictly define stored energy. Classically, the stored energy is either determined from the input impedance of the antenna or the electromagnetic fields around the antenna. The new energy expressions proposed by Vandenbosch express the stored energy in the current densities in the antenna structure. These expressions are equal to the stored energy defined from the difference between the energy density and the far field energy for many but not all cases. Here, the different approaches to determine the stored energy are compared for dipole, loop, inverted L-antennas, and bow-tie antennas. We use Brune synthesized circuit models to determine the stored energy from the input impedance. We also compare the results with differentiation of the input impedance and the obtained bandwidth. The results indicate that the stored energy in the fields, currents, and circuit models agree well for small antennas. For higher frequencies, the stored energy expressed in the currents agrees with the stored energy determined from Brune synthesized circuit models whereas the stored energy approximated by differentiation of input impedance gives a lower value for some cases. The corresponding results for the bandwidth suggest that the inverse proportionality between the fractional bandwidth and Q-factor depends on the threshold level of the reflection coefficient.},
  author       = {Gustafsson, Mats and Jonsson, B.L.G},
  issn         = {0018-926X},
  keyword      = {antenna Q,stored energy,antennas},
  language     = {eng},
  number       = {1},
  pages        = {240--249},
  publisher    = {IEEE--Institute of Electrical and Electronics Engineers Inc.},
  series       = {IEEE Transactions on Antennas and Propagation},
  title        = {Antenna Q and stored energy expressed in the fields, currents, and input impedance},
  url          = {http://dx.doi.org/10.1109/TAP.2014.2368111},
  volume       = {63},
  year         = {2015},
}