Radar device and target detecting method

1. A radar device configured to calculate an angle of a target based on a phase difference between reception signals obtained by receiving reflected waves from the target with a plurality of receiving antennae, the radar device comprising:

a transmitting unit configured to alternately transmit a first transmission wave and a second transmission wave having different beam patterns;

a calculating unit configured to calculate reception levels of the respective reception signals of the reflected waves by the first transmission wave and the second transmission wave, and an estimate angle at which the target is estimated to exist, on the basis of the reception signals;

a first determining unit configured to determine a degree of reliability of a level difference between the reception levels calculated by the calculating unit, on the basis of a comparison between the level difference with a reference value of the level difference which is associated with the estimate angle in advance; and

a second determining unit configured to determine whether the target exists at the estimate angle, on the basis of a determination result of the first determining unit and the reception level based on the first transmission wave, wherein

in a case where the first determining unit determines that the degree of reliability is high, the second determining unit sets a predetermined first threshold as a determination threshold, whereas in a case where the first determining unit determines that the degree of reliability is low, the second determining unit sets a predetermined second threshold which is greater than the predetermined first threshold as the determination threshold, and

in a case where the reception level based on the first transmission wave exceeds the determination threshold, the second determining unit determines that the target corresponding to the estimate angle is not a wrapped ghost caused by phase wrapping, whereas in a case where the reception level based on the first transmission wave is equal to or lower than the determination threshold, the second determining unit determines that the target corresponding to the estimate angle is the wrapped ghost.

2. The radar device according to claim 1 ,

wherein the first transmission wave and the second transmission wave have the same transmission axis,

wherein a transmission range of the first transmission wave is narrower than a transmission range of the second transmission wave, and a transmission distance of the first transmission wave is longer than a transmission distance of the second transmission wave, and

wherein the transmission range of the first transmission wave and the transmission range of the second transmission wave partially overlap with each other in the direction of the transmission axis.

3. The radar device according to claim 1 ,

wherein the reference value is set for each of a plurality of candidate angles at which the target may actually exist so as to be associated with the estimate angle,

wherein the first determining unit calculates difference amounts between the level difference and the reference value for each of the candidate angles, and

wherein in a case where a difference between the difference amounts exceeds a predetermined threshold, the first determining unit determines that the degree of reliability is high, whereas in a case where the difference between the difference amounts is equal to or smaller than the predetermined threshold, the first determining unit determines that the degree of reliability is low.

4. The radar device according to claim 1 , further comprising a target selecting unit configured to select the target as an object to be output to an external device, on the basis of a determination result of the second determining unit,

wherein if the second determining unit determines that the target is the wrapped ghost, the target selecting unit does not select the target as an object to be output.

5. The radar device according to claim 1 , further comprising a third determining unit configured to determine whether the target determined as the wrapped ghost by the second determining unit is a low-reflectivity object, on the basis of a movement direction of the target or whether a different target assumed to be a wrapping cause of the target exists.

6. The radar device according to claim 5 , wherein in a case where the target determined as the wrapped ghost has a relative velocity representing that the target is separating away from the radar device, and moves toward an inside of the transmission range of the first transmission wave, the third determining unit assumes the target to be the low-reflectivity object.

7. The radar device according to claim 6 , wherein in a case where a number of reflecting points existing in a predetermined range from the target determined as the wrapped ghost is equal to or larger than a predetermined value, the third determining unit determines that the target is the low-reflectivity object.

8. The radar device according to claim 5 , wherein in a case where the different target does not exist, the third determining unit assumes the target determined as the wrapped ghost to be the low-reflectivity object.

9. The radar device according to claim 5 , wherein in a case where a number of reflecting points existing in a predetermined range set on the outside of the transmission range of the first transmission wave from the target determined as the wrapped ghost is equal to or larger than a predetermined value, the third determining unit determines that the target is the wrapped ghost.

10. A target detecting method for calculating an angle of a target based on a phase difference between reception signals obtained by receiving reflected waves from the target with a plurality of receiving antennae, the target detecting method comprising:

a transmitting process of alternately transmitting a first transmission wave and a second transmission wave having different beam patterns;

a calculating process of calculating reception levels of the respective reception signals of the reflected waves by the first transmission wave and the second transmission wave, and an estimate angle at which the target is estimated to exist, on the basis of the reception signals;

a first determining process of determining a degree of reliability of a level difference between the reception levels calculated by the calculating process, on the basis of a comparison between the level difference with a reference value of the level difference which is associated with the estimate angle in advance; and

a second determining process of determining whether the target exists at the estimate angle, on the basis of a determination result of the first determining process and the reception level based on the first transmission wave, wherein

in a case where the first determining process determines that the degree of reliability is high, the second determining process sets a predetermined first threshold as a determination threshold, whereas in a case where the first determining process determines that the degree of reliability is low, the second determining process sets a predetermined second threshold which is greater than the predetermined first threshold as the determination threshold, and

in a case where the reception level based on the first transmission wave exceeds the determination threshold, the second determining process determines that the target corresponding to the estimate angle is not a wrapped ghost caused by phase wrapping, whereas in a case where the reception level based on the first transmission wave is equal to or lower than the determination threshold, the second determining process determines that the target corresponding to the estimate angle is the wrapped ghost.