Query regarding Circular polarisation

Hi all,
Does anyone know, how to ensure or test that a particular antenna is circularly polarized? Also how can we tell looking at the farfield patterns whether the antenna is linearly polised or circularly polarised?

A simple test is using your circular one and a linear antenna. Point both one to another and rotate one of them. Connect TX to the one you rotate and the other to a RX. If you observe a constant power level, then you have a linear one and a circular one. If not, the circular is not circular, but maybe elliptical or even linear. The other question I think you can't tell.