1-port measurements de-embedding adapter technique

[Juerg Ruefenacht]

We recently got a request how the 1-port measurements de-embedding technique can be done using VNA Tools.

The attached presentation gives an overview about different adapter characterization techniques and their pro and cons. The here described technique is mentioned on slide 11.

Please find below a step-by-step description:

After the two performed one-port calibrations, first: directly at the test port without adapter, second: at the adapter end, the two calibrations are calculated as normal 1-port calibration using VNA Tools.

This will result in two *.calb files in which the corresponding 'Generic Error Terms' are stored. Now select the two Generic Error Term files (assumption: first file directly at the test port, second file with adapter). With the right mouse button you activate the post-processing possibilities. Now select: Cascade / Cascade(inv(1st) and 2nd) and save the result under the desired adapter name. For example: Ada(2.4mm(m)-3.5mm(f))_1330_a.sdatb

There are two important points to consider:
a) For a calibration at port1 of a 2-port VNA the error terms are according to the implemented measurement model: S11, S13, S31, S33. For a calibration at port2 of a 4-port VNA these would be: S22, S26, S62, S66. But since you want the adapter as a TwoPort component with (S11, S21, S12, S22), you have to redefine the adapter file first. To do so, select the adapter file and choose the post-processing function 'Change Port Assignment' and define the ports accordingly by 1 and 2. Define a new file name e.g:  Ada(2.4mm(m)-3.5mm(f))_1330_b.sdatb

b) In the measurement model used, the forward transmission term is assumed to be 1 in the Error Box, and thus the entire tracking effect is taken into account in the reverse transmission term.

For this reason, the adapter must be made reciprocal (S21 = S21). You can import the attached Python script into the VNA Tools Script Tab and define the current adapter name. After executing the script the original file name will be overwritten. To better track the change, I recommend to duplicate the adapter file first and give it a new file name. For example: Ada(2.4mm(m)-3.5mm(f))_1330_corr.sdatb

The accuracy of this adapter characterization is directly dependent on the quality of the used Cal Standard definitions. To ensure that the reference planes are correctly defined, it is essential that the definitions take into account the systematic connector effects. Then the characterization comes out very well - especially since there are no cable effects involved, which are always present with the alternative TwoPort adapter characterization methods.

Best Regards, Juerg

Python script with an adapter filename example (does assume a passive and reciprocal component):

import clr

clr.AddReference('Metas.Vna.Tools')

clr.AddReference('Metas.Vna.Data')

clr.AddReference('Metas.UncLib.LinProp')

from Metas.Vna.Tools import Script

from Metas.Vna.Data import SParamData

from Metas.Vna.Data import SParamTools

from Metas.UncLib.LinProp import UncNumber

filename = 'Ada(2.4mm(m)-3.5mm(f))_1330_corr.sdatb'

s = Script(RootPath)

s1 = s.LoadSParamData(filename)

s1 = SParamTools.Reciproc[UncNumber](s1);

s.SaveSParamData(filename, s1)