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

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From: Charles Grasso (cgrassosprint1@earthlink.net)
Date: Mon Jun 04 2001 - 08:55:13 PDT


Hi there,

In my parallel universe as an EMC guy I have indeed run across
this.A series terminated transmission line does indeed radiated 6dB ( or
half as much) lower than an equivalent transmission line without the
source temination.

Chas Grasso
Ansoft
  -----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 9:05 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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