Proximity detector

Claim 1

A proximity detecting system comprising transmitter means producing a zone of radiation, receiver means having a zone of sensitivity to the radiation intersecting with the zone of radiation of the transmitter means, the transmitter means emitting and the receiver means being sensitive to infrared radiation, and indicating means indicating the amplitude of the signal from the receiver means by means of a pulsed tone the pulse frequency of which is varied, the transmitter and receiver means together comprising at least three units spaced along a line with the units being alternately transmitter units and receiver units, the zones of the transmitter units and the receiver units both being divergent and the receiver and transmitter units being spaced substantially equally along said line of units, wherein at least one type of unit has a polar diagram with at least two distinct directions of high magnitude approximately coplanar with the line of units and each such unit is constructed from a plurality of elements behind a common aperture, the axis from each element through the aperture forming one of the directions of high magnitude.