Transceiver with skewed transducers for low close-in sensitivity

Claim 1

For use in an intruder detection system in which a beam is transmitted into an area to be protected, reflections of the beam from objects in the area are received, and signals representative of the received reflections are processed to detect the presence of an intruder, a transceiver comprising: a transceiver housing; a transmitting transducer angularly mounted in said housing; a receiving transducer angularly mounted in said housing; said transmitting and receiving transducers being spaced apart in said housing by a predetermined distance and symmetrically disposed on respective opposite sides of a transceiver axis; each of said transceivers being angularly disposed in said housing outward of said transceiver axis to provide a radiation pattern symmetrical about the transducer axis angularly outward of said transceiver axis; the outward angular position of said transducers relative to the transceiver axis being of an angular extent providing substantially reduced close-in effective pattern gain and sensitivity of said transceiver and substantially the same detection-zone sensitivity outside of the close-in range, in comparison to a transceiver having parallel aligned transducers of the same spacing and same pattern.