I agree Andy! I only used the mismatched trace as one example. I also used a well matched patch antenna as another. Dr. Scott Bennett has a wonderful presentation discussing the lack of validity of the simplistic "loop area" concept of radiation. As you mentioned, if a folded dipole is laid out on a pcb, it will radiate with wonderful efficiency. Take the same loop area and design it as a transmission line and it's pretty inefficient. Well said sir, Brent -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Ingraham, Andrew Sent: Tuesday, October 14, 2003 8:44 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Traces don't cause EMI - really? Brent wrote: > ... If, in your statement, the words > "matched transmission lines" had been exchanged for "traces", I doubt anyone > would disagree. > ... As an intermediate case, I expect you would not > disagree with the concept that mis-matched transmission lines, even over a > continuous ground plane, may radiate significantly. My understanding is that it was a common but false belief that only mismatched lines radiate. Either matched or mismatched lines can radiate equally well. This popular misconception probably came about because of misunderstandings about the normal mode vs. common mode signals on the transmission lines; plus the fact that you can use a transmission line that usually doesn't radiate, as an efficient antenna element if you drive it differently, like the folded dipole antenna built from twinlead. I suppose that mismatched lines might have higher near field emissions because of the greater voltage maxima on the line; but otherwise they can both radiate. What determines how well a PCB structure radiates has more to do with its geometry than anything else. You can design geometries that radiate very well (and are designed to do so), or plain traces over continuous grounds that radiate poorly, and might be neglected because of other sources of emissions in your system. 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 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