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

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From: S. Weir (weirsp@atdial.net)
Date: Mon Jun 04 2001 - 13:51:49 PDT


Chris,

I really don't follow your reasoning:

At 11:16 AM 6/4/01 -0700, you 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. Sounds like a good case for
>simulation/measurement.
>
>Chris Rokusek
>Innoveda

The current imparted is one half for each direction, Vdelta/(Rt + Zl)
versus Vdelta/(Zl) so we have one quarter the power for twice the
time. This says one-half the total energy, and the peak amplitude is one
quarter. With the same geometries for each, what condition would ever give
rise to the series termination radiating more than the parallel termination?

Regards,

Steve.

>-----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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