GB2589867A

GB2589867A - An Aeronautical electronically steered antenna system

Info

Publication number: GB2589867A
Application number: GB1918034.8A
Authority: GB
Inventors: James Akwei Baddoo Geoffrey; Dent Gary
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2021-06-16
Anticipated expiration: 2039-12-09
Also published as: GB2589867B; GB201918034D0

Abstract

This application relates to an electronically steered antenna for an aircraft, e.g. for communication with a satellite. The antenna system comprises an array of antenna elements; an antenna controller configured to steer the antenna; and a transceiver connected to the antenna for receiving signals from or providing transmission signals to the antenna. When the antenna changes beam direction from a first beam direction to a second beam direction there is an associated phase jump. The invention lies in communicating this phase jump from the controller to the transceiver so that the transceiver can maintain a phase lock with a received (or transmitted) signal during a change in beam direction. The antenna controller may instruct the transceiver with the extent of the phase jump and the time of the beam switch, to allow the transceiver to apply the phase jump at the specified time. If multiple antennas are distributed across an aircraft, phase jump information may be provided for each antenna to allow switching between the antennas.

Description

An Aeronautical Electronically Steered Antenna System

Technical Field

This invention relates to an electronically steered antenna for an aircraft. In particular, though not exclusively, the invention relates to a low gain electronically steered antenna.

Background and Related Art

In order to have sufficient gain and reduce the generation or reception of spatial interference, antennas on aircraft for satellite communications are normally steered electronically. Electronically steered antennas have a number of advantages over mechanically steered antennas, such as higher reliability and a lower profile. Electronically steered antennas are well known in the art.

As an antenna is electronically steered, phase jumps are experienced when beam switching occurs between the elements (or patches) of the antenna. As the gain of the antenna decreases, the phase jumps can be become larger since the antenna typically has fewer elements and a simpler element selection or combination method. One way to combat the large phase jumps in low gain antennas is to apply hysteresis to switching decisions. However, although this reduces the frequency of the problem, it does not actually solve it and loss of synchronisation can still occur. Furthermore, the larger the amount of hysteresis, the less optimum the antenna pointing.

Typically, a demodulator, e.g. a modem, may be specified to handle phase jumps up to a certain level. However, low gain switched antennas typically exhibit larger phase jumps than can be accommodated by a conventional modem, which can result in the modem losing signal lock, ultimately reducing link availability.

US5559806 describes an earth station transceiver provided for communicating with at least one satellite in orbit. The earth station transceiver has an antenna with an array of antenna elements and steering circuitry for steering an antenna pattern created by the array of antenna elements. US5559806 describes a phase discontinuity compensation scheme based on having a non-coherent detector alongside the coherent detector in the demodulator. Over a phase discontinuity period, the non-coherent detector is used until the coherent detector catches up.

U36628235 describes a method for handing-off phased array antenna signals in which a phased array multiple antenna system receives and demodulates signals using one receiver. The phased array antennas are controlled electronically by an antenna controller with an antenna switch matrix to select between signals from a handing-off antenna and a handed-to antenna. A phase comparator compares the two signals and produces a phase error signal proportional to the difference between the phase angles of the two signals. A negligible phase error difference is predetermined wherein antenna handoff can occur without causing loss of phase lock on the handed-to antenna signal. When the antenna controller signals a hand-off and the phase error equals the negligible phase error difference, a fast switch performs the hand-off. However, this requires a reliable and timely output from the phase comparator which is challenging in an aeronautical satellite communication system which often has to operate at low signal levels with high noise and high levels of multipath.

The present invention seeks to provide an improved aircraft communication system and method of communicating with an aircraft electronically steered antenna.

Summary

The present invention provides an antenna system for an aircraft and a method of operating the same according to the appended claims.

Disclosed herein is an antenna system for an aircraft comprising: an antenna comprising an array of antenna elements; an antenna controller configured to steer the antenna; a transceiver connected to the antenna for receiving signals from or providing transmission signals to the antenna, wherein the antenna controller is configured to provide a predetermined phase jump (associated with a change in beam direction from a first beam direction to a second beam direction) to the transceiver so that the transceiver compensates for the change in beam direction arising from antenna steering the first beam direction to the second beam direction. The transceiver may receive the phase jump from the controller, prior to or at the same time as the change in beam direction.

The change in direction between a first beam direction and a second beam direction may represent a phase jump. The first beam direction may be an existing or current beam direction, and second beam direction may be a required beam direction.

The antenna system may further comprise at least one input for receiving information from one or more aircraft systems, wherein the antenna controller obtains information relating to the position and attitude of the aircraft relative to a transceiving entity from the aircraft systems via the at least one input.

