RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printed Circuit Boards (PCBs)"

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From: Chris Rokusek (crokusek@innoveda.com)
Date: Mon May 08 2000 - 10:35:44 PDT


Mary,

If you decide do some "off-line" research, its important to distinguish
which mechanisms the 20H may (not) be effective.

I think you'd agree that the 20H rule will reduce the size of fringing field
pattern at the board edge (for particular stackups) and therefore reduce
INDIRECT radiation where the antenna is not the planes themselves and
coupling is occurring from the fringing fields to a more efficient antenna
(other electronics/heatsinks/cables are present on the board).

Its somewhat controversial as to whether the 20H rule can reduce DIRECT
radiation from the planes (both across and along as in recent thread)
significantly. In this case there are no other conductors on the boards. I
am also interested in what noise sources on the planes and spacing would
actually be required in order to achieve 40dB far field at 3m from DIRECT
radiation mechanisms at resonant frequencies.

Chris Rokusek
Innoveda

> -----Original Message-----
> From: owner-si-list@silab.eng.sun.com
> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Mary
> Sent: Friday, May 05, 2000 2:50 PM
> To: si-list@silab.eng.sun.com
> Subject: RE: [SI-LIST] : May 9th Presentation: "Radiation from Edge
> Effects in Printed Circuit Boards (PCBs)"
>
>
> This is a fascinating discussion group. My background is in the
> microwave circuits area, so I can't be sure how much of what is
> posted here is correct. However, I have come to the conclusion
> that most of the information posted concerning the 20H rule was
> bogus.
>
> Based on what I know about microstrip patch antennas, it seems
> unintuitive to me that a small change in the size of a power
> plane would have any significant effect on the radiation from a
> power-ground plane pair. (And I am fairly certain that the
> resonant frequencies cannot be shifted by a factor of 2 to 3.)
> I tried to find out more about this, but there is virtually nothing
> in the literature about the 20H rule.
>
> I will be unable to attend the SCV EMC meeting, but I hope
> that someone will provide an overview of their presentation here
> or on the web (particularly if they discuss the 20H rule).
>
> Mary
>

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