Abstract: A proximity detector for motor cars, to aid parking, has 3 infra-red transmitter units 10-1 to 10-3 producing a zone of radiation 36 and two receiver units 20-1 and 20-2 producing a zone 46 of sensitivity to the radiation. Each transmitter unit has 3 transmitter elements housed behind a common aperture, and each receiver unit has 2 receiver elements housed behind a common aperture, giving for each unit a polar diagram with at least two distinct directions of high magnitude, the axes of peak radiation or sensitivity from the elements of a unit being divergent through the aperture and forming the directions of high magnitude. An indicating device indicates the amplitude of the combined signal from the receivers by means of a pulsed tone the pulse frequency of which is varied.

Abstract: A proximity detector for motor cars, to aid parking, has 3 infra-red transmitter units 10-1 to 10-3 producing a zone of radiation 36 and two receiver units 20-1 and 20-2 producing a zone 46 of sensitivity to the radiation. Each transmitter unit comprises 3 transmitter elements housed behind a common aperture, and each receiver unit comprises 2 receiver elements housed behind a common aperture, giving for each unit a polar diagram with at least two distinct directions of high magnitude, the axes of peak radiation or sensitivity from the elements of a unit being divergent through the aperture and forming the directions of high magnitude. An indicator indicates the amplitude of the combined signal from the receivers by providing a pulsed tone the pulse frequency of which is varied.