

Voltage Gain Determination  RF Cafe Forums

Measures 
Post subject: Voltage Gain Determination
Posted: Wed Jan 20, 2010 1:35 pm


Joined: Tue Dec 15, 2009 10:22 am
Posts: 9 
Hello I'm trying to obtain the voltage
transfer function employing an E5062A VNA.
From pages 24, 23 in:
http://cp.literature.agilent.com/litweb ...
21087.pdfI see that it can be obtained
in terms of the S parameters and the load reflection
coefficient. My question is: is it correct
to assume that the source and load impedances
are equal to the reference impedance (Zl=Zs=Zo=50
Ohm)? In this case, the expression in page
24 of the document would reduce to Av=S21/(1+S11).
Is it correct? Thank you very much.





fred47 
Post subject: Re: Voltage Gain Determination
Posted: Fri Jan 22, 2010 11:49 pm



General 

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 113 
When you measure a device with a VNA, the source
impedance from the VNA is 50 Ohms (normally,
unless you're in the TV industry, where they
use 75 Ohms a lot). Likewise, the load impedance
seen by the device you're testing is 50 Ohms,
again due to the VNA.
Remember to use
complex arithmetic when you use the equations!
Good luck!





Measures 
Post subject: Re: Voltage Gain Determination
Posted: Mon Jan 25, 2010 6:24 am


Joined: Tue Dec 15, 2009 10:22 am
Posts: 9 
So... can I assume that the reflection coefficients
of the source and the load are zero and, then
the referred expression is simplified as I said?





fred47 
Post subject: Re: Voltage Gain Determination
Posted: Mon Jan 25, 2010 1:27 pm



General 

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 113 
Basically, yes.
But it's more precise
to say that the source and load impedances (50
Ohms + j0 Ohms) determine the reference impedance.
If you connect a short piece of lowenough
loss transmission line of characteristic impedance
50 Ohms between the two ports of the VNA, then
calibrate out the length of the line, you'll
get zero for S11 and S22, and one for S21 and
S12  which I think is the answer you're looking
for, stated precisely.
Good luck!


Posted 11/12/2012



