WO2018041832A1

WO2018041832A1 - Satellite equipment

Info

Publication number: WO2018041832A1
Application number: PCT/EP2017/071665
Authority: WO
Inventors: Simon Watts; Graham Peters
Original assignee: Avanti Communications Group Plc
Priority date: 2016-08-30
Filing date: 2017-08-29
Publication date: 2018-03-08
Also published as: GB2553302A; GB201614653D0

Abstract

Subscriber equipment for use in a satellite system comprises a reflector surface arranged to reflect signals received from a satellite; receiving apparatus arranged for receiving the reflected signals at an antenna feed of the receiving apparatus; a drive mechanism coupled to at least part of the receiving apparatus for moving it relative to the reflector surface; a signal strength detector configured to determine a signal strength indicator for the signals received at the antenna feed; and an antenna controller configured to generate based on the signal strength indicator control signals at a control input of the drive mechanism, thereby moving at least part of the receiving apparatus relative to the reflector surface such that the signal strength of the signals received at the antenna feed increases.

Description

Satellite Equipment

Technical Field

The present invention relates to subscriber equipment for use in a satellite system. Background In the context of a satellite system architecture, subscriber equipment refers to equipment at the end-user side of a satellite system. The subscriber equipment communicates with a gateway, i.e. a network-side earth station, via an orbiting satellite, for example a geostationary satellite.

With reference to figures 1A and 1 B, the subscriber equipment typically includes a satellite dish 100, which is a comparatively small parabolic dish antenna. The satellite dish comprises a dish-shaped body 101 , having a parabolic reflecting surface 102. That is a surface 102 whose geometry corresponds to a section of a paraboloid (i.e. 3D parabola) - labelled 114 in figure 1 B - having an outer edge E. Typically, the reflector surface 102 has a diameter of less than 3 metres, though this is not an absolute requirement.

The paraboloid 114 is a circular paraboloid and, as such, the reflector surface 102 has an axis and a focal point F (the focus) such that any rays 103 incident on the reflector surface 102 (incoming rays, 1031) and parallel to this axis are reflected towards the focal point F, irrespective of the position at which they meet the reflector surface 102. That is, such that all rays 1031 incident on the reflector surface 102 and parallel to its axis are reflected from it such that they converge at the focus F. The reflected incoming rays are labelled 103IR. Likewise, rays emitted from the focus F in any direction such that they are incident on the reflector surface 102 (outgoing rays, 103O) are reflected from it in a direction parallel to this axis. That is, any rays emitted from the focus F and incident on the reflector surface 102 are reflected in parallel. The reflected outgoing rays are labelled 103OR. The incoming and outgoing rays 1031/1 R and 103O/OR trace the same paths in opposite directions.

The orientation of this axis relative to the reflector surface 102 and the location of the focus F relative to the reflector surface 102 are determined by its geometry. For convenience, a Cartesian coordinate system is adopted herein, with the z-axis being the axis of the reflector surface 102. However, this choice is arbitrary, and all l references to the z-axis apply in general to the axis of the reflector surface 102 as determined by its geometry.

The rays 103 denote a direction of propagation of signals in the form of

electromagnetic (EM) waves, such as radio (RF) waves. For example, a satellite may operate in the K-band of the microwave band of the electromagnetic spectrum, between 18 and 27 GHz, which lies within the wider radio frequency band. By modulating information into these EM waves, the information can be communicated between the satellite dish 100 and the satellite 107, and the EM waves are referred to as EM signals in this context. The parabolic geometry of the reflector surface 102 allows EM signals to be communicated with sufficient signal strength (i.e. with sufficient receive or transmit power as applicable) between the satellite dish 100 and an orbiting satellite 107, which may be in a geostationary orbit. This communication can be receive-only, i.e. such that incoming EM signals are received from the satellite 107 at the satellite dish 100 only, or it can be two-way, i.e. such that incoming (i.e. forward link) and outgoing (i.e. return-link) EM signals are received and transmitted respectively between the satellite dish 100 and the satellite 107. For example, the former may be sufficient when the function of the satellite dish 100 is just that of receiving television broadcasts. The latter is needed, for example, where the function of the satellite dish 100 is to provide satellite Internet access.

