Communications: directive radio wave systems and devices (e.g. – Radar transponder system – Combined with primary radar system
Reexamination Certificate
2001-09-10
2003-01-14
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
Combined with primary radar system
C342S042000, C342S044000, C342S046000
Reexamination Certificate
active
06507310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radar device in which a response signal sent from a search and rescue radar trans-ponder (SART) of a wreck ship is detected when a disaster occurs in the wreck ship at sea.
2. Description of Related Art
A search and rescue radar transponder (hereinafter, called SART) has been known as a search and rescue transceiver unit which exchanges signals with a radar device of a rescue ship. The operation of the SART mounted in a wreck ship is started when a disaster occurs in the wreck ship at sea, and the SART is set to a reception wait state to receive a question signal from a radar device mounted in the rescue ship. Thereafter, when the rescue ship approaches the wreck ship, the SART receives a question signal output from the radar device of the rescue ship, and the SART sends a response signal to the rescue ship in response to the question signal. Thereafter, in the wreck ship, to encourage crew-members of the wreck ship, the SART informs the crew-members of the reception of the question signal. Also, in the rescue ship, the response signal sent from the SART is analyzed in the radar device to detect a position of the wreck ship, and the rescue ship rescues the crew-members of the wreck ship.
FIG. 6
is a block diagram showing the configuration of a conventional radar device.
In
FIG. 6
,
101
indicates a conventional radar device mounted in a rescue ship.
102
indicates a signal producing unit for producing a question signal.
103
indicates an antenna for radiating the question signal and receiving both a response signal sent from an SART (not shown) and an echo of the question signal as a reception signal. The antenna
103
is always rotated to receive the response signal radiated from any direction.
105
indicates a signal receiving unit for analyzing the reception signal received in the antenna
103
by amplifying and phase-detecting the reception signal and producing an image signal indicating a position of the wreck ship.
106
indicates a circulator unit for sending the question signal produced in the signal producing unit
102
to the antenna
103
and sending the reception signal received in the antenna
103
to the signal receiving unit
105
.
Next, an operation of the conventional radar device
101
will be described below.
In
FIG. 6
, a question signal is produced in the signal producing unit
102
. In the circulator unit
106
, the question signal produced in the signal producing unit
102
is sent toward the antenna
103
. In the antenna
103
, the question signal is radiated into the air.
When the question signal is received in the SART of the wreck ship, a response signal is output from the SART, and the response signal and an echo of the question signal are received as a reception signal in the antenna
103
. The reception signal including the response signal is sent toward the signal receiving unit
105
by the function of the circulator unit
106
. Thereafter, the reception signal including the response signal is amplified and phase-detected in the signal receiving unit
105
to obtain an image signal. Therefore, a position of the SART can be detected according to the image signal, and an operator can visually recognize the position of the SART. That is, a distance between the radar device
101
and the SART and a direction from the radar device
101
to the SART can be visually recognized.
The detection of the position of the SART is described in detail with reference to FIG.
7
(
a
) to FIG.
7
(
c
).
FIG.
7
(
a
) shows the question signal radiated from the conventional radar device
101
, FIG.
7
(
b
) shows a frequency change in the response signal sent from the SART, and FIG.
7
(
c
) shows the image signal obtained in the signal receiving unit
105
.
As shown in FIG.
7
(
a
), the question signal is composed of pulse waves, and each pulse wave of the question signal is produced by a carrier wave set in a frequency band &Dgr;F
1
(MHz) centering around a frequency F
1
(MHz). The pulse waves of the question signal are radiated from the antenna
103
. In the SART, as shown in FIG.
7
(
b
), the outputting of the response signal is started at a reception time of each pulse wave of the question signal. The response signal is obtained by repeatedly sweeping an oscillation frequency 12 times in a sweeping frequency band from 9500 MHz to 9200 MHz. Therefore, the response signal has 12 signal waves in each response time-period, and the frequency of each signal wave uniformly changes in a saw-toothed shape. The saw-toothed-shaped signal waves of the response signal are output to the radar device
101
. The transmitting frequency band &Dgr;F
1
of the question signal is placed within the sweeping frequency band of the response signal ranging from 9500 MHz to 9200 MHz.
Thereafter, in the signal receiving unit
105
of the radar device
101
, as shown in FIG.
7
(
b
) and FIG.
7
(
c
), components of the reception signal having frequencies of the transmitting frequency band &Dgr;F
1
are extracted from the reception signal including the response signal, and an image signal having a plurality of pulse waves are obtained. The pulse waves of the image signal are placed at equal time-intervals because the saw-toothed-shaped signal waves of the response signal are output from the SART at equal time-intervals. The image signal is called an SART code.
Here, because the antenna
103
is rotated at prescribed cycles, the intensity of the pulse waves of the image signal is changed at the prescribed cycles. Therefore, a direction from the radar device
101
to the SART is detected according to the intensity change of the pulse waves of the image signal. Also, because the response signal is output from the SART when the question signal output from the radar device
101
is received in the SART, a time delay occurs between the outputting of the question signal from the radar device
101
and the reception of the response signal in the radar device
101
. Therefore, a distance between the radar device
101
and the SART is detected according to the time delay.
However, because the transmitting frequency band &Dgr;F
1
of the question signal is placed within the receiving frequency band of the response signal, a large volume of sea clutter and ground clutter indicated as the echo of the question signal is included as noise components in the reception signal, a signal-to-noise ratio of the reception signal deteriorates. Also, because components of the reception signal placed in almost the same frequency band as the transmitting frequency band &Dgr;F
1
of the question signal are extracted from the reception signal to produce the image signal, a large volume of sea clutter and ground clutter indicated as the echo of the question signal is included in the image signal. That is, the question signal is returned from the surface of the sea as the sea clutter, and the question signal is returned from the bottom of the sea as the ground clutter. Therefore, a problem has arisen that a detection performance of the position of the wreck ship is suppressed in the conventional radar device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional radar device, a radar device in which a detection performance of the position of a wreck ship is improved.
The object is achieved by the provision of a radar device comprising a signal producing unit for producing a question signal, an antenna for outputting the question signal produced in the signal producing unit and receiving both an echo of the question signal and a response signal sent from a search and rescue radar trans-ponder in response to the question signal, a filtering unit for receiving both the echo of the question signal and the response signal received in the antenna and suppressing intensity of components of both the echo of the question signal and the response signal placed in almost the same frequency band as that of the question signal to produce a filtered respon
Matuura Kioo
Nishiguchi Kenichi
Takase Kazuyosi
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