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The test channel received power level, Pr (TEST),
must be calculated to determine the approximate
maximum power level present at the output of the
antenna-under-test (AUT). The required measure-
ment sensitivity is determined from the test chan-
nel received power level, the required dynamic
range, and the required measurement accuracy.
The maximum test channel received power level
will occur when the AUT is boresighted relative to
the transmit antenna.
9
Record the estimated minimum boresight AUT
gain, G (AUT), calculate the test channel received
power level as follows and record it in Figures 16,
18, and 19.
P
(TEST) = P
+ P
/P
r
t
r
where P
(TEST) = Test channel received power level (dBm)
r
P
= Transmit power (dBm)
t
P
/P
= Range transfer function (dB, at the max-
r
t
imum test frequency)
G (AUT) = Expected minimum boresight gain of
AUT (dB)
Required measurement sensitivity
The required measurement sensitivity of the sys-
tem is a function of measurement transmit power,
range transfer function, AUT gain, required mea-
surement dynamic range, and desired measure-
ment accuracy. The previous steps have deter-
mined the approximate power level present at the
output of the AUT under boresight conditions.
The measurement dynamic range required to test
the AUT is the difference, in decibels, between
boresight and the lowest AUT level that must be
measured. Examples of these include side-lobe
level, null depth, and cross-polarization levels.
10
Record the required dynamic range in Figure 16.
+ G (AUT)
t
Measurement accuracy is also affected by the mea-
surement sensitivity of the system. The signal-to-
noise ratio will directly impact the measurement
accuracy of the system for both amplitude and
phase measurements. Figure 2 illustrates the rela-
tionship between signal-to-noise ratio and magni-
tude and phase errors.
Figure 2. Measurement accuracy as a function of signal-
to-noise ratio
11
Record the required signal-to-noise ratio in dB
in Figure 16.
The overall system measurement sensitivity
required is the test channel received power level
minus the sum of the required dynamic range and
signal-to-noise ratio.
12
Calculate the required measurement sensitivity
by subtracting the required dynamic range and sig-
nal-to-noise ratio from the test channel received
power level. Record the value in Figure 16.
The required measurement accuracy for low-
level AUT responses is not always as stringent
as the accuracy required for high-level AUT
responses.
7
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