Because the satellite 107 is a distant object, incoming EM signals received from the satellite 107 across the area of the reflector surface 102 are highly collimated, to the extent that to all intents and purposes the incoming rays 1031 can be treated as parallel to one another (that is, the satellite 107 can to all intents and purposes be treated as an object at infinity). Thus, provided the reflector surface 102 is aligned such that the z-axis lies parallel to the incoming rays 1031 from the satellite 107, these will be reflected to converge at the focus F. Moreover, any outgoing rays 103O emitted at the focus F will be reflected from the surface 102 in parallel to one another, such that outgoing EM signals are generated as a highly collimated beam, which propagates parallel to the z-axis, and directly towards the satellite 107. The greater the degree of collimation, the higher the signal strength of the outgoing EM signals at the satellite 107. The satellite 107 also has an antenna with an axis parallel to outgoing reflected rays 103OR, such that they are likewise parallel at the focal point of the satellite antenna.

The parabola 114 has a vertex V, and the focus F lies on a line intersecting the vertex V and running parallel to the axis of the reflector surface 102. For

convenience, the Coordinate system is chosen such that the z-axis lies on this line i.e. the location of the z-axis is chosen such that it intersects the vertex V and the focus F, though again it is stressed that this choice is arbitrary.

An antenna feed 105 is located at the focus F, and includes the necessary electronic components for receiving and (in some cases) emitting the outgoing and incoming EM signals respectively. For example, the antenna feed 105 may connect to an indoor modem via a coaxial cable, called the inter-facility link (IFL). The antenna feed 105 operates to convert signals between electrical and electromagnetic forms. For example, to convert the incoming EM signals to electrical signals (current and/or voltage modulations) in the IFL, and (in some cases) to convey outgoing electrical signals received via the IFL to the outgoing EM signals. A fixed, rigid support structure 116 such as a feed arm holds the antenna feed at this fixed location relative to the body 101.

The antenna feed 105 constitutes receiving apparatus 104 of the satellite dish 100. In the example of figures 1A and 1 B, the antenna feed 105 received reflected signals directly from the reflector surface 102. However, the receiving apparatus 104 of other types of satellite dish may include additional element(s). For example, some types of satellite dish include a guiding element in the receiving apparatus 104, in the form of a secondary reflecting surface, where signals are reflected from the (primary) reflecting surface 102 onto the secondary reflecting surface, and in turn from the secondary reflecting surface to the antenna feed 105. For example, Cassegrain and Gregorian dishes have a concave and convex secondary reflector respectively.

In the example of figures 1A and 1 B, the reflector surface 102 is an asymmetric section of the paraboloid 114, as can be readily seen in figure 1 B. In particular it is a section of the paraboloid 114 to one side of its vertex V and which does not include the vertex V itself. As such, the focus F and the antenna feed 105 are offset from the outer edge E of the reflector surface 102 in a plane parallel to the z-axis (the x-y plane), so that the antenna feed 105 does not disrupt the incoming or outgoing signals from the satellite 107 and reflector surface 102 respectively.

If the satellite 107 is in a geostationary orbit, its position in the sky remains fixed. Thus it is possible to perform a one-time installation of the satellite dish 100 at a fixed location, in which its orientation is carefully adjusted to properly align the z-axis with the satellite 107. The installer will typically use installation equipment, which may include a signal strength meter. The installer connects the signal strength meter to the antenna feed 105, for example to the IFL. After a course alignment of the dish 100, the installer makes fine adjustments to its orientation until a sufficiently high signal strength is achieved, which is achieved when the z-axis is closely aligned with the incoming rays 031 from the satellite 107. This requires skill, as even a small angular misalignment can result in a material degradation of the signal strength of the incoming signals received from the satellite 107 at the antenna feed 105.

However, if the satellite dish 100 is moved for any reason, it needs to be realigned. For example, a satellite dish installed on a moving object, such as a mobile home, boat, or other vehicle, requires re-alignment every time the object moves.

So that it does not have to be manually realigned every time, the satellite dish may be installed on a motorized mount, an example of which is shown in figure 1A (120). The body 101 of the dish 100 is attached to the motorized mount 120. The mount 120 includes a drive mechanism, which is controllable to change the pitch P of the dish (i.e. to rotate it vertically) and its yaw Y (i.e. to rotate it horizontally). Thus, instead of a manual re-installation, the drive mechanism can be controller to realign the dish 100 with the satellite 107 as needed.

Summary The present invention is targeted at satellite dishes to be installed at a fixed location, and in particular provides a greater tolerance to small misalignments of a satellite dish installed at a fixed location. Such misalignments may occur because the dish has not been installed carefully enough, or because it has been disturbed sometime after it has been installed. As such, it de-skills the installation process and provides robustness to subsequent disruption. One way of addressing the problem of small misalignments would be to mount the satellite dish on a motorized mount at the fixed location, such as mount 120 in figure 1 A. However, this is not an optimal solution. Such mounts need large motors, which in turn require a significant amount of power, in order to be able to move the whole satellite dish. This is because the satellite dish has a relatively large mass, the bulk of which stems from the relatively large dish-shaped body 101 which provides the reflector surface 102. In addition such motors need to have sufficient power to hold the dish 100 still against the pressure of wind. Moreover, such mounts are expensive, and the flexibility afforded by them is far more than is needed to correct small misalignments.

