Run down a copy of Polarization in Electromagnetic Systems, Stutzman to read more than you ever imagined existed about antenna polarization determination.
hello
you can plot rEx and rEy versus frequency, if the difference between them is large, the polarization is linear, if the difference between rEx and rEy is lower than 3-dB then you reach circular polarization, else you have elliptic polarization
Be cautious, you could also have a slant linear polarization. When you are looking at components, phase is important too. Pay close attention to the comments above. In other words, Ex approximately equal to Ey does not guarantee (close to) circular polarization. It is necessary but not sufficient.
The reference above would be helpful. There are numerous other references on the subject as well.
hello Azulykit, your comment is right, but in must antenna, i don't think have a slant polarization, for example in microstrip antenna , for circular polarization we must excite TM10&TM01 modes that those vectors are in x and y direction, on this base i say you can plot rEx and rEy
I have a circular patch and it's being feed by a single source. I'm usong CST. the radiation pattern - polar plot for Phi = 0 and phi = 90 are nearly the same. can I assume that it's Circular Polarized? Will all circular patch have circulat polarization (in Tm11 case) ?