GB2259210A

GB2259210A - Ground movement monitor

Info

Publication number: GB2259210A
Application number: GB9118621A
Authority: GB
Inventors: Paul Kevin Kimber; Ian James Forster
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1991-08-30
Filing date: 1991-08-30
Publication date: 1993-03-03
Anticipated expiration: 2011-08-30
Also published as: GB9118621D0; GB2259210B

Abstract

Airport surface detection equipment employs a plurality of interrogating beacons 6, 7, 8, 9 located adjacent taxiways 3, 4 and runways 1 and a transponder 11 on an aircraft 10. The beacons transmit an AMCW interrogation signal and the transponder retransmits it modulated in accordance with the contents of a memory (17, fig 2). The position of the aircraft can be determined at a central control point by determining which beacon receives the retransmitted signal. In an alternative embodiment (fig 4) the interrogator (31) is on board the aircraft (10) and a plurality of transponders (11) are adjacent the runway (1) and taxiways (3, 4). Each transponder modulates the retransmitted signal distinctively, enabling the aircraft to determine its position. The transponders may be located adjacent the taxiway and runway lights and may share their power supply. The claims refer to passive transponders. <IMAGE>

Description

Ground Movement Monitor This invention relates to a ground movement monitor and specifically to a ground movement monitor for use at airports.

A number of accidents have occurred due to collisions between aircraft on the ground, generally this has been due to the ground controller not knowing the position of an aircraft or the aircraft crew becoming lost.

One solution to this problem is to use ground surveillance radar to track aircraft movements on the ground. This approach has a number of problems associated with it. One problem is that not all aircraft on the airport will necessarily be visible to the radar. Some parts of the airfield may be obscured by buildings, which is predictable and permanent, but also aircraft and other vehicles may unpredictably obscure one another temporarily.

In addition fading of the radar signals due to environmental conditions such as rain can prevent detection of aircraft even when a clear line of sight between the aircraft and radar exists.

Another problem of ground surveillance radar is that it cannot identify which return corresponds to which specific aircraft, which complicates the issuing of instructions by the ground controller.

The final problem with ground radar is its great expense.

This invention was intended to produce a ground movement monitor at least partially overcoming these problems.

This invention provides a ground movement monitor comprising a beacon and a passive transponder, one being mounted on a vehicle and one being fixed, the beacon being arranged to radiate an interrogation signal and the transponder being arranged to reflect this signal and to transmit data to the beacon by altering the characteristics of the reflected signal.

This provides a relatively cheap ground movement monitor which can easily be set up. The use of a passive transponder helps to keep the cost of the monitor down and reduces any possible electromagnetic interference problems.

Ground movement monitors embodying the invention will now be described by way of example only with reference to the accompanying diagrammatic Figures in which; Figure 1 shows a first ground movement monitoring.

system; Figure 2 shows a passive transponder suitable for use in the system of Figure 1 or Figure 4; Figure 3 shows a beacon suitable for use in the system of Figure 1; Figure 4 shows a second ground movement monitoring system; and Figure 5 shows a beacon suitable for use in the system of Figure 4, similar parts having the same reference numerals throughout.

Referring to Figure 1 a first airport ground movement monitor is shown.

An airport includes a runway 1 and two associated taxiways 2 and 3 which meet at a junction 4.

Interrogator beacons 5, 6, 7, 8 and 9 are situated adjacent the runway 1 and taxiways 2 and 3. Each interrogator beacon transmits a weak R.F. signal continuously.

When an aircraft 10 mounting a passive transponder 11 is near to one of the interrogator beacons 5 to 9 it provides the aircraft's identity to the beacon 5 to 9.

Referring to Figure 2 the aircraft passive transponder 11 is shown. This comprises an antenna 12 linked to an antenna matching network 13 formed by an inductor 13A and two diodes 13B and 13C.

when the aircraft 10 is within range of one of the beacons 5 to 9, in Figure 1 the beacon 6, the amplitude modulated interrogation signal transmitted continuously by the beacon 6 is received by the antenna 12. The signal then passes through the antenna matching network 13 to an amplitude modulation (AM) detector 14 which selects the AM signal from the beacon and supplies it to a conditioner 15.

