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