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Gap between Microstrip and Ground Plane - RF Cafe Forums
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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?
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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!
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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.
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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
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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.
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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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