help on smart antenna calibration

I have got a smart antenna system. At the bottom of the system (beneath the circular array) is a calibration system comprised of a 1:8 wilkison power divider and directional couplers. I have read a lot of articles and found that it is used the calibrate the time-varying channel errors.

But my tutor told me it is used to calibrate the mutual coupling between the antenna elements!!!

So if you know the calibration theories, can you tell me if the mutual coupling must be calibrated using an online method, or and the system be used to calibrate the mutual coupling error, or I am right and my tutor is wrong!

Thank you very much