The antenna may be a low gain antenna.

The antenna system may further comprise at least one memory, wherein the at least one memory includes a model of the antenna for determining a required phase jump The memory may be located within the antenna or the antenna controller.

The antenna system may further comprise a plurality of antennas. The plurality of antennas may be connectable to a common transceiver via a switch. The plurality of antennas may be distributed about the aircraft The transceiving entity may comprise a satellite.

Also disclosed herein is a method of controlling an electronically steered antenna in an aircraft, comprising: obtaining information relating to the position and attitude of the aircraft relative to a transceiving entity; determining a required beam direction for the antenna using the information relating to the location and attitude of the aircraft relative to the transceiving entity; and, providing the required phase jump (associated with steering the beam) to a transceiver so that the transceiver can maintain a phase lock with a received signal during a transition to the required beam direction.

A controller may determine a required change in the direction of the beam. The change in direction may result in a phase jump. Determining the phase jump for a change in beam direction may comprise obtaining a model for the antenna. The model may be a phase model. The model may be used by the controller to determine the phase jump required for the change in direction.

The phase model may be determined analytically for the antenna.

The phase model may be determined prior to installation of the antenna.

The method may further comprise determining the phase model for an antenna and providing the controller with the phase model.

The antenna may comprise at least one memory, and the phase model may be stored within the memory of the antenna.

Determining the phase jump may comprise obtaining a geometric arrangement of the antenna elements.

The geometric arrangement may be the installed geometric arrangement.

The antenna may comprise a plurality of sub-antennas. The sub-antennas may be distributed about the aircraft.

The method may further comprise executing the transition to the required beam direction in the antenna.

The required beam direction may be determined in accordance with a predetermined manoeuvre of the aircraft.

Obtaining information relating to the position of the aircraft relative to a transceiving entity may comprise determining a location of the aircraft; an attitude of the aircraft and a position of the transceiving entity.

The transceiving entity may be a satellite.

The geometrical arrangement of the antenna may specify the position and orientation of the different antenna elements relative to one another.

The method may further comprise the controller requesting phase information from the antenna.

The number of antenna may be between 2 and 5.

The phase jump between an existing beam direction and a required beam direction may be greater than 20 degrees.

The antenna may be a low gain antenna.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the aspects, examples or embodiments described herein may be applied to any other aspect, example, embodiment or feature. Further, the description of any aspect, example or feature may form part of or the entirety of an embodiment of the invention as defined by the claims. Any of the examples described herein may be an example which embodies the invention defined by the claims and thus an embodiment of the invention.

The invention allows lower gain antennas to be employed without the risk of large phase jumps on beaming switching causing a loss of synchronisation on receive signals or a significant degradation to transmit signals. Thus, it may increase the link availability where low gain switched antennas are deployed. Further, the invention may give more freedom in the design of antennas since the antenna no longer needs to minimise phase discontinuities.

The invention may also allow switching between multiple antennas without loss of phase synchronisation on receive or the introduction of phase shifts on transmit. This can reduce the number of receiver modules where multiple antennas are deployed.

Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic overview of an aircraft communication system which incorporates an electronically steered antenna; Figure 2 shows a flow diagram of a communication method according to an embodiment of the present disclosure; Figure 3 shows a schematic representation of a communication system according to an

embodiment of the present disclosure;

Figure 4 shows yet a further schematic representation of a communication system; Figure 5 shows a schematic representation of an alternative communication system having a plurality of antennas; Figure 6 shows a flow diagram of a communication method which may be implemented by the system shown in Figure 5; and, Figure 7 shows a schematic representation of an alternative communication system.

Detailed Description

The present invention provides an improved communication system and method of communicating between an aircraft and a transceiving entity. The communication system includes at least one antenna comprising an array of antenna elements (which may be referred to as patches) and a controller for controlling the antenna, or more particularly, for steering the antenna. That is, the controller may be configured to control the respective relative phases of the antenna elements so as to control the direction of the beam emitted from the antenna, or configure the antenna to receive a beam from a particular direction.

References are made throughout this disclosure relating electronically steered antennas. It will be appreciated the that the electronically steered antennas may be configured to operate as a phased array antenna.

The antenna may be a low gain antenna. By low gain it will be understood to mean approximately less than 5 dBi.

It will be appreciated that the communication methods and systems disclosed herein may be advantageously used with higher gain antennas (e.g. high or intermediate gain antennas) and the disclosure is not limited to applications in low gain antennas.

