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| Gap between Microstrip and Ground Plane - RF Cafe Forums | ||||||
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Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
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Below are all of the forum threads, including all the responses to the original posts. ljoseph Post subject: Gap between Microstrip and Ground Plane Posted: Tue Sep 04, 2007 8:03 am Captain Joined: Tue Sep 04, 2007 7:54 am Posts: 13 Location: Dallas Hello I have microsrtip line on the PCB with following specifications: Er = 4.25 H = 0.3mm T = 32.5um With this, width of 50 ohms line is 0.56mm. On the PCB it is better to provide ground fill on both sides of Microstriop line so that fields radiating from the line will be terminated on the ground fill. But, depnding on the distance between the Mcirostrip line and Gnd plane, CPW effects will take over. What is the ideal distance between the Microstrip line and the ground fill so that CPW effects won't dominate and affect characteristics impedance of the line? Top IR Post subject: Posted: Tue Sep 04, 2007 2:19 pm Site Admin Joined: Mon Jun 27, 2005 2:02 pm Posts: 373 Location: Germany Hello ljoseph, From my experience, the best distance from both sides of the Microstrip line is 1.5 to double the line width. Don't forget to stitch plated vias in a distance which is around 1/10 wavelngth along the GND fills. Hope this helps. Good luck! Top ljoseph Post subject: Posted: Tue Sep 04, 2007 6:00 pm Captain Joined: Tue Sep 04, 2007 7:54 am Posts: 13 Location: Dallas Hello Thanks for your reply. Could you please explain the function of ground fill. Still, I am not very clear about it. Top Noise Post subject: Posted: Wed Sep 05, 2007 2:06 am Captain Joined: Tue May 02, 2006 4:59 am Posts: 15 hello, In my opinion the distance from GND should be 4 time the copper width. Else it will act like Coplanar and not as microstrip. For Coplanar as far as ratio a\b is bigger , the characteristic impedance is bigger. It can be seen as two parallel impednace (Coplanar and microstrip) Noise Top IR Post subject: Posted: Wed Sep 05, 2007 2:28 pm Site Admin Joined: Mon Jun 27, 2005 2:02 pm Posts: 373 Location: Germany The function of the GND planes is exactly as the shielding of a coaxial cable. Top madengr Post subject: Posted: Tue Sep 11, 2007 4:55 pm Captain Joined: Fri Feb 02, 2007 5:22 pm Posts: 5 Location: Overland Park, KS I use a spacing of one or two substrate heights, depending on how long the trace is. Often people use N*trace_witdth, however lets say you have a low impedance line of Z0=10 ohms, would you still space at N*trace_width? EM simulators are inexpensive or free these days. Maybe try your configuration and see how much you can get away with. http://www.sonnetusa.com/products/lite/ Posted 11/12/2012 | ||||||
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