A signal receiver unit includes a first receiver unit which is designed to receive reflected electromagnetic waves created by a main lobe and two grating lobes of projected electromagnetic wave. The signal receiver unit includes a second receiver unit which is designed to receive reflected electromagnetic waves created by the main lobe and one grating lobe of the projected electromagnetic wave. The signal receiver unit includes a third receiver unit which is designed to receive reflected electromagnetic waves created by the main lobe and the other grating lobe of the projected electromagnetic wave. The signal processor unit identifies the reflected electromagnetic waves based on combinations of the received signals of the first receiver unit, the second receiver unit, and the third receiver unit, and calculates a distance to an object.