# RE: [SI-LIST] : Question on transmission line simulation by AGILE NT ADS /Momentum

From: ABOULHOUDA,SAMIR (A-England,ex1) (samir_aboulhouda@agilent.com)
Date: Mon Apr 30 2001 - 06:23:49 PDT

Hi,

To answer to Nianci question: LineCalc vs. Momentum? I would say, it
depends!
It depends on the frequency range, the dimensions and above all, on the
complexity of your circuit. First of all, we should be aware that sims in
Momentum are less accurate a low frequencies than sims at high frequencies.
At high frequency and for the long structures, where radiation effect can no
longer be neglected, Momentum is definitively more accurate and may be
recommended. To overcome the limitation at low frequencies, there is now
something called "Momentum RF Modes". With Momentum RF Mode, you can expect
sims solutions stable down to DC. Momentum RF mode is usually more efficient
mode when a circuit is electrically small, complex, and does not radiate...
and due to the difference of method used to mesh the structures, Momentum RF
Mode requires less CPU time and memory.

Rdg

Samir.

-----Original Message-----
From: Dan Swanson [mailto:DSWANSON@BartleyRF.com]
Sent: Monday, April 30, 2001 1:08 PM
To: 'Nianci Wang'; 'si-list@silab.eng.sun.com'
Subject: RE: [SI-LIST] : Question on transmission line simulation by HP

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: d.swanson@ieee.org
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:nwang@amcc.com]
> Sent: Friday, April 27, 2001 4:24 PM
> To: 'si-list@silab.eng.sun.com'
> 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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