Patent ID: 7649491

Claim:
A distance measuring apparatus, comprising: a transmitter that transmits a request signal from an antenna to the outside via radio waves having a plurality of different carrier frequencies; a receiver that receives a reflection signal which is a signal composed of one frame and is obtained when the request signal transmitted from the transmitter is reflected by a reflector while being modulated; a phase information acquirer that calculates a phase change amount between the reflection signal received by the receiver and the request signal for each of the carrier frequencies transmitted from the transmitter; and a distance calculator that calculates a distance between the antenna and the reflector on the basis of the carrier frequencies and the phase change amount for each of the carrier frequencies acquired by the phase information acquirer, wherein: the receiver comprises a frequency converter that converts the received reflection signal to an I signal and a Q signal; the reflection signal is transmitted from the reflector via three or more different carrier frequencies; and the phase information acquirer extracts, as a minimal component, one of the I signal and the Q signal that has a smaller signal level for each of the carrier frequencies, selects two carrier frequencies having minimal components greater than that of at least one of the other carrier frequencies, and acquires the phase change amount for each of the selected two carrier frequencies.