RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe...

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From: Chris Padilla (cpad@cisco.com)
Date: Thu May 11 2000 - 08:22:25 PDT


Hi Chris,

The stack-up was a simple 4-layer one: S-P-G-S

A microstrip on top, via through the planes, to a microstrip
on the bottom.

The via radiated in a raidal TEM mode as described below. The
whole presentation was very eye-opening for myself.

----->Chris

At 02:12 PM, you wrote:
>Peter,
>
>Do you recall what stackup(s) were tested?
>
>Chris Rokusek
>Innoveda
>
>
>> -----Original Message-----
>> From: owner-si-list@silab.eng.sun.com
>> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of ARNOLD,PETER
>> (HP-Cupertino,ex3)
>> Sent: Wednesday, May 10, 2000 9:39 AM
>> To: 'si-list@silab.eng.sun.com'
>> 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:dmckean@corp.auspex.com]
>> Sent: Tuesday, May 09, 2000 3:27 PM
>> To: si-list@silab.eng.sun.com
>> 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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>>
>
>
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