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5-11 HOT S22 The output match of a power amplifier under excited conditions is critical
information that has a strong bearing on efficiency, output power, stabil
-
ity, and often the economic viability of the design. One way of dealing
with this information—primarily in power devices operating well away
from compression or in somewhat matched amplifiers— is a quasi-linear
measurement of S
22
while the amplifier is operating under normal drive.
Such a measurement is termed hot S
22
, and it can provide (1) some infor
-
mation on the degree of mismatch in the system, (2) potential operational
stability, and (3) the effects of the amplifier’s performance on subsequent
stages or an antenna. In the PATS, the Hot S
22
measurement uses one
source (Source 2) to provide stimulus to the amplifier-under-test (AUT)
input port while the other source (Source 1) provides a pilot tone injected
to the output of the AUT for measuring S
22
at the AUT output port.
Procedure
Prepare the ME7840A as shown in Chapter 3.
Enter the appropriate test values in the displayed
User Input screen. The input fields are described
below:
n S Parameter: Already set to “Hot S
22
” for test –
input disabled.
n
Data Points: Drop down options - number of data
points in frequency sweep.
n
Frequency 1 (MHz): Lower frequency to be dis-
played. Typically set to a value less than or equal
to the main tone. Can be reset using slider control.
n
Frequency 2 (MHz): Upper Frequency to be dis
-
played. Set to a value less than the system’s maxi
-
mum frequency (for example, for MS4623C set to a
max of 5000 MHz). Can be reset using slider con
-
trol.
n
Src 1 Power (dBm):Source 1 power level, in dBm.
n
IF Bandwidth (Hz):Intermediate frequency
value, in Hertz.
HOT S22 OPERATIONS, MEASUREMENT
5-32 ME 7840A OMM