Keysight N9923A, User Manual, Page: 103 / 276

Keysight N9923-90001 User’s Guide
103
Calibration for NA, CAT, and VVM Modes
Why and When to Calibrate
There are well-defined and understood systematic errors that are measured
and calculated during the calibration process. These errors are caused by
leakage signals inside the FieldFox, by the frequency response of the FieldFox
receivers, and by reflections inside the FieldFox that interact with the DUT.
After calibration, these errors are removed from subsequent measurements.
To maintain highest measurement accuracy, perform a new calibration when
any of the following changes occur:
— When any of the following measurement settings change: Frequency
Range, Power Level, IF BW, and Resolution. Therefore, make these
measurement settings before calibrating. Increased Averaging, lower IF BW,
and higher Resolution all cause slower sweeps and slower calibration times.
Learn about Interpolation and Questionable Accuracy in
“Interpolation *”
on page 119
.
— When the FieldFox temperature changes more than about 10°F (5°C). Learn
more in
“How to monitor the internal FieldFox temperature:” on page 24
.
— When the connection to the DUT changes, requiring a different jumper
cable or adapter.
Definitions
DUT (Device Under Test)
The cable, antenna, transmission line, amplifier, or
anything else that is connected to the FieldFox that is to be measured.
Calibration Standards - OPEN, SHORT, LOAD, and THRU
—
OPEN, SHORT,
and
LOAD
are ‘reflection’ standards that are used during
calibration. When an RF signal ‘hits’ these components, the signals are
reflected in a predictable manner. These components can also be used to
terminate a DUT port during some measurements.
—SHORT and OPEN standards both cause 100% of an RF signal to be
reflected. The difference between these two standards is what
happens to the phase of the reflected signal, which is beyond the
scope of this discussion. Although an OPEN standard is a precision
component, simply leaving
nothing
connected at the end of a cable
can be a reasonable substitute for an OPEN.
—A LOAD standard absorbs almost ALL of the incident signal and very
little signal is reflected back to the source.