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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 (Enr and
Enn),
transmission tracking (Err
and
Em),
and reflection tracking
(Em
and E
RR
) terms may be derived from the TRL error
terms. This leaves the isolation
(EXF
and
ExR),
source match
(Esr
and
Esn)
and load match
(ELF
and
ELR)
terms to
dkUSS.
IsoIation
Two additional measurements are required to solve for the isolation terms
(EXF
and
ExR).
Isolation is 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
dE8).
Note
If an isolation calibration is performed, the
ikture
leakage must be the
same during the isolation calibration and the measurement.
.
.
. .
.
r
El0
s21
'32
,,Eoo
Eli,,
,,Sll
S22,\
,,&22
E33,,
EOl
%2
&23
I
*
/
.
.
.
I
I
EioEoi
=
ERF
E23E33
= ERR
%o=
EDF
E33
=
EDR
91
=
k~,
ELR
E22
=
&.R,ELF
'IO&32
=
bF
'01'23 =
%R
pb6121d
Figure 6-53. S-term
TRL
error model and generalized
coefkients
644
Application and Operation Concepts