VNA concepts and features
R&S
®
ZNL/ZNLE
278
User Manual 1178.5966.02 ─ 19
9.6.1
Offset parameters
Offset parameters compensate for the known length and loss of a (non-dispersive and
perfectly matched) transmission line between the calibrated reference plane and the
DUT.
The analyzer can also auto-determine length and loss parameters, assuming that the
actual values should minimize the group delay and loss across a configurable fre-
quency range.
9.6.1.1
Definition of offset parameters
The
delay
is the propagation time of a wave traveling through the transmission line.
The
electrical length
is equal to the delay times the speed of light in the vacuum. It is a
measure for the length of the transmission line between the standard and the actual
calibration plane. For a line with permittivity ε
r
and
mechanical length
L
mech
the delay
and the electrical length are calculated as follows:
In the [OffsetEmbed] > "Offset" softtool tab, "Delay","Electrical Length" and "Mech.
Length" are coupled parameters. When one of them is changed, the other two are
adjusted accordingly.
For a non-dispersive DUT, the delay defined above is constant over the considered fre-
quency range and equal to the negative derivative of the phase response for the fre-
quency (see mathematical relations). The length offset parameters compensate for a
constant delay, which is equivalent to a linear phase response.
9.6.1.2
Definition of loss parameters
The loss is the attenuation a wave experiences when traveling through the transmis-
sion line. In logarithmic representation, it can be modeled as the sum of a constant and
a frequency-dependent part, where the frequency dependence is due to the skin effect.
In the limit case, where the length of the transmission line is considered to be "almost
zero", the loss is considered constant:
Otherwise, if the loss at DC and one additional frequency
f
1
is known (or measured),
the loss at frequency f is approximated by:
Offset parameters and de-/embedding
