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

  • From: Steve Corey <steve@xxxxxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Tue, 26 Feb 2002 10:48:38 -0800

Sainath -- I'll see what I can do without getting too embroiled in the 
details:

1. What makes the two T-lines support even or odd kind of modes? and the
one T-line support the TEM kind of modes?

For the first part of #1, I would refer to the book by Paul.  A system 
doesn't really support modes, it has modes.  Sometimes in analysis we 
break down voltages and currents into the system modes to simplify 
analysis.  If you come up with a good answer to the first part of #1, 
you will understand that the even and odd are also TEM modes in the same 
way that a single line has a TEM mode.

2.  Is it not possible to have TEM kind of mode propagation in a two 
T-line system?

Yes, as you will see in my previous post.

3.  How would you define a MODE when it is meant even or odd mode ? and 
when it is meant TEM mode?

For the first part of #3, you can refer to Paul's book for a rigorous 
mathematical definition.  You can also refer to Eric Bogatin's post to 
this thread for what may be a more intuitive definition.  For the second 
part of the question, refer to my earlier post for a short definition, 
or to Paul's book or any E/M book that covers waveguides for a longhand 
definition.


 > >
 > >



Sainath Nimmagadda wrote:

> Steve,
> 
> I suppose your message was to address my questions to Arpad.
> 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
>>-------------------------------------------
>>
>>
>>Muranyi, Arpad wrote:
>>
>>
>>>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,
>>>
>>>Arpad
>>>=================================================================
>>>
>>>-----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
>>>
>>>
>>>
>>>Arpad,
>>>
>>>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 -----
>>>From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
>>>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!
>>>>
>>>>Arpad Muranyi
>>>>Intel Corporation
>>>>=================================================================
>>>>
>>>>
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>>
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>>
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-- 
-------------------------------------------
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
-------------------------------------------

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