'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 ?
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.
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