By contrast, the inventors of the present invention have devised a solution to this problem that does not suffer from these deficiencies. The solution stems from the realisation that a small angular misalignment can be accounted for without moving the reflector surface, and thus without moving the bulk of the dish's mass. Instead, the receiving apparatus of the dish is moved relative to its reflector surface.

The principles underlying this are described in detail below. For now, and with reference to figures 1 A and 1 B, suffice it to say that, when there is a non-zero angle between the axis of the reflector surface 102 (i.e. the z-axis) and the incoming rays 1031 from the satellite (a), then the incoming rays 1031 once reflected from the reflector surface 102 will no longer exactly coverage at a single point (as they do at F for a=0), i.e. each pair of reflected rays will intersect at a slightly different point.

However, for a small misalignment (small a), they will intersect near a point (denoted G, below and in the figures) that is offset from the focus F in space. This is evident, for example, in the ray-tracing diagram of figure 2B, which is described in detail below. By moving at least part of the receiving apparatus relative to the reflector surface 102- for example by moving the antenna feed itself and/or a guiding element(s) of the receiving apparatus (if any) - the antenna feed 105 can be made to coincide with this point G (or the separation between the feed 105 and the point G can at least be reduced) resulting in a significant increase in the signal strength at the antenna feed 105.

A first aspect of the present invention is directed to subscriber equipment for use in a satellite system, the subscriber equipment comprising: a reflector surface arranged to reflect signals received from a satellite; receiving apparatus arranged for receiving the reflected signals at an antenna feed of the receiving apparatus; a drive mechanism coupled to at least part of the receiving apparatus for moving it relative to the reflector surface; a signal strength detector configured to determine a signal strength indicator for the signals received at the antenna feed; and an antenna controller configured to generate based on the signal strength indicator control signals at a control input of the drive mechanism, thereby moving at least part of the receiving apparatus relative to the reflector surface such that the signal strength of the signals received at the antenna feed increases.

For example, using the present invention, in practice it may be possible to account for an angular misalignment between the axis of the reflector surface and the satellite where a is equivalent to a pointing loss of 0.5dB or less. Although small, a misalignment of this size could nonetheless cause a material degradation in the signal strength of signals received at the antenna feed if not properly accounted for - a degradation that can be prevented, or at least reduced, using the present invention.

In embodiments, the drive mechanism may be coupled to the antenna feed, and the antenna feed may be moved relative to the reflector surface to increase the signal strength.

The receiving apparatus may comprise at least one guiding element arranged to guide the reflected signals to the antenna feed.

The drive mechanism may be coupled to the guiding element, which is moved relative to the reflector surface to increase the signal strength.

The subscriber equipment may comprise a demodulator connected to the antenna feed and a data interface connected to the demodulator, wherein the demodulator is arranged to demodulate signals received at the antenna feed thereby generating incoming data accessible via the data interface. The subscriber equipment may comprise a modulator connected to the antenna feed and a data interface connected to the modulator, wherein the modulator is configured to modulate outgoing data received via the data interface thereby causing it to be transmitted from the antenna feed. A second aspect of the present invention is directed to the use of the subscriber equipment of the first aspect or any embodiments thereof to receive signals from and/or transmit signals to a satellite. That is, a method comprising a step of using the subscriber equipment in this way. For example, the use of the subscriber equipment to access the Internet via a satellite. The reflector surface and receiving apparatus may be integrated in a satellite dish.

For example, a third aspect of the present invention is directed to a satellite dish, in which the subscriber equipment of the first aspect or any embodiment thereof is integrated. That is, in which not only the dish and receiving apparatus are integrated, but the other components as well. A fourth aspect of the present invention is directed to a method of controlling subscriber equipment in a satellite system, the method comprising the following steps: receiving, at an antenna feed of receiving apparatus of the subscriber equipment, satellite signals reflected from a reflector surface of the subscriber equipment; determining a signal strength indicator for the satellite signals at the antenna feed; and generating based on the signal strength indicator control signals at a control input of a drive mechanism of the subscriber equipment to move at least part of the receiving apparatus relative to the reflector surface such that the signal strength of the signals received at the antenna feed increases.

