Communications: directive radio wave systems and devices (e.g. – Presence detection only
Patent
1992-08-19
1996-07-09
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
340850, G01S 1300
Patent
active
055348696
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to open transmission line systems of the kind used for determining the location of objects, things or people moving along a pathway and is especially applicable to so-called "guided radar" intrusion detection systems which use leaky cables as a transducer to detect human intrusions.
Aspects of the invention are applicable whether the objects, things or people carry a radio transmitter, a receiver, a transponder or no electronics whatsoever.
BACKGROUND ART
Known perimeter security sensors or intrusion detection systems utilizing open transmission lines incorporate a source of radio frequency energy as a component of the system. This can be used to set up a field around a transmission line which is monitored by a second parallel line or to set up a field from a central antenna which is monitored by an open transmission line. Guided radar type of intrusion detection systems have been developed using leaky coaxial cables. In most guided radar systems there are two parallel cables. One is used to distribute an electromagnetic field along the desired pathway and the parallel receive cable is used to monitor the field coupling between the two cables and thereby to detect movement of people or objects which disturb the coupling. Both continuous wave (cw) and pulsed type guided radars using leaky coaxial cables have been developed. Canadian patents numbers 1,216,340 and 1,014,245 by Keith Harman et al, both of which are incorporated herein by reference, describe two such guided radar systems.
An alternative form of guided radar which uses a leaky coaxial cable to monitor the field set up by a central antenna is disclosed in Canadian patent No. 1,169,939, by Keith Harman et al. In order to minimize the number of nuisance or false alarms, this system tracks the phase angle which changes as the intruder crosses the cable.
A disadvantage of both such systems is that the transmitter which generates the field is part of the system and in general requires radio regulatory approval.
The present invention seeks to overcome this disadvantage and to this end contemplates the use of an independent transmitter, for example an existing commercial radio or television station, as the source of the field which is subsequently used to detect intruders or other moving objects.
DISCLOSURE OF INVENTION
According to one aspect the invention comprises an open transmission line system for locating a mobile entity along a defined pathway, said system being adapted to utilize transmissions from a remote independent transmitter, for example a commercial radio or television station transmitting at a known frequency, said system comprising an open transmission line extending along said pathway, radio receiver means connected to said transmission line, said radio receiver means including a first receiver for receiving a first signal coupled into and transmitted along said transmission line from said remote station, a second receiver for receiving a second signal directly from said remote station, and means for correlating the first and second signals, said system further comprising signal processing means coupled to said radio receiver means for processing said first and second signals to determine the location of said mobile entity relative to said open transmission line.
Preferably the first and second receivers share a common local oscillator, thus ensuring that they are both tuned to the same frequency and phase information is preserved at the intermediate frequency.
The system may be adapted to use transmissions from a plurality of such remote transmitters. Selector means may then tune both receivers to the different transmission frequencies. In one embodiment, the selector means switches the receivers, alternately between two frequencies of a pair of remote transmitters. Provision may be made for selecting a third frequency so that a third transmitter can be used if one of the others fails. This also minimizes the effects of multipath signals by effectively operating at two or more freq
REFERENCES:
patent: 4612536 (1986-09-01), Harman
patent: 5019822 (1991-05-01), Kirkland
Adams Thomas
Auratek Security Inc.
Hellner Mark
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