Communications: directive radio wave systems and devices (e.g. – Determining direction – Scanning
Reexamination Certificate
1999-08-25
2001-06-12
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining direction
Scanning
C342S070000, C342S118000, C342S127000, C342S128000, C342S133000, C342S147000, C342S195000
Reexamination Certificate
active
06246359
ABSTRACT:
TECHNICAL FIELD
The prevent invention relates generally to a radar device for detecting the azimuthal direction of a target on the basis of the signal reflected from the target and received by the plural receiving antennas, and more particularly to the radar device in which the plural transmitting antennas are sequentially switched.
BACKGROUND ART
Various types of radar have conventionally been used to detect the relative distance and relative speed of a target. For example, radar is commonly used to detect the relative distance and relative speed of a lead-vehicle on a road. One type of radar used for this purpose is a phase monopulse radar. In a phase monopulse radar, a plurality of receiving antennas receive reflected waves from a target obtained by sending radio waves from one transmitting antenna. Because the receiving antennas have different spatial positions, even signals reflected from the same target differ in phase. The azimuthal direction of the target can then be detected by detecting this phase shift. In principle, this phase monopulse radar has an advantage in that the sending and receiving antennas need not be physically moved.
However, using a phase monopulse radar does result in the generation of ambiguities. Specifically, in the phase monopulse method, as shown in
FIG. 1
, the azimuthal direction &thgr; of a target is obtained from the phase difference &Dgr;&phgr; of a signal (wavelength: &lgr;) received by two receiving antennas (assume the interval is L) in accordance with the following formula:
&thgr;=(180/&pgr;)sin
−1
{(&Dgr;&phgr;/360)·(&lgr;/L)}
When &Dgr;&phgr; satisfies −180 degrees<&Dgr;&phgr;≦+180 degrees, a unique value for the azimuthal direction &thgr; of the target can be obtained. However, when the receiving antennas have wide directional beams and the distance L between the receiving antennas is long, the value of the phase difference may be beyond this range. Therefore, a phase difference can only be detected within a practical range of −180 to +180 degrees: &Dgr;&phgr; and &Dgr;&phgr;+360 degrees, for example, cannot be discriminated.
Accordingly, when the azimuthal directions of the two targets are &thgr;
1
and &thgr;
2
, respectively, and the phase difference &Dgr;&phgr;
1
that corresponds to &thgr;
1
is within the above range while the phase difference &Dgr;&phgr;
2
that corresponds to &thgr;
2
is beyond the range, as shown in
FIG. 2
, although the azimuthal direction &thgr;
1det
to be detected regarding &thgr;
1
is correct, the azimuthal direction &thgr;
2det
detected regarding &thgr;
2
will differ from the original azimuthal direction. This is what is meant by ambiguity.
In other words, when the phase shift exceeds this range, the detected azimuthal direction will differ from the true azimuthal direction. For example, if a phase monopulse radar is mounted on a vehicle and used to detect an advancing vehicle, a non-existent advancing vehicle may be incorrectly detected.
In an attempt to prevent this, a phase monopulse radar commonly only operates within a range where no ambiguity problems occur.
Another type of monopulse radar is an amplitude monopulse radar. Amplitude monopulse radar receives signals reflected from a target by a plurality of receiving antennas with different beam directions. The azimuthal direction of the target is then detected in accordance with the amplitude of the waves received by the receiving antennas. For example, if the amplitudes of the received waves received by two receiving antennas are the same, the azimuthal direction of the target is determined to be in the middle between directions of the signals, and the azimuthal direction of the target is determined from difference of the amplitude between the received waves.
Such an amplitude monopulse antenna also has a theoretical advantage in that the transmitting antenna and the receiving antennas need not be physically moved. However, operation of an amplitude monopulse antenna requires assuming that multiple targets having the same distance and speed does not exist. In other words, if waves reflected from a plurality of targets are received, these signals cannot be discriminated. Accordingly, the amplitude monopulse antenna is used only for detecting the azimuthal direction of a target in rather a narrow angle of visibility and only in the case of a single target.
It is therefore an object of the present invention to provide radar device that can accurately detect the azimuthal direction of a target using a combination of the phase and amplitude monopulse methods.
DISCLOSURE OF THE INVENTION
The present invention comprises plural transmitting antennas with mutually different directional beam directions. These antennas are sequentially switched and the radio waves they radiate, are received by a plurality of receiving antennas after the waves are reflected from a target with reference to the radio waves radiated from these plural transmitting antennas. Also included is an azimuthal direction detection device for detecting the azimuthal direction of the target based on the phase difference or amplitude difference between the waves received in the plurality of receiving antennas.
In this manner, more information is obtained by receiving through the plural receiving antennas the reflected waves from the target that are based on the waves sent from the plural transmitting antennas, than in a radar device where only a single transmitting antenna is used. In the present apparatus, the azimuthal direction of the target can then be accurately determined based on this information.
It may be preferable for the final azimuthal direction detection device to detect the azimuthal direction of the target detected based on the phase difference or amplitude difference between the received waves in the plurality of receiving antennas and the azimuthal direction of the target based on the azimuthal direction of the beam when this target azimuthal direction was detected. For example, the amplitude monopulse antenna may obtain two received signals when a single receiving antenna receives reflected waves originating from two transmitting antennas having differing beam azimuthal directions. The azimuthal direction of the target can then be determined from the amplitude difference of the two received signals and the azimuthal direction of the directional beam. The two received signals are also obtained by receiving the reflected waves that are based on the radio waves from a single transmitting antenna by the two receiving antennas having a different beam azimuthal direction. The azimuthal direction of the target can also be detected from the amplitude difference of the two received signals and the azimuthal direction of the directional beam.
It may also be preferable that the azimuthal direction detection device should further detect the final target azimuthal direction in consideration of the width of the direction beam. Moreover, it may be preferable that the azimuthal direction detection device should output the final target azimuthal direction when the azimuthal direction of the target detected based on the phase difference or amplitude difference between the received waves in the plurality of receiving antennas be contained in the radiation azimuthal direction range of the radio waves determined depending on the azimuthal direction of the directional beam and the width of the directional beam when the azimuthal direction of the target was detected.
Further, it may also be preferable that the azimuthal direction detection device should detect the azimuthal direction of the target based on the phase difference between waves received by a plurality of receiving antennas and comprise a decision devices for deciding that the target is true when the azimuthal direction of the detected target almost coincides with the azimuthal direction indicated by the target that was detected by radiating radio waves from the transmitting antenna having a directional beam azimuthal direction approximate to the azimuthal direction.
T
Asano Yoshikazu
Ohshima Shigeki
Gregory Bernarr E.
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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