The antenna may be located on an aircraft and may form part of a larger communication system. The communication system may be a satellite communication system comprising one or more aircraft antennas and one or more satellites. The satellites may, in turn, communicate with one or more ground stations as is well known in the art. For the purposes of the disclosure, the satellite and/or ground station may be considered to be the transceiving entity within a satellite communication system.

Although the disclosure is centred on a satellite communication system, it will be appreciated that other transceiving entities may form part of the communication system in addition or an alternative to one or more satellite. For example, the one or more aircraft antennas may transmit and/or receive signals to and from another aircraft and/or a ground station directly.

The method and communication systems described here are considered to be used generally for two way communication and as such involve a transmitter and receiver.

The transceiving entity should be taken to mean a receiving entity and/or a transmitting entity with which the antenna transmits to or receives from. The transceiving entity may be configured to transmit and receive, but this may not be the case in some instances with the operation being limited to one or the other of a receiver or transmitter. The transceiving entity may comprise a plurality of transceivers which may be collocated or geographically distributed.

Figure 1 shows a communication system which may include the communication system of the disclosure and provide infrastructure for carrying out the method of communication of the disclosure. The communication system 10 may include an aircraft 12, one or more satellites 14, one or more by ground stations 16 and one or more clients 18, 20. The ground stations 16 may receive or transmit communications to the satellite 14 or may receive or transmit communications directly to the aircraft 12. The ground stations 16 may be connected by any suitable network 22 such as a global, wide area or local area network. The network may comprise the Internet or an intranet, for example. The ground stations 16 may also be in connected to the one or more client 18 for which the communications are received or sent. The connection between a client 18 and the transceiving entities, e.g. one of the ground stations, may be achieved by any suitable means, such as a global, wide area or local area network. One or more clients 20 may be provided within or as a part of one of the ground stations 16.

In addition to communicating with one or more ground based clients 18, the system described herein may also be applicable to air-to-air communications in which an originating or primary aircraft 12 communicates with a receiving or second aircraft 26.

The communication with the second aircraft 26 may be direct air-to-air communication, or may be via one or more of the communication networks such as the satellite 14 or one or more of the ground stations 16 according to the methods described herein. The second aircraft 26 may also include the necessary antennas and controller(s) to embody a method described herein.

It will be appreciated that the aircraft 12, 26 may be civil, commercial or military aircraft and may take the form of unmanned aerial vehicles, aeroplanes, helicopters or any other form of aircraft which may benefit from the improved communication system and method described herein. The one or more satellites 14 and ground stations 16 may be distributed across an area. The ground stations, for example, may be located in different jurisdictions or marine based. The types of ground stations 16 which form part of the communication networks are well known in the art and not discussed in detail here.

The aircraft may include one or more transceiving antenna 28, 29. The one or more transceiving antenna 28, 29 are typically electronically steered antenna having a plurality of antenna elements. The number of the antenna may depend on the number of separate communications which are required and/or the coverage which is required, as described in more detail below. Other factors may affect how many antennas an aircraft may include. In one example, the number of antennas may be between 2 and 5.

As is known from existing communication systems, as an aircraft moves relative to the receiving or transmitting entity, a satellite 14 for example, the antenna 28, 29 needs to be controlled so as to change the beam direction of the electronically steered antenna to track the transceiving entity 14 so as to maintain the communication link therebetween. Changes in direction may be required due to the constantly changing relative location of the transmitting and receiving entities due to the relative velocities.

Changes may also occur in the attitude of the aircraft 12 relative to the receiving or transmitting entity. Thus, if the aircraft 12 banks, the spatial relationship between the aircraft antennas 28, 29 and the transceiving entity 14, 16 will be altered and the antenna 28, 29 must be electronically steered to track the transceiving entity 14, 16 to ensure a link can be maintained and the communications continuous. As an antenna 28, 29 is electronically steered, phase jumps are experienced when beam switching occurs between the elements (or patches) of the antenna 28, 29.

The present disclosure relates to the provision of obtaining phase jump information for a particular antenna 28, 29 and using this information to predict when a phase jump will be required. Thus, the compensation of the phase jump may be made on a predictive basis rather than using feedback from the antenna or communications received or transmitted therefrom. That is, the amount and timing of a phase jump may be predetermined in advance of the phase jump or a degradation of the link between the transceiving entities.

The phase jump information may include information about the antenna design and operating characteristics. For example, the antenna may comprise a specific geometric arrangement (or model) of antenna elements and/or phase pattern and/or a characteristic model. These models may be used to determine the amount of the phase jump when the antenna is in a particular orientation or position relative to the transceiving entity.

