Product specifications

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Active-Device Measurements with Calibrated Stimulus
Devices that operate under pulsed conditions are often discrete active
devices or modules that consist of amplifiers and/or mixers. The performance
of these devices is typically power-dependent. Therefore, they are character-
ized in linear and nonlinear operating conditions. Inaccurate stimulus power
may introduce considerable measurement errors. In this section we will dis-
cuss source leveling techniques in pulsed measurements that minimize errors
caused by inaccurate pulsed-RF stimulus.
The stimulus power of every PNA-X has been calibrated at the factory with
continuous-wave (CW) with a default setting to cover the entire frequency range
of the analyzer. This allows reasonably accurate stimulus power level at the test
ports even without source power calibration. The PNA-X monitors and adjusts
the source’s automatic level control (ALC) internally to maintain the specified
power level. This is called “internal” leveling mode and is used in most mea-
surement setups. However, the internal detectors do not measure correct peak
power of the pulsed stimulus resulting in ALC-unleveled errors. For pulsed-RF
measurements the internal leveling has to be turned off by changing the leveling
mode to “open loop”. This prevents the ALC errors but at a cost of source level
accuracy. There are three accuracy errors with open loop leveling mode: level
offset, sweep-to-sweep, and band-crossing level inconsistency. The level offset
and band-crossing level inconsistency are typically within a few dB and they
are repeatable. This means that the source power calibration can correct these
errors. The power-sensor-loss feature must be used to calibrate the pulsed-RF
power, because the average pulse power is lower than the peak pulse power by
10*log (duty cycle); refer to the next section for how to calibrate pulsed stimulus
power. The sweep-to-sweep error is typically very small (typically less than 0.1
dB but it could be larger), appears as a short-term drift which the source power
calibration cannot correct. All of these open loop errors can be minimized by
using the “receiver” leveling mode, which uses a VNA receiver to monitor the
pulsed-RF power and correct the source power level on every measurement
sweep. Once receiver leveling is selected, the source level is adjusted with the
receiver readings, thus the source power correction coefficients are ignored
(source power calibration is not used even if it is turned on). The leveling mode
can be setup in Power and Attenuators, and Receiver Leveling Setup dialog boxes
as shown in Figure 22.
Power leveling modes
Figure 22. Power and Attenuator,
and Receiver Leveling
Setup dialog boxes