In embodiments, the receiving apparatus may be located in the first receiving step such that a difference between a receive power of the reflector surface and the receiving apparatus along a propagation direction of the satellite signals and a maximum receive power of the reflector surface and receiving apparatus is more than 0.5dB. Preferably, such that this difference is more than 0.5dB but no more than 15dB. A fifth aspect of the present invention is directed to a method comprising steps of: installing, by a user, the subscriber equipment of the fourth aspect; and using the method of the fourth aspect to control the subscriber equipment once installed;

wherein the installing step comprises installing the reflector surface and the receiving apparatus at an outdoor location such the difference between the receive power along the propagation direction of the satellite signals and the maximum signal strength is more than 0.5dB but no more than 15dB.

A sixth aspect of the present invention is directed to a method of installing the subscriber equipment of any of the above aspects of any embodiment thereof, the method comprising a step of a user installing the reflector surface and the receiving apparatus at an outdoor location such a difference between a receive power of the reflector surface and receiving apparatus along the propagation direction of the satellite signals and a maximum receive power of the reflector surface and receiving apparatus is more than 0.5dB but no more than 15dB.

In embodiments, a measurement device may automatically output to the user, in the installation step, a notification in response to detecting that said difference does not exceed a threshold value, the threshold value being between 10dB and 15dB.

A seventh aspect of the present invention is directed to a computer program product comprising code stored on a computer readable storage medium and configured when executed by an antenna controller to implement any of the functionality disclosed herein, and in particular the determining and generating steps of the fourth aspect.

Brief Description of Figures

For a better understanding of the present invention, and to show how embodiments of the same may be carried into effect, reference is made to the following figures in which; Figure 1A is a perspective view of a satellite dish having a known configuration;

Figure 1 B shows a cross-section of the satellite dish of Figure 1A;

Figure 2A shows a perspective view of a satellite dish having a configuration according to embodiments of the present invention;

Figure 2B shows a ray tracing diagram illustrating the effects of a satellite dish misalignment; δ Figures 2C and 2D demonstrate how an antennae feed of a satellite dish can be moved relative to its reflector surface in order to correct a misalignment;

Figure 3 is a cross-section diagram illustrating a first alternative arrangement of the satellite dish according to embodiments of the invention; Figure 4 is a highly schematic block diagram representing an alternative

configuration of a receiving apparatus of the satellite dish, which comprises a guiding element.

Figure 4A is a cross-section diagram illustrating a second alternative configuration of a satellite dish according to embodiments of the invention; Figure 4B is a cross-section diagram illustrating a third alternative configuration of a satellite dish according to embodiments of the invention;

Figure 4C is a cross-section diagram illustrating a fourth alternative configuration of a satellite dish according to embodiments of the invention;

Figure 4D is a cross-section diagram representing a fifth alternative configuration of a satellite dish according to embodiments of the invention;

Figure 5 is a schematic function block diagram representing functionality of satellite equipment according to embodiments of the present invention; and

Figure 6 shows a schematic illustration of a receive power distribution of a satellite dish. Detailed Description of Example Embodiments

Figure 2A shows a perspective view of a satellite dish 200, which has many of the same components as the satellite dish 100 of Figures 1A and 1 B, such as the dish- shaped body 101 , and receiving apparatus 104 comprising the antenna feed 105. Note that all description pertaining to these components with reference to Figures 1 A and 1 B applies equally to the satellite dish 200. In contrast to Figures 1 A and 1 B, the satellite dish 200 is shown to be misaligned with the satellite 107, in that there is a non-zero angle a between the z-axis and the incoming rays 1031 from the satellite 107. So that this misalignment a can be accounted for without moving the heavy body 101 of the satellite dish 200, the satellite feed 105 is attached to the body 101 by a motorised support structure 216. The motorised support structure 216 includes a drive mechanism (not shown in Figure 2A) which can be controlled in order to move the antenna feed 105 relative to the reflector surface 102 of the body 101. In particular, the drive mechanism can be controlled to move the antenna feed 105 from the focus F to a point G at which the incoming 1031 once reflected from the surface 102 approximately (but not exactly) coincide, as this is the point at which the received signal strength will be maximised. This in turn allows the satellite dish 200 to be mounted on a much simpler mount 220, which need not be motorised. This key to this is a moving sub-assembly of the satellite dish 200, rather than moving the whole dish 200. To further illustrate the principles underlying this technique, reference is made to Figure 2B which is an optical ray tracing diagram for the reflection of the incoming rays 1031 at the reflector surface 102 for different values of a. An arbitrary

