On 10/21/2013 08:55 AM, W5DXP wrote:
On Monday, October 21, 2013 5:45:48 AM UTC-5, J.B. Wood wrote:
I would think by "magnetic" loop antenna there must also be a
"non-magnetic" loop antenna.
The opposite would actually be an "electric loop antenna". According to Kraus, there exists a "small electric antenna", i.e. a physically short dipole. The physically short loop and the physically short dipole are both standing wave antennas. The short loop operates close to a standing wave current maximum point, i.e. near a *magnetic loop* (electric node). The short dipole operates close to a standing wave voltage maximum point, i.e. near an *electric loop* (magnetic node). Full-size antennas have both magnetic loops/nodes and electric loops/nodes. Here's a quote from Kraus:
"The small horizontal loop antenna ... may be regarded as the *magnetic* counterpart of the short vertical (*electric*) dipole ... Booth loop and dipole have identical field patterns but *with the E and H interchanged*."
Note that the H field is directly proportional to the M field and that there are two distinctly different uses for the word "loop" above. One is physical, the other is electromagnetic. A "magnetic loop antenna" could just as easily be described as an "electric node antenna" and a small dipole could be called an "electric loop antenna" or a "magnetic node antenna".
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73, Cecil, w5dxp.com
Hello, and no issues here. My OP was addressing practical ham antenna
(not usually electrically small) dimensions. I still contend though
that even if one shrinks a loop antenna to something approaching a
magnetic dipole, it still should be called a "loop antenna" vice
"magnetic loop antenna". Or you can call it a "magnetic dipole" if the
dimensions apply. None of my antenna textbooks, including Kraus, uses
the term "magnetic loop antenna". Frankly, I don't know how this
terminology ever got started, but it seems to be in somewhat common use
in the ham radio community. Perhaps it is the confusion between
operation of a coil of wire as an inductor immersed in a magnetic field
vs the operation of that same coil as an antenna). Sincerely, and 73s
from N4GGO,
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J. B. Wood e-mail: