[SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz frequency

Stuart, for common dielectrics, somewhere in the high hundreds of MHz 
dielectric loss overtakes loss from skin effect.

Steve.
At 05:16 PM 11/24/2003 -0500, Stuart Brorson wrote:
>True enough, but aren't the dielectric losses in FR-4 more or less
>frequency independent (i.e. to the <10% level that the dielectric
>function is constant)?
>
>Anyway, Tom is right:  you need to consider the frequency variation of
>both Dk (the dielectric function) and Df (the dielectric loss
>function).   However, both are typically dominated by skin effect
>losses, particular in the GHz range.
>
>Stuart
>
>
> > To make the answer complete you need also to include dielectric losses 
> which
> > also are frequency dependent.
> >
> > Tom Dagostino
> > Teraspeed Consulting Group LLC     Teraspeed Consulting Group LLC
> > 2926 SE Yamhill St.                Device Modeling Division
> > Portland, OR 97214                 13610 SW Harness Lane
> >                                    Beaverton, OR 97008
> > http://www.teraspeed.com           503-430-1065
> > tom@xxxxxxxxxxxxx
> >
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Stuart Brorson
> > Sent: Monday, November 24, 2003 1:22 PM
> > To: andyk@xxxxxxxxxx
> > Cc: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Dielectric constant for FR4 at above 1Ghz
> > frequency
> >
> >
> > If I am not mistaken, your question is equivalent to this one:  Is the
> > dielectric function constant over the 1 MHz -- 1 GHz range?  The
> > answer is: It is not constant, but varies by several percent or more
> > over that range for many FR-4s.  (FR-4 is not a single material, but
> > is a family of materials, each different depending upon your PCB
> > vendor, and whatever batch of materials he was shipped on any
> > particular day.)
> >
> > However, the bigger problem for you to think about is the loss due to
> > the skin effect in your copper traces.  The skin effect losses vary as
> > the square root of the frequency, IIRC.  The frequency-dependent loss
> > due to the skin effect dominates over the frequency variation of the
> > FR-4's dielectric constant.
> >
> > Here are some references:
> >
> > http://www.tdasystems.com/library/appnotes/siml0803.pdf
> > http://signalintegrity.com/Pubs%5Cnews%5C4_5.htm
> >
> > Stuart
> >
> >
> > > Hi all,
> > >
> > > I am designing a high speed PCB at over 1Ghz frequency using FR4 
> material=
> > > .
> > > I am wondering how much the dielectric constant will be affected by the
> > > frequency over 1Ghz as compared to 1Mhz?
> > >
> > > Thank you
> > >
> > > Regards,
> > > Andy
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