Controlling directivity and Q of small ideal antennas by the surface reactance of nearby boundary

Johan Sten, Arto Hujanen

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Directivity and radiation Q of dipole sources placed very close to a reactive impedance boundary are considered. By means of complex image theory, dominant low-frequency multipoles for fields radiated by point currents are evaluated. The multipole expansion is applied when the source region containing the currents and their images is reasonably compact and small in terms of wavelengths, which is when excitation of surface waves is unimportant. Such is the case when the surface reactance compared to the impedance of free space is very small and positive or very large and negative. Analytical expressions for directivity and Q are then written in order to study the influence of the surface reactance, and approximate expressions are derived for the surface reactance, which optimises either Q or directivity. The relation between directivity and Q is studied graphically.
Original languageEnglish
Pages (from-to)1493-1511
Number of pages19
JournalJournal of Electromagnetic Waves and Applications
Volume17
Issue number10
DOIs
Publication statusPublished - 2003
MoE publication typeA1 Journal article-refereed

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reactance
directivity
antennas
Antennas
multipoles
impedance
Surface waves
surface waves
Radiation
Wavelength
dipoles
low frequencies
expansion
radiation
wavelengths
excitation

Cite this

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title = "Controlling directivity and Q of small ideal antennas by the surface reactance of nearby boundary",
abstract = "Directivity and radiation Q of dipole sources placed very close to a reactive impedance boundary are considered. By means of complex image theory, dominant low-frequency multipoles for fields radiated by point currents are evaluated. The multipole expansion is applied when the source region containing the currents and their images is reasonably compact and small in terms of wavelengths, which is when excitation of surface waves is unimportant. Such is the case when the surface reactance compared to the impedance of free space is very small and positive or very large and negative. Analytical expressions for directivity and Q are then written in order to study the influence of the surface reactance, and approximate expressions are derived for the surface reactance, which optimises either Q or directivity. The relation between directivity and Q is studied graphically.",
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Controlling directivity and Q of small ideal antennas by the surface reactance of nearby boundary. / Sten, Johan; Hujanen, Arto.

In: Journal of Electromagnetic Waves and Applications, Vol. 17, No. 10, 2003, p. 1493-1511.

Research output: Contribution to journalArticleScientificpeer-review

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AU - Sten, Johan

AU - Hujanen, Arto

PY - 2003

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AB - Directivity and radiation Q of dipole sources placed very close to a reactive impedance boundary are considered. By means of complex image theory, dominant low-frequency multipoles for fields radiated by point currents are evaluated. The multipole expansion is applied when the source region containing the currents and their images is reasonably compact and small in terms of wavelengths, which is when excitation of surface waves is unimportant. Such is the case when the surface reactance compared to the impedance of free space is very small and positive or very large and negative. Analytical expressions for directivity and Q are then written in order to study the influence of the surface reactance, and approximate expressions are derived for the surface reactance, which optimises either Q or directivity. The relation between directivity and Q is studied graphically.

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