Graphics Programs Reference
In-Depth Information
The Radar Ambiguity
Function
Chapter 4
4.1. Introduction
The radar ambiguity function represents the output of the matched filter, and
it describes the interference caused by the range and/or Doppler shift of a tar-
get when compared to a reference target of equal RCS. The ambiguity function
evaluated at is equal to the matched filter output that is
matched perfectly to the signal reflected from the target of interest. In other
words, returns from the nominal target are located at the origin of the ambigu-
ity function. Thus, the ambiguity function at nonzero and represents
returns from some range and Doppler different from those for the nominal tar-
get.
(
τ
f
d
,
)
=
(
00
,
)
τ
f
d
The radar ambiguity function is normally used by radar designers as a means
of studying different waveforms. It can provide insight about how different
radar waveforms may be suitable for the various radar applications. It is also
used to determine the range and Doppler resolutions for a specific radar wave-
form. The three-dimensional (3-D) plot of the ambiguity function versus fre-
quency and time delay is called the radar ambiguity diagram. The radar
ambiguity function for the signal
s
()
χτ
f
d
is defined as the modulus squared of its
)
2
2-D correlation function, i.e.,
(
;
. More precisely,
∞
∫
2
)
e
j
2π
f
d
t
)
2
s
()
s
∗
t
χτ
f
d
(
;
=
(
τ
d
(4.1)
∞
In this notation, the target of interest is located at , and the
ambiguity diagram is centered at the same point. Note that some authors define
the ambiguity function as
(
τ
f
d
,
)
=
(
00
,
)
χτ
f
d
(
;
)
. In this topic,
χτ
f
d
(
;
)
is called the uncer-
tainty function.
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