[SI-LIST] Re: Buried Microstrips
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Ty Beeman <ty.beeman@xxxxxxxxx>
- Date: Thu, 16 Jul 2009 07:45:22 -0700
3D field solvers like Simberian, Ansoft, CST, when properly set-up yield
very accurate results. If the object is to develop CF equations that
are more accurate than existing over some data range, I think you need
to do the leg work of obtaining / generating the data set, and then
performing the fit. To put it another way: If there was a straight
forward way to yield accurate results from CF equations over a wide data
range, there wouldn't be much demand for 3D solvers in this space.
Ty Beeman wrote:
> Hello,
> As part of a class project, we have been given the assignment of using
> closed loop equations to "accurately" predict the characteristic impedance,
> etc. of microstrips.
>
> To solve for surface microstrips, we have used the equations from: E.
> Hammerstad and O. Jensen, "Accurate models for microstrip computer-aided
> design." These equations give us results that are very close to field
> solvers.
>
> However we're kind of stuck in getting accurate results for a buried
> microstrip. We are using the equations found in: Brian C. Wadell,
> "Transmission Line Design Handbook." When we use the surface microstrip
> equations above to solve for Z-buried we can get close, end up with some
> errors as much as 4% and off by as much as 3 ohms or more.. If we use the
> Wadell equation for surface microstrip to solve for Z-buried, our error is
> around 5% when comparing to field solvers.
>
> Looking at it a little closer, we find that our calculated effective er is
> different than that given by the field solvers.
>
> All we can seem to find in the reference materials is the same (or similar)
> calculation that is in Wadell's book or old IPC equations.
>
> So our questions are:
>
> 1. Are there any other equations for buried microstrips that others have
> found to be more accurate, especially for effective er and impedance?
>
> 2. Can anyone recommend any other reference material on buried microstrips?
> Are there any good IEEE papers on the subject?
>
> We know we may have to settle for what we have now, given the reference
> material, but we're hoping there's something a little more accurate
> available.
>
> Thank you,
> Ty Beeman
> Logan Talada
> Students
> Tompkins-Cortland Community College
>
>
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