Power coupled in to different modes inside waveguides using CST

Hi everyone,

I'm trying to find the power being coupled in to different modes at a particular surface/area inside a waveguide using CST. The waveguide itself is being excited by a probe inside of it. And the surface/area to which the amount of power being coupled in to by different modes, could be defined as a waveguide port set across the cross section of the waveguide. But so far, I've been unable to solve this issue.

If any one knows how to solve this, please enlighten me

Thanks in advance