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

From: Michael Khusid <mkhusid@xxxxxxxxxxxxxxxxxx>
To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
Date: Tue, 26 Feb 2002 17:49:12 -0500
That also assumes that the tramission line has no discontinuities and both
lines are perfectly length matched.

This assumption is rarely true in the real world.

> -----Original Message-----
> From: Christman, Timothy (STP) [mailto:Timothy.Christman@xxxxxxxxxxx]
> Sent: Tuesday, February 26, 2002 5:43 PM
> To: 'haedge@xxxxxxxxxxxx'; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> 
> 
> 
> Each propagates undistorted, but at different velocities?
> 
> Timothy J. Christman
> Test Engineer
> Tel 651.582.3141  Fax 651.582.7599
> timothy.christman@xxxxxxxxxxx
> Guidant Corporation 
> 4100 Hamline Ave. N.  
> St. Paul,  MN   55112  USA 
> www.guidant.com
> 
> 
> -----Original Message-----
> From: David G Haedge [mailto:haedge@xxxxxxxxxxxx]
> Sent: Tuesday, February 26, 2002 3:56 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion
> 
> 
> 
> 
> Eric and all,
> 
> My understanding of a transmission line that has  +1 volt 
> signal on one
> line and
> 0 volts on the other is actually the superposition of an even 
> mode signal
> of +0.5 volt / +0.5volt and an odd mode signal of 
> +0.5volt/-0.5volt, giving
> you
> the +1volt/0volt signal on the line, in which case each mode should
> propagate
> undistorted.  Is this not what in fact is occurring in a line 
> excited in
> this nature?
> 
> David Haedge
> Raytheon
> 
> 
> 
> 
> 
> 
> In a nutshell, odd and even modes, and any modes in general,
> are special voltage patterns that propagate undistorted down
> a pair of transmission lines. For example, in a pair of
> microstrip traces, if you send a +1 v on one line and a 0v
> signal on the other, the actual voltage on the two lines
> will change, as the signals move down the line. The 0v line
> will see a growing negative signal as the far end cross talk
> builds up and the +1v signal will drop and distort as it
> looses energy to the quiet line. This voltage pattern is not
> a mode. It is just a particular driven voltage pattern.
> There is nothing special about it.
> 
> However, there are two special voltage patterns that you can
> impose on the lines which will not change as the signals
> propagate down the lines. If you put a +1v on each line, wrt
> the return plane below, there will be no voltage difference
> between the two signal lines and the voltage pattern will
> continue undistorted. The other voltage pattern is a +1v and
> a -1v applied to the two lines, wrt the return plane.
> 
> 
> 
> 
> 
> 
> 
> 
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[SI-LIST] Re: Even mode, common mode, and mode conversion

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