Concepts and features
R&S
®
ZND
127
User Manual 1173.9557.02 ─ 61
In practice, the analyzer calculates an approximation to the derivative of the phase
response, taking a small frequency interval Δf and determining the corresponding
phase change ΔΦ. The delay is thus computed as:
f
deg
meas
g
360
,
The aperture Δf must be adjusted to the conditions of the measurement.
If the delay is constant over the considered frequency range (non-dispersive DUT, e.g.
a cable), then τ
g
and τ
g,meas
are identical and:
c
L
t
f
d
t
f
d
mech
g
360
)
360
(
where Δt is the propagation time of the wave across the DUT, which often can be
expressed in terms of its mechanical length L
mech
, the permittivity ε, and the velocity of
light c. The product L
mech
· sqrt(ε) is termed the electrical length of the DUT and is
always larger or equal than the mechanical length (ε > 1 for all dielectrics and ε = 1 for
the vacuum).
4.4
Operations on traces
The R&S
ZND can perform more complex operations on the measured traces. Some
of the operations, e.g. the time domain transform, require additional software options;
see
Chapter 4.7, "Optional extensions and accessories"
The R&S
ZND can also check whether the measured values comply with specified lim-
its and export trace data, using different file formats.
4.4.1
Limit check
A limit line restricts the allowed range for some or all points of a trace, i.e. for a certain
range of stimulus values. Typically, limit lines are used to check whether a DUT con-
forms to the rated specifications (conformance testing).
●
An upper limit line defines the maximum allowed values for the related stimulus
range.
●
A lower limit line defines the minimum allowed values for the related stimulus
range.
●
A ripple limit defines the maximum difference between the largest and the smallest
response value for the related stimulus range. A ripple limit test is suitable, e.g., to
check whether the passband ripple of a filter is within acceptable limits, irrespective
of the actual transmitted power in the passband.
●
A circle limit defines the acceptable values as a circular area within a complex dia-
gram.
Operations on traces
www.allice.de
Allice Messtechnik GmbH