How to calculate S21, S11
S21 calculation
Connect a 2V, 50Ω source to the input of the two port network.
Connect 50Ω load to the output.
Calculate the voltage at the output.
This voltage is S21.
In dB, S21 magnitude = 20*log (Vout)
S11 calculation
Terminate output with 50Ω.
Calculate input impedance and reflection coefficient.
r = (Zin - 50Ω)/(Zin + 50Ω)
S11 (dB) = 20*log(r)
Single element two port networks
For a network with a single element (Z) in series between the input and output.
S21=2/(2+Z/Zo)
S11=Z/(2*Zo+Z)
For a network with a single shunt element (Y)
S21=2/(2+Y*Zo)
S11=-Y*Zo/(2+Y*Zo)
posted by MyTravels @ 10:53 AM
3 Comments:
in order to measure s21 and s11 by using VNA and the antenna apparatus, does the distance between the antennas will affect the results?
to the magnitude, it won't change. but as the length of transmite line changes, the phase of RF signal will change accordingly. so if you watch the wave in the smith chart, you will get a different waveform
Great page! thanks for the info...
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