The conditioner 15 filters and amplifies the signal and makes it suitable for analysis by a digital processor 16.

When the digital processor 16 detects an interrogation signal from the beacon 6 it extracts the aircrafts identification code from a memory 17. This code identifies the aircraft type and flight number, which is set before the aircraft 10 leaves its parking area for each flight.

The processor 15 emits a digital signal corresponding to the aircraft identification code and this signal is passed to an output conditioner 18 which operates on the signal to make it suitable for a modulator 19 and then supplies it to the modulator 19. In response to the signal from the output condition 18 the modulator 19 varies the voltage across the diodes 13B and 13C in the antenna matching network 13.

This change in voltage across the diodes 13B and 13C alters the signal reflected by the antenna 12 back to the beacon 6. This works by the beacon 6 transmitting continuously at a first frequency F1, the modulator 19 changes the voltage across the diodes 13B and 13C at a second frequency F2 and this causes the reflected signal to have sidebands at frequencies F1-F2 and F1+F2. The modulator 19 frequency modulates frequency F2 to produce a frequency modulation in the sideband signals so that the aircraft identification code is represented by the variations in the sideband frequencies.

Referring to Figure 3 the beacon 6 is shown, the other beacons 5, 7, 8, 9 are identical. The beacon 6 has two parts, a transmission assembly 20 and a receiving assembly 22.

The transmitting assembly consists of an AM signal generator 23 and a transmission antenna 24 and radiates a continuous interrogation signal at a frequency F1 carrying a repeated AM modulation which the passive transponder 11 is set to detect and respond to.

The receiving assembly consists of a receiving antenna 25 which picks up the reflected signal and passes it to a band-stop filter 26 which rejects a narrow band of frequencies centred on F1, the frequency F2 and its modulation are selected so that the sideband frequencies are always outside the frequency band blocked by the filter 26.

The signals passed by the filter 26 are supplied to a demodulator 27 which extracts the modulation applied to the sidebands and passes this modulation signal to a conditioner 28 which filters and amplifies the modulation signal into a suitable form for the processor 29.

The processor 29 identifies the modulation signal as a data stream identifying an aircraft and transmits the aircraft identification code together with the identifying number of the beacon 6 along a line 30 to the controller.

The modulated sidebands picked up by the beacons 5 to 9 are generated by reflection of the signal emitted by the beacon, as a result the strength of these sidebands drop as the forth power of distance between the aircraft 10 and the beacon. As a result with low transmitted powers the area from which replies are received from transponders 11 can be small and precisely defined.

The beacons 5 to 9 are placed adjacent to junctions, such as beacons 6, 7, 8 on each access route to the junction 4, at entrances and exits of runways, such as beacon 5 and periodically along taxiways, such as beacon 9. Thus although the controller only knows the positions and identities of aircraft when they are adjacent a transponder a record can be kept of the identity of all aircraft and what region of the airfield they are in. In Figure 1 for example the controller will know that aircraft 10 has just cleared junction 4 and is between beacons 5 and 6 on the taxiway 2.

This allows aircraft to be kept safely clear of one another in a similar manner as the block system of operation used on railways.

The aircraft 10 can be instructed in its movement by the controller and tracked, if it moves incorrectly, taking the wrong exit at a junction for example, the controller can inform the pilot of this and take whatever corrective action is needed.

This system can be set up relatively cheaply, only a relatively small number of beacons are required and the passive transponder can be simply bolted on to aircraft.

The transponder is passive and so will not interfere with other electronic systems aboard the aircraft and can be constructed to have minimal power, weight and space requirements. Using off the shelf components a volume of approximately 240 cc would be required with a power requirement of some tens of milliwatts, allowing the transponder to be made entirely self contained running on battery power without any connection to the aircraft's electrical system.

