Quote from the ADS knowledge center. Does it make sense at all to all of you? I don't understand why there are two sets of Z-parameters at all
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Why (Z11)s are different?
Issue
I have a two port network. It is set up to run S-parameter simulation and with 50 ohm terms at both input and output ports. I want to calculate the z11 parameter use the following methods:
· Z11-params calculated directly from the S-parameter controller:Z11=real(Z11)
· Z11-params calculated using stoz(): Z11=real(stoz(S,50)(1,1))
· Z11-params calculated using stoz(): Z11=real(stoz(S11,50))
· Z11-parameter calculated using Zin(): Z11=real(Zin(S11,50))
But the method 1 and method 2 give one answer and method 3 and method 4 give a different answer, which one is right and why?
Solution
All the 4 methods are give the right answers for their setups. The reason the simulation results are different is due to the different loading impedances are used based on different method. The results for the method 1 and method 2 are two port simulation while the results for method 3 and method 4 are one ports simulation.
For the method 1 and method 2, the loading condition is based on the Z parameter definition that is Z11 is V1/I1 with port 2 open. So to calculate the Z11 impedance, the method 1 and method 2 assume there is no loading impedance, the load is open circuited.
For method 3 and method 4, the loading condition is based on the S parameter definition that is S11=b1/a1 with a2=0 that means the port 2 is loaded with Z0, in this case Z0=50 ohm.