FreeLists / si-list / [SI-LIST] Help Explaining Microstrip

[Paul Levin <levinpa@xxxxxxxxxxxxx>]

Dear SI-LIST'ers,

I'm working on a presentation to explain transmission line to 
non-engineers and I
find myself stumbling over some of the basics. (There's nothing like 
explaining
something to bring out all of the glitches in what you were sure you 
understood!)
I'm hoping that one of you may be able to supply the missing link.

Nearly two hundred years ago Oersted and Ampere figured out that if you 
have
two conductors carrying current in the same direction, they would would 
to pull
in close to each other whereas if you had two conductors carrying 
current in
opposite directions, they would want to separate.

If one were to apply just these observations to microstrip, you would 
expect to
see all of the trace current bunched on the side away from the ground 
plane and
the return plane current in two bunches to either side of the trace and 
as far away
from the trace as possible, if not on the bottom.

Of course, this is almost exactly opposite from what we know happens.

What is the force that overcomes Oersted and Ampere and causes the trace and
return currents to be so heavily attracted to each other?

Thank you in advance.

Regards,

Paul Levin
Senior Principal Engineer
Xyratex


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