The communication system may be configured to determine the phase jump using real time data taken from the aircraft systems. The real time data may include one or more of the aircraft location, the aircraft velocity and/or trajectory, the aircraft attitude, the intended path of travel of the aircraft, the transceiver location, the location of the antenna on the aircraft (including the location of the antenna elements), the antenna type and/or one or models of the antenna.

Alternatively or additionally, the communication system may include at least one memory which is configured to store information relating to the aircraft systems. The storage of the information may be located in non-volatile memory. The information relating to the aircraft systems may be stored prior to use of the communication systems. For example, one of more antenna model may be stored in the memory of the communication system during installation, commissioning, initialisation and/or starting the system for use. Thus, the one or more model may not be real-time data. The models may be updated when required.

The geometric model may be provided by the antenna manufacturer and provide the relative positions of the antenna elements, such as the spacing between the phase centres of the elements. The geometric model may be used to analytically determine a phase model for the antenna.

The phase model may be referred to as a phase map and provide information relating to the phase pattern for the antenna and the associated antenna patches. Hence, the phase model may also be referred to as a phase pattern. The phase model may comprise a three dimensional model of the phase pattern, as known in the art. As noted above, the phase model may be determined analytically, or may be determined empirically. The phase model may be provided by the antenna manufacturer. In some instances, the phase model may be combined with gain information to provide a characteristic model.

The characteristic model may comprise a phase model and a gain model, which may also be referred to as a gain and phase pattern. The gain and phase pattern may be provided by a manufacturer or determined empirically or analytically. The empirical determination may be performed prior to the installation of the antenna, for example, using methods known in the art.

In addition to obtaining the characteristics of the antenna 28, 29, the methods disclosed herein may comprise obtaining information about the location and orientation of the antenna 28, 29 relative to the aircraft fuselage. Thus, when mounted on an aircraft 12 at a particular position and orientation, the system can determine, or obtain, the relative position and orientation of the antenna 28, 29 during an in-flight manoeuvre and use this in conjunction with the RF frequency to determine a predicted phase jump.

The phase jump information may be obtained and/or determined by a controller 30. The controller 30 may be provided by an antenna controller or any other suitable entity within the communication system or aircraft 12. Thus, the phase jump information may be determined by a controller 30 which is remote to the antenna controller and passed to the antenna controller when required. The controller 30 which determines the phase jump information may form part of the antenna 28, 29, for example, or another onboard system of the aircraft 12. As such, the controller may be distributed between different computing devices.

The phase jump information may be stored in the antenna 28, 29 and/or the controller 30 and/or a computer memory provided elsewhere in the communication system or aircraft 12. The phase jump information may be transmitted between the antenna 28, 29 and the controller via one or more intervening entities. The phase jump information may be passed from the antenna 28, 29 to the controller 30 (or some other storage device in the communication system) after installation and prior to a use of the antenna. Thus, the phase jump information may be determined and stored in one or more memory storage devices of the antenna 28, 29 at the time of manufacture or as a result of determining the geometric model or characteristic model of the antenna prior to installation on the aircraft 12. Once the antenna 28, 29 is installed, the controller 30 may obtain the phase jump information from the antenna 28, 29. The obtaining of the phase jump information may be carried out as part of an installation procedure, such as an initialisation procedure or may be requested during operation of the communication system.

Thus, the present disclosure may provide a method of configuring an antenna for an aircraft by storing an antenna model in a memory of the antenna. The antenna model may be one or more of a geometric model and a characteristic model of the antenna. The antenna model may be for use in a communication system of an aircraft. The antenna model may be used by a controller which controls the phases of antenna cells in the antenna. The antenna model may be passed to the controller from the memory storage of the antenna after installation of the antenna on the aircraft. The controller may form part of a transmitter or a receiver.

The aircraft 12 may include a plurality of antennas 28, 29, each having a plurality of elements to provide an electronically steered antenna. The separate antennas 28, 29 may be distributed around the aircraft 12 at suitable locations. For example, as shown in Figure 1, there may be an antenna 28, 29 on either side of the fuselage (e.g. on opposing sides of a central vertical plane of the aircraft fuselage) such that at least one of the antennas faces sufficiently skywards (or towards the ground as the case may be) during a banking manoeuvre.

