In a message dated 7/29/2002 5:08:51 PM Pacific Standard Time, leeritchey@xxxxxxxxxxxxx writes: > What I show in my class is that guard traces are always LC networks that > resonate at some frequency and can and do turn into bandpass filters at > some > frequencies. I demonstrate this will actual failed circuits. Lee: It should be clear to most designers that providing either ungrounded guard traces or traces grounded at both ends will create a resonant structure that will be stimulated by transient (fast rise time) signals. These resonant structures allow reinforcement of signal strength (at their resonant frequency) and will couple this energy into other nearby traces. These resonant structures are commonly used to match impedances and therefore transfer maximum power into patch antennas. That is why one must use vias to ground at spacings on the order of 1/20 wavelength of the highest frequency of concern on the guard traces for them to be effective as a shielding mechanism. When properly implemented, guard traces are very effective at improving isolation between signal traces. For a 50 ps test signal rise time, I have achieved isolation improvements of 20-40 dB for stripline and 12-14 dB for microstrip using via-grounded guard traces with the same center-to-center signal trace spacing as non-guarded traces. Going on travel for a couple of days now, be back soon. Mike Michael L. Conn Owner/Principal Consultant Mikon Consulting *** Serving Your Needs with Technical Excellence *** ------------------------------------------------------------------ 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