[SI-LIST] symmetric coupled striplines...
- From: "Ishwar Hosagrahar" <ishwarh@xxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 28 Aug 2009 18:47:36 -0500
Folks,
I was pondering about PCB trace losses in general to assess the impact of
migrating a couple of transmission lines to various dielectrics, and hoping that
some of the experts here can provide some inputs.
As a part of the pondering process, I messed about with a HFSS model of a
symmetric differential stripline, and solved the differential transmission
loss/1inch of two different cases :
case1 : FR4_epoxy, Dk = 4.4, Er = 0.02
case2 : Nelco-4000-13SI, Dk = 3.4, Er = 0.01
(model had a 8mil thick dielectric for the symmetric stripline on the top and
bottom, and I adjusted the (default copper) trace widths to get a 100ohm
differential impedance for both cases. With a trace gap of about 9mils, the
traces were between 6mils to 8mils wide depending on dielectric. The simplistic
material definitions were from the default Ansoft library, ie.nothing too
intelligent was attempted. A picture of the model is attached here)
Without getting into the numerous technical details of the solver or the setup
(choice of solution and port types, excitations, boundary conditions, complex
dielectric definitions, surface roughness factors/layered impedance etc.etc.),
do the HFSS results look believable to folks here with more experience on all
this sort of complicated thing?
My questions are :
(a) does anyone have measured data (or an intuitive feel) to judge if the FR4
and Nelco4000-SI results are realistic in terms of what I'd get from a VNA
measurement if I were able to ideally deembed any connections and measure the
uniform symmetric stripline characteristics for this specific topology?
(b) anyone on this list know of published data for loss/inch characteristics of
different trace topologies (uniform symmetric stripline) for different
dielectrics? I am looking for actual measured or simulated data for different
dielectrics on the lines of Joel Goergen's qualitative comparison to the IEEE at
:
http://grouper.ieee.org/groups/802/3/ap/public/may04/goergen_01_0504.pdf
The Sdd21 plot of my analysis is attached. I'll be happy to send anyone the
actual Touchstone-formatted S-parameters [S4P] if you want to take a deeper peek
at the data. (I can't figure out how to post the data zipfile to the si-list
reflector submissions area, so please email me directly at this time)
Thanks for inputs.
Cheers,
Ishwar Hosagrahar
ishwarh@xxxxxxxx
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