RF calibration
RF and microwave calibration refers to the process
of verifying the performance of, or adjusting/
deriving corrections for, any instrument or
component that will be used in the measurement
or testing of RF and microwave parameters.
This discipline is usually referred to as RF and
microwave metrology. Principal parameters include
RF voltage, RF power, impedance, modulation,
distortion, time, frequency and phase. High
dynamic range ratiometric comparisons are
often performed and results are expressed in the
logarithmic dB form.
As with any other calibration, RF and microwave
calibration compares a device or unit under test
(DUT or UUT) to a traceably calibrated standard or
reference device. The process typically involves
comparing a measuring UUT to a reference source;
a sourcing UUT with a measuring reference; or
quite commonly a measuring UUT with a measuring
reference, using a stable but unknown source.
In each case, the uncertainty or stability of the
reference should significantly exceed the specified
performance of the device or unit under test. RF
metrologists typically look for performance margins
of 4:1, however, test uncertainty ratios lower than
this usual target are more frequently encountered
in RF than in other calibration disciplines.
Conversion from logarithmic (dB) to linear units
is recommended practice when combining
uncertainty contributions and considering test
uncertainty ratios.
Precision devices that are commonly used in RF
and microwave calibration fall broadly into four
categories:
Sourcing instruments. Reference signals and/or
modulation sources, frequency references, pulse or
arbitrary waveform generators, reference attenuators.
Measuring instruments. Power sensors, spectrum
analyzers, measuring receivers, oscilloscopes, RF
voltmeters, frequency counters.
Source-measure instruments. Vector or scalar
network analyzers.
Precision components
• Power splitters, power dividers or couplers,
attenuating pads
• Inter-series, polarity or sacrificial cables and
adapters
• Short, open, load or sliding terminators
• Reflection bridges or directional couplers
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