Istvan Novak Wrote: > > As it was stated above, the lowest parallel modal resonance from a pair of > FR4 10x5" planes is around 288MHz. If the planes are ideal: perfectly > rectangular, no cutouts, plane separation does not change with location, and > the dielectric material is homogenious, this parallel modal resonance > frequency can be readily calculated as fres=1/(2*tpd), where tpd is the > propagation delay along the longer side of the rectangular. So as long as > these idealization assumptions are valid, calculating the modal resonance > frequencies is easy. Dear Istvan: Thank you for excellent comments. In a paper by T. H. Hubing et al., (reference 1) on Page 158, equation 7 is: fp = fs * sqrt(1 + n * C1/Cb ) Where fp and fs are parallel and series resonant frequencies respectively; Cb represents capacitance between power and ground planes, and n is the number of decoupling caps having capacitance C1. It is interesting to examine under what conditions above fp formula simplifies to your expression for parallel modal resonance fres=1/(2*tpd). This seems to require setting n = 0 (causes fp = fs) but leads to a mismatch factor of 1/pi; assuming fp = fs = 1/[2 * pi * sqrt(L * C )] and tpd = sqrt(L * C). Reference: [1] T.H. Hubing, J.L. Drewniak, T.P. Van Doren and D.M. Hockanson, "Power Bus Decoupling on Multilayer Prined Circuit Boards", IEEE Transactions on Electromagnetic Compatibility, Vol 37. No. 2, May 1995, PP. 155 - 166. Best Regards, Abe Riazi ServerWorks ------------------------------------------------------------------ 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