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 >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu