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October 3, 2012
RE: Clarification of Content of RF/μwave Scopes
The following detail of scopes in the RF/μwave area is to be included in the “Comments”
column to ensure proper presentation of the technical capability:
1) If a calibration activity is performed in accordance with a published standard then the
standard is to be referenced. For example:
antenna calibration: ANSI C63.5-2005
calibration of LISNs: ANSI C63.4-2003
current probes: IEC 61000-4-6 or ISO 11452-3
EMI receivers: CISPR 16-1-1 (2006)
Some assessors are of the opinion that such standards are not to be included – or be
relegated to a foot note. This is not correct since these standards call out the exact
method how to perform calibrations. Different methods of these activities result in
different correction factors!
2) If a laboratory measures the Reflection and/or Transmission coefficient (e.g., with a
Vector Network Analyzer) the characteristics of the EUT that is actually calibrated has a
direct impact on the test result. Therefore, the relevant EUT parameter must be included
on the scope for the uncertainty estimate to be meaningful. For example:
A highly reflective device will cause a larger measurement uncertainty for a
A low loss device will cause a larger measurement uncertainty for a reflection
There are two ways (in my opinion) to exactly state the situation:
a) It can be stated that the relevant EUT parameter is assumed to be ideal (e.g., the
mismatch uncertainty is assumed to be zero for a transmission measurement).
Werner Schaefer Page 1 of 2 10/3/2012
This does not indicate a practical measurement uncertainty number – but is the
(theoretically) achievable uncertainty with a given measurement system.
b) Stating the uncertainty as an “equation”. For example: 0.15 + M with a foot note
on the scope explaining the meaning of M and how to combine it with the stated
uncertainty value. This approach has the advantage that the clients of the
calibration laboratory can actually determine the expected uncertainty for any
device that undergoes calibration.
3) the achievable uncertainty is very much dependent on the test equipment used.
For example, there are vast differences between network analyzers as far as the
achievable uncertainty is concerned. Furthermore, specially for network
analyzers the connector interface(e.g., Type N, APC7, APC 3.5 or K) is crucial to
the achievable accuracy, and so is the calibration kit for network analyzers. The
stated uncertainty on a scope is to be supported by the information about the test
equipment used in order to be meaningful and to describe the technical ability of
a calibration laboratory.
4) Specific installations like for example a (50 x 80) square meter ground plane,
used for antenna calibrations. is also to be included to explain relatively low best
uncertainty values. Such installations are not common and, if not stated on the
scope, will immediately call the uncertainty estimate into question.
Werner Schaefer Page 2 of 2 10/3/2012