5.1 General Information
5.1.1 Measurement Errors
S-parameter measurements are influenced by various measurement errors, which can be
broken down into two categories:
§systematic errors, and
§random errors.
Random errors comprise such errors as noise fluctuations and thermal drift in electronic
components, changes in the mechanical dimensions of cables and connectors subject to
temperature drift, repeatability of connections and cable bends. Random errors are
unpredictable and hence cannot be estimated and eliminated in calibration. Random
errors can be reduced by correct setting of the source power, IF bandwidth narrowing,
sweep averaging, maintaining constant environment temperature, observance of the
Analyzer warm-up time, careful connector handling, and avoidance of cable bending
after calibration.
Random errors and related methods of correction are not mentioned further in this
Systematic errors are the errors caused by imperfections in the components of the
measurement system. Such errors occur repeatedly and their characteristics do not
change with time. Systematic errors can be determined and then reduced by performing
mathematical correction of the measurement results.
The process of measurement of precision devices with predefined parameters with the
purpose of determination of measurement systematic errors is called calibration, and
such precision devices are called calibration standards. The most commonly used
calibration standards are SHORT, OPEN, and LOAD.
The process of mathematical compensation (numerical reduction) for measurement
systematic errors is called an error correction.
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