Thanks, Nizar. There is almost no difference between the two methods for Z (|Z|), a bit more for R and I. This suggests that the residual shunt capacitance in your test fixture is negligible. The S21 method is noted as Ser, which stands for series-through (Snt for the shunt-through method comes next). I include R because some builders judge choke performance by it rather than |Z|. The I plot shows where the choke changes from being inductive to capacitive.
Brian
