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s-parameter calculation using ac analysis (Read 6711 times)
R. Zakai
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s-parameter calculation using ac analysis
Feb 14th, 2010, 9:21am
 
Hello,
Just wondering if anyone knows where I can find formulas to manually compute s-parameters using nodal voltages from ac analysis. I have taken a shot at calculating these formulas myself but I have run into some ambiguities with s21 and Ap. If someone already has those formulas and has used them with confidence, I'll greatly appreciate if you can share them with me.
Rehan
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pancho_hideboo
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Re: s-parameter calculation using ac analysis
Reply #1 - Feb 14th, 2010, 9:39am
 
R. Zakai wrote on Feb 14th, 2010, 9:21am:
Just wondering if anyone knows where I can find formulas to manually compute s-parameters using nodal voltages from ac analysis.
It is very easy. You can find such formula in any basic circuit or filter theory text book.
See http://www.designers-guide.org/Forum/YaBB.pl?num=1215827287/3#3

As direct method, assume port impedances(=reference impedances), R01 and R02 are all real.
Available power of port1 is Pa=(|E|/2)2/R01
Power delivered to port2 is Pload=|V2|2/R02

|S21|2=Pload/Pa=(2*|V2/E|)2*R01/R02

S21=(2*V2/E)*sqrt(R01/R02)=(V2/(E/2))*sqrt(R01/R02)

Here "E" is an open circuit voltage of port1. And E/2 is not equal to V1 generally.

S21 is different from conventional voltage gain V2/V1 even if R01 is equal to R02.
Also |S21|2 is different from conventional power gain Pload/Pin.

About meaning of "E", see the following and my related previous posts.
http://www.designers-guide.org/Forum/YaBB.pl?num=1237656418/3#3

As another method, evaluate Y or Z parameters by AC analysis.
Then convert them to S parameters.
See http://www.rfcafe.com/references/electrical/s-h-y-z.htm
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« Last Edit: Feb 15th, 2010, 5:38am by pancho_hideboo »  
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Frank Wiedmann
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Re: s-parameter calculation using ac analysis
Reply #2 - Feb 15th, 2010, 12:57am
 
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