From: Chris Rokusek ([email protected])
Date: Wed May 10 2000 - 14:12:45 PDT
Peter,
Do you recall what stackup(s) were tested?
Chris Rokusek
Innoveda
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of ARNOLD,PETER
> (HP-Cupertino,ex3)
> Sent: Wednesday, May 10, 2000 9:39 AM
> To: '[email protected]'
> Subject: RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge
> Effects in Printe...
>
>
> Doug,
>
> Here is what I think I heard at the EMC society presentation. The
> simulations presented showed that 20H structures they examined actually
> resulted in more emission at the board edge. However, the presenters were
> neutral on whether this was detrimental to compliance for the system as a
> whole, pointing out that EMC solutions are rarely universally
> applicable. I
> hope they post this on the web, I found it most instructive.
>
> The main points I remember:
>
> 1) Time-varying currents on vias can inject radial TEM-mode waves into the
> space between planes.
>
> 2) The energy thus injected bounces around the cavity volume between the
> planes. The board edge is a discontinuity in the medium and so results in
> partial reflection of the propagating wave and partial transmission, i.e.
> radiation from the board edge.
>
> 3) Fencing the board edge with grounded vias is equivalent to changing the
> PCB-edge discontinuity to a short to ground, so the reflection coefficient
> becomes -1 and all energy is kept inside of the fenced area.
>
> 4) By contrast, a 20H-rule example showed that that structure,
> which looks a
> little like a patch antenna, allows for more efficient radiation from the
> edge. The exposed area allows a propagation mode where energy can travel
> around the outside edges of the board also. Thus less energy is trapped
> within the board area and more gets radiated.
>
> 5) Is this good? Energy bouncing around between planes can be picked up by
> structures like the one that initially injected it, e.g. vias, and then
> travel along conductors to outside surface components where it can be
> emitted. This is not especially desirable. On the other hand, the more
> efficient radiatiing edge (20H) puts more energy into the system chassis,
> which moves the problem one level higher.
>
> 6) Closely spaced ground vias all across the board had the effect
> of fencing
> in the injected energy to a small area. This seems to cut
> radiation from the
> edges drastically. I would like to know more about this particular case.
>
> The data was obtained from an FDTD simulation of a small board
> with a single
> off-center via as the point of injection. Excitation was with both a
> continuous sine-wave at 1GHz and also a Gaussian-derivative pulse.
> Dielectric losses were included in the FR4 model. The results of lengthy
> simulations were presented as captivating animations, with color variation
> showing the magnitude of the Poynting vector across the whole board. The
> test setup was of necessity rather artificial but it did help to
> give a feel
> for the physical behavior underlying radiation from board edges.
>
> peter.
>
> -----Original Message-----
> From: Doug McKean [mailto:[email protected]]
> Sent: Tuesday, May 09, 2000 3:27 PM
> To: [email protected]
> Subject: Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge
> Effects in Printe...
>
>
> I won't be able to make the meeting.
> Any chances of having what's presented
> put up on a website? - Doug
>
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