Acquisitions For Uncorrected S-Parameters

The following example scenario is measuring the S11 of a two port DUT using a two port VNA. With error correction turned off, the VNA measures the uncorrected S11 of the DUT by stepping through the configured frequency points, returning the uncorrected S11 as the following ratio:

where

  • the subscript m in S11m stands for measured,
  • Sij denotes the intensity of the scattered wave traveling away from the DUT at port [i] when the VNA generates the stimulus signal at port [j],
  • rij denotes the intensity of the incident wave traveling away from the DUT at port [i] when the VNA generates the stimulus signal at port [j].

,Computing the uncorrected S11, that is S11m, requires the VNA source to measure the DUT response by generating the signal only at port 1.

Note In the context of a two port DUT, measurements performed when the source is set to port 1 are forward measurements, while measurements performed when the source is port 2, are referred to as reverse measurements.
Note S11m and S21m require measuring the DUT in the forward direction, that is, measuring the scattered and incident waves when the source is set to port 1.
Note S12m and S22m require measuring the DUT in the reverse direction, that is, measuring the scattered and incident waves when the source is set to port 2.

Acquisitions For Corrected S-Parameters

Computing an error-corrected s-parameter of a two port DUT using a two port VNA requires measuring the DUT in both the forward and reverse port directions. The error corrected s-parameters S〈i〉〈j〉 are obtained from uncorrected S〈i〉〈j〉m as shown in the equations below.

Note Computing the common denominator term D requires all four uncorrected s-parameters, that is, S11m, S12m, S21m and S22m. Obtaining any error corrected s-parameter requires measuring the DUT in both forward and reverse port directions.

Port Subset For Error Correction

When measuring the error-corrected S11 of a 1-port DUT connected to port 1 of a two-port VNA, the VNA still performs both forward and reverse sweeps. However, since the DUT is a 1-port network connected to port 1 of the VNA and is completely isolated from port 2 of the VNA, the reverse sweep is unnecessary.

You can avoid this extra sweep by setting the Correction:Port Subset:Enabled property to True and the Correction:Port Subset:Ports property to port 1. With error-correction limited to the specified set of ports, the VNA performs only a forward sweep to compute the error corrected S11 of the DUT.