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I was searching for helical antenna designs and stopped here to look around when I saw this antenna (below). I am guessing it has a somewhat omnidirectional characteristic that would be advantageous to put on a car/plane/helicopter to communicate with a helical "command station" antenna which can be manually pointed back.

  • What is this antenna design called?
  • What does the radiation pattern look like in three dimensions? Is it somewhat similar to a vertical dipole with isotropy in the horizontal plane and nulls at the top and bottom, or is it substantially different?
  • What about polarization - linear? circular? azimuthal? mixed?

I've tried a translation, but it does not seem to describe the antenna itself. These can also be seen at the extreme left of the second image.

enter image description here

enter image description here

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  • \$\begingroup\$ It is clearly intended to be circularly-polarized. That means it sacrifices radiation at all the specific angles in order to cover many. In other words, it would probably work equally well with horizontal as well as vertical receiving antennas. This is similar to how FM radio broadcasters do it. It is a compromize in order to cover the widest variety of receivers, at the expense of range. On FM that is no problem because they just pump a lot of power into them or add antenna bays. This one is set up vertically, but they often hang off the side of towers to cover specific directions. \$\endgroup\$
    – SDsolar
    Commented Jul 1, 2017 at 8:59
  • \$\begingroup\$ @SDsolar "clearly" because why? In what way is this clear? Clear to everybody? Is there some way one can tell by looking at an antenna that it is or isn't circularly polarized? Can you tell if the antenna in the question is right- or left-circularly polarized clearly as well? \$\endgroup\$
    – uhoh
    Commented Jul 1, 2017 at 9:13
  • \$\begingroup\$ Clearly - because of the shape and arrangement of the elements. They are generally curved instead of straight, and not all in one plane.. When you say right or left you are likely thinking about satellite antennas built like a helix where the whole thing is built to twist in one direction. But an antenna like this is both, as you can tell by the shape. Do some Googling about FM broadcast antennas and you will see that they are more like this example. The whole idea is to make it easier for the listener by removing their polarization considerations. \$\endgroup\$
    – SDsolar
    Commented Jul 1, 2017 at 16:44
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    \$\begingroup\$ @SDsolar Sorry, you are saying that this antenna is both right-hand and simultaneously left-hand polarized? I don't think any amount of googling can reconcile that. Can you show any existing evidence of a roughy omnidirectional antenna (within a horizontal plane) that transmits simultaneously equal amounts of power in both circular directions, that isn't actually just radiating linear polarization? I think it's not mathematically possible, and I don't think you will be able to find any. \$\endgroup\$
    – uhoh
    Commented Jul 1, 2017 at 16:53
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    \$\begingroup\$ @SDsolar thanks, that's the link in the accepted answer where the benefits of rejecting one CP sense is discussed, for example to reduce sensitivity to reflected relative to direct signals. In that case by about 10 and 12 dB at 1.3 and 2.4 GHz. I think FM broadcast is sometimes polarized in both linear directions (with a phase lag) to make a single circular polarization, so that FM receivers (with typically linearly polarized antennas) will receive a signal with fewer dropouts caused by reflections and rotations along the path. \$\endgroup\$
    – uhoh
    Commented Jul 2, 2017 at 3:00

2 Answers 2

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Cloverleaf antenna, circular polarization.

An introduction, more or less: https://www.antenna-theory.com/antennas/cloverleaf.php

A paper: Rexiramdhan & Thalib (2020) "Design and Analysis of Circular Polarized Receiver Antenna as Video Stabilizer in UHF Television" Int. J. Comp. App. (0975 – 8887) v. 175, No. 30.

Although they call it "design", they don't happen to provide any design formulas, everything was simulated... go figure. Their VSWR seems to suggest the impedance could be a bit better tuned (perhaps by adjusting wire diameter?). Bandwidth will also be affected by wire diameter.

The pattern is toroidal, like that of a vertical dipole, but has circular polarization, meaning it's relatively independent of angular orientation. I believe they are popular for remote control applications, drones and such, for this reason.

There's probably something to be said for multipath as well, which might not tend to cancel out as well (have as deep nulls) as linear polarization, thus maintaining some link quality even under those conditions. Multipath may also create linear polarization from circular, thus not canceling out completely with the original, or other random angles. And some multipath may indeed cover for the axial nulls of the antenna, so it may still be fairly omnidirectional in a real environment.

The other antennas, in the second picture, appear to be helical type.

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  • \$\begingroup\$ That would make sense. It reminds me of a presentation I saw of an omnidirectional UHF(?) antenna that was designed for and used on the US Space Shuttle, to allow communications with astronauts when they were outside the shuttle. The presentation was proprietary, so I cannot post anything from it. \$\endgroup\$
    – SteveSh
    Commented Oct 30, 2022 at 12:30
  • \$\begingroup\$ @SteveSh a simple crossed dipole with one element 90° to the other (perpendicular and fed 90° out of phase) will be truly omnidirectional. It does this by smoothly varying from CP on axis to LP in the plane of the dipoles. \$\endgroup\$
    – uhoh
    Commented Nov 2, 2022 at 21:56
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That appears to be a cloverleaf antenna.

It is circularly polarized. And the radiation pattern is similar to a dipole antenna.

Here are some more details: https://www.antenna-theory.com/antennas/cloverleaf.php

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    \$\begingroup\$ To avoid this being a link-only answer, could you describe the radiation pattern here in your post instead of sending people off-site for the answer? A screen shot of the radiation pattern would be helpful as well. Thanks! \$\endgroup\$
    – uhoh
    Commented Oct 30, 2022 at 12:45

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