will the person who wrote this response please contact me? I need info on RF also.(P.S. Jack, sounds like the new job is a challenge.) Pete Waddell Printed Circuit Design Mag voice: 770- 952-1303 fax: 770-952-6461 e: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: RF Design - Plating and Routing Author: [log in to unmask] at Internet Date: 6/24/97 5:45 PM Jack Olson wrote: <snipped material> > Many of the RF designs here were done in AutoCAD, and the only reason I > have been given for this was that it was easier to chamfer the corners > of the delay lines (fairly wide 50 ohm traces on 20mil teflon). I may be > wrongly assuming that the reason for the chamfer was to minimize the > effect of the impedance change "around the corner", but my new CAD > package can do curved traces which suggests NO mismatch around bends... > constant width everywhere, right? > Unfortunately, no one here has any data to support the need for > chamfers. (I have to painstakingly enter precise polygons if chamfers > are really required, so I would rather avoid it). > We are working with 1.9GHz, and are moving to Rogers 4003 material. > > Can anyone with RF experience comment on this? Hi Jack, The issue of corners comes up every now and then. Part of the issue is that as frequency goes up, the turn of the trace is part of a turn for a loop. i.e. inductor. The other part I have always used I will try to address in the following. A side trace-end-on point of view, current distribution in the ground plane will look like the following... ______ Trace | | |______| ........ . . . . . . . . Ground Plane .____________________________. Strongest underneath, dropping off exponentially as you move away from the trace to some other point in the ground plane. Put two traces very close to one another and their respective current distributions in the ground plane will conflict with one another. Now, let's add a right angle turn to your trace and you get more of a mess. The current distribution on the outside bend drops off much more rapidly than the above. Why? It's spread across a 270 degree angle. The current on the inside of the bend does not drop off so rapidly. Why? It's compressed into a 90 degree angle. This spreading and compression causes an "impedence bump". The current is not evenly distributed as before. The only way this can be explained is if there is a discontinuity. In this case, it's a discontinuity in the current that "appears" as a discontinuity in impedence. Put another trace close to your first and it just adds to the mess. 90 degree corners modified to two 45 degree corners or a corner with a radius helps. And keep your traces fairly spaced from one another. Hope this helped... *************************************************************************** * 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.* *************************************************************************** * If you are having a problem with the DesignerCouncil, please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * 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.* *************************************************************************** * If you are having a problem with the DesignerCouncil, please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************