Specifications

158 Chapter 15
Concepts
Stimulus Response Measurement Concepts
Concepts
Stimulus Response Measurement Concepts
NOTE Stimulus response measurements require option 1DN or 1DQ with ESA
spectrum analyzers.
Stimulus Response Overview
Stimulus response measurements require a source to stimulate a device
under test (DUT), a receiver to analyze the frequency response
characteristics of the DUT, and, for return loss measurements, a
directional coupler or bridge. Characterization of a DUT can be made in
terms of its transmission or reflection parameters. Examples of
transmission measurements include flatness and rejection. Return loss
is an example of a reflection measurement.
A spectrum analyzer combined with a tracking generator forms a
stimulus response measurement system. With the tracking generator
as the swept source and the analyzer as the receiver, operation is the
same as a single channel scalar network analyzer. The tracking
generator output frequency must be made to precisely track the
analyzer input frequency for good narrow band operation. A narrow
band system has a wide dynamic measurement range. This wide
dynamic range will be illustrated in the following example.
There are three basic steps in performing a stimulus response
measurement, whether it is a transmission or a reflection
measurement. The first step is to set up the analyzer, the second is to
normalize, and the last step is to perform the measurement.
Tracking Generator Unleveled Condition
When using the tracking generator, the message TG unleveled may
appear. The TG unleveled message indicates that the tracking
generator source power (
Source, Amplitude) could not be maintained at
the selected level during some portion of the sweep. If the unleveled
condition exists at the beginning of the sweep, the message will be
displayed immediately. If the unleveled condition occurs after the sweep
begins, the message will be displayed after the sweep is completed. A
momentary unleveled condition may not be detected when the sweep
time is short. The message will be cleared after a sweep is completed
with no unleveled conditions.
The unleveled condition may be caused by any of the following:
• Start frequency is too low or the stop frequency is too high. The
unleveled condition is likely to occur if the true frequency range
exceeds the tracking generator frequency specification (especially
the low frequency specification).