[RFI] Far Field, Near Field

Cortland Richmond ka5s at earthlink.net
Mon Jan 24 19:06:48 EST 2005

An article in the IEEE Antennas and Propagation Magazine for October 2004
discusses the near field/far field distinction for dipoles of  various
lengths up to one wavelength. It concludes that the lower boundary of the
far field is 9 wavelengths for 0.1 wavelength and 0.25 dipoles, 9.5
wavelengths for a half wave dipole,  and 12 wavelengths for a one
wavelength dipole.

The authors define the very near field zone as that region inside which the
wave impedance is both different than  377 ohms and reactive power is
non-negligible with respect to the active power.   They conclude that the
upper boundary of the very-near-field zone is 1.6 wavelengths from a 0.1
wavelength dipole, 1.75 wavelengths from a 0.25 wavelength dipole, 2.05
wavelengths from a half wave dipole and   2.85 wavelengths for a full-wave

This may have implications for measurements taken at Amateur stations and
also of BPL emissions.  

"On Radiating-Zone Boundaries of Short, ?/2 and ? Dipoles"
S. Laybros and P.F. Combes
IEEE Antennas and Propagation Magazine, Volume 45, Number 5, October 2004 

Cortland Richmond

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