GB2341504A

GB2341504A - Vehicle tracking system

Info

Publication number: GB2341504A
Application number: GB9821716A
Authority: GB
Inventors: Ian Benjamin Hopley
Original assignee: ASG TECHNOLOGY Ltd
Current assignee: ASG TECHNOLOGY Ltd
Priority date: 1998-09-11
Filing date: 1998-10-07
Publication date: 2000-03-15
Anticipated expiration: 2018-10-07
Also published as: GB2341504B; GB9821716D0; GB9819792D0

Abstract

A vehicle tracking system utilising GPS satellite signals, includes a plurality of radio communication antennas (101, 102) mounted within the vehicle, and arranged so that if one antenna is disabled the other or remainder are capable of continuing to function. A control unit (111) which receives GPS signals from a separate antenna (115), is adapted to sense a change in the impedances of the communication antennas (101, 102) and to initiate the generation and transmission of vehicle position data signals (113) to a base tracking station (114). The antennas may be connected to a junction/splitter unit (109) by respective transmission lines (103, 104, 107, 108) which may include respective balance to unbalance transformers (105, 106). The communication and GPS aerials (101, 102, 115) may also be protected by capacitive proximity detectors (116, 117, 118) to detect unauthorised screening of the antennas which is recorded by sealed recorder unit (119).

Description

2341504 A VEHICLE TRACKING SYSTLY.

The present invention relates to vehicle tracking systems in which vehicle position signals are relayed by radio to a central tracking station, and more specifically to such systems in which the position of the vehicle is determined using signals from a global positioning satellite, known by the acronym GPS, and which also form part of the security system of the vehicle.

At present, vehicle mobile data com:,. i-.-,.nication systems operating at frequencies in the region of 450MHz tend to use a quarter wavelength whip antenna mounted above a ground plane which is provided by a surface of the body of the vehicle concerned. This arrangement is vulnerable to damage, accidental or deliberate, and to a large extent negates the value of such a system as a security aid, because a vehicle thief seeking to steal a vehicle in which the system is fitted merely to disable the antenna in order to sever communication between the vehicle and a tracking base station. Such disablement of the antenna may be by physically breaking it off, or by bending or deforming it in such a way that it no longer functions, or by screening the antenna.

It is an object of the present invention to provide a more secure vehicle radio tracking system.

2 According to the present invention there is provided a vehicle tracking system including means for receiving global positioning satellite signals, means for determining the position of a vehicle therefrom and for producing vehicle position data signals, and means for communicating the vehicle position data signals from the vehicle to a tracking base station, in which there is included a plurality of electrically balanced receiving/transmitting antennae adapted to be mounted within the vehicle structure, the arrangement being such that in the event of one antenna being disabled the other or remainder of the antennae are capable of functioning.

Preferably, at least one of the antennae is adapted to 15 form an integral part of a window of the vehicle, such as the windscreen or rear window.

In one embodiment of the invention the mobile control unit is adapted to respond to the activation of the vehicle's normal alarm system to generate and transmit alarm signals and vehicle position data signals to the tracking base station.

In another embodiment there are included means responsive to a change in the impedance of the ant-,nnae systems to initiate the operation of producing the vehicle position data signals and communicating them to the base tracking station. The said means may also be responsive to the 3 operation of the vehicle's normal alarm system to initiate the production and transmissi-cn of the vehicle position data signals to the tracking b-ise station.

one advantage of a device which responds to a change in the impedance of the antenna system is the ability to counter the activities of a dishonest driver of a haulage vehicle intent on disabling the system temporarily for example during an unscheduled delivery. This would be sufficient if only the antennae involved in transmission and reception of signals between the vehicle and the tracking base station are affected. 'rLf the GPS antenna were to be disabled instead (or as well), for example by screening, the vehicle's position signal would be lost, thereby making an undetected unscheduled delivery possible. The present invention provides means by which this can be detected and recorded so that an analysis can be made, at least ex post facto for discovery. This would make it impossible for a delivery driver to claim that atmospheric conditions or the effect of nearby metal buildings had caused a. failure of the system.

In order to disable an antenna temporarily and reversibly so as to leave no obvious evidence of tampering, there is in practice only one available technique, namelyto screen an antenna by placing a metal article between it and the satellite or radio network with which it is 4 communicating. once removed such a screen would be undetectable. However, by placing a capacitive sensor capable of detecting a change in capacitance due to the presence of such a screen close to the antenna it becomes possible to detect a screening attempt. A recorder, together with a timing device, may also be provided, preferably in a sealed housing, to provide a record of the times and duration of such screening with which a driver can be confronted upon his return. Such housing may be provided with its own internal battery so that it is not dependent on the general power supply to the system, and would thus provide an entirely independent check on any attempt to corrupt the operation of the system.

one embodiment of the invention will now be described, by way of example, with reference to 1-he accompanying drawing which is a diagrammatic representation of a vehicle security tracking system embodying the invention.

