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ADS Momentum Simulation Problem - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

 Post subject: ADS Momentum Simulation problem
Posted: Sun Oct 09, 2005 10:43 pm 
i'm having a big problem in displaying the gamma and impedance values of a transmisison line. i've a simple microstrip and i attached a substrate definition and ran the simulation. it worked fine and i got the s-parameters but when i do Momentum-->Post Processing -->Visualization to see the gamma and impedance graphs versus frequency, i get impedance being 50 ohm throughout the frequency range and gamma being zero throughout.

The s-params make sense but for some reason i'm not getting the right transmission line data. does any one know what's going on? i read the momentum manual and it said that if it didn't recognize the ports as 'Single' it sets the gamma=0 and impedance=50. So, i'm assuming that might be the case but how do I fix that. My ports are single with 50 ohms. I did Momentum--> Port Editor... I also read in the manual that if you define a 'Single' port your 'substrate definition must include at least one infinite metal layer: a top cover, ground plane, or a slot layer, or a ground reference must be used in addition to the port'. Now, I've a ground plane because i'm simulating a microstrip and i've mapped the ground plane as a slot layer. so, i think i'm meeting the requirement but i'm still unable to see the right gamma and impedance.

Any help will be much appreciated.

 Post subject: Re: ADS Momentum Simulation problem
Posted: Sun Oct 23, 2005 12:32 am 
Hi, What you see is the impedance which is connected to the port , which
is usually assumed to be 50 ohm. If you want the input impedance and vswr they automatically does not appear on the list. You need to calculate them through eqn. option of ads. i.e. zin=(1+s11)/(1-s11)*z0

 Post subject: Re: ADS Momentum Simulation problem
Posted: Thu Feb 25, 2010 2:44 pm 

Joined: Tue Dec 15, 2009 10:22 am
Posts: 1
Is that a general expression, or is it assuming a terminated network?

Posted  11/12/2012

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