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

• To: <si-list@xxxxxxxxxxxxx>
• Date: Tue, 26 Feb 2002 09:59:43 -0800

```Steve,

There are 3 questions and I'm not clear which one is addressed.
Is it possible to say few simple words about each question separately?

Thanks,
Sainath

----- Original Message -----
From: "Steve Corey" <steve@xxxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Tuesday, February 26, 2002 7:20 AM
Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion

>
> Sainath -- I will give you the short answer, and refer you to the texts
> for the long answer.  The even and odd modes are TEM modes, or at least
> quasi-TEM.  TEM vs. higher order modes describes the field distribution
> across a single transmission line or waveguide structure.  Quasi-TEM is
> a basic assumption of the transmission line theory on which we rely,
> including characteristic impedance and RLGC matrices.  It requires that
> to first order, no field has a component in the direction of
> propagation.  I usually rely on "Analysis of Multiconductor Transmission
> Lines" by Clayton R. Paul when I have questions of this sort.
>
> The higher order modes are significant to transmission line theory for
> the most part in that we try to make sure they don't exist, since they
> each propagate with their own velocities and make a mess of our nice
> clean square waves.  Any E/M text with a waveguide section will describe
> the physics behind this.
>
> On the other hand, all TEM modes propagate.  Analysis of the different
> TEM modes supported on a multiconductor transmission line structure is
> from my perspective more of a mathematical tool for breaking down a
> system into its most basic components.  In the case of even/odd, this
> has a very practical application in differential signaling, but once we
> step outside of the symmetric coupled two-line regime, the math gets
> pretty complicated to try and define signaling schemes which coincide
> with any particular modes.
>
> So-called "full-wave" analysis, which essentially means "non-TEM
> analysis" for our purposes, is necessary for situations where we can't
> count on quasi-TEM assumptions.  These situations occur when we step
> outside of the strict geometries of uniform transmission lines, or into
> certain loss regimes.  Again, I would refer you to the book by Clayton
> R. Paul.
>
>    -- Steve
>
> -------------------------------------------
> Steven D. Corey, Ph.D.
> Time Domain Analysis Systems, Inc.
> "The Interconnect Modeling Company."
> http://www.tdasystems.com
>
> email: steve@xxxxxxxxxxxxxx
> phone: (503) 246-2272
> fax:   (503) 246-2282
> -------------------------------------------
>
>
>
> > To all,
> >
> > Sainath addressed his question to me, but I am going on vacation
> > and don't have the time to answer it.  Could someone please
> > give him a good explanation to his questions?  Thanks,
> >
> > =================================================================
> >
> > -----Original Message-----
> > From: sainath@xxxxxxxxxxxxx [mailto:sainath@xxxxxxxxxxxxx]
> > Sent: Monday, February 25, 2002 11:18 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> >
> >
> >
> >
> > This two T-lines vs one T-line mode distinction is confusing to me.
> > What makes the two T-lines support even or odd kind of modes? and the
one
> > T-line support the TEM kind of modes?
> > Is it not possible to have TEM kind of mode propagation in a two T-line
> > system?
> > How would you define a MODE when it is meant even or odd mode ? and when
it
> > is meant TEM mode?
> >
> > Thanks,
> > Sainath
> >
> > ----- Original Message -----
> > To: <si-list@xxxxxxxxxxxxx>
> > Sent: Monday, February 25, 2002 10:26 AM
> > Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> >
> >
> >
> >>What may be confusing to some is that the word "mode" is used
> >>in different ways in different contexts, both involving
> >>transmission lines.
> >>
> >>So far most responses mentioned the even or odd mode, where
> >>the signals of ***two*** T-lines go either in the same or the
> >>opposite direction.
> >>
> >>The other usage of this word involves only one T-line (or
> >>wave guide or optical fiber) and describes how the electro
> >>magnetic waves propagate inside that line, one of the most
> >>familiar mode being the TEM (Transverse Electro Magnetic)
> >>mode.  Don't confuse the two meanings of the word MODE!
> >>
> >>Intel Corporation
> >>=================================================================
> >>
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> >
>
>
> --
>
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