Communications: radio wave antennas – Antennas – With coupling network or impedance in the leadin
Reexamination Certificate
2001-01-31
2002-11-19
Phan, Tho G. (Department: 2821)
Communications: radio wave antennas
Antennas
With coupling network or impedance in the leadin
C342S372000
Reexamination Certificate
active
06483478
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radar systems, and more particularly to monopulse radar systems.
BACKGROUND OF THE INVENTION
Monopulse radar systems are widely used for radar surveillance and tracking, and for missile tracking or homing systems.
Monopulse radar systems are advantageous by comparison with the use of single-function surveillance radars combined with altitude-determining radar systems, because a single radar system provides the information required not only to establish the presence of a target in surveillance operation, but also provides the information required to determine both azimuth and elevation angle of the target relative to the boresight of the sum beam. It should be noted that the terms “azimuth” and “elevation” are conventional terms used to designate two orthogonal directions, which are not necessarily associated with true azimuth or true elevation.
FIG. 1
is a simplified block diagram of a prior-art monopulse antenna system using an array antenna. In
FIG. 1
, the monopulse radar receiving system
10
includes a set
12
of individual antenna elements
12
1
,
12
2
, . . .
12
N
. The individual receive antenna elements
12
1
,
12
2
, . . .
12
N
are formed into a receive array having two dimensions. The individual antenna elements
12
1
,
12
2
, . . .
12
N
receive signals reflected from a target, and couple the received signals r
1
, r
2
, . . . , r
N
to various input ports
14
i
1
,
14
i
2
, . . . ,
14
i
N
of an analog beamformer
14
. Beamformer
14
processes the signals as generally described in conjunction with
FIG. 2
to produce analog sum (&Sgr;) signals, azimuth difference signals (&Dgr;
A
) and elevation difference signals (&Dgr;
E
). The analog sum signals represent the summation of all the signals received by the array of individual antenna elements. The analog azimuth difference signals represent the difference between the signals received by the antenna elements of the right and left halves of the array of antenna elements, while the analog elevation difference signals represent the difference between the signals received by the antenna elements of the upper and lower halves of the array. The analog sum signals are applied from beamformer
14
to a radio-frequency (RF) receiver illustrated as a block
16
&Sgr;
of a &Sgr; processing channel, which performs standard analog receiver functions such as low-noise amplification and or downconversion to an intermediate frequency (IF). The received analog signals from receiver
16
&Sgr;
are applied to an IF receiver
18
&Sgr;
which performs further standard functions such as IF amplification and detection, to produce baseband analog signals. The baseband signals from IF receiver
18
&Sgr;
are applied to an analog-to-digital converter (ADC)
20
&Sgr;
, which converts the analog signals into quantized or digital signals representing the signals received by the sum channel. The digital signals from analog-to-digital converter
20
&Sgr;
are applied to conventional sum-channel waveform digital processing illustrated as a block
22
&Sgr;
, which produces the processed sum-channel signal for evaluation by a conventional threshold or other detector
24
, which evaluates for the presence of absence of a target in the receive sum beam.
The analog azimuth difference signals &Dgr;
A
of
FIG. 1
are applied from beamformer
14
to a radio-frequency (RF) receiver illustrated as a block
16
&Dgr;A
of a &Dgr;
A
processing channel, which performs standard analog receiver functions. The received analog signals from receiver
16
&Dgr;A
are applied to an IF receiver
18
&Dgr;A
which performs further standard functions such as IF amplification and detection, to produce baseband analog signals for the &Dgr;
A
channel. The baseband signals from IF receiver
18
&Dgr;A
are applied to an analog-to-digital converter (ADC)
20
&Dgr;A
, which converts the analog signals into quantized or digital signals representing the signals received by the azimuth difference channel. The digital signals from analog-to-digital converter
20
&Dgr;A
are applied to conventional azimuth-difference-channel waveform digital processing illustrated as a block
22
&Dgr;A
, which produces the processed azimuth-difference signal for evaluation by a conventional azimuth monopulse ratio detector
26
, which evaluates the ratio of the azimuth difference signal to the sum signal to determine the azimuth angle of the target relative to boresight.
The analog elevation difference signals &Dgr;
E
of
FIG. 1
are applied from beamformer
14
to a radio-frequency (RF) receiver illustrated as a block
16
&Dgr;E
of a &Dgr;
E
processing channel, which performs standard analog receiver functions. The received analog signals from receiver
16
&Dgr;E
are applied to an IF receiver
18
&Dgr;E
which performs further standard functions such as IF amplification and detection, to thereby produce baseband analog signals for the &Dgr;
E
channel. The baseband signals from IF receiver
18
&Dgr;E
are applied to an analog-to-digital converter
20
&Dgr;E
, which converts the analog signals into quantized or digital signals representing the signals received by the elevation difference channel. The digital signals from analog-to-digital converter
20
&Dgr;E
are applied to conventional azimuth-difference-channel waveform digital processing illustrated as a block
22
&Dgr;E
, which produces the processed elevation-difference signal for evaluation by a conventional elevation monopulse ratio detector
30
, which evaluates the ratio of the elevation difference signal to the sum signal to determine the elevation angle of the target relative to boresight.
In the arrangement of
FIG. 1
, the RF receiver blocks and the IF receiver blocks are ordinarily assumed to introduce no perturbation of the received signals, so that the analog signals at the output of the beamformer and the digital signals at the outputs of the analog-to-digital converters can be deemed to be the same, although represented in different form. In the conventional arrangement of
FIG. 1
, the beamformed signal (either at the beamformer outputs or at the ADC outputs) can be expressed as
Σ
=
∑
k
=
1
N
w
∑
(
k
)
r
(
k
)
1
Δ
A
=
∑
k
=
1
N
w
Δ
A
(
k
)
r
(
k
)
2
Δ
E
=
∑
k
=
1
N
w
Δ
E
(
k
)
r
(
k
)
3
where w
&Sgr;
, w
&Dgr;A
, and w
&Dgr;E
are the sum, azimuth-difference and elevation-difference beamforming weights, and {r(k)} are the received signals at each antenna element of the array.
As mentioned, the target detection in block
24
of
FIG. 1
is conventional, and amounts to some type of thresholding. When a target is identified by block
24
, the azimuth and elevation angles of the target, m
A
and m
E
, are determined from a monopulse table look-up
m
A
=
Re
(
Δ
A
∑
)
4
m
E
=
Re
(
Δ
A
∑
)
5
The corresponding antenna patterns for the sum, azimuth and elevation beams are given by
g
∑
(
T
x
,
T
y
)
=
∑
k
=
1
N
w
∑
(
k
)
exp
(
ⅈ
2
π
λ
(
T
x
x
k
+
T
y
y
k
)
)
6
g
Δ
A
(
T
x
,
T
y
)
=
∑
k
=
1
N
w
Δ
A
(
k
)
exp
(
ⅈ
2
π
λ
(
T
x
x
k
+
T
x
y
k
)
)
7
g
Δ
E
(
T
x
,
T
y
)
=
∑
k
=
1
N
w
Δ
E
(
k
)
exp
(
ⅈ
2
π
λ
(
T
x
x
k
+
T
y
y
k
)
)
8
where (T
x
, T
y
) are the dire
Murrow David Jay
Yu Kai-Bor
Duane Morris LLP
Lockheed Martin Corporation
Phan Tho G.
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