On 10/23/2013 03:26 PM, W5DXP wrote:
On Wednesday, October 23, 2013 6:07:45 AM UTC-5, J.B. Wood wrote:
So I think using a term like "magnetic loop antenna" or "electric dipole
antenna" is misleading.
A short loop antenna responds more to the magnetic field than the electric field. A short dipole responds more to the electric field than the magnetic field. A full-sized dipole or loop responds equally to both fields - that's why they are the most efficient.
I'm also a EE and maybe my experience with receiving antennas will shed some light. I have, in the past, been involved with 75m mobile shootout measurements. At first, we tried to use a 75m hamstick but human bodies close to the antenna affected the receive signal strengths considerably because of the effect of human bodies on the electric field. We switched over to ferrite rod antennas which, because they respond primarily to the magnetic field, are more immune to the effects of human bodies. Although you are correct in stating that all radio waves in free space are ElectroMagnetic waves, some antennas are more sensitive to the magnetic portion of the EM wave and some are more sensitive to the electric portion of the EM wave. Since antennas are, in general, reciprocal for receiving/transmitting, I can understand why some antennas are associated with the magnetic field of an EM wave and some are associated with the electric field of an EM wave.
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73, Cecil, w5dxp.com
Sorry, Cecil, that while I usually agree with you I would take exception
to the "responds more" comment, if taken in the sense that it applies
everywhere. If the loop is being used as an inductive pickup, IOW in
the near field of a radiator or mutually coupled to another coil in
close proximity, then I can see that view. But not in the far field. In
the far field it would be just as correct to say that the loop responds
to the electric field. A better way of putting this IMO would be that
the loop (as a receiving antenna) in the far field (several wavelengths
removed from the transmitter) captures a portion of the E-M energy
incident upon it (what isn't captured is scattered). The amount of
energy captured is a function of the antenna's "effective area", which
depends upon antenna geometry and its orientation relative to the
incident energy (E/H field direction). Sincerely,
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J. B. Wood e-mail: