Concepts and features
R&S
®
ZNB/ZNBT
176
User Manual 1173.9163.02 ─ 62
Offset parameters
The offset parameters have the following physical meaning:
●
The
delay
is the propagation time of a wave traveling through the standard. The
electrical length
is equal to the delay times the speed of light in the vacuum. It is a
measure for the length of transmission line between the standard and the actual
calibration plane. For a waveguide with permittivity ε
r
and mechanical length L
mech
,
the following relations hold:
r
mech
r
mech
L
c
L
Length
Electrical
;
Delay
The default delay is 0 s, the default step width is 1 ns, corresponding to a step
width of 299.792 mm for the electrical length. The relations hold for one-port and 2-
port standards.
●
Z
0
is the characteristic impedance of the standard. If the standard is terminated
with Z
0
, then its input impedance is also equal to Z
0
. Z
0
is not necessarily equal to
the reference impedance of the system (depending on the connector type) or the
terminal impedance of the standard. The characteristic impedance of the standard
is only used in the context of calibration.
The default characteristic impedance is equal to the reference impedance of the
system.
●
The
loss
is the energy loss along the transmission line due to the skin effect. For
resistive lines and at RF frequencies, the loss is approximately proportional to the
square root of the frequency.
In Keysight mode, the
offset loss
is expressed in units of Ω/s at a frequency of 1
GHz. The following formula holds for two-port standards:
s
delay
dB
Z
dB
Loss
s
Loss
Offset
/
/
3429
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4
/
/
/
/
0
The conversion formula for one-port standards has an additional factor ½ on the
right-hand side. The reason for this factor is that the Loss in dB accounts for the
attenuation along the forward
and
the reverse path. It does not depend on how
often the wave actually propagates through the line, whereas the offset loss is pro-
portional to the attenuation of the line.
To determine an offset loss value experimentally, measure the delay in seconds
and the loss in dB at 1 GHz and use the formula above.
The default loss or offset loss is zero.
The impedance for waveguides is frequency-dependent. If a waveguide line type is
selected in the "Cal Connector Types" dialog, the "Char. Imp." field is disabled and indi-
cates "varies" instead of a definite impedance value. Moreover no loss or offset loss
can be set.
Calibration
