Agilent Technologies E4438C - Manual (Page 69)

Performance Tests
Power Level Accuracy
3- 21
Power Level Accuracy
A power meter is used to verify performance over the +13 to
−
45 dBm range. The absolute power level
measured at
−
40 dBm is used as a reference for all lower level measurements.
For power levels below
−
45 dBm, a vector signal analyzer is used to make relative power measurements. A
low noise amplifier (LNA) and step attenuator are connected in series to control the absolute power level
input to the signal analyzer. For power level settings
≥ −
90 dBm, the step attenuator is set to approximately
cancel the gain of the LNA. Below
−
90 dBm, the step attenuator is set to 0 dB, which keeps the signal level
well above the signal analyzer’s noise floor.
Relative measurements are accomplished by setting the DUT amplitude. For example:
Set the DUT to a specific frequency, and an amplitude of
−
40 dBm. For the purpose of this example, assume
the power meter measures
−
40.1 dBm at these settings. The signal analyzer does a peak search, sets the
reference level, and sets the marker to delta mode (0 dB). The DUT amplitude then changes to
−
50 dBm, and
the signal analyzer makes a relative power measurement (assume it to be
−
10.15 dB). The absolute power
measured is
−
40.1 dBm + (
−
10.15 dB), or
−
50.25 dBm.
To determine power level accuracy below
−
90 dBm, the signal analyzer makes the 0 dB marker delta
measurement with the amplitude set to
−
90 dBm, and all lower level measurements are made relative to this
reference. The previously measured error for the
−
90 dBm setting is then accounted for in the measurement.
For frequencies above 2 GHz, an Agilent 8563EC Option 001 spectrum analyzer is used to downconvert the
frequency to 321.4 MHz.
Recommended Equipment
• Agilent E4418B E-Series power meter
• Agilent E9304A E-Series power sensor
• Agilent 89441A vector signal analyzer with Options AYA, AYH, AY7, AY9, B7A, UFG or UTH
• Agilent 8563EC Option 001 spectrum analyzer
• Agilent 8495G programmable step attenuator (0 to 70 dB)
• Agilent 11713A step attenuator driver
• See Chapter 2, “Required Equipment,” on page 2-1 for details on the following:
— Low Frequency Low Noise Amplifier (LNA)
— High Frequency Low Noise Amplifier (LNA)