Concepts and Features
R&S
®
ZNB/ZNBT
144
User Manual 1173.9163.02 ─ 53
The following restrictions apply to this export type:
–
the reference resistance of the Touchstone option line is fixed to 50 Ω - regard-
less of the reference impedance setting of the involved port
–
the data file type of the Touchstone option line is fixed to S (for S-parameter)
although the trace can represent a different parameter type
●
Touchstone files containing S-parameters
–
For a one-port Touchstone file, the reflection coefficient for the specified port
(S
ii
for port i) must be measured. If a full one-port (Refl OSM) or a full n-port
(TOSM, ...) calibration is available for the specified port, it is possible to export
the data even when the trace is not displayed.
–
For a multiport Touchstone file
*.s<n>p
, either a full multiport system error
correction or a complete set of n
2
S-parameter traces must be available.
If the port configuration contains balanced ports, the exported Touchstone file
contains the converted single-ended S-parameters.
–
If balanced (symmetric) S-parameters shall be exported, you have to make
sure that all these parameters are actuially measured, and that for each
involved balanced port, both physical ports are part of the export.
This type of export can be initiated from the GUI by using the "s<n>p Port ..." or
"snp Free Config. ..." functions of the TRACE > [TRACE
CONFIG] > "Trace Data"
softtool or by the remote command
MMEMory:STORe:TRACe:PORTs
.
Renormalization of S-parameters
Renormalization means that the S-parameters at connector impedances are converted
into S-parameters at certain target impedances. During export the S-parameters can
be renormalized in two ways: either a common target impedance is used for all ports or
the individual port reference impedances are used.
If the reference impedances are identical and real this common resistance value is
used as reference resistance of the Touchstone option line. Otherwise the value 50 Ω
is used.
●
Common Target Impedance
For multi-port S-parameters, the reference resistance of the Touchstone option line
is taken as common target impedance and the data is renormalized to the common
target impedance, regardless of the port reference impedances. Thus in case of
ambiguous port reference impedances the data is always renormalized to 50 Ω.
●
Port Reference Impedance
The
Chapter 5.3.2, "Reference Impedances"
on page 119 of the individual ports
are used as target impedances for the renormalization. The target impedances are
listed in a comment line in the Touchstone file. If the related ports use different ref-
erence impedances, an additional comment with a warning is added that the
Touchstone option line contains a non-matching reference resistance (see example
below).
Note
that when reimporting this type of file into standard applications (including the
R&S
ZNB/ZNBT itself), the reference resistance from the Touchstone option line is
used and the impedance system underlying the data is not interpreted correctly.
Operations on Traces
