HP 8712ES User Manual page 250

Calibrating for Increased Measurement Accuracy
Measurement Calibration Overview
Frequency response errors (transmission and reflection tracking) are
caused by differences between the frequency response of the receivers
used during ratio measurements.
Leakage errors result from energy leakage between signal paths. In
transmission measurements, this leakage is due to crosstalk between
test ports. In reflection measurements, it is due to imperfect directivity of
internal signal-separation devices.
Mismatch errors are due to the fact that the analyzer's port
impedances are not exactly equal to the system impedance across the
frequency range. Source match errors are produced on the source side of
the DUT; load match errors on the load side. If the DUT is not connected
directly to the port, the mismatch errors due to cables, adapters, etc. are
considered part of the source or load match errors.
Figure 6-2 Mismatch Errors in a Forward Reflection Measurement
6-4 ES User's Guide