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EMPower impedance over-estimate

Question asked by mburfo on Feb 22, 2007
Latest reply on Mar 1, 2007 by JERRY_MARKETOS
Dear all,
I have been trying to simulate stripline in EMPower. Using the top and bottom covers as the top and bottom metal layers for coupled stripline,I can for the geometry: w=6, seperation=5, dielectric height=20 (metal to metal), Er=3.48, tand=0.004.

Using the above geometry I can achieve Z0dd=54ohms and Zeven=79ohms from a mixed mode EMPOwer simulation. TLine gives 54 and 74 ohms respectively.

I find that decreasing the grid size to 1x1 and 0.5x0.5mil pushes the impedances for odd and even modes even further from their true value.

I tried creating stripline without the top and bottom covers and inserting two extra metal layers and drawing these layers in by hand. This pushed impedances very high indeed. Stitching vias had no effect that I could see.

PLease could someone tell me how to simulate stripline in EMpower so it gives the same answer as TLINE. Otherwise I cannot trust EMPower results.
I really want to be able to look at the effect of increasing size of the metal planes above and below the coupled stripline. Also the effect of stitching vias on the amount radiation that leaks from the traces.

All help appreciated