Figure 2 shows a flow diagram of a method 200 of controlling an electronically steered antenna in an aircraft, according to the present disclosure. The method 200 may comprise: obtaining information relating to the position (e.g. location and/or attitude) of an aircraft relative to a transceiving entity 202; determining a required beam direction and a corresponding phase jump for the antenna using the information relating to the position of the aircraft relative to the transceiving entity 204 as the antenna switching occurs; and, providing the phase jump to a transceiver prior to, immediately after or simultaneously with (i.e. at approximately the same time) a phase jump so that the transceiver can maintain a phase lock with a received signal during the phase jump 206.

Figure 3 shows a communication system 300 according to an embodiment of the present disclosure. The communication system 300 is for an aircraft and may comprise: an antenna 328 comprising an array of antenna elements 330a-c; a controller 330 configured to control the respective phase of the antenna elements; a transceiver 310 connected to the antenna 328 for receiving received signals from and/or providing transmission signals to the antenna 328, wherein the antenna controller 330 is configured to provide a predetermined phase jump to the transceiver prior to or at the same time as the phase jump. In addition to this, the phase jump may be provided to the transceiver immediately after the phase jump but at a timing which is sufficient for the transceiver to adjust for the phase jump. For the purpose of the present disclosure, it can be assumed that prior to and simultaneously can be taken to include all changes which are provided within an appropriate window for the transceiver to correct for the phase jump and may include the transceiver receiving the corrections immediately after the phase jump.

The communication system 300 may also include one or more aircraft systems 302 which may be configured to provide information relevant to the determination of the phase jump. The aircraft systems 302 may be connected to the antenna controller 330 and the transceiver 310 to provide data required for the communication system to operate. Thus, the aircraft systems 302 may pass or receive communication data to or from the transceiver, e.g. data for transmitting over the communication network or data which has been received. Additionally or alternatively, the aircraft systems may provide information or data relating to the aircraft flight situation, such as positional data including location and attitude, to the antenna controller 330.

The aircraft systems 302 may include on-board or other communications systems which can provide one or more of the aircraft position, the aircraft attitude, and the transceiving entity position. The systems which can provide this information are well known in the art and, with the exception of the satellite position, may be required for flight and navigation purposes. Thus, for the purpose of the disclosure, the aircraft systems 302 may include, for example, on-board flight or navigation computers, for example. The satellite position may be provided from a signal received from the satellite or satellite network. The satellite position may be provided as part of a global positioning system, for example, which may form part of the aircraft systems 302 for navigation or other purposes. The satellite position may be provided as part of the satellite communication system.

The aircraft systems 302 may also be considered to include one or more clients (not shown) which provide or receive the communications which are transmitted. The clients may nominally form part of one or more aircraft systems 302 and provide data, requests or other information necessary for flight or navigation purposes to a receiving entity. Alternatively, or additionally, the clients may include one or more passengers which provide personal communications or other data. The network connection between the client(s) and transceiver may use any known method in the prior art and include, for example, one or more aircraft local area networks which communicate using conventional protocols such as Ethernet.

The antenna controller 330 may be conventional in many respects and may be configured to control the antenna to allow directional transmission and reception of signals via the electronically steered antenna elements. Thus, the antenna controller 330 may include hardware or software to allow the antenna 328 to be reconfigured during use such that electronically steered signals between the antenna elements 330a-c is achieved. The antenna controller 330 may comprise one or more processors 330p and a memory 330m for storing instructions to be executed by the one or more processors 330p. The execution of the instructions may cause the one or more of the method steps of the present disclosure to be carried out. For example, the processor may be configured to receive the phase jump information from the antenna 328 (or some other source) and cause the phase jump information to be stored in the memory for future use. The processor 330p may be further configured to recall the phase jump information and use it to determine the phase jump required in any particular instance.

Determining the phase jump may be done using conventional methods. Thus, in the case of a switched antenna, switching from patch A to patch B, the geometrical arrangement of the phase centres of each patch will be separated by a distance D in the direction of the transceiving entity. If the delays between the patches and the feed into the transceiver are equal (which can be configured accordingly or compensated for through calibration and calculation) the remaining phase differences are determined by D. The phase difference on switching between the patches will be zero if D is an integral number of wavelengths of the RF frequency of interest. In general, the phase difference in degrees will be 3600 multiplied by the fraction of the wavelength above the integer wavelengths.

Once the phase jump has been calculated and passed to the modem in the transceiver, the modem can apply it by, for example, making an oscillator in the receive (or transmit) chain jump by the specified phase jump, so as to remain synchronised. A convenient method for doing this is to adjust a numerically controlled oscillator in the digital domain.

