How to remove effect of antenna from measurement result

hello friends
can you tell me how to remove the antenna effect from measurment results?
i measured S21 with dipole antenna but this antenna have a little difference between simulation and measurment.
experimental setup for S21 measurment like this figure.

You might find the Wheeler Cap measurement technique useful. I suspect that you might be after an efficiency measurement or a method for separating directivity and gain.

Regards,

Azulykit