Concepts and Features
R&S
®
ZNB/ZNBT
194
User Manual 1173.9163.02 ─ 38
4.7.2.2
Band Pass and Low Pass Mode
The analyzer provides two essentially different types of time domain transforms:
●
Band pass mode: The time domain transform is based on the measurement results
obtained in the sweep range between any set of positive start and stop values. The
sweep points must be equidistant. No assumption is made about the measurement
point at zero frequency (DC value). The time domain result is complex with a gen-
erally undetermined phase depending on the delay of the signal.
●
Low pass mode: The measurement results are continued towards f = 0 (DC value)
and mirrored at the frequency origin so that the effective sweep range (and thus
the response resolution) is more than doubled. Together with the DC value, the
condition of equidistant sweep points implies that the frequency grid must be har-
monic. Due to the symmetry of the trace in the frequency domain, the time domain
result is harmonic.
See also
Chapter 4.7.2.4, "Harmonic Grid"
Two different types of response are available in low pass mode; see below.
Table 4-17: Comparison of band pass and low pass modes
Transform
type
Band pass
Low pass
Advantages
Easiest to use: works with any set of equi-
distant sweep points
Higher response resolution (doubled)
Includes information about DC value
Real result
Impulse and step response
Restrictions
No step response
Undetermined phase
Needs harmonic grid
Use for...
Scalar measurements where the phase is
not needed
DUTs that don't operate down to f = 0 (e.g.
pass band or high pass filters)
Scalar measurements where the sign is of
interest
DUT's with known DC value
Impulse and step response
In low pass mode, the analyzer can calculate two different types of responses:
●
The impulse response corresponds to the response of a DUT that is stimulated
with a short pulse.
●
The step response corresponds to the response of a DUT that is stimulated with a
voltage waveform that transitions from zero to unity.
The two alternative responses are mathematically equivalent; the step response can
be obtained by integrating the impulse response:
Integrate impulse
response
Obtain step
response
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