| 摘要 |
<p>PROBLEM TO BE SOLVED: To correct a decrease in electric field strength of reception of a reflected wave due to multipath disturbance. SOLUTION: The length of a wireless transmission path of transmitted and reflected waves is increased or decreased periodically in a dislocation cycle W15 as a consequence of a periodical change in the installation positions of antennas 13, 14 in a vehicle. A mixing circuit 18a mixes a local oscillation signal from a local oscillator 15b and a received signal of a reflected wave from a receiving antenna 14, and generates a beat signal having a beat frequency. After a beat signal is deprived of its direct current component by a filter 21 and a signal level change of a beat frequency by an intensity detection circuit 22, a level change due to a path length change and multipath disturbance is removed as a consequence of the smoothing of cut-off frequencies below a normal frequency corresponding to a cycle W15. A comparator 26 discriminates outputs by levels, decides whether an object of detection is present or not, and computes a relative distance and speed using the beat signal.</p> |
