Measures 
Post subject: Input Impedance
Posted: Mon Mar 01, 2010 6:57 am


Joined: Tue Dec 15, 2009 10:22 am
Posts: 9 
How can I obtain the input impedance of my circuit
from the measured Sparameters?
Is the
expression Zin=Zo*(1+S11)/(1S11) a general
expression, or it is only valid in the cases
in which GammaL is zero? I don't obtain the
input impedance using this expression. Is
GammaL zero occurs only when the load impedance
is equal to the impedance of the network? Or
does it occur whenever the load impedance is
equal to the reference impedance?
Does
anybody know which is the expression than ADS
uses to obtain the Zin from the S11 parameter?
I know this expression works perfectly, but
I would like to obtain Zin by myself from the
measured Sparameters, not using ADS (I cannot
use touchstone files).
Thank you very
much





david1hitch

Post subject: Re: Input Impedance
Posted: Mon Mar 15, 2010 10:35 pm


Joined: Mon Jan 04, 2010 1:12 am
Posts: 5 
The input impedance of any network is determined
by the combination of the real and imaginary
elements combined , real being the resistive
element and the imaginary being the reactive
elements . Your results should be in the for
z=R+jwl or z=RjwC . I have spent over 30 years
dealing with practical examples





SunshineDesign

Post subject: Re: Input Impedance
Posted: Wed Apr 07, 2010 3:28 pm


Joined: Sat Nov 08, 2008 11:35 pm
Posts: 30 Location: Ramona, CA

David didn't answer your question, of course
impedance is a complex value. But the question
was is the formula he posted the general expression
for Input impedance from S11 and the answer
is yes. Do remember to convert the S11 from
dB to linear terms, where it is a voltage ratio.
This can be used to convert the S11 measurement
of the Zo =50 or 75 ohms of the measurement
instrument plane to the Zload of the device.
GammaL zero occurs when the load impedance is
equal to the reference impedance i.e. when both
impedances are exactly matched.
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Posted 11/12/2012
