How to properly define Circular TE11 waveguide mode in CST and HFSS?

I'm designing a rectangular to circular taper transition in HFSS and CST, but doesn't seem to get it right. How should I define the TE10 for rectangular and the TE11 for circular (they say this is degenerate but i dont undestand what that means) in CST? or HFSS? Can someone explain this to me, and how to do this properly? Thanks!

I already modeled a transition like this in CST, but I got stuck at the error produced by the degenerative mode at the circular port. It said that I should add more ports. In HFSS however I did get to simulate it, but it doesn't seem to produce proper results. :/

Looks like I found some answers from searching the previous threads in this forum:

https://www.edaboard.com/thread169660.html#post739622
https://www.edaboard.com/thread4606.html#post18059
and here
https://www.edaboard.com/thread200143.html#post930151 (Hash answered me in this thread directly, thanks)

Basically I just need to define 2 modes (TE11) for the circular port using Alignment thru Integration lines placed perpendicular with each other; then 1 Integration line to set the polarization for the 1 mode (TE10) in the rectangular port. This is in HFSS 13.

For CST MWS, I just configured the circular port with 2 modes and checked the Polarization angle to set the angle of the 1st of the 2 degenerative modes to 90 deg. Automatically the 2nd degenerative mode will be set perpendicular with this one (0 deg).

That's it! If you feel there's something wrong with what I've said here, feel free to correct or add any additional info. I hope this would help any potential waveguide engineer in the future. :)