VNA Concepts and Features
R&S
®
ZNL/ZNLE
261
User Manual 1178.5966.02 ─ 07
For a lossless transmission line, Loss
DC
= Loss(f
ref
) = 0 dB. In practice, the frequency-
dependent loss often represents the dominant contribution so that Loss
DC
can be set to
zero.
Experimentally, the two loss values Loss
DC
and Loss(f
ref
) are determined in two sepa-
rate measurements at a very low frequency (f --> 0) and at f = f
ref
.
8.6.1.3
Auto Length
The "Auto Length" function ([Offset Embed] > "Offset" > "Auto Length") adds an electri-
cal length offset to a test port with the condition that the residual delay of the active
trace (defined as the negative derivative of the phase response) is minimized across
the entire sweep range. If "Delay" is the selected trace format, the entire trace is shif-
ted in vertical direction and centered on zero. In phase format, the "Auto Length" cor-
rected trace shows the deviation from linear phase.
Length and delay measurement, related settings
"Auto Length" is suited for length and delay measurements on transmission lines.
1. Connect a (non-dispersive) cable to a single analyzer port no. n and measure the
reflection factor S
nn
.
2. In the [Offset
Embed] > "Offset" softtool tab, select "Auto Length".
The delay is displayed in the "Delay" field, the cable length (depending on the
"Velocity Factor") in the "Mech. Length" field.
It is also possible to determine cable lengths using a transmission measurement. Note
that "Auto Length" always provides the
single
cable length and the delay for propaga-
tion in
one
direction.
The analyzer provides alternative ways for delay measurements:
1. Measure the reflection factor and select [Format] > "Delay" .
This yields the delay for propagation in forward and reverse direction and should
be approx. twice the "Auto Length" result. For transmission measurements, both
results should be approx. equal.
2. Measure the reflection factor and select [Format] > "Phase" . Place a marker to the
trace and activate [Trace] > "Trace Statistics" > "Phase/El Length".
This yields the delay in one direction and should be approx. equal to the "Auto
Length" result.
The measurement results using trace formats and trace statistics functions depend on
the selected delay aperture and evaluation range. "Auto Length" is particularly accu-
rate because it uses all sweep points. For non-dispersive cables, aperture and evalua-
tion range effects are expected to vanish.
Use [Mkr] > "Set by Marker" > Zero Delay at Marker to set the delay at a special trace
point to zero.
Offset Parameters and Embedding
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