Referring to the drawing, a vehicle security radio tracking system consists of two centre-fed half-wave transmit/receive dipole antennae 101, 102 each of which has a characteristic impedance of approximately 10C ohms.

The antennae 101, 102 are adapted to form an integral part of a window of a vehicle.

The antennae 101, 102 are connected via lengths of parallel conductor transmission line 103, 104, baluns 105, 106 and lengths of coaxial feed cable 107, 108 respectively, to a junction/ splitter lbox 109 and thence via a coaxial feed line 110 to a mobilp control unit 111.

The mobile control unit 111 contains the circuitry necessary to process global positioning satellite (GPS) signals received by an antenna 115 and to produce vehicle position data signals 113 for transmission by the antennae 101, 102 to a tracking base station 114. The tracking base station itself may transmit signals 112 to the vehicle for a number of purposes including setting the regular transmission update rate either in terms of time or of distance travelled, sending a message to the driver, adjusting the interval for wInich the central processing unit remains operative when the ignition is switched of f and setting the vehicle immobiliser. The signals 112 may also be used to enable the base station operator to obtain the vehicle position at any time.

For the system to operate effectively, the separation of the conductors in the lengths of parallel conductor transmission lines 103, 104 are chosdii to optimise the impedance match to the coaxial f eed cables 107, 108, which are of the 75ohm type. The lengths of the coaxial feed cables 107, 10841 as measured between the junction/splitter 109 and the respective baluns 105, 106 are required to be equal to each other and also to be equal to an integral number of half wavelengths of the 6 operating signal within the coaxial feed cables 107, 108.

The first criterion ensures that signals radiated from the antennae 101, 102 are in phase, the second criterion ensures that each length of coaxial feed cable 107, 108 acts as a 1:1 transformer and that the impedance of each length of coaxial feed cable 107, 108 at the junction/ spl itter 109 is equal to the impedance at the respective antennae 101, 102. If one antenna is disabled, for example by severance of the connection to the dipole, either accidentally or as a result of a deliberate attempt at damage, for example by forcible entry into the vehicle to which the system is fitted, then the impedance at the junction/splitter 109 of that half of the antennae system will become infinite but the other half of the system will continue to operate, albeit with some mismatch at the antennae side of the junction/splitter 109.

The function of the baluns 105, 106 is to match the balanced dipole feed lines 103, 104 to the unbalanced coaxial feed cable 107, 108. Each balun consists of a length of seamless copper tube the length of which is one quarter wavelength of the signals in the associated coaxial cable, arranged to enclose the end of the coaxial cable at its junction with the respective balanced dipole feed. Each balun is connected to '1.he sheath of the associated coaxial cable at the end remote from the 7 junction with the associated balanced dipole feed.

The dipoles 101, 102 can be disposed in a number of ways. For example, in the case of a car, one may be mounted on the inside of the windscreen and the etfler on the inside of the rear window. Alternatively, if it is practicable, one or both of the antennae may be mounted on the inside of a lens of a headlamp or rear light cluster of the car. In both cases, the screening effect of the metal of the body of the car between the windows, or the lamp cluster or lamp clusters would reduce the interference between the two antennae.

In the case of heavy haulage vehicles, where an antenna mounted on the rear window is likely be screened by the metal of a trailer or pantechnicon body, the antennae can be mounted vertically at each side of the windscreen, as close to the windscreen pillars as is practicable. Such a mounting arrangement also may be used with motor cars.

In the case of a heavy haulage vehicle, the separation of the two antennae is likely to be about two wavelengths for 450MHz signals. Consequently. the forward interference pattern produced by the ant. ennae has maxima at X=00 and X=300and minima at X=14.50 and X=480where X is the angle between the normal to the windscreen and the direction of the radiation received or transmitted by the 8 antennae.

In the case of a motor car, with the antennae mounted at opposite sides of the windscreen, the separation is 5 approximately one wavelength for 450MHz signals. Consequently, the forward interference pattern of the antennae has first maxima and minima at X=00 and X=300 respectively.

If the windscreen or other window of the vehicle is of the laminated type, then the antennae and their parallel conductor feed lines can be incorporated into the window glass during manufacture in the manner of heating/demisting wires. Alternatively, the antennae and is f eed wires can be attached to an existing window of a vehicle. Another method of manufacture of the antennae would be to deposit the antennae/feed conductors directly on the surface of the window glass.

As mentioned above, if the system is provided with means for detecting a change in the impedance of the antennae it can provide significant benefits. One cause of such imbalance (apart from external violent damage by a car thief) may be the result of a covert attempt by the vehicle driver to conceal the vehicle's whereabouts for a period of time. This may be done, f or example, by introducing metal elements into the vicinity (if the antennae to distort their field patterns and/or to screen

9 them. After the diversion the driver may then remove the distorting/screening metal elements. However, as soon as a routine position transmission takes place the system detects the change in antenna impedance. This may act to transmit a signal (one example of the signal 113 in the drawing) to the base station warning the operator that the antenna system had been tamperel.. with. This information, which is automatically recorded at the base station, would counter any suggestion by the driver that any gaps in transmission were the result of poor reception.