convention is adopted, whereby negative and positive a correspond to clockwise and anti-clockwise rotation away from the z access respectively. Figure 2B is

approximately to scale, and in this example the cross-section of the reflecting surface 102 visible in Figure 2B corresponds to a section of the paraboloid z = x² where the x axis runs horizontally along the page. However, this is just an example for the purposes of illustration. An expanded view of the region surrounding the focus F as shown in which the effect of the misalignment for different values of a on the reflected incoming rays, labelled 103IR, is most evident. As can be seen, as the magnitude of a increases from zero, the reflected rays 103IR no longer exactly coincide at a single point (whereas for a = zero they exactly coincide at the focus F); they do however approximately coincide at a point G which is offset from the focus F in space. As the magnitude of a increases, the separation between points F and G also increases as does the spread of points at which different pairs of reflected rays 103IR coincide. Note that Figure 2B is intended to illustrate the effect of the misalignment for different values of a; not all of the rays shown in Figure 2B would ever be received simultaneously, rather rays would only be received from the satellite in a single direction, i.e. for a single value of a at any one time. Thus, as shown in Figures 2C and 2D, by moving the antenna feed 102 slightly relative to the reflector surface 102, to locate it at the point G rather than the focus F, the misalignment can be accounted for resulting in a significant increase in signal strength at the antenna feed 105, provided the angle a is relatively small. Note that, with the antenna feed 105 moved thus, not only are incoming reflected rays 103IR approximately focused on the new location of the antenna feed 105, but also outgoing rays 103O of signals emitted by the antenna 105 in this location will follow approximately the same path as the incoming rays but in the opposite direction. Accordingly, the paths traversed by the incoming rays 1031 in Figure 2B are the same as those traversed by the outgoing rays generated by the antenna feed at the point G, at least approximately.

Like the satellite dish 100 of Figures 1 A and 1 B, the satellite dish 200 of Figures 2A to D is an off axis satellite dish where, as noted, the reflecting surface 102

corresponds to an asymmetric section of paraboloid 114 in Figure 1 B. However, the present invention is not limited in this respect. Moreover, whilst in the example of Figures 2A to 2D the misalignment a is accounted for by moving the antenna feed 105, the present invention is not limited in this respect either.

For example, in the alternative configuration of Figure 3, the reflector surface 102 instead corresponds to a symmetric section of a paraboloid centred on the vertex V of the paraboloid. In this configuration, the focus F is located at or approximately at the geometric centre of the reflector surface 102 when viewed in plan. With this configuration the underlying principles are essentially unchanged; by moving the antenna feed 105 to the point G shown in Figure 3, both incoming and outgoing rays (generally denoted 103) will trace approximately the same paths between the antenna feed 105 and the satellite 107 via the reflector surface 102. In this case, it can for example be sufficient to move the antenna feed perpendicular to the z axis only (the x direction as shown) though in some cases the drive mechanism may be such that the antenna feed can also be moved in a direction parallel to the z axis. As another example, Figure 4 shows a highly schematic block diagram representing an alternative configuration of the receiving apparatus 104, wherein the receiving apparatus comprises at least one guiding element 402.

For example, in the configuration of Figure 4A, the guiding element 402 is a secondary convex reflecting surface located directly above the vertex V of the reflector surface 102, which is a symmetric paraboloid section equivalent to that of Figure 3. In this context the reflector surface 102 is referred to as the primary reflector surface. As shown incoming rays incident on the primary reflector surface 102 are reflected onto the secondary reflector surface 402, which in turn reflects the rays onto the antenna feed 105 which is located on or near the primary reflector surface 102 itself. As such, the focus F now lies near to the primary reflector surface

102 between the primary reflector 102 and the secondary reflector surface 402. As is readily evident from Figure 4A, a misalignment a has an equivalent effect of causing the twice reflected incoming rays to approximately focus at G, rather than exactly focus at F. This can be accounted for as shown in Figure 4A by moving the antenna feed to the point G, and with the antenna feed moved to this location outgoing rays emitted by the antenna feed 105 will traverse approximately the same path as the incoming rays but in the opposite direction.

However, as illustrated in Figure 4B, an alternative means of correcting this misalignment a is to instead move the secondary reflector surface 402 relative to the primary reflector surface 102. For example, by rotating the secondary reflector surface 402 about an axis perpendicular to the plane of the page in Figure 4B

(corresponding to the y axis) it is possible to effectively move the point G to the location of the antenna feed 105, rather than moving the antenna feed 105 to G.

