coupled microstripline odd impedance

Hi all
I am trying to design a microstrip coupled line bandpass filter and have determined the length of the lines and the even and odd mode impedances.

But eventually I ran into a problem with the EM simulator.
The question is:

How do I determine the odd and even impedances of a coupled microstrip line?

Iam using Momentum and I did the following:

1.Drew a simple coupled line of length (L), width(W) and spacing(S).
2. Defined the network as a differential 2-port network (Each port pair at each end is driven differentially). Determined the S Parameters as [S]even.
3. Defined the network as a common-mode 2-port network (Each port pair at each end is driven common-mode). Determined the S Parameters as [S]odd.
4. The question is: How to determine Zeven and Zodd from [S]odd and [S]even? Is this formulation correct? Does the answer depend on the impedance of the port and should an extra length be added to eliminate mode mismatch? What should be the port impedances for a 50 ohm system?
5.I am not able to get an answer anywhere close to that computed by Line Calc.

Distinguished members, I seek your help.

Thank you very much.
Rajesh

I suggest you get a copy of SonnetLite at www.sonnetsoftware.com (free, no time-out, I work for Sonnet), install, go to Help->Tutorial. About 45 minutes later you will have a solid working knowledge of Sonnet.

Then go to Help-> Search for Help On, then type in "even mode". Click on the first document found, "Using Even and Odd Mode Parameters". This gives a very detailed answer to your question. You can then proceed in Sonnet, or in Momentum, or even in both to be sure you are doing it correctly. The Sonnet analysis actually calculates the impedances and displays them right after the S-parameters, so you don't have to figure it out from the S-parameters.

also need the answers
any comment will be appreciated.

actually I find the reason
when you use differential port, the impedance you get is twice the odd mode impedance, whereas if you use common port, the impedance is half the even mode impedance.

Hello Rajesh,

Yes, Try with Sonnet em, you get the ansers, go through the following article page no 19 you will see the analysis results similar to what you want...

Microstrip Filter Design Using Electromagnetics (emtalkb.pdf)

http://palgong.kyungpook.ac.kr/~ysyoon/Pdf/emtalkb.pdf


---manju---

hi
iam too seatrching for the same even and odd mode impedances, i just found a site it might be helpful to u,visit this site u may get some idea about it. if u get it reply me, i need a small help regarding this
Coupled Microstrip Analysis/Synthesis

This looks good. Thank you for the reference

hi my project is design of band pass filter for ku band using ie3d simulator, if you need any help regarding this ask me, if possible i will do.