Anritsu 37 C Series, Руководство по эксплуатации, Страница: 180 / 603

8-4
GROUP DELAY Group delay is the measure of transit time through a device at a par-
ticular frequency. Ideally, we want to measure a constant—or rela-
tively constant—transit time over frequency. The top waveform shown
in Figure 8-13 is measured at one frequency. The bottom waveform is
identical to the first, simply delayed in time.
Referring to Figure 8-14, the first waveform shown is the original
waveform. It is made up of many frequency components. After travel-
ing through a device the signal is delayed in time. Some frequencies
are delayed more than others and thus our waveform does not have
exactly the same shape as before.
When delay is nonlinear, as shown above, distortion occurs. By meas-
uring group delay with a network analyzer you can characterize the
distortion that occurs from a signal traveling through your test device.
GROUP DELAY MEASUREMENTS
8-20 37XXXC OM
M A G N I T U D E
T I M E
t
0
t
1
Figure 8-13. Two Waveforms Delayed in Time
I N P U T
O U T P U T
M A G N I T U D E
T I M E
Figure 8-14. Waveform with Frequency Differences
NONLINEAR DELAY = DISTORTION