Electronic – Skew planar wheel antenna – is it circularly polarised or not

antennaelectromagnetismham-radioradiationradio

'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

Best Answer

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