"Wimpie" wrote in message
...
On 26 ago, 19:38, qrk wrote:
On Tue, 26 Aug 2008 10:02:47 -0700 (PDT), Wimpie
wrote:



Hello,

Most formulas for microstrip transmission line assume that there is
dielectric all over the ground plane.

Does somebody know a formula (or graphical solution) for the
characteristic impedance of a microstrip where there is only
dielectric material under the strip (so you can see the ground
plane)?

Best regards,

Wim
PA3DJS
www.tetech.nl
The mail address is valid when you remove abc

http://atlc.sourceforge.net/
The above link is a wonderful arbitrary solver for transmission lines.
This is primarily a Unix program. If you need a Windows build of the
program, I probably have version 4.4 somewhere.

--
Mark

Hello Mark,

This is good one (I found it via google also). You can enter both
metallics and dielectrics as you want. It would be very nice when you
can mail me a Windows Build (I hope it is not that big). A link would
also be useful.

My address is valid when you remove abc.

Best regards and thanks,

Wim
PA3DJS
www.tetech.nl

AFAIK dielectric between the strip and GP is the most significant unless
stripline is to couple to other stuff. Anytime you change board material
there are subtle changes in VF. For proto, I always like to allow for
trimming where it has to be critical, but best to make it less critical so
you don't have to spend time on every board. Air is better, but spacing
variations come into play, and what will happen if you drop it. The
calculations only get you so far unless you have your constants handy.