Concepts and Features
R&S
®
ZNB/ZNBT
195
User Manual 1173.9163.02 ─ 38
The step response is recommended for impedance measurements and for the analysis
of discontinuities (especially inductive and capacitive discontinuities). The impulse
response has an unambiguous magnitude and is therefore recommended for most
other applications.
4.7.2.3
Windows in the Frequency Domain
The finite sweep range in a frequency domain measurement with the discontinuous
transitions at the start and stop frequency broadens the impulses and causes side-
lobes (ringing) in the time domain response. The windows offered in the "Define Trans-
form" dialog can reduce this effect and optimize the time domain response. The win-
dows have the following characteristics:
Table 4-18: Properties of frequency windows
Window
Sidelobe suppres-
sion
Relative impulse
width
Best for...
No Profiling (Rect-
angle)
13 dB
1
–
Low First Sidelobe
(Hamming)
43 dB
1.4
Response resolution: separation of
closely spaced responses with compara-
ble amplitude
Normal Profile
(Hann)
32 dB
1.6
Good compromise between pulse width
and sidelobe suppression
Steep Falloff (Boh-
man)
46 dB
1.9
Dynamic range: separation of distant
responses with different amplitude
Arbitrary Sidelobes
(Dolph-Chebychev)
User defined
between 10 dB and
120 dB
1.2 (at 32 dB side-
lobe suppression)
Adjustment to individual needs; tradeoff
between sidelobe suppression and
impulse width
4.7.2.4
Harmonic Grid
A harmonic grid is formed by a set of equidistant frequency points f
i
(i = 1...n) with
spacing Δf and the additional condition that f
1
= Δf. In other words, all frequencies f
i
are
set to harmonics of the start frequency f
1
.
If a harmonic grid, including the DC value (f = 0), is mirrored to the negative frequency
range, the result is again an equidistant grid.
The point symmetry with respect to the DC value makes harmonic grids suitable for
lowpass time domain transformations.
Optional Extensions and Accessories