R&S ZNB Series User Manual page 225

®
R&S ZNB/ZNBT
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 4-20: Properties of frequency windows
Window
No Profiling (Rect-
angle)
Low First Side lobe
(Hamming)
Normal Profile
(Hann)
Steep Falloff (Boh-
man)
Arbitrary Side lobes
(Dolph-Chebychev)
4.7.2.4 Harmonic grid
A harmonic grid is formed by a set of equidistant frequency points f
spacing Δf and the additional condition that f
set to harmonics of the start frequency f
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.
Visualization of the harmonic grid algorithms
The R&S ZNB/ZNBT provides three different algorithms for harmonic grid calculation.
The three harmonic grids have the following characteristics:
●
Keep "Stop Frequency and Number of Points" means that the stop frequency and
the number of sweep points is maintained. The sweep points are redistributed
across the range between the minimum frequency of the analyzer and the stop fre-
quency; the step width can be increased.
User Manual 1173.9163.02 ─ 62
Side lobe sup- Relative impulse
pression width
13 dB 1
43 dB 1.4
32 dB 1.6
46 dB 1.9
User defined 1.2 (at 32 dB side
between 10 dB and lobe suppression)
120 dB
.
1
Concepts and features
Optional extensions and accessories
Best for...
–
Response resolution: separation of
closely spaced responses with compara-
ble amplitude
Good compromise between pulse width
and side lobe suppression
Dynamic range: separation of distant
responses with different amplitude
Adjustment to individual needs; tradeoff
between side lobe suppression and
impulse width
= Δf. In other words, all frequencies f
1
(i = 1...n) with
i
are
i
225