Product specifications

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Reference receivers are typically used for the receiver leveling, although any
receiver or a power sensor (if added as a receiver to the PNA-X) can be used.
The source level accuracy in receiver leveling mode depends on the receiver’s
absolute power measurement accuracy, therefore receiver calibration is strongly
recommended. There are three ways to calibrate the reference receivers – per-
form a receiver calibration independently, as a part of a source power calibra-
tion, or as a part of a guided S-parameter calibration. When performed inde-
pendently, the receiver readings are compared to the calibrated source settings
(note that an independent receiver calibration requires a calibrated source).
Source accuracy and drift introduce additional errors to the receiver calibra-
tion. Thus performing receiver calibration either as a part of a source power or
S-parameter calibration is recommended. This way the reference receiver read-
ings are compared to the power sensor readings regardless of the source accu-
racy when the correction coefficients are computed. As a result it transfers the
power sensor accuracy to the receiver with minimal errors. The open loop level-
ing mode must be used during calibration in order to keep the source settings
the same between calibration and measurements. The pulse modulation can
remain on if sensor loss compensation is used during the calibration. However,
a calibration with the pulse modulation off is recommended, because the sensor
loss value may add some errors (refer to the next section for more details). Also
the receiver setting such as attenuators, IF bandwidth, and gate widths must be
the same between the receiver calibration and the pulsed measurements, oth-
erwise, the receiver calibration is turned off and then the source level becomes
inaccurate. Once the receiver is successfully calibrated, it accurately measures
the peak pulse power in wideband detection, and it adjusts the source power
until it’s within the specified tolerance or reaches the maximum number of
iterations before the measurement sweep.
Pulsed stimulus power calibration
Although turning off the pulse modulation is recommended during calibration, it
may not be possible in some cases such as using a booster amplifier that has a
different response between pulsed and non-pulsed signals. In this case, the pulse
modulator needs to stay on during calibration. The PNA-X uses power meters only
in average power measurement mode, regardless of an average or peak-power sen-
sor. Therefore, under pulsed-RF stimulus, the power meter will read a value that is
lower than the peak pulse power (defined as the power during the time the pulse
is on) by 10*log (duty cycle). This difference is specified as a sensor loss to avoid
the PNA-X’s source to go unleveled as it tries to bring the test port power to the
desired level. For example, if the pulse duty cycle is 5%, then the power sensor
reading is 10*log (0.05) = -13 dB lower than the peak pulse power.
Note that the pulse desensitization (power sensor loss value) calculated from pulse
duty cycle introduces errors due to the pulse rise and fall time. If the pulse rise and
fall time are relatively large compared to the pulse width, the power sensor loss
value may need to be adjusted. The PNA-X’s internal pulse modulators provide
approximately 4 ns pulse rise time and 10 ns fall time. When the pulse width is 1
us and the duty cycle is 1% (100 us PRI), the average power is calculated as 20 dB
lower than the pulse peak power. The actual pulsed stimulus adds some RF energy
for 14 ns to the ideal pulsed stimulus, which makes the actual duty cycle 1.01%
approximately, and the average pulse power is 19.96 dB lower instead of the typical
20 dB. However, if the pulse width is 300 ns and the duty cycle is 1% (30 us PRI),
then the duty cycle is approximately 1.033% and the average pulse power is 19.85 dB
lower than the peak pulse power.
Accurate pulsed stimulus
using receiver leveling