In the defense of Microstrip Topologies, I would offer the following:=20 For a given impedance and the same signal to plane spacing, the width of the microstrip should be roughly twice what it would be for a stripline. So the skin effect loss should be approximately the same. The resistive loss will be lower as the cross section is twice that of the stripline and the dielectric loss should be lower as well. If the signal could be routed entirely on the outer layer with no vias, it would surely be better for signal quality. Also microstrips offer faster propagation delays so they can be used to improve timing margin on busses. =20 --Prakash.=20 -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Lee Ritchey Sent: Tuesday, December 13, 2005 12:04 PM To: Hassan O. Ali; babid_a@xxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Microstrip/Stripline The higher skin effect loss for the same width microstrip transmission line over the same width stripline is more likely due to the fact that most of the current in the microstripline is confined to the side of the trace exst to the plane over which it runs while the stripline trace has current distributed over both sides. The under side of a surface microstripline is roughened in order to make it bond to the prepreg layer, increasing the loss. This is offset, somwhat, by the fact that a surface microstripline has air on one side which has a lower loss tangent that the dielectrics of the stripline version. As someone pointed out, there isn't a simple answer to this question. I rarely use surface microstriplines because the impedance control on outer layers is so poor, so this question doesn't come up.=20 Lee W. Ritchey Speeding Edge P. O. Box 2194 Glen Ellen, CA 95442 Phone- 707-568-3983 FAX- 707-568-3504 I just used the energy it took to be angry to write some blues. Count Basie > [Original Message] > From: Hassan O. Ali <hassan@xxxxxxxx> > To: <babid_a@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx> > Date: 12/12/2005 10:45:38 PM > Subject: [SI-LIST] Re: Microstrip/Stripline > > Babid, > > You can always find a microstrip line that is more lossy than a stripline. You can also=20 > find a stripline that is more lossy than a microstrip line. You'll=20 > have to fix some=20 > parameters of interest and then ask the same question. > > For example, you can fix the trace width, trace thickness, dielectric constant, electric=20 > loss tangent, metal conductivity, and characteristic impedance for=20 > both line types=20 > (allowing the trace height to vary to give rise to the required characteristic=20 > impedance). You may also need to specify whether or not the stripline=20 > is symmetric, i.e.=20 > the center strip is the same distance from the two reference planes.=20 > You should also fix=20 > a frequency band of interest - low frequency loss behavior can be different from high=20 > frequency loss behavior. > > In general though, a microstrip is more lossy than a stripline. The fundamental reason is=20 > that a stripline provides two planes through which the return currents could pass, hence=20 > less resistive loss (two resistors in parallel). But at higher frequencies where=20 > dielectric loss dominates over skin-effect (resistive) loss, the story can be different.=20 > That's pretty much material-dependent. > > Now go find a book if you need more info. > > Best regards. > > Hassan.=20 > > > > On Dec 12, "Tom Dagostino" <tom@xxxxxxxxxxxxx> wrote: > >=20 > > There are many good books that describe this. I would suggest you=20 > > try the > > "Transmission Line Design Handbook" by Brian C. Wadell as a good source. > >=20 > > Tom Dagostino > > Teraspeed(R) Labs > > 13610 SW Harness Lane > > Beaverton, OR 97008 > > 503-430-1065 > > tom@xxxxxxxxxxxxx > > www.teraspeed.com > >=20 > > Teraspeed Consulting Group LLC > > 121 North River Drive > > Narragansett, RI 02882 > > 401-284-1827 > >=20 > > -----Original Message----- > > From: si-list-bounce@xxxxxxxxxxxxx > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Babid A > > Sent: Monday, December 12, 2005 5:44 PM > > To: si-list@xxxxxxxxxxxxx > > Subject: [SI-LIST] Microstrip/Stripline > >=20 > >=20 > > Which is more lossy between microstrip and stripline? why? > >=20 > > Thanks, > > -Babid > >=20 > > ------------------------------------------------------------------ > 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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > List technical documents are available at: > http://www.si-list.org > > List archives are viewable at: =20 > //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 > =20 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //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 =20 ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ 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