In some embodiments, it may be possible to switch between a plurality of antennas. Thus, the communication system may include one or more switches for switching the RE line from the transceiver to one or more of the plurality of antennas. The switching of the antennas may be controlled by the antenna controller 330. Figure 5 shows an example of an arrangement having a plurality of antennas and an associated switching arrangement, which will be described in more detail below. It will be appreciated that in some embodiments, an aircraft may include a plurality of antennas each with dedicated transceiver circuitry and antenna controllers.

In some embodiments, the antenna controller 330 may incorporate one or more field programmable gate array, FPGA, which can be configured to carry out one or more steps of the methods disclosed herein.

The antenna controller 330 may be connected to the transceiver 310 to provide the determined phase jump to the transceiver such that the signal processing can be matched to the signals received from the antenna. The antenna controller 330 may be connected to the antenna 328 to provide the beam forming control signals to the one or more antenna 328.

The transceiver 310 may include one or more of modulator, a demodulator, a modem, a diplexer to allow transmission and reception, and other additional or alternative RF signal processing circuits which may be required or desirable for the signal processing of signals for transmission and reception by the electronically steered antenna 328 as known in the art.

The antenna controller 330 may instruct the transceiver 310 with the extent of the phase jump and time of the switch. The transceiver 310 may apply the determined phase jump at the specified time, which allows it to seamlessly track the signal and correct the transmissions. It is to be noted that the phase jump timing implemented in the transceiver 310 does not have to be exactly synchronised with the timing of the antenna switch since the receive tracking loops on the transceiving entity may accommodate an amount of offset. The offset may result in phase discontinuities for a short period and the maximum amount of tolerable offset will be determined by the characteristics of the relevant tracking loops. In addition to maintaining lock, it may also be desirable to have a short enough offset that the channel interleaving and forward error correction handles the burst of errors during the offset period. A typical offset period might be 10 ms, for example.

The antenna may be any suitable conventional antenna as known in the art and will not be described further here.

Figure 4 shows an embodiment of the present disclosure in which there is a communication system 400 comprising: an antenna controller 430; a transceiver which may include: a modem 410a, a diplexer and RF circuits 410b; and, an antenna 428. The antenna controller 430 is in communication with the modem 410a so as to provide the phase jump 432 information to the modem 410a. The antenna controller 430 is also in communication with the antenna 428 so as to provide the beam control/beam steering control signals 434. The antenna controller 430 receives information from the aircraft systems (or elsewhere) relating to the satellite position 402a, the aircraft location 402b, the aircraft attitude 402c and the installed antenna model 402d. The installed antenna model 402d may include geometric or phase and gain information, as described above. Generally, the components included in the embodiment of Figure 4 may include some or all of the features of the corresponding components described above and the description of these will not be repeated here.

As described above with reference to Figure 1, the communication system 10 of the present disclosure may include a plurality of antennas 28, 29. The antennas 28, 29 may be distributed about the aircraft 12 to increase the spatial coverage provided by the communication system 10. Thus, a first antenna 28 may be provided at a first location of the aircraft 12 and a second antenna 29 may be provided at a second location of the aircraft 12. The first and second locations may be provided on opposing sides of the fuselage (e.g. symmetrically positioned on either side of a principal central plane which extends vertically along the central axis of the fuselage). The plurality of antennas 28, 29 may be selected in accordance with the actual or expected attitude of the aircraft 12 and the required beam direction with respect to the transceiving entity.

Thus, a first antenna 28 may be locked to the transceiving entity, e.g. satellite 14, during a first phase of flight and the antenna controller 30 may switch to the second antenna 29 during the transition to a second phase of flight. For example, the aircraft 12 may have a first trajectory during the first phase of flight and be required to navigate to a new heading which represents the second phase of flight. To transition between the two phases, the aircraft 12 may be required to bank which may obscure the line of sight between the first antenna 28 and the transceiving entity 30 thereby reducing the quality of the transmitted signal. In this instance, the antenna controller 30 may switch to the second antenna 29 which may have a direct line of sight.

The transition between the first and second antenna 28, 29 may be carried out in real time in which the attitude of the aircraft 12 is continually monitored and the relative positions of the respective antennas calculated to determine whether a switch from an existing locked antenna needs to be transitioned to another one of the plurality of antennas. Alternatively, or additionally, the antenna controller 30 may be provided with a route and planned manoeuvres to enable the antenna controller 30 to determine when a change of antenna may be beneficial along the course. Thus, the antenna controller 30, may determine a plurality of waypoints or other markers at which to transition between the antennas.

As noted above, the first and second antenna 28, 29 may be connected to the same transceiver. Thus, there may be a plurality of antennas and a single transceiver connected to the plurality of antennas to receive therefrom and transmit signals thereto. In some embodiments of the present disclosure, there may be M antennas and N transceivers, wherein M and N are integers and M is greater than N. Hence, there may be a plurality of transceivers, but at least two of the antennas are connected to the same transceiver.

