User`s guide

7-77
Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
TRL Options
The softkey accesses the TRL/LRM options menu. There are two
selections under this menu:
• (calibration Z
0
)
• (set reference)
The characteristic impedance used during the calibration can be referenced to either the
line (or match) standard ( ) or to the system ( ).
The analyzer defaults to a calibration impedance that is equal to the line (or match)
standard.
When the is selected, the impedance of the line (or match) standard is
assumed to match the system impedance exactly (the line standard is reflectionless). After
a calibration, all measurements are referenced to the impedance of the line standard. For
example, when the line standard is remeasured, the response will appear at the center of
the Smith chart. When is selected, the values entered for
(under menu) and (within the define standard menu) are ignored.
is selected when the desired measurement impedance differs from
the impedance of the line standard. This requires a knowledge of the exact value of the Z
0
of the line. The system reference impedance is set using under the calibration
menu. The actual impedance of the line is set by entering the real part of the line
impedance as the within the define standard menu. For example, if the line
was known to have a characteristic impedance of 51 Ω ( = 51 Ω), it could still
be used to calibrate for a 50 Ω measurement ( = 50 Ω). After a calibration, all
measurements would be referenced to 50 Ω, instead of 51 Ω. When the line standard is
remeasured, the center of the Smith chart is at the current value of (in this case,
50 Ω). Since only one value of offset Z
0
can be selected for the line standard, the value of Z
0
should be a constant value over the frequency range of interest in order to be meaningful.
The location of the reference plane is determined by the selection of and
. By default, the reference plane is set with the thru standard which
must have a known insertion phase or electrical length. If a non-zero length thru is
specified to have zero delay, the reference plane will be established in the middle of the
thru. The reflect standard may be used to set the reference plane instead of the thru
provided the phase response (offset delay, reactance values and standard type) of the
reflect standard is known and is specified in the calibration kit definition.
TRL/LRM OPTION
CAL ZO:
SET REF:
CAL ZO: LINE ZO
CAL ZO: SYSTEM ZO
CAL ZO: LINE ZO
CAL ZO: LINE ZO
SET ZO
Cal
OFFSET ZO
CAL ZO: SYSTEM ZO
SET ZO
OFFSET ZO
OFFSET ZO
SET ZO
SET ZO
SET REF: THRU
SET REF: REFLECT