Note that the techniques of Figure 4A and Figure 4B are not mutually exclusive, and a misalignment can for example be corrected by moving both the antenna feed 105 and the secondary reflector surface 402 relative to the primary reflector surface 102. In the examples of Figures 4A and 4B, the secondary reflector surface is a convex reflector surface. However, as illustrated in Figures 4C and 4D, which correspond to Figures 4A and 4B respectively, the secondary reflector surface 402 can instead by a concave reflector surface located above the vertex V of the reflector surface 102 as shown. Exactly the same principles apply and all description pertaining to Figures 4A and 4B applies equally to Figures 4C (moveable feed 105) and 4D (moveable convex reflector 402).

Note that the dotted lines shown Figures 2B through to 4D correspond to the rays

103 for the case that a = zero (i.e. no misalignment), and are included for ease of reference. Figure 5 shows a functional block diagram of a set of subscriber equipment 500 which includes the satellite dish 200 described above. As indicated the drive mechanism, labelled 506, is mechanically coupled to at least part of the receiving apparatus 104 for example to the feed 105 and/or one or more guiding elements of the receiving apparatus 1054 should it include such components. That is, to which ever component(s) of the receiving apparatus 104 that are moveable relative to the reflector surface 102. In addition, an antenna controller 510 and a signal strength detector 512 of the subscriber equipment 500 are shown. The signal strength detector 512 determines a signal strength of incoming signals received at the antenna feed 105 from the satellite 107 via the reflector surface 102 automatically. The signal strength indicator denotes an estimated signal strength of those signals, and is inputted to the antenna controller 510. The antenna controller 510 is connected to a control input of the drive mechanism 506, and generates based on the signal strength indicator control signals which cause the drive mechanism 506 to move at least part of the receiving apparatus 104 according to the principles described above such that the signal strength of the signals received at the antenna feed 105 increases. That is, the antenna controller 510 moves at least part of the receiving apparatus 104 relative to the reflector surface 102 based on feedback from the antenna feed 05 itself, as conveyed by the signal strength detector 512. This can for example be in response to the antenna controller determining that the estimated signal strength has fallen below a signal strength threshold. In that event, it can for example continue to relocate the part of the receiving apparatus 104 in question until the estimated signal strength as conveyed by the signal strength detector 512 reaches or exceeds this threshold (or at least until it has exhausted all possible locations thereof). Alternatively, the antenna controller 510 can for example move the at least part of the receiving apparatus 104 over a range of locations relative to the reflector 102, determine at which of these locations the signal strength is maximised, and then return the at least part of the receiving apparatus to that location if necessary. For example these steps could be performed periodically to ensure that the configuration of the dish is optimized at all times.

In this example, the subscriber equipment 500 also comprises a modulator 534 and a demodulator 532, and a data interface 530 connected to both the modulator 532 and demodulator 534. The modulator 534 and demodulator 532 are also both connected to the antenna feed 105. The demodulator 532 receives the incoming signals from the antenna feed 105 after they have been converted by the antenna feed 105 into an electrical form, such as voltage and/or current modulations. The demodulator 532 demodulates these signals so as to generate incoming data that is accessible via the data interface 530, for example by a user device or user devices 536 connected to the data interface.

Outgoing data received at the modulator 534 via the data interface 530, for example from the user device or devices 536, is modulated by the modulator 534 in order to generate electrical signals that are supplied to the antenna feed 105. The antenna feed converts these signals to electromagnetic form and transmits them to the satellite 107 via the reflector surface 102. This allows two-way communication between the subscriber equipment 500 and the satellite 107. However, this is not essential and if receive only communication is all that is desired the modulator 534 can be omitted from the subscriber equipment 500. The incoming signals

transmitted from the satellite 107 to the subscriber equipment 500 are received at the satellite 107 from an earth station gateway 540. Similarly, outgoing signals received at the satellite 107 from the subscriber equipment 500 are transmitted to the gateway 540. This in turn allows two-way communication between the subscriber equipment and the gateway 540. This can for example allow the gateway 540 to provide an Internet access service, whereby a user or users of the user devices 536 can access the Internet 542 (or some other packet based computer network) via the satellite 107. Note that Figure 5 is highly schematic, and does not necessarily show all

components of the subscriber equipment 500 in particular. For example, the demodulator 532 and modulator 534 may connect to the antenna feed 105 via additional circuitry, such as amplifiers, filters and/or frequency converters. The demodulator 532 and modulator 534 and data interface 530 can for example by integrated in a modem device, for example an indoor modem configured to connect to the satellite dish 200 via an IFL that links the indoor environment to the outdoor environment. Alternatively, these components can be integrated in the satellite dish 200 itself, for example to provide a self-contained satellite 200 housing an outdoor modem. The antenna controller 510 and signal strength detector 512 can for example be integrated into the dish 200 itself, or these may also be components of the indoor modem and may also communicate with the outdoor dish 200 via the IFL or a separate connection means.

