Periphery monitoring radar device

1. A periphery monitoring radar device that is mounted to a vehicle to monitor a periphery of the vehicle, comprising:

a transmission unit that is configured to transmit a combination of transmission signals modulated using a plurality of modulation modes as a radar wave;

a reception unit that is configured to generate a reception signal from a reflected wave from an object in the periphery of the vehicle, the object reflecting the radar wave transmitted by the transmission unit as the reflected wave;

a spectrum generation unit that is configured to, for each of the plurality of modulation modes, generate a frequency spectrum based on the reception signal generated by the reception unit;

an azimuth calculation unit that is configured, for each of the plurality of modulation modes, to:

extract one or more peaks corresponding to the object from a corresponding frequency spectrum generated by the spectrum generation unit, and

subject the extracted one or more peaks to azimuth development to accordingly calculate an azimuth of the object;

an environment determination unit that is configured to, for each of the plurality of modulation modes, determine whether a peripheral environment of the vehicle is a complex environment with a decrease in calculation accuracy of the azimuth for a corresponding modulation mode, based on a degree of randomness of the corresponding frequency spectrum generated by the spectrum generation unit; and

a position calculation unit configured to:

remove, upon the peripheral environment of the vehicle for at least one modulation mode in the plurality of modulation modes being determined to be the complex environment, at least one azimuth corresponding to the at least one modulation mode from the azimuths respectively calculated for the plurality of modulation modes to thereby obtain at least one target azimuth that is at least one of remaining azimuths except for the at least one azimuth that is removed; and

calculate a position of the object based on the at least one target azimuth.

2. The periphery monitoring radar device according to claim 1 , wherein the environment determination unit is configured to determine, for each of the plurality of modulation modes, that the peripheral environment of the vehicle is the complex environment when at least one of the following conditions is satisfied:

(i) in a preset determination range, a number of the one or more peaks in the frequency spectrum is larger than a preset threshold;

(ii) in the determination range, an average value of peak power obtained by averaging values of power at the respective one or more peaks in the frequency spectrum is larger than a preset peak threshold; and

(iii) in the determination range, average power in the frequency spectrum is larger than a preset average threshold.

3. The periphery monitoring radar device according to claim 1 , wherein the position calculation unit is configured to, when there are two or more of the modulation modes where the environment determination unit does not determine that the peripheral environment of the vehicle is the complex environment, calculate the position of the object using an average value of the azimuths calculated by the azimuth calculation unit using a corresponding two or more of the modulation modes.

4. The periphery monitoring radar device according to claim 3 , wherein the plurality of modulation modes includes an FMCW mode and a 2FCW mode.