Quality factor of an electrically small antenna radiating close to a conducting plane

Johan Sten, Arto Hujanen, Päivi Koivisto

Research output: Contribution to journalArticleScientificpeer-review

48 Citations (Scopus)

Abstract

Expressions are derived for the smallest achievable radiation quality factor (Q) of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of non-propagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation Q is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the method of moments), and the approximate Q obtained from their fractional bandwidth are compared to the corresponding theoretical minima.
Original languageEnglish
Pages (from-to)829-837
Number of pages9
JournalIEEE Transactions on Antennas and Propagation
Volume49
Issue number5
DOIs
Publication statusPublished - 2001
MoE publication typeA1 Journal article-refereed

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Antennas
Radiation
Dipole moment
Method of moments
Wire
Decomposition
Bandwidth
Wavelength

Cite this

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title = "Quality factor of an electrically small antenna radiating close to a conducting plane",
abstract = "Expressions are derived for the smallest achievable radiation quality factor (Q) of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of non-propagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation Q is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the method of moments), and the approximate Q obtained from their fractional bandwidth are compared to the corresponding theoretical minima.",
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Quality factor of an electrically small antenna radiating close to a conducting plane. / Sten, Johan; Hujanen, Arto; Koivisto, Päivi.

In: IEEE Transactions on Antennas and Propagation, Vol. 49, No. 5, 2001, p. 829-837.

Research output: Contribution to journalArticleScientificpeer-review

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AU - Koivisto, Päivi

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AB - Expressions are derived for the smallest achievable radiation quality factor (Q) of an electrically small antenna in front of a conducting plane. Applying the low-frequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of non-propagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation Q is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the method of moments), and the approximate Q obtained from their fractional bandwidth are compared to the corresponding theoretical minima.

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