Michael, Resonance conditions are formed between sections of transmission lines that have discontinuities, due to reflections at the boundary between two impedances. These are generally quarter-wave and half-wave resonances and multiples thereof, and are described quite well in books such as Pozar's Microwave Engineering. As for ground shields, or ground traces, the trace portion is "just a transmission line" that is periodically terminated to ground through a via. At the via, the impedance is 0, and causes a discontinuity at the point where the ground traces connects with the ground via. This discontinuity will set up a reflection and a corresponding resonance. If the other end of the ground trace is left open, then a quarter-wave resonator is formed. If the other end of the ground trace is also tied to ground through a via, then a half-wave resonator if formed. At the resonant frequency and integer multiples the trace will no longer operate as an effective ground shield, and instead will cause a peaking of crosstalk. Much more on this phenemenona can be found by searcing the SI archives. Several of us, including Mike Conns and myself have written about this in the past. best regards, scott -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com Michael Smith wrote: Hi guys, I found this thread very interesting and informative. I was hoping someone could explain what is meant by "exciting half-wave resonance" and how via spacing would affect this. Thanks for your help, Michael Smith Hardware Engineer iZ Technology Corp. -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com ------------------------------------------------------------------ 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