Calibration Process and Clarifying S-Parameter Representation

Updated Oct 30, 2018

Reported In

Hardware

  • PXIe-5632
  • N-type

Issue Details

What do the s-parameters represent before and after calibration?

Solution

The VNA itself has 2 ports that can both be used to emit or detect a RF signal, this data is then put through a series of calculations to determine the s-parameters.
S-parameters describe the magnitude and phase relationship between incident and reflected waves.

If the value of S11 = 0, this indicates 0% being reflected back
If the value of S11 = 1, this indicates 100% being reflected back
In the situation of S11 > 1 prior to calibration, this is theoretically impossible, which indicates the s-parameters mean nothing prior to calibration. For example:
If there was a situation where S11= 0.99 with a calibration error of 0.05, the measurement will show to be 1.04 which explains why you would see a value greater than 1. 

 

Additional Information

In its simplest form, a network analyzer is an instrument used to measure impedance.
Calibration capabilities are required to eliminate systematic errors and compute the appropriate ratios necessary to produce S11, S12, S21 and S22, (the S-parameters).
Determination of scattering parameters, or S-parameters, is the basic measurement capability of vector network analyzers. The S-parameters describe the magnitude and phase relationship between incident and reflected waves and are numbered according to where a wave originates from and where it is propagating to.

There is a possibility, with S11(or others) >1, that this could be caused by an active device, with an external power source. 

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