Radar apparatus and object sensing method

1. A radar apparatus comprising:

an antenna that receives echo signals, each echo signal being a radar signal reflected by one or more objects;

a Doppler-frequency acquirer that acquires Doppler frequencies at each range from the received echo signals;

a direction correlation power-value calculator that calculates direction correlation power values for respective combinations of the Doppler frequencies and at least one of a distance to the one or more objects and an arrival direction of the echo signals, each direction correlation power value indicating a strength of a corresponding echo signal; and

a normalized direction correlation-value calculator that calculates, for the respective combinations, normalized direction correlation values, each normalized direction correlation value indicating a probability of the arrival direction of the corresponding echo signal.

2. The radar apparatus according to claim 1 , further comprising:

an object sensor that senses the at least one object that reflects the radar signal, based on the direction correlation power values and the normalized direction correlation values.

3. The radar apparatus according to claim 2 ,

wherein the one or more objects includes a first object and a second object; and

wherein the object sensor includes:

an object detector that detects a range in which the first object and the second object that reflect the radar signal are located, based on the direction correlation power values; and

an object separator that separates the region into a first region in which the first object is located and a second region in which the second object is located, based on whether or not a width of spread of the Doppler frequency at which the normalized direction correlation value exceeds a first threshold exceeds a second threshold.

4. The radar apparatus according to claim 3 ,

wherein the first object includes a vehicle, and the second object includes a human, and

the object separator determines a portion of the region as the second region, the portion being an area where the width of the spread of the Doppler frequency exceeds the second threshold.

5. The radar apparatus according to claim 4 ,

wherein the antenna is an array antenna consisting of a plurality of antenna elements;

wherein the Doppler-frequency acquirer acquires Doppler frequencies in each range from the received echo signals, for each of the plurality of antenna elements; and

wherein, by using a relative positional relationship of the plurality of antenna elements, the normalized direction correlation-value calculator calculates the normalized direction correlation values, based on the received echo signals.

6. The radar apparatus according to claim 5 ,

wherein the direction correlation power-value calculator calculates an inner product of a direction vector and a correlation vector as each of the direction correlation power values, the direction vector indicating complex responses of the plurality of antenna elements for each combination of a Doppler frequency, the distance, and the arrival direction, when the echo signals arrive from the arrival direction, and the correlation vector indicating components of the received echo signals for each combination of the Doppler frequency and the distance; and

the normalized direction correlation-value calculator calculates, as the normalized direction correlation value, a value obtained by normalizing the inner product by using a value of the correlation vector, for each combination of the Doppler frequency, the distance, and the arrival direction.

7. The radar apparatus according to claim 6 , further comprising:

a power-value-data shrinker that compresses a predetermined component of a distance component and a direction component in direction correlation power-value data including the direction correlation power values corresponding to combinations of the Doppler frequencies, the distances, and the arrival directions; and

a correlation-value-data shrinker that compresses the predetermined component in normalized direction correlation-value data including the normalized direction correlation values corresponding to the combinations,

wherein the object detector detects the region, based on the direction correlation power-value data on which the compression was performed, and

the object separator separates the region into the first region and the second region, based on the normalized direction correlation-value data on which the compression was performed.

8. An object sensing method comprising:

receiving echo signals, each of the echo signals being a radar signal reflected by one or more objects;

acquiring Doppler frequencies at each range from the received echo signals;

calculating direction correlation power values for respective combinations of the Doppler frequencies and at least one of an distance from a radar apparatus to the object and an arrival direction of the echo signals, each direction correlation power value indicating a strength of a corresponding echo signal; and

calculating, for the respective combinations, normalized direction correlation values, each indicating a probability of the arrival direction of the corresponding echo signal.