Circular waveguide in CST

Hi all,
I'm trying to simulate a circular waveguide in CST. I have drawn my cylinder, picked the end faces and added waveguide ports to them.
I want to excite this with circular polarization, do I do this by defining a plane wave from the menu and selecting circular from the option?
When I simulate, I get a warning message that says, "2 degenerated mode(s) at port 1 is/are not included in time domain calculation! It may be better to increase the number of modes at port 1."
Can anyone explain this to me? I have increased the number of modes up to 20, and I still get this warning! This is with no CP plane wave, just the default excitation (which I assume is linear)
Thanks.

hi，
i think you should use the waveport to excite the circular waveguide, a plane wave is used for scatting case.

Hi,
Thanks for the reply. How do I excite the waveguide with c.p. in CST if I don't use a plane wave?
Thanks.

hello RTNI,
Mostly, a waveport is excited by liner polarization, if you want to get c.p. I think maybe you should define two ports with two l.p. excitations that have 90 degree phase delay.
BR

hye all..
actually i dont understand about how to define two ports with two lp?and how to know the result is CP?