Re: [SI-LIST] : 20-H Rule for Power Planes

Douglas McKean ([email protected])
Thu, 27 May 1999 17:27:38 -0700

At 06:44 PM 5/27/99 -0500, Bill Dempsey wrote:
>I must be dumb....

No such thing ...

> If anyone can explain this in basic terms I'd love to hear it.

The hypothesis goes that with a two dimensional
transmission line with a peripheral slot, i.e.
two parallel plates, said slot launches the wave
straight off the edge of the planes.

*Highly exaggerated* of course and
me ASCII ain't good but here goes ....


) ) ) ) -->


If the 20-H cutback is employed, then the launching
of any waves or even the resonance of the slot is
launched, then the wave does not launch straight
off from the plates. It gets launched at an
angle. That angle drives the wave into the
ground plane.


> Or better yet if you've got some near
> field and far field measurements on boards
> with and without the 20H rule in effect
> I'd love to see the results.

I wish I could but I can't ...

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