**From:** ARNOLD,PETER (HP-Cupertino,ex3) (*[email protected]*)

**Date:** Wed May 10 2000 - 09:38:46 PDT

**Next message:**Kowal, Keith: "RE: [SI-LIST] : VeriBest / Mentor Tools"**Previous message:**[email protected]: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Next in thread:**Doug McKean: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Doug McKean: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Chris Rokusek: "RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Bob Davis: "RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**rachild.chen: "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

**** To unsubscribe from si-list or si-list-digest: send e-mail to

[email protected] In the BODY of message put: UNSUBSCRIBE

si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.

si-list archives are accessible at http://www.qsl.net/wb6tpu

****

**** To unsubscribe from si-list or si-list-digest: send e-mail to

[email protected] In the BODY of message put: UNSUBSCRIBE

si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.

si-list archives are accessible at http://www.qsl.net/wb6tpu

****

**Next message:**Kowal, Keith: "RE: [SI-LIST] : VeriBest / Mentor Tools"**Previous message:**[email protected]: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Next in thread:**Doug McKean: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Doug McKean: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Chris Rokusek: "RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**Bob Davis: "RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."**Reply:**rachild.chen: "Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe..."

*
This archive was generated by hypermail 2b29
: Wed Nov 22 2000 - 10:50:16 PST
*