Agilent Technologies 8753ET User Manual page 436

Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
In total, ten measurements are made, resulting in ten independent equations. However, the TRL error model
has only eight error terms to solve for. The characteristic impedance of the line standard becomes the
measurement reference and, therefore, has to be assumed ideal (or known and defined precisely).
At this point, the forward and reverse directivity (E
reflection tracking (E and E
RF
(E and E ), source match (E
XF XR
Isolation
Two additional measurements are required to solve for the isolation terms (E
characterized in the same manner as the Full 2-port calibration. Forward and reverse isolation are measured
as the leakage (or crosstalk) from port 1 to port 2 with each port terminated. The isolation part of the
calibration is generally only necessary when measuring high loss devices (greater than 70 dB).
NOTE If an isolation calibration is performed, the fixture leakage must be the same during the
isolation calibration and the measurement.
Figure 7-44 8-term TRL (or TRL*) Error Model and Generalized Coefficients
Source match and load match
A TRL calibration assumes a perfectly balanced test set architecture as shown by the term which represents
both the forward source match (E
both the reverse source match (E
source and load match terms are not equal because the transfer switch presents a different terminating
impedance as it is changed between port 1 and port 2.
Because the standard network analyzer is based on a three-sampler receiver architecture, it is not possible
to differentiate the source match from the load match terms. The terminating impedance of the switch is
assumed to be the same in either direction. Therefore, the test port mismatch cannot be fully corrected. An
assumption is made that:
7- 68
and E
DF
) terms may be derived from the TRL error terms. This leaves the isolation
RR
and E ) and load match (E
SF SR
) and reverse load match (E
SF
) and forward load match (E
SR
), transmission tracking (E
DR
and E ) terms to discuss.
LF LR
and E
XF
), and by the 
term which represents
LR 22
). However, in any switching test set, the
LF
and E ), and
TF TR
). Isolation is
XR