Pulse profile measurements are not valid, because in
this mode the analyzer sweep begins before the RF pulse
begins, so again the analyzer measures the characteris-
tics of the pulse modulator instead of the DUT for some
portion of the sweep. Figure 9 shows an example of this.
The return loss when the pulse is off should equal the
directivity of the analyzer, about 46 dB in this case, but
it clearly does not. Instead we see the pulse arising from
a baseline level of approximately –16 dB
Measurement Conditions:
Frequency: 10.25 GHz
Number of points: 101
IF bandwidth: 6000 Hz
Pulse width: 5 ms
Pulse period: 200 ms
Trigger: external on sweep
Delay: 2 ms
Figure 9. Invalid reflection measurement in pulse-profile mode
So is it possible to use the 8720ES to make valid reflec-
tion measurements in pulse-profile mode or at a high
PRF? One way to do so is to use an external coupler
between the pulse modulator and the DUT. Another way
is to use the 8720ES configurable test set (Option 014)
to make many such measurements possible. This option
provides an external access to the RF signal path prior
to the transfer switch and couplers. The insertion points
are labeled in and out in Figures 1 and 10. With the
pulse modulator in this position, it is no longer present
in the reflected signal path since it precedes the port 1
coupler. This permits reflection measurements to be
made using the same techniques described for transmis-
sion measurements. It has the added benefit of allowing
full two-port error correction to be performed, which is
an advantage in many transmission measurements as
well.
Figure 10. Pulse modulator in rear access loop (Option 014)
9
To Next Page
Loading...
Need help?
General
