if I use a round patch antenna, does it create a circular polarisation since a round patch is nothing more than a lot of single lines originating from the middle with different lentgh and thus different phases? Or what kind of polarisation do I get?
For excitation I would assume a koax feed right in the middle of the patch.
A center feed obviously does not involve length differences and thus neither a circular nor linear polarisation in the patch plane, just an omnidirectional radiation pattern and polarisation normal to the plane.
To generate circular polarisation, you'll need some kind of asymmetry in the patch design.