Hi, Mailgavenkat: I checked your .doc file. Following are the comments:
1. I noticed you have defined 3 substrates (50 nm, 10 nm and 30 nm). However, your strip is defined on z = 245 microns. It is very far away from the ground. It will be a very high impedance TLN no matter what.
2. You use Fmax = 20 GHz and Ncells = 200 cells per wavelength. It is very coarse for such a tiny structure. I tried to increase it to Fmax = 20000 and Ncell = 30 to mesh a length of 1 micron into a few cells in the longitidual direction. When the meshing is too coarse, it may cause accuracy problem.
3. The strip thickness is 10 nm. For such a thin strip, the loss is very high. It is talking about 2 ohms/square. You will find the Zc to be very big even for a normal dimensions which you will expect the Zc to be around 50-ohms.
The thickness of the strip is no longer very small compared to the width. It is possible building the thickness model may improve accuracy.
I have attached my models in this posting.
Best regards,