I have problem with TML calibration in FEM simulation.
In a 20 Ohm line simulation on er=36 substrate with 5 um gold conductors and line width of 15.88mil, MoM givers 30dB return loss while FEM can not give better than 20 dB return loss.
When I go into details, I figure out that in FEM the TML calibration is not accurate and the wave have deformation while injecting into the structure (figure below the left side of the transmission line)
I think this is the main reason for different return losses from Mom and FEM in a simple transmission line with similiar calibration.
Any advise how to resolve TML calibration problem in FEM?