GUI Reference
R&S
®
ZNC
139
User Manual 1173.9557.02 ─ 13
Calculation of Δf and ΔΦ
With a given number of aperture steps n the delay at sweep point no. m is calculated as
follows:
●
If n is even (n = 2k), then Δf (m) = f (m+k) – f (m–k) and ΔΦ(m) = ΔΦ (m+k) – ΔΦ
(m–k).
●
If n is odd (n = 2k+1), then Δf (m) = f (m+k) – f (m–k–1) and ΔΦ (m) = ΔΦ (m+k) –
ΔΦ (m–k–1).
The calculated phase difference (and thus the group delay) is always assigned to the
frequency point no. m. For linear sweeps and odd numbers of aperture steps, the center
of the aperture range is [f (m+k) + f (m–k–1)] / 2 = f (m–1/2), i.e. half a frequency step
size below the sweep point f (m). This is why toggling from even to odd numbers of
aperture steps and back can virtually shift the group delay curve towards higher/lower
frequencies. It is recommended to use even numbers of aperture steps, especially for
large frequency step sizes.
The delay calculation is based on the already measured sweep points and does not slow
down the measurement.
Δf is constant over the entire sweep range, if the sweep type is a Lin. Frequency sweep.
For Log. Frequency and Segmented Frequency sweeps, it varies with the sweep point
number m.
Application:
The aperture must be adjusted to the conditions of the measurement. A
small aperture increases the noise in the group delay; a large aperture tends to minimize
the effects of noise and phase uncertainty, but at the expense of frequency resolution.
Phase distortions (i.e. deviations from linear phase) which are narrower in frequency than
the aperture tend to be smeared over and cannot be measured.
Remote command:
SWR
Calculates the Standing Wave Ratio (SWR) from the measured quantity (primarily: from
a reflection S-parameter) and displays it in a Cartesian diagram.
Properties:
The SWR (or Voltage Standing Wave Ratio, VSWR) is a measure of the
power reflected at the input of the DUT. It is calculated from the magnitude of the reflection
coefficients Sii (where i denotes the port number of the DUT) according to:
|
|
1
|
|
1
ii
ii
S
S
SWR
The superposition of the incident and the reflected wave on the transmission line con-
necting the analyzer and the DUT causes an interference pattern with variable envelope
voltage. The SWR is the ratio of the maximum voltage to the minimum envelope voltage
along the line.
Interpretation of the SWR
The superposition of the incident wave I and the reflected wave R on the transmission
line connecting the analyzer and the DUT causes an interference pattern with variable
envelope voltage. The SWR is the ratio of the maximum voltage to the minimum envelope
voltage along the line:
SWR = V
Max
/V
Min
= (|V
I
| + |V
R
|) / (|V
I
| – |V
R
|) = (1 + |S
ii
|) / (1 – |S
ii
|)
Trace Settings