The means for achieving this are illustrated in the drawing. If an unauthorised attempt is made to screen the communication antennae 101 and 102 or the GPS antenna for the purposes of making an unaul.horised journey, it is important to be able to detect that this has been done, and preferably to provide reliable evidence of the occurrence. Otherwise the failure of the system could be attributed to poor reception caused by the particular location, screening by buildings or temporary failure of the communication network or the GPS system. In order to counter this form of attack the antennae 101, 102 and 115 are protected by capacitive proximity detectors, 116, 117 and 118 respectively. The presence of.screening in the vicinity of the antennae is detected y a change in the capacitive sensors and this is recorded by a sealed recorder unit 119. The sealed recorder unit 119 contains a rechargeable battery which is maintained by the vehicle electrical system to enable the unit to continue to operate for many hours even if the charging supply is interrupted. Unit 119 also contaihs a clock which functions to record the time and duration of any interval during which the antennae have been screened. In the event of an apparent failure of the tracking system the seals of the recorder could be removed when the vehicle returns to its base and the recorder data noted. From this it can be established whether the presence of any screening material within the range of the proximity detected is recorded. All connectors associated with the tracking and proximity systems should be sealed to guard against any attempt to tamper with the interconnection cables of the system.

Claims

A vehicle tracking system including means for receiving global positioning satellite signals, means for determining the position of a vehicle therefrom and producing vehicle position data signals and means for communicating the vehicle position data signals to a base tracking station, wherein there is in.::.',-uded a plurality of electrically balanced and matched receiving/ transmitting antennae adapted to be mounted within the vehicle, the arrangement being such that in the event of one antenna being disabled the other or the remainder are capable of continuing to function.
2. A vehicle tracking system according to Claim 1, wherein the antennae are connected to a junction/splitter unit by respective lengths of conditcllor transmission lines.
3. A vehicle tracking system according to Claim 2, wherein the said respective lengths of conductor transmission lines include respective baluns between each antenna and the said junction/splitter unit.
4. A vehicle tracking system according to Claim 3, wherein the lengths of conductor transmission lines between the junction/ spl itter unit and the respective baluns are equal to one another.

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5. A vehicle tracking system according to claim 4, wherein the lengths of the conductor transmission lines between the junction/ spl itter unit and the respective baluns is equal to an integral number of half wavelengths of the operating signal within the conductor transmission lines.
6. A vehicle tracking system according to any preceding claim, wherein the said conductor transmission lines are coaxial feed cables.
7. A vehicle tracking system according to any preceding claim, wherein there are included means responsive to a change in the impedance of an antenna to initiate the production and communication of the vehicle position andlor warning signals to the base tracking station.
8. A vehicle tracking system according to Claim 7, further including means at the tracking base station responsive to reception of the vehicle position and/or warning signals initiated upon detection of a change in the impedance of an antenna to transmit a vehicle immobilising command, there being p.l:c.vided means for receiving the said immobilising command operable to effect immobilisation of the vehicle upon the occurrence of predetermined conditions after reception of the said immobilising command.

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9. A vehicle tracking system according to Claim 8, in which the said predetermined conditions include switching off the vehicle ignition.
10. A vehicle tracking system according to any preceding Claim, wherein there are included means responsive to the actuation of an alarm system f itted to the vehicle to initiate the production and communication of the vehicle position signals to the base tracking station.
11. A vehicle tracking system according to any preceding Claim, wherein each antenna is associated with a transparent member of the vehicle.
12. A vehicle tracking system according to Claim 11, wherein the transparent member is a window of the vehicle.
13. A vehicle tracking system according to claim 12, wherein at least one antenna is associated with the windscreen of the vehicle.
14. A vehicle tracking system according to Claim 13, wherein there is an antenna disposed at each side of the windscreen of the vehicle such that the limbs of the antennae are parallel to side windscreen support members.
15. A vehicle tracking system accordirg to any of Claims 14 11 to 14, wherein the antennae are integral with the said transparent member, or members of the vehicle.
16. A vehicle tracking system according to any of Claims 11 to 14, wherein the antennae are formed on an adhesive transparent substrate for attachment to the transparent member of the vehicle.
17. A vehicle tracking system according to Claim 15, when dependent on Claim 11, wherein the transparent member is the lens of a lamp unit of the vehicle.
18. A vehicle tracking system according to any preceding claim, wherein the antennae are half-wave dipoles.
19. A vehicle tracking system according to any preceding claim, further including a capacitive sensor in the vicinity of the or each antenna for detecting the presence of a screening conductor by sensing a change in capacitance.
20. A vehicle tracking system substantially as hereinbefore described and with reference to the accompanying drawing.
21. A vehicle including a vehicle tracking system according to any preceding claim.