R&S ZNB Series User Manual page 195

®
R&S ZNB/ZNBT
4.5.6.1 Source power calibration
A source power calibration ensures accurate power levels of the generated waves at
an arbitrary calibration plane in the measurement path. Typically the calibration plane
corresponds to the input of the DUT.
In a frequency sweep, the power at the calibration plane is maintained at a constant
"Cal Power" value. The source power calibration eliminates frequency response errors
in the signal path between the source and the calibration plane. It is possible to intro-
duce an arbitrary attenuation or gain into the signal path so that the cal power is not
restricted to the power range of the source. A typical application for a power calibration
in a frequency sweep is the measurement of the gain of an amplifier across a fre-
quency range but at a fixed input power.
In a power sweep, the power calibration ensures that the power at the calibration plane
is either constant or a linear function of the stimulus power. A typical application for a
power calibration in a power sweep is the measurement of the gain of an amplifier
across a power range but at a fixed frequency. The correction data acquired in a fre-
quency or power sweep is re-used if a "Time" or "CW Mode" sweep is activated.
Calibration procedure
The source power calibration requires an external power meter, to be connected via
GPIB bus, USB or LAN interface. The power sensor can be connected directly at the
calibration plane or to any other point in the test setup where the signal power is known
to be proportional to the power at the calibration plane.
By default, the source power calibration involves several steps:
1. Reference receiver calibration: The analyzer performs a first calibration sweep at
the source power that is likely to produce the target power ("Cal Power") at the cali-
bration plane. A known attenuation or gain at the source port and in the signal path
between the source port and the calibration plane can be specified:
The power which the external power meter measured at the calibration plane is
displayed in the calibration sweep diagram, together with the reference receiver
reading. The firmware uses the difference between the two traces to correct the
reference receiver reading.
2. Internal source power flatness calibration: In the following steps, the calibrated
reference receiver is used to adjust the source power. To this end, the R&S ZNB/
ZNBT performs a series of calibration sweeps at varying source power until the
number of "Total Readings" is reached or until the deviation between the calibrated
reference receiver power and the cal power is below a specified "Tolerance". The
external power meter is no longer used for these repeated calibration sweeps;
everything is based on the previously calibrated reference receiver. This speeds up
the calibration procedure but does not impair its accuracy.
User Manual 1173.9163.02 ─ 62
Concepts and features
Calibration
195