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

From: Charles Grasso ([email protected])
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: [email protected]
[mailto:[email protected]]On Behalf Of [email protected]
Sent: Sunday, June 03, 2001 9:05 PM
To: [email protected]; [email protected]
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.

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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