Consider a center-fed dipole antenna. It‘s well understood how the bottom element can be replaced by a ground plane (in practice, generally a few rods but in principle a conducting plate would work as well), creating a „groundplane antenna“.

From a dipole to a ground plane

I was wondering whether it would be possible to do the same transformation for directional antannas with either parasitic (Yagi-Uda) or active (HB9CV) directors.

Illustration of suggested Yagi transformation

Are there any publications out there discussing this idea? What consequences would this change have in terms of antenna properties, and how would antenna theory explain radiation?

  • $\begingroup$ Also, please excuse the quality of those sketches ;-) $\endgroup$ – jstarek May 6 at 11:32
  • $\begingroup$ See my earlier answer to a similar question here: ham.stackexchange.com/a/14509/2988 $\endgroup$ – tomnexus May 6 at 13:11
  • $\begingroup$ @jstarek I like your sketches -- very refreshing! $\endgroup$ – Brian K1LI May 6 at 15:11
  • $\begingroup$ @jstarek If appropriate, please remember to mark a response as "Answered" so that it comes off the list of "Unanswered" questions. $\endgroup$ – Brian K1LI May 6 at 22:40
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    $\begingroup$ @MikeWaters That’s just bad drawing, the line is supposed to be connected to the ground plane and the radiator. $\endgroup$ – jstarek May 8 at 7:45

Yes, this is a time-honored practice, particularly at the longer wavelengths where horizontal antennas need to be mounted quite high to provide low-angle radiation for DX work. Callum, M0MCX, presents a nice gallery of information about his three-element parasitic array for 40-m:

enter image description here

The radiating elements are the three black verticals in the foreground behind the fence.

While a "vertical yagi" can be an effective solution for low-angle radiation, it's important to remember:

  • the ground screen consumes considerable area
  • you lose the reflection gain attendant upon horizontal antennas
  • ground conductivity near the antenna strongly affects efficiency and feedpoint impedance
  • ground conductivity out to several wavelengths from the antenna determines how low the radiation angle will be

M0MCX demonstrates the advantage he hopes to achieve:

enter image description here

but this comparison doesn't tell the whole story:

  • the text says the feedpoint shows a very low SWR across the entire 40-m band without any matching circuitry, indicating substantial losses in the system which may reduce radiation more for a vertical than for a horizontal antenna
  • the comparison puts a dipole at 20-ft, while the vertical elements are at least 50% taller

I point this out only to illustrate the complexity of an antenna system in the real world, not to criticize the efforts of M0MCX, who is obviously enjoying his fine antenna. All antennas require compromises, so carefully consider your goals and resources, then set your expectations accordingly.

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    $\begingroup$ There are even examples of log-periodic arrays using monopole vertical elements driven against a ground screen. See, e.g. Vertical Log Periodic Antenna for 80m, 40m. $\endgroup$ – Brian K1LI May 6 at 15:23
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    $\begingroup$ Good answer. I would also note that even if the losses are high, the losses don't matter so much as the improvement to directivity in the receive case. As an example, W8JI has a circular array for rx only. $\endgroup$ – Phil Frost - W8II May 6 at 15:29

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