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

  • From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxxxxxx>
  • To: <haedge@xxxxxxxxxxxx>
  • Date: Tue, 26 Feb 2002 17:42:53 -0500

> 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?

Not necessarily.  In general, the two modes would have different
propagation velocities, and then the combination would experience
some distortion of the original waveshape.

For stripline, the two modes (if you would even call them "modes"
for stripline) have exactly the same velocity, so any combination
would arrive undistorted.  For microstrip, the two modes do not have
quite the same velocity.

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