Accurate Absolute and Relative

Introduction
The Agilent N5531S measuring receiver system is the
successor to the venerable (and now discontinued) 8902A
measuring receiver. The center piece of the N5531S is
an optional fi  rmware personality module for the Agilent
PSA Series spectrum analyzers (Option 233). The N5531S
measuring receiver system matches or outperforms the
8902A in every operating mode, while extending the
fundamental operating frequency range from 1.3 GHz
(8902A) to as high as 50 GHz. 
Accurate power-level measurement was a key capability in
the 8902A that has been carried over to the N5531S. This
capability is essential for the calibration of signal-generator
output level and step-attenuator accuracy.
Among the more important performance parameters for any
signal generator are the absolute and relative accuracies of
its output power level. The highest-accuracy measurement
of the output level of a signal generator requires a power
meter and sensor. However, modern power sensors can
measure only part of the output range of modern signal
generators. Below −70 dBm, some other method must
be used. The traditional approach has been to check the
relative accuracy of the generator’s output level for power
levels below the range of power sensors. The power meter
is employed to establish a reference power level, and a
sensitive, linear measuring receiver is used to verify level
accuracy relative to that reference down to −140 dBm.