Is there a name or common descriptive term for a linearly loaded dipole or end-fed, where a (near) parallel loading element or elements are not connected (galvanically isolated) to the fed element or ground, but are much closer than a director or reflector element (much less than 0.03 wavelength)?

On example might be a low NVIS wire dipole with similar (but not necessarily identical) length wire below it or near the ground. But can this be useful with a higher (non-NVIS) antenna or a vertical?

Where might there be descriptions or technical articles on this type of antenna loading?

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    $\begingroup$ What is "linear loading"? $\endgroup$ – Phil Frost - W8II Jun 13 at 18:19
  • $\begingroup$ I've heard conductive elements parallel to the driven antenna element(s) (but far closer than a director or reflector) called linear loading. As opposed to capacitive loading (hats) or inductive loading (inline coils somewhere). All in order to try an improve one or another antenna characteristic (bandwidth, SWR, feed impedance, Rr, pattern, etc.) Is there a better or more common term? $\endgroup$ – hotpaw2 Jun 13 at 22:02

I've never heard the term "linear loading", and searching for it I can only find amateur definitions, many of them contradictory.

Many reference J-poles and some reference (although they don't use the words) folded monopoles. What these have in common are transmission line stubs with the objective of modifying the feedpoint impedance.

Calling parallel wires in proximity to other wires "loading" is something to be avoided, in my opinion.

Loading, as with a loading coil, or a capacitive hat, are techniques for changing the electrical length of antenna, usually to make it electrically longer than it is physically. A loading coil at the base, or a capacitive hat at the top of an antenna has a predictable effect: it makes the antenna electrically longer. Since the effect is predictable and the technique commonly used, generalizing these techniques as "loading" is a useful terminology.

However, adding some parallel wire can have myriad effects. It might be mostly like a transmission line (like in a folded dipole) or it might be a parasitic element (like in a Yagi). It might change the impedance seen at the feedpoint (in any direction), or it might make the antenna more or less directional, or it might just be a balun which might be designed to avoid altering the impedance and radiation pattern from the idealized free-space case. The function of some parallel wire will depend on the spacing, the relative diameter, whether it's short, open, or something else at each end, where it's connected, and many other factors.

Since the effects of some parallel wire are so diverse, and there are so many possible variables, and there appears to be no solid consensus or professional literature to establish a definition of "linear loading", I would not any kind of parallel wire "loading" if my objective was to communicate clearly. Moreover, in some cases such as the J-pole the function of the parallel element is not "loading" (changing the electrical length of the antenna) but rather matching: the radiating element of the J-pole is already the desired electrical length, but the impedance is too high. "Folding" as in folded dipoles and monopoles is pretty well defined, but these designs rely on the parallel elements being shorted at the end farthest from the feedpoint, which seems to be a different thing than you are asking.

As for your question about an antenna with another wire nearby and what it might be called, I'm not aware of a name for any such thing. As explained, the behavior of such an arrangement would depend quite a bit on just how far apart the wires are and their lengths. I think a professional would call this "a low dipole with a wire buried under it", and the properties of such an antenna would be determined by modeling or empirically measuring such an arrangement of the particular geometry under consideration.

  • $\begingroup$ This blog article by W6BSD simply calls it an antenna with a parasitic element: 0x9900.com/807540-meter-antenna-for-field-day The antenna was constructed, matched its modeling quite well, and was successfully used by the SM(A)RC(W6UQ) on Field Day. $\endgroup$ – hotpaw2 Jul 21 at 0:20

In the May 2011 and October 2011 issues of ARRL's QST magazine, Joel Hallas, W1ZR, described a "Folded Skeleton Sleeve Antenna" as well as its "unfolded" companion:

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The antenna is constructed from "window line" - a two-wire transmission line created by polyethylene dielectric - with shorted ends and wires cut at appropriate places. The October article includes dimensions for band pairs from the 80-meter to 6-meter bands.

I have used 80/40, 20/15 and 17/12-meter versions of this antenna at my home station and taken them on some pretty far-flung expeditions as primary and/or backup antennas. The folded versions are more compact than a dipole for the same lower-frequency band - between 96-ft and just over 111-ft long on 80-meters, depending on the higher-frequency band. Compared to single-wire, untrapped antennas, they have the benefit of delivering the same dipole-type pattern on both of the design bands.


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