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Confusing on Z11 and input impedance

Question asked by stanleymyc on Jun 18, 2009
Latest reply on Jun 19, 2009 by Dr_joel
hi all, good day to you.

i am using PNA to do some characteristic impedance measurement, and with my DUT connecting to the front panel input, assuming i set S11 measurement, in smith chart format, and i managed to get 50ohm result, which indicate good absorption power of the DUT.

However, i feel abit confuse that can i claim Z11 is the input impedance characteristic? and from below documents:

http://contact.tm.agilent.com/data/stat ... n-95-1.pdf

i find out we have two different formula, on the page 13 we have Z1 = [(1 + S11)/ (1-S11) ] * Zo

while on the page 65 i have
Z11 = (1+S11)(1-S22)+ S12*S21  /  (1-S11)(1-S22)+ S12*S21

which when i apply this formula, it is not identical to the result i measure in the smith chart but Z1 seems working fine.

Can anyone help on this issue?

thanks for your help.  

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