Hello All! Reading the different contributions to this thread I hat to think back to my studies. Our Professor lecturing High Frequency Design talked of Microstrip Antennas. After a short search on google I found the below article (sorry for clipping the URL): http://www.navicpmart.com/advice/advicetmp.cfm/s/C7A13B2C9F173CF2E034080020B 4BBE117272197/v/001~~%2E%2E%2Fnews%2Fmw%5F200103%5F1%2Ecfm~~~~~~~~~~~~.html The article describes well the principle of radiation of this type of antenna. I think that the frequency range is an important. This could help to sort out at which frequency which part of a PWB will possibly act as source. Best regards, Michael > -----Original Message----- > From: Chris Cheng [mailto:chris.cheng@xxxxxxxxxxxx] > Sent: Dienstag, 21. Oktober 2003 02:58 > To: 'bdewitt@xxxxxxxxxxxxx'; leeritchey@xxxxxxxxxxxxx; > si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > > Brent & Lee, > > Nice spin on the issue but unfortunately you both tried to avoid the > original problem that Lee stated : > > >As far as EMI is concerned, it has been demonstrated many > times, once in > >the paper done by Doug Brooks with the staff at UMR, that > traces traveling > >over planes are not a detectable source of EMI. Therefore, > constraining > >the routing of differential pairs to prevent them from > creating EMI is not > >appropriate or necessary. > > I have seen and explained how surface trace can both fail EMI > and signal > integrity even if it is referencing to a solid plane and perfectly > terminated. If the edges are fast enough and the reference plane is > unrelated to the I/O power, the image current will be denied > a low impedance > return path and will exhibit strong EMI and power/ground > bounce. This is the > exactly reason why tight coupling differential traces can > help. This is also > the original claimed by proponents of coupled differential > signals and Lee > has chosen not to response to me. Whether the image current is flowing > between the differential traces or on the reference plane, > they cancel each > other out at both the driving and receiving end and thus > minimize both EMI > and power/ground bounce. Whether the reference plane is > related to the I/O > power or not does not affect the outcome in differential case > but make a big > difference in the single end signal case. > > To hide behind claims that since PC's or workstations have > surface trace > passing EMI and magically deduced that traces does not cause > EMI problem > makes as much sense as driving in the highway seeing no cops > pulling people > over for speeding and extending that to no one is speeding in > the highway. > Let me ask you this way, have you seen a highspeed system > that has surface > trace referencing to the wrong voltage plane pass EMI with an > open enclosure > without those crazy highspeed decoupling caps or thin core > planes to return > the image current ? I have seen plenty of them fail that way. > And yet I have > seen plenty of coupled differential signals route that way > and pass EMI or > signal quality. This is the fundamental advantage of coupled > differential > signals that you are so ignorant about. > > Lee, > > You seem to like to make claims that I can easily counter but > when face with > the rebuff you like to ignore it and continue to repeat your > flawed claim as > if no one can give you a counter example. > > In this forum, you have been asked many times the following question : > > "If tomorrow you are going into a client's office to consult > on designing a > 2.4GB/s differential signal system. Will you recommend them to "routed > thousands of differential signal where each member of the pair is on a > different layer". Do you think that is good engineering > practice ? Do you > think you can still keep your job as a consultant after making that > statement ?" > > And you seem to ignore the fact that this is how all these > differential > traces vs. single un-coupled lines discussion starts. > > This is a simple yes or no question. I don't even want to throw in any > technical point or science into it. You either do it or > don't. If you do, I > would propose you put that in your lecture notes and whatever > book you are > writing and call it "Lee Ritchey technique" or may be even > patent it as I > sure haven't seem anyone designing >GHz signals doing that. > As an inventor > of that technique, you deserve to publize it and make sure > people follow it. > > > On the other hand, you silence suggests you may have > something to hide in > you claim. It is plain wrong and even you yourself won't dare > to do that. > > Which way is it ? > > -----Original Message----- > From: Brent DeWitt [mailto:bdewitt@xxxxxxxxxxxxx] > Sent: Sunday, October 19, 2003 8:28 PM > To: leeritchey@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Traces don't cause EMI - really? > > > It seems this has become something of a tempest in a teacup. > As I mentioned > in an earlier post, I believe much of the energy of the dispute has > developed over differences in terminology. > > First, in the vast majority of cases, I agree with Mr Ritchey. In the > twenty five years or so I've been involved in EMC, I've never seen the > radiation from surface trace fail a product. That said, > I've only worked > on old/slow boards with fundamental clocks less than 1.5 GHz, > although I've > worked with 900 MHz intentional radiators to their 10th > harmonic. Rules of > thumb only work until the thumb is too fat to see the problem > underneath it. > As I mentioned in an earlier post, resonant patch antennas and other > intentional radiating pcb structures are nothing more than fat, well > designed traces. Somewhere between them and our ideal EMC > designs lies > practicality. As frequency increases, I find myself needing > increasingly > closer inspection of detail. > > In somewhat oblique support of Mr. Ritchey, most failing EMC > issues I've > observed have been associated with L di/dt induced voltages > on the reference > plane caused by surface traces. I/O cables, using said > poorly controlled > reference planes out to the world, are often a major > emissions issue, but > that is entirely another subject for discussion. > > Finally, I believe Mr. Ritchey is correct, but using the following > assumptions: > > - The trace structure and geometry does not approach a > resonant structure at > the fundamental or appreciable harmonics of the operating frequency. > - The reference plane structure supporting the return currents of the > surface trace does not significantly contribute to reference > plane resonance > and induced voltage on attached cables. > > Respectfully, > > Brent DeWitt > > ------------------------------------------------------------------ > 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 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 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