
ES User’s Guide
3-69
Making Measurements
Measuring Group Delay
Measuring Group Delay
The phase linearity of many devices is specified in terms of group delay.
This is especially true of telecommunications components and systems
where phase distortion is critical.
Group delay is a measure of transit time through the DUT as a function
of frequency. It is approximated by:
where
∆φ
is the phase difference between two adjacent frequencies
∆
f.
The quantity
∆
f is commonly referred to as the aperture. The minimum
aperture is equal to the analyzer's frequency span divided by the number
of points minus one, and can be entered as a frequency or a percent of
span. To measure group delay correctly, the phase difference at a specific
aperture must be less than 180 degrees, satisfying the following
relationship:
If this relationship is not satisfied, incorrect measurements will occur
since the measurement of the phase difference at adjacent points will be
undersampled.
This section uses an example measurement to describe how to calibrate
for and make a basic phase-derived delay (group delay) measurement.
An S
21
measurement is demonstrated in this example, but the same
general concepts apply for an S
12
measurement.This example uses a
two-port calibration, but other calibration choices are also available. For
example, a response calibration could be used for this measurement.
Though not quite as accurate as two-port error correction, a response
calibration offers the advantage of faster measurement speeds than
when using a two-port calibration. In this example, an insertable
bandpass filter like the one that was supplied with your network
analyzer is used.
∆φ
–
∆
f
( )
360
(
)
-------------------------
frequency span
number of points
1
–
2 approx. DUT delay
(
)
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Summary of Contents for HP 8712ES
Page 8: ...viii ES User s Guide ...
Page 17: ...ES User s Guide 1 1 1 Installing the Analyzer ...
Page 34: ...1 18 ES User s Guide Installing the Analyzer Preventive Maintenance ...
Page 35: ...ES User s Guide 2 1 2 Getting Started ...
Page 52: ...2 18 ES User s Guide Getting Started Performing the Operator s Check ...
Page 53: ...ES User s Guide 3 1 3 Making Measurements ...
Page 135: ...ES User s Guide 4 1 4 Using Instrument Functions ...
Page 159: ...ES User s Guide 4 25 Using Instrument Functions Using Markers Figure 4 15 Delta Marker Mode ...
Page 165: ...ES User s Guide 4 31 Using Instrument Functions Using Limit Testing Figure 4 16 Limit Lines ...
Page 224: ...4 90 ES User s Guide Using Instrument Functions Using an External VGA Monitor ...
Page 225: ...ES User s Guide 5 1 5 Optimizing Measurements ...
Page 246: ...5 22 ES User s Guide Optimizing Measurements Measuring Devices with Long Electrical Delay ...
Page 247: ...ES User s Guide 6 1 6 Calibrating for Increased Measurement Accuracy ...
Page 281: ...ES User s Guide 7 1 7 Front Rear Panel ...
Page 306: ...7 26 ES User s Guide Front Rear Panel Line Module ...
Page 307: ...ES User s Guide 8 1 8 Hardkey Softkey Reference ...
Page 410: ...8 104 ES User s Guide Hardkey Softkey Reference Z ...
Page 411: ...ES User s Guide 9 1 9 Specifications ...
Page 469: ...ES User s Guide 10 1 10 Safety and Regulatory Information ...
Page 475: ...ES User s Guide 10 7 Safety and Regulatory Information Regulatory Information ...
Page 476: ...10 8 ES User s Guide Safety and Regulatory Information Regulatory Information ...
Page 477: ...ES User s Guide 11 1 11 Factory Preset State and Memory Allocation ...