Concepts and features
R&S
®
ZNA
262
User Manual 1178.6462.02 ─ 20
Compared to calculations using noise factors (or noise figures), this method can easily
account for different physical temperatures of the involved components. Furthermore,
with noise temperatures there is no need to apply corrections factors, if the compo-
nents are on a different temperature than the reference temperature
T
0
(= 290 K). The
equivalent circuit, which is internally used for the calculation of the DUT noise factor
F
D
ext
comprises the total external loss (net gain) between
the R&S
ZNA port and the calibration plane, including connecting cables, additional
external attenuators, adapters, etc.
Figure 4-29: Equivalent circuit used for the calculation of the DUT noise factor
A noise temperature
T
is converted into the corresponding noise factor
F
using the
equation:
Source noise temperature
As already mentioned, it is important to have precise knowledge of the noise present at
the input of the DUT. The input noise temperature
T
Source
is derived from the internal
temperature of the R&S
ZNA (typically around 38
°C) and the ambient temperature
T
amb
of the measurement environment. The ambient temperature is by default chosen
to 296
kelvins, which is close to a typical laboratory temperature of 23
°C. However, for
precise measurements the ambient temperature can be adjusted to the actual room
temperature (see
To calculate the effective noise temperature
T
Source
at the DUT input, the external
attenuation (net gain) must be considered. Depending on the total external attenuation,
the “hot” internal temperature of the R&S
ZNA is suppressed:
T
VNA
represents the internal temperature of the R&S
ZNA and
G
ext
is the external net
gain (cables, additional external attenuators, adapters, etc.) connected during calibra-
tion and measurement. The external net gain is automatically determined during cali-
bration.
Receiver noise temperature
The noise present at the output of the DUT cannot be measured directly. In fact, the
measured noise is always the sum of the noise emitting from the DUT and the noise
Optional extensions and accessories