Providing the phase jump information for the plurality of antennas allows switching between multiple antennas without loss of phase synchronisation on receive or the introduction of phase shifts on transmit. Thus, the number of transceivers as described above can be reduced where multiple antennas are deployed. That is, in prior art systems, multiple receiver modules are deployed with multiple antennas to allow concurrent reception through different antennas which in turn facilitates a smooth switch over from one to another. If the phase jumps are predetermined and the transceiver synchronised with the change of the antennas, there is no need to provide multiple transceivers.

In accordance with the above, Figure 5 shows a further embodiment of the present disclosure in which there is an aircraft communication system 500 comprising a plurality of antennas 528, 529. The antennas are connected to a common transceiver via an RF switch 511 which may be configured to connect each of the antennas to the transceiver under control of an antenna controller 530. Thus, the antenna controller 530 may issue an antenna selection signal 536 in accordance with the relative positions of the antennas and the required beam direction.

The communication system of Figure 5 may also comprise: an antenna controller 530; a transceiver which may include: a modem 510a, a diplexer and RF circuits 510b; and, an antenna 528. The antenna controller 530 is in communication with the modem 510a so as to provide the phase jump information 532 to the modem 510a. The antenna controller 530 is also in communication with each of the antennas 528, 529 so as to provide the beam control/beam steering control signals 534. The antenna controller 530 receives information from the aircraft systems (or elsewhere) relating to the satellite position 502a, the aircraft location 502b, the aircraft attitude 502c and the installed antenna model 502d. The installed antenna model 502d may include geometric or phase and gain information, as described above. Generally, the components included in the embodiment of Figure 5 may include some or all of the features of the corresponding components described above and the description of these will not be repeated here.

It will be appreciated that multiple transceivers may be provided in the arrangement of Figure 5. Further, each of the antennas 528, 529, may receive beam control signals from different antenna controllers 530 Figure 6 provides depiction of a method of operating a communication system having a plurality of antennas. The communication system could be that shown in Figure 5, for example. Thus, there is shown a flow diagram of a method 600 of controlling an electronically steered antenna in an aircraft which may comprise: obtaining information relating to the position (e.g. location and/or attitude) of an aircraft relative to a transceiving entity 602; determining the direction of the beam required to point at the transceiving entity such that the antenna controller can steer a given antenna or select a different antenna to point the beam at the transceiving entity 604; determining whether the current antenna is a preferred antenna for the beam direction 605. Where the locked antenna is the preferred antenna, the antenna controller may provide phase jump information to the transceiver (or modem within the transceiver) prior to the phase jump occurring so that the modem can correct for the phase jump and maintain a phase lock with a received signal during the phase jump 606. If the currently locked antenna is not preferred for the required direction then the antenna controller may determine whether another of the available aircraft antennas may provide the necessary beam direction 608. When the antenna of choice has been selected, the antenna controller may issue the control signal to adjust the electronic steering of the antenna and provide the phase jump information to the transceiver 609. In another example, the method may comprise determining a required direction and assessing whether the direction is achievable with the current antenna 605. Where the required direction is determined to be achievable with the currently locked antenna, the antenna controller can provide phase jump information to the transceiver (or modem within the transceiver) prior to the phase jump occurring so that the modem can correct for the phase jump and maintain a phase lock with a received signal during the phase jump 606. If the currently locked antenna cannot achieve a suitable lock for the required direction then the antenna controller may determine whether another of the available aircraft antennas may provide the necessary beam direction 608. When the antenna of choice has been selected, the antenna controller may issue the control signal to the switching array; provide the phase jump to the transceiver, and adjust the beam direction of the antenna.

The selection of the antenna may be based on real time data as described immediately above, or on predicted performance of the antenna within an approaching time frame. The time frame may be a phase of a flight plan for example. In some embodiments, the antenna controller may determine that one of the antennas is preferable in the short term, but a further antenna may be preferable in the long term. This assessment may be based on an intended flight path for example. In such a case, the antenna controller may select the antenna with the long term stability, rather than choosing a second antenna and having to switch again, for example, after a manoeuvre has been carried out.

