Environmental Engineering Reference
In-Depth Information
0.6
T
w
=
100 ns
T
w
=
40 ns
T
w
=
32 ns
T
w
=
10 ns
|
S
11, r
e
f
(
f
)|
0.4
0.2
0.0
810
840
870
900
930
960
f
(MHz)
(a)
180
90
0
T
w
=
100 ns
T
w
=
40 ns
T
w
=
32 ns
T
w
=
10 ns
|
S
11, ref
(
f
)|
-90
-180
810
840
870
900
930
960
f
(MHz)
(b)
Fig. 6.5
Comparison between the
S
11
(
f
)
measured through the TD/FD combined approach
(for different time windows) and the
S
11
,
ref
(
f
)
.
a
magnitude.
b
phase
the
S
11
,
ref
), that the AUT presents two resonant frequencies in its operating fre-
quency range. The analysis of the FD-transformed data in the 810-960 MHz range,
confirmed that for
T
w
(
f
)
=
=
=
30 ns, the corresponding fre-
quency resolution ensures the presence of one, three, and four spectral components,
respectively. As a matter of fact, for
T
w
>
10 ns,
T
w
20 ns and
T
w
20 ns the frequency resolution seems to be
adequate for discriminating the two resonant peaks. Additionally, Fig. 6.3(b) shows
that at low times (
20 ns), multiple reflections effects are still considerable and
thus they cannot be windowed out, since the related spectral content is relevant. The
frequency resolution requirements, along with the aforementioned considerations,
suggest that the lowest limit for the windowing is
T
w
,
LOW
>
<
30 ns.
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