simulating even mode impedance in ads

Can anyone advise me if they have had luck in simulating the odd and even mode impedances of parallel coupled stripline ( with a top and bottom ground plane as per stripline). CST gives values that I dont completely trust.

Are there any open source programs that use the method described in R. R. Gupta "Accurate Impedance Determination of Coupled TEM Conductors" IEEE MTT vol 17 No 8 August 1969

Any advice would be appreciated.

Hello Terrorhertz,

Try this AWR free utility TXLINE...
http://web.appwave.com/Products/Micr...hp?bullet_id=9
Download it & use for coupled microstrip or stripline impedence calculations...
see the attached picture...


---manju---

Download AppCAD utility, it was initially design by HP. Very good and reliable.

I think maju's advice to get a transmission line caculator first is a very good idea. TxLine and AppCAD are both good transmission line calculators that provide coupled line models. That will get you close to a reasonable result.

To test the result for higher accuracy, you can get a free 3D planar EM simulator to build and test it. I would probably recommend Sonnet Lite, since they have really good ports, very deep dynamic range and are by nature a shielded domain simulator which is good for modeling striplines. In Sonnet Lite you can get the odd-mode impedance and S-parameters by setting the ports to 1 and -1 on one end and 2 and -2 on the other. Then, to get the even mode impedance and S-parameters, set the ports to 1 and 1 on one end, and 2 and 2 on the other.

Using this method should result in very accurate structures.

--Max

can you upload an example using sonnet free to show even and odd modes.
Thanks

Thanks for the advice. TXline is good for coupled lines on the same plane, however, I did use CST with a short length of line (performing a port mode calculation only)and a very fine mesh to obtain good results.

Add Polar's Si9000 to the list of Zo calculators and also look at the on line help in HFSS on impedance calculation for guidance on setting up the calculation.

I also usually look at the fields at the port to make sure I have the mode I want.

good luck, it is easy to go astray.