**From:** ABOULHOUDA,SAMIR (A-England,ex1) (*samir_aboulhouda@agilent.com*)

**Date:** Mon Apr 30 2001 - 06:23:49 PDT

**Next message:**Degerstrom, Michael J.: "RE: [SI-LIST] : Plane short"**Previous message:**Javin Olson: "FW: [SI-LIST] : RE: 2.5 GHz in FR4"

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

AD S /Momentum

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
*

*> ADS /Momentum
*

*>
*

*> 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
*

*> ADS
*

*> 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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**Next message:**Degerstrom, Michael J.: "RE: [SI-LIST] : Plane short"**Previous message:**Javin Olson: "FW: [SI-LIST] : RE: 2.5 GHz in FR4"

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