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

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From: RMELLISON@aol.com
Date: Sun Jun 03 2001 - 20:04:41 PDT


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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