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Is the S21 plot result given in the voltage ratio or the power ratio in ADS Momentum?

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raebrm

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Hi,

Just a simple question. Is the S21 plot result we get from momentum in dB the voltage ratio or the power ratio? Is there a method to convert one to another in ADS?

Thanks!
 

S21 in ADS Momentum

S-Parameters are voltage ratios
 

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    raebrm

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Re: S21 in ADS Momentum

S parameters are actually power-wave ratios [W]^1/2. You cannot assume that all you reference port impedances are the same. I know, I know, we all are working with Z0i=50 but I'm a little academy biased :)
 

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    raebrm

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Re: S21 in ADS Momentum

To see the power of a certain node in your circuit you must give a name at the node, run the simulation and than from datadisplay you can write the expression dbm(nodename) than you can also plot this
see also
www.uwaverf.altervista.org/forum
 

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    raebrm

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Re: S21 in ADS Momentum

thanks for the replies. I did some tests on ADS and i think that S21 gives the voltage ratio when we display the S21 in terms of its magnitude (V0/V1). But if we display the S21 in terms of dB, it's converted into 20*log(V0/V1), so the plot in dB is the same for power or voltage, since the power in dB is 10*log(P0/P1) and P0=V^2.

hope i didnt have a huge misconception here.
thanks!
 

Re: S21 in ADS Momentum

raebrm said:
I did some tests on ADS and i think that S21 gives the voltage ratio when we display the S21 in terms of its magnitude (V0/V1). But if we display the S21 in terms of dB, it's converted into 20*log(V0/V1), so the plot in dB is the same for power or voltage, since the power in dB is 10*log(P0/P1) and P0=V^2.
Click to expand...

Yes, this is correct.

Chinaski mentioned the special case where you have mixed reference impedances, and then it gets a little bit more complex. But for the normal case with identical reference impedance on all ports, your description is correct.
 

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    raebrm

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Re: S21 in ADS Momentum

wonderful! thanks so very much
 

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