Method and apparatus for rejecting rain clutter in a radar system

Abstract

A method and apparatus for detecting the presence of objects in a vehicle operator's blind spots. The apparatus comprises a side-facing Doppler radar system using continuous wave (CW) transmission with frequency modulation (FM) operation from a frequency modulation switching technique. The radar system determines the presence, range and closing rate of detected targets. The radar system detects targets even when operated in adverse weather conditions and will not generate false warnings due to rain clutter caused by wet roads and other wet surroundings. The radar system uses ranging techniques to reject false targets that are detected outside of a predetermined target detection zone. In accordance with the present invention, the radar system indicates that a target is detected if and only if any part of the target is within the detection zone and it: (1) remains in front of the antenna for at least TH1 seconds; (2) is at a range between Range.sub.min and Range.sub.max ; and (3) is moving faster than Closing-Speed.sub.min relative to the antenna. By rejecting targets that are closer than Range.sub.min feet to the antenna, false alarms due to rain clutter are dramatically reduced. Also, by rejecting targets that are further than Range.sub.max feet from the antenna, the radar system reduces false alarms caused by wet foliage and other wet 'non-road' surroundings. In one embodiment, the radar system uses a patch array antenna oriented into a diamond-shape configuration to effectively create a natural linear amplitude taper that aids in rejecting clutter caused by wet road surfaces.