In order to further reduce the power requirements of the transponder 11 its electronics can be normally switched off with only the AM detector 14 powered and the rest of the circuitry switched on, on instruction from the AM detector 14 when a beacon signal is sensed, in this switched off and listening mode the transponder power requirements could be below 100 microwatts.

Another system is shown in Figure 4, in this system the aircraft 10 carries a beacon 31 while a large number of passive transponders 11 are placed adjacent the airports runways and taxiways. The passive transponders 11 are attached to the already existing runway and taxiway lights and the transponders 11 draw their power requirements from the power supply to the lights. This is an insignificant extra load on the lighting power supply.

The beacon 31 on board the aircraft 10 is shown in Figure 5, and is similar to the beacon 6. The beacon 31 comprises a transmission antenna 24 and a continuous interrogation signal generator 23 as before.

When a passive transponder 11 receives this continuous interrogation signal it waits for a preset period of time and then responds. This response delay time is stored permanently in the memory 17 together with an identity code which specifies the position of the transponder, for example taxiway 2, 200 m from junction 4. The processor 16 is programmed not to respond to the interrogation signal if it detects another transponder responding before its own delay time expires. In this case it waits its own delay time again before responding after the detected response has finished. The processor 16 is also programmed not to respond for a preset period after it has responded, this period is many times the period required for response.

This ensures that a beacon is not overwhelmed by simultaneous responses from all of the transponders in its vicinity.

The beacon 31 picks up the transponder responses using a receiving antenna 25, filter 26, demodulator 27 and conditioner 28 are before, and supplies the response signals to a processor 32. The processor 32 stores the responses in a memory 33, which also contains a code identifying the aircraft 10.

After a preset period the processor 32 compares all of the responses received and held in the memory 33 with the positions of all of the transponders 11 at the airport stored in the memory 33 and calculates the position of the aircraft 10. The position of the aircraft 10 can be calculated because the range from which the responses of transponders 11 can be sensed is limited and predictable, so in Figure 4 transponders l1A, llB, llC and llD only will respond to the beacon 31 on the aircraft 10. From this it can be deduced that the aircraft 10 is on the taxiway 2 between the positions represented by dashed lines 34A and 34B. The processor 32 produces a digital signal identifying the aircraft 11 and it's calculated position.This signal passes through a conditioner 35 which transforms it into a suitable format for transmission and then to an amplifier 36 which amplifies it. The digital signal from the processor 32 is simultaneously passed along a line 37 to a display unit (not shown) on the flight deck of the aircraft 11 which displays the current aircraft location.

As the processor 32 produces this digital signal it also instructs a switch 38 to change state, disconnecting the signal generator 23 from the transmission antenna 24 and connecting the amplifier 36 to the transmission antenna 24, this stops the interrogation signal being transmitted and allows the signal from the amplifier 36 to be transmitted from the transmission antenna 24.

The signal transmitted from the antenna 24 gives the identity and position of the aircraft and is received by the controller.

The processor 32 then clears all of the received responses from the memory 33 and changes the switch 38 back to its original state, allowing the interrogation signal.

from the signal generator 23 to be transmitted again, triggering a new set of responses from the transponders 11.

This cycle is repeated continuously while the aircraft is on the ground, A manual inhibit control 39 is provided to switch the beacon 31 off when the aircraft is parked for long periods, such as in a hanger for maintenance or loading or unloading on a ramp and after take-off.

With this system, both the aircraft and the controller know the aircraft position. However this requires the aircraft to carry a radiating beacon.

A further refinement to the system is for the aircraft and any ground service vehicles allowed onto the airfield to also carry transponders 11, although each aircrafts transponder 11 should be programmed not to respond to its own aircrafts beacon 31. This will not help the aircraft to establish its position, but will provide a warning when another aircraft or vehicle is in the vicinity.

Alternatively or additionally, ground vehicles could be fitted with interrogation beacons 31 to inform their drivers of their position.

