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Chapter 2 71
Making Complex Measurements
Making Stimulus Response Measurements
Making Stimulus Response Measurements
What Are Stimulus Response Measurements?
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.
Using An Analyzer With A Tracking Generator
There are three basic steps in performing a stimulus response
measurement, whether it is a transmission or a reflection
measurement. The steps are to set all the analyzer settings, normalize,
and measure.
The procedure below describes how to use a built in tracking generator
system to measure the rejection of a band pass filter, a type of
transmission measurement. Illustrated in this example are functions in
the tracking generator menu such as adjusting the tracking generator
output power. Normalization functions located in the trace menu are
also used. Making a reflection measurement is similar and is covered in
“Making a Reflection Calibration Measurement” on page 84.
Stepping Through a Transmission Measurement
1. To measure the rejection of a band pass filter, connect the equipment
as shown in Figure 2-1. This example uses a 200 MHz bandpass
filter as the DUT.