Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1998-04-10
2000-10-03
Wu, Daniel J.
Communications: electrical
Condition responsive indicating system
Specific condition
340541, 340565, 340552, 340522, 340528, 340553, 340556, 340567, 34082532, G08B 1300
Patent
active
061279269
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to intrusion sensing systems and components therefor and is particularly concerned with intrusion sensors and intruder detectors for use in protecting vertical surfaces.
SUMMARY OF THE INVENTION
By a "vertical surface" we mean a real or imaginary surface which extends with its major component of direction vertically and which itself is not necessarily a flat surface. In particular, a vertical surface may be represented by a face of a building or by an imaginary surface defined by the face of scaffolding or of a scaffolding tower. Thus a horizontal plane or surface is to include any plane extending substantially at right angles to such vertical surface.
According to one aspect of the invention there is provided an intrusion sensor comprising a microwave transmitter, with an associated microwave aerial, and a microwave receiver, with associated microwave aerial, for receiving radiation transmitted by the transmitter, the receiver having means responsive to variation of the received radiation outside a given range to produce a signal to represent the presence of an intruder, the transmitter and receiver aerials each having an aperture which has an extent, in a direction substantially at right angles to a vertical surface, of not less than 0.50 meters (20 inches) to provide a microwave beam pattern between the aerials in a substantially horizontal plane, the aerials being mounted adjacent to a vertical surface at opposite ends of a path to be monitored for intruder presence.
In a preferred embodiment, each aerial is provided by a horizontally extending array of radiating elements co-acting to provide the required horizontal beam pattern. Preferably the beam pattern has a half-power beam width not greater than 2.degree..
Thus, according to a second aspect of the invention there is provided an intrusion sensor comprising a microwave transmitter having a microwave aerial, and a microwave receiver having a receiving microwave aerial and which receiver includes means responsive to a variation in received signal to provide an alarm signal, each of the aerials comprising an array of radiating elements extending in a horizontal plane and co-acting to provide a substantially horizontal beam pattern having a half-power beam width not greater than 2.degree., the aerials being mounted spaced apart in the vicinity of a vertical surface so that each element of the receiver array receives radiation components directly from each element of the transmitter array together with vertical-surface-reflected components from at least some of the elements of the transmitter array, the direct and surface-components adding vectorially at the receiver aerial.
Possible aerial components for use in these aspects of the invention have already been disclosed in the UK Patent Specification No. 1475111 and accordingly the technical content of that specification is incorporated herein. That specification is a prior art form of microwave beam sensor in which the importance of reducing ground reflection is incorporated. The aerial arrangements were designed with the objective of reducing ground sensitivity, thus to reduce problems of false alarms created by moving and growing vegetation etc.
The prior art microwave transmitter and receiver are designed to be mounted vertically above the ground and have beam aerials of extended vertical aperture, of at least 0.75 meters (30 inches), to mitigate the effects of ground reflection. The preferred vertical aerials used were a slotted waveguide array with circular polarisation to minimise beam spreading.
Investigations revealed however that, whilst ground reflected components are less sensitive, the prior art sensor's capabilities are reduced. Whilst a walking, running or crawling intruder is detected, a rolling intruder, minimising his cross-sectional body area, will normally be undetected. Despite that problem, the system can be adapted for use in the present invention without the problem materialising Preferred embodiments of the above aspe
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Pham Toan
Wu Daniel J.
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