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In the HF bands loop antennas are common, which, if I understand correctly, emit most of their radio energy into the magnetic field, whereas most dipoles emit largely into the electric field.

To take advantage of propagation effects, would one prefer electric field emissions over magnetic field emissions?

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[This is not my best area of knowledge, but I figured I'd give answering a try; please correct me if this is wrong.]

Electric and magnetic fields are only usefully distinguished from each other in steady-state (DC or static charge) or “near field” (distances comparable to the wavelength) conditions. Propagating radio waves are both electric fields and magnetic fields, equally and inseparably.

At a distance, the only things the design of your antenna can affect are gain and polarization. (And polarization matters only if the type of propagation you're hoping to use does not randomize polarization.)

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    $\begingroup$ You have a false dichotomy: DC vs propagating radio waves. There is another option: non-propagating AC circuits, which are, I'm told, kind of a big deal. There are components which don't radiate electromagnetic energy very well because they have a strong electric field but very little magnetic field, and we call them capacitors. They have a dual, called inductors. The two are definitely usefully distinguished. But for radiation you are right: the two can't be separated. They can be distinguished, though since they are the same thing, that isn't useful. $\endgroup$ – Phil Frost - W8II Dec 19 '13 at 22:15
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In a traveling plane wave the ratio of the electric ($\vec{E}$) and magnetic field ($\vec{H}$) is always the wave impedance of the medium (377 $\Omega$ for air or vacuum). Further, the fields are always perpendicular to each other and to the direction of the wave ($\vec{k}$) This is a very fundamental property of electromagnetic radiation. The wave you transmit propagates always the same way without knowing what kind of an antenna you used to transmit it.

However, the notion that loops are more "magnetic" and the dipoles "electric" is totally correct: in the near field, or close to the antenna as name suggests, a part of the power you feed to your antenna is stored in the electric and magnetic fields. In loop antenna the magnetic fields dominate and with dipoles the electric fields. In other words, close to the loop antenna $\frac{E}{H} < 377 \Omega$.

http://en.wikipedia.org/wiki/Near_and_far_field

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  • $\begingroup$ I think the comparison between loops and dipoles can only hold in all cases for the electrically small variants of the two. Even so, at some definitions of "close", the field impedance of a small loop is higher than the equivalent small dipole. See w8ji.com/magnetic_receiving_loops.htm $\endgroup$ – Phil Frost - W8II Dec 19 '13 at 21:29

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