Graphics Programs Reference
In-Depth Information
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Figure 4.14. Binary phase code of length 7.
TABLE 4.1.
Barker codes.
Code
symbol
Code
length
Side lode
reduction (dB)
Code elements
2
1 -1
1 1
6.0
B
2
3
1 1 -1
9.5
B
3
4
1 1 -1 1
1 1 1 -1
12.0
B
4
5
1 1 1 -1 1
14.0
B
5
1 1 1 -1 -1 1 -1
7
16.9
B
7
1 1 1 -1 -1 -1 1 -1 -1 1 -1
11
20.8
B
11
1 1 1 1 1 -1 -1 1 1 -1 1 -1 1
13
22.3
B
13
In general, the autocorrelation function (which is an approximation of the
matched filter output) for a Barker code will be wide. The main
lobe is wide; the peak value is equal to . There are side-
lobes on either side of the main lobe. This is illustrated in
Fig. 4.15
for a
B
N
2
N
∆τ
2∆τ
N
(
N
1
)
⁄
2
B
13
.
Notice that the main lobe is equal to 13, while all sidelobes are unity.
The most sidelobe reduction offered by a Barker code is , which
may not be sufficient for the desired radar application. However, Barker codes
can be combined to generate much longer codes. In this case, a
22.3
dB
B
m
code can be
used within a
B
n
code (
m
within
n
) to generate a code of length
mn
. The
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