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'Skew planar wheel' antennas are popular for uhf. They are often described as circularly polarised, but I don't see how they would be. Are they instead just a mixed polarisation omnidirectional antenna ?

enter image description here

If they are circularly polarised, where would the equivalent 90 degree phase shift come from, as used in a normal circularly polarised antenna.

This account of testing this antenna indicated strong circular polarisation:

The results showed that this Skew-Planar is strongly right-hand circularly polarized, as expected. At my end, Clare's signal was S8 with his right-hand helix, and dropped to S1 when he switched to his left-hand helix.

http://www.ve3byt.com/SkewPlanarAntenna/

Practical designs discussed here, also noteworthy is that the polarization is apparently determined by the direction of lean(skew?) of the four elements : http://www.slvrc.org/902band/skewplanar.htm

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  • \$\begingroup\$ Hi and welcome! Please can you paste in a picture or diagram of one of these antennas, to get us started? \$\endgroup\$ – tomnexus Nov 29 '16 at 17:57
  • \$\begingroup\$ Updated with an image \$\endgroup\$ – Paul George Nov 29 '16 at 17:59
  • \$\begingroup\$ Hmm. If we only had two "blades" instead of four, and if each one emits in a dipole pattern (like any loop antenna,) then we actually have two vertical dipole antennas with a 1/2lambda separation, with a 90deg twist. In a horizontal line through the two, we'd expect pure circ-polarized emission. Cool! Two "propellors" with opposite screw, they can't hear each other! \$\endgroup\$ – wbeaty Dec 2 '16 at 4:59
  • \$\begingroup\$ @wbeaty I don't follow. Where is the 90 degree phase difference coming from between the elements? \$\endgroup\$ – Paul George Dec 4 '16 at 23:39
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Figure 10 of this excellent explanation boils down to this:

If you ignore all the currents that cancel each other out due to symmetry, you can physically guide (via the copper) three currents Ez of similar magnitude and phase in the z-direction and one equivalent current in the y-direction, the resulting two equal and orthogonal currents being spaced a quarter wavelength apart.

So, with currents of equal magnitude and phase, orthogonal and spaced a quarter wavelength apart - voila, circular polarization!

Planar Wheel Antenna Primary Currents

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  • \$\begingroup\$ Interesting, I've added a link to slvrc.org/902band/skewplanar.htm with practical designs. While I follow both of the ways you describe, I can't reconcile that with what I see on that site - apparently symmetrical designs - there doesn't appear to be a transmission line different, and with consistent element lengths? Also noteworthy is that the polarization direction appear to be determined by the lean or 'skew' of the elements themselves, this I still do not understand! \$\endgroup\$ – Paul George Dec 17 '16 at 1:02
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    \$\begingroup\$ Agreed. I watched your reference & then dug further for a good explanation that considers the perfect symmetry, then edited my response. Pretty cool once you see Figure 10! \$\endgroup\$ – neonzeon Dec 17 '16 at 13:38
  • \$\begingroup\$ Thanks, I think that explanation is as good as it's going to get, although it is still challenging to 'visualize' coherently. The explanation highlights a need for symmetry, what is interesting is that 3 and 5 lobe designs are being sold. Also some that are not curved but with straight lobes. It's hard to see how these would work well or be beneficial. A good gallery is at maxmyrange.com/assumptions.html \$\endgroup\$ – Paul George Feb 20 '17 at 10:40

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