The data interface 530 can for example comprise a wired network interface, such as an Ethernet interface and/or a wireless interface such as a WI-FI interface. As such, the user device or devices 536 may communicate with the subscriber equipment 500 via wireless and/or wired means.

As illustrated in figure 8, the satellite dish 200 has an angular receive power distribution 602 defined by its physical geometry, and in particular by the geometry of the reflector surface 102, the location of the antenna feed 105 and the location of any guiding element(s) 402. The power distribution 602 is a function of angles (θ,φ), and Ρ(θ,φ) denotes the receive power of the dish 200 at (θ,φ). The receive power distribution 602 has plurality of lobes including a main lobe 604, which in turn has a peak receive power P_max along a direction denoted by line 606 - corresponding to (θ,φ)=(0,0) - at which the receive power of the dish 200 is highest. That is,

P(0,0)=P_max. Along the main lobe 604, Ρ(θ,φ) decreases from P_max as Θ or φ increase, corresponding to rotation away from and about line 606 respectively.

The dish 200 has a pointing relative to the satellite, which can be expressed as the angle Θ between line 606 and the direction of the incoming rays 3021 from the satellite 107. When the antenna feed 105 is located at the focus F of the dish 200, line 606 corresponds to the z-axis and α=θ.

By way of illustration, assuming the pointing Θ of the dish 200 is initially on the main lobe 604 and within about 15dB of peak P_max then the principles described herein can be applied straightforwardly. That is, an initial pointing such that:

P_max dB - Ρ(θ,φ) dB < 15 dB at least approximately, along the direction of the incoming rays 302I.

Thereafter, fine adjustments can then be performed entirely automatically by the antenna controller 210 in the manner described in order to achieve the increased signal strength at the antenna feed 105. For the upper limit of 15dB, this equates to about 1.2cm of movement for a 74cm antenna with an f/D ratio of 0.8 - f being the distance from the vertex V to the focus F and D being the diameter of the reflector surface 102. Note these figures are provided purely for the purposes of illustration to give a feel for the geometric scales involved in a certain context. They are not in any way exhaustive or limiting.

This initial pointing can for example be the pointing with which the dish 200 is installed. The dish may be installed with the antenna feed 105 located at the focus F.

This relatively high 15dB margin of error de-skills the installation process significantly to the extent that, whilst it can be performed by a trained installer, is may equally be viable for an end-user to perform it himself; by contrast, for a conventional satellite dish, a trained installer is tasked to be within 0.5 dB of P_max, i.e. with only a 0.5dB margin of error.

For example, it may be relatively straightforward for an untrained user to achieve an initial pointing such that:

P_max dB - 0.5dB > Ρ(θ,φ) dB > P_max dB-15dB

That is, such that P_max dB - Ρ(θ,φ) dB is in the range (0.5dB,15dB], where "(" and "]" denote exclusive and inclusive range boundaries respectively. For example such that P_max dB - Ρ(θ,φ) is in the range [1dB,15dB], or in the range [5dB,15dB], or in the range [10dB,15dB].

A user (trained or untrained) installing the satellite dish can, for example, perform signal strength measurements using a measurement device to perform a course alignment of the dish 200, to achieve the initial pointing within this 15dB power limit. For example, using a dedicated signal strength meter, a general-purpose user device such as a smart phone executing a signal strength measurement application, or the device in which the signal strength detector 512 of the subscriber equipment 500 itself is incorporated. For example, the measurement device may output, via an output device (such as a display or loudspeaker), a notification when a sufficient receive power Ρ(θ,φ) has been achieved as a result of the user moving the dish 200. For example when P_max - Ρ(θ,φ) no longer exceeds a threshold value, where the threshold value can for example be between 10dB and 15dB.

As will be apparent, the drive mechanism 506 can be configured in numerous different ways, depending to a large extent on which components of the receiving apparatus 104 are moveable. The drive mechanism 506 can comprise one or more electrical motors arranged so that it can perform this function, and in the case of multiple motors this can be spatially distributed throughout the dish 200 in any suitable fashion that allows this function to be performed. Whatever the precise configuration of the drive mechanism 506, it is always the case that the drive mechanism 506 does not need to move the dish-shaped body 101 of the satellite dish 200, which as noted makes up the bulk of the mass of the satellite dish 200. Thus it is always possible to implement the drive mechanism 506 with reduced electrical power and physical size requirements, as compared with a drive

mechanism that needs to move the whole satellite dish 200. The antenna controller 510 can for example be implemented in software, i.e. as code executed on a processor or processors of the subscriber equipment 500.

