How to fix port impedance in HFSS?

Hi HFSS users,
I am using HFSS to simulate WR-90 hollow waveguide (a=2.286cm,b=1.016cm). For the first five modes, we know theoretically the waveguide characteristic impedance (defined by Ex/Hy) is like the attached plot. It should converge to free space impedance (377 ohm). But when I plot PortZ0 in HFSS, the values of all the modes are very different from the theoretical values, some go to above 1000 ohm, some go to below 10 ohm.
I know it may because HFSS use Zpi to calculate the port impedance. I tried to define different integration lines for the five modes and use Zpv or Zvi to calculate port impedance. It seems not working, still gives crazy values. Or there are other methods to fix this problem, like renormalize port impedance? Thanks for any information!

Hello,

The characteristic impedance is badly implemented in HFSS to my opinion: the only way to find the same value of the analytic characteristic impedance of the TE10 mode is to define an integration line and set the impedance calculation to Zpv. Then, you will find the same analytic value for the ratio b=a/2 only. If b is different from a/2, then you won't find the analytic value.

I've send the problem (bug?) to HFSS support, but never had a clear answer if is normal or not.

Best regards

Thank you Hash. I even cannot reach HFSS support. Do they have a support phone number that I can directly talk with a technician? I am using a academic license bought in bulk by my university. It seems I even cannot have a user account with HFSS support.

I have, but I presume you may not have support with academic license...