Standing wave radar, occupant detection system, and object detection method

An object detection method executed by a standing wave radar including:

• a transmitter configured to set a frequency of a transmission signal to multiple frequencies, and output the transmission signal taking the respective frequencies in a time-division manner;
• a receiver configured to receive a reflected signal taking the multiple frequencies in a time-division manner, the reflected signal being the transmission signal taking the multiple frequencies reflected by an object;
• and
• a processor,
• the object detection method comprising:
• obtaining reflection coefficients of the multiple frequencies by obtaining each reflection coefficient of the transmission signal and the reflected signal taking a same frequency with each other, for the transmission signal taking the multiple frequencies and the reflected signal taking the multiple frequencies,
• executing a first inverse Fourier transform process of calculating a first distance spectrum for the object by executing an inverse Fourier transform on the reflection coefficients of the multiple frequencies, and a first distance measurement process of determining presence or absence of the object and calculating a distance to the object, based on the first distance spectrum,
• wherein standing wave radar further includes a storage, and
• wherein the object detection method further comprising:
• obtaining the reflection coefficients of the multiple frequencies repeatedly determined at predetermined time intervals, and storing the reflection coefficients in the storage,
• obtaining, for each of the multiple frequencies, a difference between a reflection coefficient stored in the storage in a previous storing process and a reflection coefficient stored in the storage in a current storing process,
• executing a second inverse Fourier transform process of calculating a second distance spectrum for a non-stationary object by executing an inverse Fourier transform on the difference obtained for each of the multiple frequencies, and
• executing a second distance measurement process of determining presence or absence of the non-stationary object and calculating the distance to the non-stationary object, based on the second distance spectrum.