Alternatively or in addition at least part of its functionality may be implemented in dedicated hardware, such as an application specific integrated circuit or an FPGA. Similarly, the signal strength detector 512 can be implemented in dedicated hardware, such as application specific integrated circuit or an FPGA, or part of its functionality may also be implemented in software, for example as code executed on the same processor or a different processor of the satellite subscriber equipment 500. The modulator 532 and demodulator 534 can be implemented in any suitable manner, as will be readily apparent to the skilled person. The above embodiments of the present invention have been described by way of example only, and other variations that are within the scope of the present invention will be apparent to the skilled person. The scope is not limited by the described examples but only by the accompanying claims.

Claims

1. Subscriber equipment for use in a satellite system, the satellite terminal equipment comprising:

a reflector surface arranged to reflect signals received from a satellite;

receiving apparatus arranged for receiving the reflected signals at an antenna feed of the receiving apparatus;

a drive mechanism coupled to at least part of the receiving apparatus for moving it relative to the reflector surface;

a signal strength detector configured to determine a signal strength indicator for the signals received at the antenna feed; and

an antenna controller configured to generate based on the signal strength indicator control signals at a control input of the drive mechanism, thereby moving at least part of the receiving apparatus relative to the reflector surface such that the signal strength of the signals received at the antenna feed increases.

2. Subscriber equipment according to claim 1 , wherein the drive mechanism is coupled to the antenna feed, and the antenna feed is moved relative to the reflector surface to increase the signal strength.

3. Subscriber equipment according to claim 1 or 2, wherein the receiving apparatus comprises at least one guiding element arranged to guide the reflected signals to the antenna feed.

4. Subscriber equipment according to claim 3, wherein the drive mechanism is coupled to the guiding element, which is moved relative to the reflector surface to increase the signal strength.

5. Subscriber equipment according to any preceding claim, comprising a demodulator connected to the antenna feed and a data interface connected to the demodulator, wherein the demodulator is arranged to demodulate signals received at the antenna feed thereby generating incoming data accessible via the data interface.

6. Subscriber equipment according to any preceding claim, comprising a modulator connected to the antenna feed and a data interface connected to the modulator, wherein the modulator is configured to modulate outgoing data received via the data interface thereby causing it to be transmitted from the antenna feed.

7. Use of the subscriber equipment of any of claims 1 to 7 to receive signals from and/or transmit signals to a satellite.

8. Use of the subscriber equipment of any of claims 1 to 7 to access the Internet via a satellite.

9. A satellite dish, in which the subscriber equipment of any preceding claim is integrated.

10. A method of controlling subscriber equipment in a satellite system, the method comprising the following steps:

receiving, at an antenna feed of receiving apparatus of the subscriber equipment, satellite signals reflected from a reflector surface of the subscriber equipment;

determining a signal strength indicator for the satellite signals at the antenna feed; and

generating based on the signal strength indicator control signals at a control input of a drive mechanism of the subscriber equipment to move at least part of the receiving apparatus relative to the reflector surface such that the signal strength of the signals received at the antenna feed increases.

11. A method according to claim 10, wherein the receiving apparatus is located in the first receiving step such that a difference between a receive power of the reflector surface and the receiving apparatus along a propagation direction of the satellite signals and a maximum receive power of the reflector surface and receiving apparatus is more than 0.5dB.

12. A method according to claim 1 1 , wherein the receiving apparatus is located in the first receiving step such that said difference is more than 0.5dB but no more than 15dB.

13. A method of installing the subscriber equipment of any preceding claim, the method comprising a step of a user installing the reflector surface and the receiving apparatus at an outdoor location such a difference between a receive power of the reflector surface and receiving apparatus along the propagation direction of the satellite signals and a maximum receive power of the reflector surface and receiving apparatus is more than 0.5dB but no more than 15dB.

14. A method according to claim 13, wherein a measurement device automatically outputs to the user, in the installation step, a notification in response to detecting that said difference does not exceed a threshold value, the threshold value being between 10dB and 15dB.

15. A computer program product comprising code stored on a computer readable storage medium and configured when executed by an antenna controller to implement the determining and generating steps of claim 10.