Abstract: An antenna apparatus for use as in an automobile collision warning system has a primary radiator for radiating a high-frequency radio wave beam, a reflecting member for reflecting the radio wave beam, an actuating mechanism for actuating the reflecting member, and a lens such as a dielectric lens for converging the radio wave beam reflected by the reflecting member to reduce an angle of divergence of the radio wave beam.

Abstract: An FM signal generator generates a frequency-swept FM signal, which is radiated as a beam from a transmission and reception antenna. The transmission and reception antenna is angularly moved by an antenna actuator to scan the beam. An echo signal reflected from a target and a signal related to the frequency-swept FM signal are mixed into a beat signal, whose frequency spectrum is analyzed by a frequency analyzer. A target detector determines the distance up to the target based on the frequency spectrum of the beat signal. A BPF processor comprises a bandpass filter which extracts a frequency component corresponding to the distance up to the target from the beat signal. A bearing calculator compares the level of a signal that has passed through the BPF processor with a threshold level to determine a bearing and a width of the target.

Abstract: An FM-CW multibeam radar apparatus includes a plurality of antennas designed to serve both for beam transmission and receiving are arranged in such a manner that radiated beams overlap in part with each other. For sensing a short-distance-away target, a beam is transmitted by means of one of the antennas and a reflected beam is received by a separate adjacent one of the antennas to thereby obtain a beat signal. For sensing a long-distance-away target, one and the same beam transmitter-receiver is used. Upon sensing the short-distance-away target, the per-unit-time amount of change of the frequency of a frequency modulated transmitted signal is set to be larger than that for sensing the long-distance-away target so that a beat signal becomes higher, whereby the distance resolution is improved.