Concepts and Features
R&S
®
ZNA
72
User Manual 1178.6462.02 ─ 12
Both "Imb Start Phase" and "Imb Stop Phase" must be in the range between -180°
dBm and 180°. The analyzer generates a balanced signal with configurable fre-
quency and power, however, the relative phase of the two components is varied
according to this range.
The selected sweep range applies to all source and receive ports of the analyzer.
In arbitrary mode (with option R&S
ZNA-K4), you can define port-specific frequencies
Chapter 6.12.2.2, "Port Settings Dialog"
5.1.5
Automatic Level Control
Automatic Level Control (ALC) keeps the level of the a waves (source level) at a con-
stant value, irrespective of the DUT's input impedance. The measurement speed is
slightly reduced.
Control Loop Parameters
The analyzer uses a proportional-integral (PI) controller as a feedback controller for
ALC. PI controllers provide two control parameters:
●
The proportional gain
K
r
controls the change of the controller output in response to
the current error value. If the value is too high, the ALC may become unstable. If it
is too low, the ALC may not respond sufficiently to errors and become too slow.
●
The integration time
T
i
controls the change of the controller output based on the
integral of the error over time. If the value is high, the ALC becomes slower. If it is
too low, the ALC may overshoot and thus become unstable.
The proportional and integration terms are summed to calculate the controller out-
put, so there is a tradeoff between the two terms.
T
control
is the (maximum) time the level control is performed – per sweep point. After
it has elapsed, the VNA proceeds with the measurement.
T
control
cannot be set by
the user.
The control parameters can be set manually, or selected automatically by the ana-
lyzer. With automatic ALC parameter setting, the control parameters are deter-
mined by the selected ALC bandwidth as shown in the following table.
ALC IF
band-
width
IF Filter (analog): Normal
IF Filter (analog): Wideband, Narrowband
K
r
(dB)
T
i
(ms)
T
control
(ms)
K
r
(dB)
T
i
(ms)
T
control
(ms)
20 Hz
0.225
9.5
112.5
0.225
9.5
105.57
30 Hz
0.29
7.5
62.345
0.275
7
60.495
50 Hz
0.3
4.5
36.155
0.275
4.5
48.075
100 Hz
0.34
2.5
29.6
0.6
3.5
26.6
200 Hz
0.85
2.5
20.12
0.0043
0.03
20
500 Hz
1.2
2
13.955
0.65
0.75
5.167
1 kHz
0.8
0.5
3.835
0.3
0.25
1.9
Basic Concepts