Figure 7 shows an embodiment of a communication system 700 in which the phase information is provided by the antenna, rather than being stored within a memory of the aircraft or of the antenna controller or the like. Thus, Figure 7 shows a communication system comprising: an antenna controller 730; a transceiver which may include: a modem 710a, a diplexer and RF circuits 710b; and, an antenna 728. The antenna controller 730 is in communication with the modem 710a so as to provide the phase jump 732. The antenna controller 730 is also in communication with each of the antennas 728 so as to provide the beam control/beam steering control signals 734. The antenna controller 730 receives information from the aircraft systems (or elsewhere) relating to the satellite position 702a, the aircraft location 702b and the aircraft attitude 702c. The phase information 702d for the antenna may be stored in and provided by the antenna to the controller upon start-up of the system or on request from the controller. The phase information may include installed antenna geometric or phase and gain information, as described above. Generally, the components included in the embodiment of Figure 7 may include some or all of the features of the corresponding components described above and the description of these will not be repeated here.

It will be appreciated that the embodiments described above may be combined where possible. Thus, for example, the embodiment of Figure 7 may include a plurality of antenna, as shown in Figure 5, or the modem and diplexer and RF circuits of Figures 4 to 7 may be replaced by an alternative form of transceiver/transmitter/receiver.

It will be understood that the invention is not limited to the examples and embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

CLAIMS: 1. An antenna system for an aircraft comprising: an antenna comprising an array of antenna elements; an antenna controller configured to steer the antenna; a transceiver connected to the antenna for receiving signals from or providing transmission signals to the antenna, wherein the antenna controller is configured to provide a predetermined phase jump to the transceiver prior or simultaneously to the phase jump occurring in the transceiver so that the transceiver compensates for the phase jumps arising from antenna steering.
2. An antenna system as claimed in claim 1, further comprising at least one input for receiving information from one or more aircraft systems, wherein the antenna controller obtains information relating to the position and attitude of the aircraft relative to a transceiving entity from the aircraft systems via the at least one input.
3. An antenna system as claimed in either of claims 1 or 2, wherein the antenna is a low gain antenna.
4. An antenna system as clamed in any preceding claim, further comprising at least one memory, wherein the at least one memory includes a model of the antenna for determining a required phase jump.
An antenna system as claimed in claim 4, wherein the memory is located within the antenna or the antenna controller.
6 An antenna system as claimed in any preceding claim, further comprising a plurality of antennas.
7 An antenna system as claimed in claim 6, wherein the plurality of antennas are connectable to a common transceiver via a switch.
8 An antenna system as claimed in either of claims 6 and 7, wherein the plurality of antennas are distributed about the aircraft.
9 An antenna system as claimed in any of claims 6 and 8, wherein the number of of antennas is between 2 and 5.
10. An antenna system as claimed in any preceding claim, wherein the transceiving entity comprises a satellite.
11. A method of controlling an electronically steered antenna in an aircraft, comprising: obtaining information relating to the position and attitude of the aircraft relative to a transceiving entity; determining a required phase jump for the antenna using the information relating to the location and attitude of the aircraft relative to the transceiving entity; and, providing the phase jump to a transceiver prior to or simultaneously with a phase jump so that the transceiver can maintain a phase lock with a received signal during the phase jump.
12.A method as claimed in claim 11, wherein determining the phase jump comprises obtaining a phase model for the antenna.
13. A method as claimed in claim 12, wherein the phase model is determined analytically for the antenna.
14. A method as claimed in claim 13, wherein the phase model is determined prior to installation of the antenna.
15. A method as claimed in any of claims 12 to 14, further comprising determining the phase model for an antenna and providing a controller with the phase model, wherein the controller is configured to steer the antenna.
16. A method as claimed in any of claims 12 to 14, wherein the antenna comprises at least one memory, and the phase model is stored within the memory of the antenna.
17.A method as claimed in claim 11, wherein determining the phase jump comprises obtaining a geometric arrangement of the antenna elements.
18.A method as claimed in claim 17, wherein the geometric arrangement is the installed geometric arrangement.
19. A method as claimed in any preceding claim, further comprising executing the phase jump in the antenna.
20. A method as claimed in any preceding claim, wherein the phase jump is determined in accordance with a predetermined manoeuvre of the aircraft.
21. A method according to any preceding claim, wherein obtaining information relating to the position of the aircraft relative to a transceiving entity comprises determining a location of the aircraft; an attitude of the aircraft and a position of the transceiving entity.
22. A method according to any preceding claim, wherein the transceiving entity is a satellite.
23. A method according to any preceding claim, wherein the geometrical arrangement of the antenna specifies the position and orientation of the different antenna elements relative to one another.
24 A method according to any preceding claim further comprising the controller requesting phase information from the antenna.A method according to any preceding claim wherein the phase jump is greater than 20 degrees.