Agilent Technologies 4395A, Manual Change

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Network Measurement Basics
Figure A -8. Constant Group Delay
Note , however , that the phase characteristic typically consists of both linear (rst order) and
higher order (deviations from linear) components . The linear component can be attributed to
the electrical length of the test device and represents the average signal transit time . The
higher order components are interpreted as variations in transit time for dierent frequencies ,
and represent a source of signal distortion (Figure A -9).
Figure A -9. Higher Order Phase Shift
The 4395A computes group delay from the phase slope . Phase data is used to nd the
phase deviation, 1', at the center point of a specied frequency aperture , 1f, to obtain an
approximation for the rate of change of phase with frequency (Figure A -10 ). This value ,
g
,
represents the group delay in seconds assuming linear phase change over 1f.
Basic Measurement Theory A-17