Specifications

14
Figure 13. Swept power gain compression measurement
Swept-power gain compression
By applying a fixed-frequency power sweep to the
input of an amplifier, the gain compression can be
observed as a 1 dB drop from small signal gain.
The power sweep should be selected such that the
AUT is forced into compression.
The S
21
gain will decrease as the input power is
increased into the nonlinear operating region of
the amplifier. The 8510C network analyzer has a
power sweep range as defined earlier in Table 1.
The fixed frequency chosen could be the frequency
for which the 1 dB drop first occurs in a swept-
frequency gain compression measurement. The
swept-power gain compression and corresponding
output power (P
out
) can be displayed simultaneously
on the 8510C network analyzer. A power flatness
correction over a power sweep range (at a fixed
frequency) may be performed first if very accurate
power is required at the input to the AUT.
1. Configure the system as shown in Figure 2.
2. Perform a power flatness correction, if neces-
sary.
3. Set up channel 1 for an absolute power measure-
ment and channel 2 for an S
21
gain measurement
as described earlier.
4. Turn on a dual channel split display.
[DISPLAY] {DISPLAY MODE}
{DUAL CHAN SPLIT}
5. Set the marker to the CW frequency point of
interest, and set the power low enough to avoid
driving the device into compression.
6. Turn on power domain. Set the start and stop
power points to drive the amplifier into compres-
sion.
[DOMAIN] {POWER}
[START] –22 [x1]
[STOP] –12 [x1]
7. Connect the AUT and apply bias, if necessary.
8. Move a marker to the flat portion of the trace. If
there is no flat portion the AUT is in compression
throughout the sweep, and power levels must be
decreased. Use the marker search to find the
power for which a 1 dB drop in gain occurs. Read
the marker value for channel 1 to determine the
absolute input power (P
in
) or output power (P
out
)
where the 1 dB gain compression occurs.
[MARKER] {MORE} {MINIMUM}
[CHANNEL 1]
PARAMETER [MENU]
{USER 1 a1} or {USER 2 b2}
In this example, the 1 dB gain compression at
26.255 GHz occurs at an output power level of
16.006 dBm and an input power level of –14.7
dBm.