Cross polarization discrimination

I am simulating antenna radiation patterns using FEKO. I have the far field radiation patterns. But i Do not know how to calculate the cross polarization discrimination. If someone can let me know it will be great help. Also if there are some references please let me know.

thanks
abhishek

For my knowledge, FEKO gives the isotropic gain on both mag and phase.
Simply plot on the same graph |Gi [dB]| at Phi=0 and Phi=90.
The X-pol is the difference between max Co-pol and Max X-pol

Hi,

Just to confirm Phi=0 is the co-pol and PHI=90 is the cross-pol right?