Additional circuitry can be added to the beacons 31 and transponders 11 to allow interrogation of a specific transponder 11 by a beacon 31 so that the range of specific transponder 11 from the beacon 31 can be precisely calculated. Once the precise ranges to several transponders 11 have been calculated by this procedure the exact position of the aircraft can be calculated by triangulation.

This is particularly useful for collision warning where aircraft carry beacons 31 and transponders 11 or ground vehicles carry transponders 11.

If aircraft each carried several beacons, for example at each wingtip and at the end of the tail and their identity codes identified their position on the aircraft, precise ranging would allow the orientation of aircraft relative to one another to be calculated and the risk of collision estimated taking this into account.

Although the invention has been discussed in terms of aircraft and ground vehicles at an airport, it could be used to find the positions of any vehicle.

The transponder 11 described frequency modulates the reflected signal to transmit data to a beacon, the signal could be modulated in any other known manner, such as amplitude modulation for example.

Claims

1. A ground movement monitor comprising a beacon and a passive transponder, one being mounted on a vehicle and one being fixed, the beacon being arranged to radiate an interrogation signal and the transponder being arranged to reflect this signal and to transmit data to the beacon by altering the characteristics of the reflected signal.

2. A monitor as claimed in claim 1 in which the vehicle is an aircraft.

3. A monitor as claimed in claim 1 or claim 2 in which the vehicle carries the beacon.

4. A monitor as claimed in claim 3 in which a plurality of passive transponders are distributed about an area.

5. A monitor as claimed in claim 4 and claim 2 in which the passive transponders are attached to airport lights.

6. A monitor as claimed in claim 5 in which the passive transponders are supplied with power from the existing power supply to the lights.

7. A monitor as claimed in any of claims 3 to 6 in which the vehicle also carries a passive transponder.

8. A monitor as claimed in claim 1 or claim 2 in which the beacon is fixed and the vehicle carries a passive transponder.

9. A monitor as claimed in claim 8 in which a plurality of beacons are distributed about an area.

10. A monitor as claimed in claim 9 where the area is an airport and the beacons are situated adjacent runways and taxiways.

11. A monitor as claimed in any preceding claim in which each beacon is equipped to transmit data to a remote location.

12. An aircraft ground movement monitor substantially as shown in or as described in with reference to Figures 2, 4 and 5 of the accompanied drawings.

12. A ground movement monitor substantially as shown in or as described with reference to Figures 1 to 3 of the accompanying drawings.

13. A ground movement monitor substantially as shown in or as described in with reference to Figures 2, 4 and 5 of the accompanied drawings.

Amendments to the claims have been filed as follows

1. An aircraft ground movement monitor comprising a beacon and a passive transponder, one being mounted on an aircraft and one being fixed, the beacon being arranged to radiate an interrogation signal and the transponder being arranged to reflect this signal and to transmit data to the beacon by altering the characteristics of the reflected signal.

2. A monitor as claimed in claim 1 in which the aircraft carries the beacon.

3. A monitor as claimed in claim 2 in which a plurality of passive transponders are distributed about an area.

4. A monitor as claimed in claim 3 in which the passive transponders are attached to airport lights.

5. A monitor as claimed in claim 4 in which the passive transponders are supplied with power from the existing power supply to the lights.

6. A monitor as claimed in any of claims 2 to 5 in which the aircraft also carries a passive transponder.

7. A monitor as claimed in claim 1 in which the beacon is fixed and the aircraft carries a passive transponder.

8. A monitor as claimed in claim 7 in which a plurality of beacons are distributed about an area.

9. A monitor as claimed in claim 8 where the area is an airport and the beacons are situated adjacent runways and taxiways.

10. A monitor as claimed in any preceding claim in which each beacon is equipped to transmit data to a remote location.

11. An aircraft ground movement monitor substantially as shown in or as described with reference to Figures 1 to 3 of the accompanying drawings.