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Power Flow From a Short Antenna Lossy Uniaxial Medium
Author(s) -
Galejs Janis
Publication year - 1967
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/rds19672121419
Subject(s) - poynting vector , lossy compression , antenna (radio) , physics , flow (mathematics) , lossless compression , power (physics) , optics , mathematics , acoustics , mechanics , telecommunications , computer science , magnetic field , statistics , algorithm , quantum mechanics , data compression
The power flow from a short linear current element is computed by integrating the Poynting's vector over concentric cylindrical surfaces of various radii ρ . An effective antenna resistance is defined as the ratio between the integrated power flow and the mean square source current. In a lossless medium the integrated power flow is independent of ρ , and the conventional expression is obtained for the radiation resistance. In a slightly lossy medium, and at moderate distances ρ the effective resistance R remains unaltered for frequencies ω above the plasma frequency ω ρ . For ω < ω ρ , a simple asymptotic approximation shows that R which is inversely proportional to the antenna length ℓ for ρ small is gradually changed to R ∼ ℓ 2 / ρ 3 with increasing values of ρ . There is an optimum antenna length ℓ ∼ ρ which maximizes the power flow for this value of ρ . For very large distances from the source the power flow is proportional to ℓ 2 / ρ 4 and it remains of the same form for frequencies above and below the plasma frequency.