## [SI-LIST] Re: Even mode, common mode, and mode conversion

• From: Ege Engin <engin@xxxxxxxxxx>
• To: fred@xxxxxxxxxxxxx
• Date: Thu, 28 Feb 2002 09:00:08 +0100

```Fred,
I was wondering, whether the equations that you stated for the odd and even mode
impedance are an approximation? Or are these exact solutions that can be
obtained from the eigenmodes of the system?
Say, you have somehow obtained the characteristic impedance matrix:

Z11 Z12
Z21 Z22

In case of symmetrical geometry Z11=Z22, Z12=Z21. But now one can define
Odd = Z11-Z12
Even = Z11+Z12
In my opinion, one of these approches must be an approximation.

Best Regards
Ege

Fred Balistreri schrieb:

> There have been excellent responses on this subject. Perhaps one may better
> understand the
> meaning of odd, even modes by looking at the equations from where they
> originate:
> Given that there are 2 lines wrt gnd or some plane or in the microwave
> description 3 lines, with
> one being a reference and given the Maxwell's LC matrix then:
>
> Odd = sqrt  L11-L12/C11+|C12|
> Even = sqrt  L11+L12/C11-|C12|
>
> Note that the loop inductance is minimized and capacitance maximized for odd
> mode. The opposite is
> true for the even mode. Thus the differences in impedance. The coupling is
> the key.
> Note that in Maxwell's C matrix the mutual capacitance is desginated as
> negative, therefore the absolute brackets.
>
> Best Regards,
>
> ----- Original Message -----
> From: "Doug Brooks" <doug@xxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Sent: Monday, February 25, 2002 9:31 AM
> Subject: [SI-LIST] Even mode, common mode, and mode conversion
>
> >
> > Gurus,
> >
> > I've been following the thread on mode conversion and suspect I am not the
> > only one with this question. Can someone explain, in layman's terms:
> >
> > The distinction between even mode and common mode?
> >         between odd mode and differential MODE (not to be confused with
> > differential traces)
> >
> > And does the existence of differential traces add any complications to
> > these distinctions?
> >
> > Thanks for bringing the dummies along with you!
> >
> > Doug Brooks
> >
> >
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