The 90 degree angle problem is real. I have done some antenna design/modeling using the method of Moments (Full wave technique) and found the radiation efficiency is higher when a 90 degree bend exists. The data was compared to actual measurements and matched well. Regards, Ross Jatou U.S. Robotics ______________________________ Reply Separator _________________________________ Subject: Re: EMI Author: Joe Zdybowicz <[log in to unmask]> at Internet Date: 8/26/96 12:54 PM > Point 6. Has anybody measured a difference in radiation using 90 degree > angles? Or is this based on heresay (an electronics "Urban Myth")? >> 6. Eliminate ALL 90 degree angles on traces, and planes. All 90 degree >> angles radiate, it is important to run your clean up utilities if you >> haven't already. Also consider the planes as capable of radiation >> especially at higher frequecies, so 45 all the corners. I am not a Phd, but have taken some classes and hope my response is adequate. The radiation at a 90 degree bend is based on theory. I know of two sources which discusses the importance of chamfering corners. How much the right angle bends radiate is a good question, and I will try to uncover some tests or discuss with people who may have some greater information on how much does the 90 degree bend radiate. Please reference: High-Speed Digital Design by Howard W. Johnson & Martin Graham section 4.4.4 Right-Angle Bends "At the right angle bend the effective transmission line width increases. An increase in width contributes extra unwanted parasitic capacitance. The right-angle bend looks like a capacitive load attached to the transmission line." The wider line also effects impedance and this causes reflections. The reflection causes the signal to bounce back along the transmission line toward where it came from. Once reflections are introduced the trace on the board will seem longer because the signal is bouncing around. Designing traces to be short will make a difference. However we can not always make all traces short in length, sometimes it is physically impossible, which is why I fall back on good design practice. Some suggested reading "Field and Waves in Communication Electronics" by Simon Ramo, John R. Whinnery, and Theodore Van Duzer. Specificly chapter 5 on transmission lines. In general, I found having some education in communications, and transmission line theory a tremendous help when it come to high speed design. I would recommend PC designers look into these coarses. To me understanding is better then just following some rules, and understanding can come from college coarses, or experience, or testing. I think my point is, evan though theory tells us something and testing provide us with more information, it seems to me that if the design rules cause little additional effort on the part of the pc designers then why not just make it a standard practice. If there is something we can do a little differently and it causes no more work, then why not just do it. Although we are discussing design practices for pc designers to use on circuit boards, my opinion is most of the issues related to EMI radiation has to do with the enclosure and how well the enclosure acts as a shield. Unfortunately my field is pcb design and not enclosure design. joez ----------------------------------------------------------------- Joseph Zdybowicz FORE Systems CAD Engineer 174 Thorn Hill Road Email: [log in to unmask] Warrendale, PA 15086-7586 Direct: 412-772-6552 ----------------------------------------------------------------- **************************************************************************** * The mail list is provided as a service by IPC using SmartList v3.05 * **************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * **************************************************************************** **************************************************************************** * The mail list is provided as a service by IPC using SmartList v3.05 * **************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ****************************************************************************