114 Installation and User’s Guide
AEnhancing Measurement Accuracy
Understanding System Measurement Calibration
Measurement accuracy is degraded by the effects of three different types
of measurement errors: systemic, drift, and random.
Systemic errors are caused by imperfection in the test equip ment and test
setup.
Drift errors occur when a test system’s performance ch anges after a
calibration has been performed. Drift er rors are caused primarily by
variations in the ambient temperature of the measurement environment.
Random errors are caused by instrument noise (sampler noise, IF noise
floor, etc.), switch repeatability and co nnector repeatability. These errors
vary randomly as a function of time.
You can compensate for systemic and drift errors by performing a syst em
measurement calibration prior to measuring a device. (Performing a
measurement calibration has no effect upon random errors.)
To increase the accuracy of your measurements, perform a system
measurement calibration before performing device measurements. Repeat
the measurement calibration if the ambient temperature of the
measurement environment has deviated ±1°C since the last measurement
calibration.
This procedure performs a modified full 2-port measurement calibration to
remove the following errors:
Directivity
Source-load matc h
Reflection tracking
Transmission tracking
The isolation calibration (crosstalk correction) has been omitted. Isolatio n
calibration is only required when measuring high- isolation devices such as
a switch in the open position or high- dynamic range devices such as
filters with a high level of rejection.
Required Tools
Agilent 85225F performance modeling system
Agilent 85056A 2.4 mm calibration kit, or
Agilent 85056D 2.4 mm calibration kit