# RE: [SI-LIST] : Question on transmission line simulation by HP AD S /Momentum

From: Dan Swanson ([email protected])
Date: Mon Apr 30 2001 - 05:08:12 PDT

Nianci,

In Lince Calc, the basic calculation for microstrip impedance
assumes an infinetly thin strip. To account for thickness, a
corrected strip width is computed internally. The equations they
use were developed by curve fitting to a large data base of
field-solver runs.

In Momentum, the basic calculation is again for an infinitely thin
strip. If they ask you for thickness at any point ( I don't remember)
it will be a correction to the surface impedance for loss. You can
approximate thick strips by adding a ficticious air layer that is
the thickness of your strip and then add a second layer of metal
on top. Depending on the length in wavelengths, you may want
to stitch the sides together at a few points. For large, complicated
circuits this is not very efficient because you have doubled the
number of unknowns and forced the solution time to be 6 to 8 times
greater.

In the end, you are comparing two field-solvers.

Dan

Dan Swanson EMAIL: [email protected]
Bartley RF Systems, Inc. TEL: 978-834-4085
37 South Hunt Road FAX: 978-388-7077
Amesbury, MA 01913

> -----Original Message-----
> From: Nianci Wang [SMTP:[email protected]]
> Sent: Friday, April 27, 2001 4:24 PM
> To: '[email protected]'
> Subject: [SI-LIST] : Question on transmission line simulation by HP
>
> Hi,
>
> I have a question on simulating finite metal thickness transmission line
> by
> using HP ADS Line Calc and Momentum.
>
> Basically I did simulation by using both line Calc and Momentum for
> several
> different structures, I found that Momentum always give me a higher
> characteristic impedance than that of Line Calc. The thicker the metal is,
> the
> larger the difference between two simulation results. I did talk with HP
> help line and got the answer was that Momentum gave more accurate
> simulation
> results. I wonder if any one did the simulation by each line Calc or
> Momentum
> and compared the result with that of the measurement.
>
> Thank you
>
> Nianci
>
>
>
>
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