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Adapter Characterization Macro for s2p Measurements

Question asked by drdroege Employee on May 5, 2016
Latest reply on May 9, 2016 by Dr_joel

I'm using T-matrices to cascade S-parameters and am having problems with the s2p measurements.

 

I've started with a cascade of SMA male-to-female adapters (PE9506).

To get accurate measurements of these adapters I have been attaching them directly to the front test port on our PNA and using the Adapter Characterization macro to calculate the S-parameters.  I have found that I can correctly CALCULATE the S-parameters for cascaded components if I characterize the adapters in the following manner:

1) Perform a one port cal at TP1 (save to file: Reference, for example)

2) Attach Adapter A1 to TP1

3) Perform a one port cal at Adapter A1 (file: A1)

4) Use the Adapter Char. Macro to subtract Reference from A1 (file: A1.s2p)

5) Attach Adapter A2 to Adapter A1

6) Perform a one port cal at Adapter A2 (file: A2)

7) Use the Adapter Char. Macro to subtract A1 from A2 (file: A2.s2p)

8) Use the Adapter Char. Macro to subtract Reference from A2, to get the cascade S parameter,

    (file: A2_From_A1.s2p)

 

The T-matrix cascade calculation using the two Adapter s2p files is nearly identical to the cascade data collected in step 8 above, which should be the measured cascade value.  So that makes sense.

 

The measurement method that doesn't work for some reason, but I'd would rather use (because then I can cascade any S-parameter data I may have) is the following:

1) Perform a one port cal at TP1 (File: Reference)

2) Attach Adapter A1 to TP1

3) Perform a one port cal at Adapter A1 (file: A1)

4) Remove Adapter A1 and Attach Adapter A2 at TP1.

6) Perform a one port cal at Adapter A2 (file: A2)

7) Use the Adapter Char. Macro to subtract A1 from A2 (file: A2.s2p)

 

The A2 S-parameters retrieved from these two methods differ from each other and the T-matrix cascade calculation for these last two adapter files will under-estimate the actual Insertion and return losses.  I've attached charts of the measurements using the two techniques.

 

I can understand why the phase measurements for A2 may differ from the two measurements methods but I don't understand why the magnitudes are different.

 

Any thoughts?

 

Thanks,

David

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