RE: [SI-LIST] : Antenna Problem on the Board

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From: Bill Owsley (owsley@cisco.com)
Date: Mon Jun 04 2001 - 12:34:48 PDT


At 11:16 AM 06/04/2001 -0700, Chris Rokusek wrote:
>Richard,
>
>Your first paragraph sounds good to me.
>
>Something else that to consider is that with parallel termination, the wave
>flows down the line without a reflection but with source termination the
>wave has to travel _twice_ as far before it is absorbed. This seems loosely
>like doubling the loop area.

not quite, but the time involved is doubled...

> Sounds like a good case for
>simulation/measurement.
>
>Chris Rokusek
>Innoveda
>
>
>-----Original Message-----
>From: owner-si-list@silab.eng.sun.com
>[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of RMELLISON@aol.com
>Sent: Sunday, June 03, 2001 8:05 PM
>To: crokusek@innoveda.com; si-list@silab.eng.sun.com
>Subject: Re: [SI-LIST] : Antenna Problem on the Board
>
>
>To Chris Rokusek, Jian-X. Zheng, Jason Leung, Andrew Martwick and others.
>Thanks for the feedback.
>The replies got me to really thinking about radiation and impedance. I went
>to my ARRL handbook to check out the quarterwave transformer reasoning, and
>this seems valid for a special case. But after reading a new book
>(Controlling Radiated Emissions by Design by Michel Mardiguian), I'm more
>convinced than ever that it is not the higher impedance that gives rise to
>greater EMI--it's the height of the trace above the ground plane that is the
>governing factor. The common assumption of the replies was that a higher
>impedance was caused by a larger height above the ground plane. Obviously
>you can get higher or lower Zo by varying the width of the trace while
>holding h constant. In this instance, I would say that for a given voltage
>across the transmission line, the lower impedance line would produce more
>EMI
>due to higher line current. This is stated various places in Mardiguian's
>book, also.
>
>Nobody replied to my question about the radiation comparison of source
>terminated lines to end terminated lines. It seems to me that since you
>have
>half as much current in a source terminated line, the EMI should be half as
>much as a parallel terminated line would produce. Does anyone agree with
>me?
>I appreciate the help.
>Richard Ellison
>972-569-8317
>
>
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----------------------------
Bill Owsley, owsley@cisco.com
919) 392-8341

Compliance Engineer
Cisco Systems
7025 Kit Creek Road
POB 14987
RTP. NC. 27709

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