Itzhak, The coupling through a small hole is extremely broadband and almost frequency independent. Though, the value of the coupling is very small to worry about for digital signal integrity problems. However it is considerably larger comparing to coupling through a solid metal plane. It may be important to put some restrictions on distance from strip to holes for digital to analog interference problems. That can be done with the electromagnetic analysis. Best regards, Yuriy Yuriy Shlepnev www.simberian.com -----Original Message----- From: Hirshtal Itzhak [mailto:ihirshtal@xxxxxxxxxx] Sent: Thursday, July 14, 2011 4:49 AM To: shlepnev@xxxxxxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] More About Plane Isolation Hello Yuriy, Thanks again. As I understand the Bethe hole directional coupling you mentioned (and I admit to be far from an expert on this issue), it seems to be of a narrow band nature. If I'm right, then it seems relatively irrelevant to regular wide-band digital signals I'm concerned with, isn't it? Best Regards Itzhak Hirshtal -----Original Message----- From: Yuriy Shlepnev [mailto:shlepnev@xxxxxxxxxxxxx] Sent: Wednesday, July 13, 2011 4:06 AM To: Hirshtal Itzhak Cc: si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] More About Plane Isolation Itzhak, In addition to Steve's response, I can add a few things. A hole much smaller then the wavelength may serve as a coupling structure. Search for Bethe hole directional coupler or see the original H.A. Bethe paper (Phys. Rev. vol. 66, 1944, Oct. p. 163-182) for more details. With appropriate location of a hole and strips, the coupling may be much larger then coupling through the solid conductive planes even at lower frequencies. Coupling through a hole filled with a metal post (screw) may be larger or smaller - it depends on whether the screw is connected to the solid conductive planes or not (and other elements of geometries of coupled structures). If multiple holes appear along a strip line, the coupling will increase substantially comparing to the case with one hole or to the solid plane. Periodicity will increase the coupling, but only at frequencies with the distance between the holes equal to a quarter of wavelength. Only electromagnetic analysis may provide guidelines for the isolation in your design. Best regards, Yuriy Yuriy Shlepnev www.simberian.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Hirshtal Itzhak Sent: Tuesday, July 12, 2011 12:02 AM To: shlepnev@xxxxxxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] More About Plane Isolation Hello Yuriy, It took me a while, because I've lost my SI-LIST correspondence, but still, I would like to question your note about through-plane coupling via PCB holes, which I cite below (from the SI-LIST Archive). First, is it true that the coupling through a single hole will be very low at frequencies that correspond to wavelengths longer than twice the hole diameter? Second, what if the hole isn't really a hole, since it's filled with copper, or "filled" with a screw? This will turn the hole to a much less coupling structure, isn't it? Third, can you explain the issue of periodic hole pattern? Is it an issue at several GHz frequencies? Thanks Itzhak Hirshtal Your Note: Note, that these results are for the solid copper planes. If planes have holes in vicinity of the traces, the coupling may substantially increase at high frequencies even for much shorter segments. If small holes form a periodic pattern, the structure may behave as very effective directional coupler with substantially larger coupling at microwave frequencies. As Scott already pointed out, you have to do numerical analysis for a structure that represents your particular design. Best regards, Yuriy www.simberian.com The information contained in this communication is proprietary to Israel Aerospace Industries Ltd., ELTA Systems Ltd. and/or third parties, may contain classified or privileged information, and is intended only for the use of the intended addressee thereof. If you are not the intended addressee, please be aware that any use, disclosure, distribution and/or copying of this communication is strictly prohibited. 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