GB2452082A

GB2452082A - Mount with rotational axes at an oblique angle relative to one another

Info

Publication number: GB2452082A
Application number: GB0716534A
Authority: GB
Inventors: John Christie Male
Original assignee: Vislink Communications Ltd
Current assignee: Vislink Communications Ltd
Priority date: 2007-08-24
Filing date: 2007-08-24
Publication date: 2009-02-25
Also published as: GB0716534D0

Abstract

A mount 1, suitable for an antenna 5, comprises at least two axes A - C for rotational movement. One of the said axes B is at an oblique angle relative to the other axis or axes A, C. The axes A - C may be an azimuth axis A, a central axis B and a polarisation axis C. The central axis B may pass through an elliptical surface, with a wire type roller bearing, which extends through a hollow cylindrical member 2, 3 at an angle in the range of thirty to sixty degrees and preferably forty five degrees. The polarisation axis C and azimuth axis A may pass through circular surface with bearings. Rotational movement at the axes A - C may be provided manually or may be automatically controlled via electric drive systems. Rotational adjustments may be performed in a set sequence where the central axis B rotation is performed first. The lightweight and rigid mount structure 1 may be controlled to support and rapidly steer an antenna as it tracks a satellite across an arc in the sky.

Description

This invention relates to a mount. In particular it relates to a mount for a satellite antenna, which provides three axes of movement. A mount is also termed a positioner and the term encompasses these.

A large number of communication satellites are currently positioned in geostationary or geosynchronous orbit. In order to transmit to or receive from a given satellite it is necessary to point a dish or flat panel antenna directly at the satellite and usually to track its passage across the sky. Satellite antennas are generally used outside and are therefore subject to environmental conditions, particularly wind, which can move the antenna away from its desired direction resulting in loss of signal or interference on adjacent satellites. This can be a particular problem with portable antennas, which are carried by man or are vehicle mounted. A stiff antenna mount is required that limits the impact of environmental conditions and that is lightweight to maximise portability.

Mounts presently used for portable antennas generally comprise elevation over azimuth mounts. These have a first (azimuth) axis that has its axis perpendicular to the ground, a second (elevation) axis that has its axis perpendicular to the azimuth axis and a third (polarisation) axis that has its axis perpendicular to the elevation axis. These mounts presently suffer from several significant drawbacks. A typical mount of this type is shown in Figure 5.

All of the wind and weight-induced loads about the elevation axis are transferred through an elevation drive mechanism. Accordingly, it is necessary to provide a large, heavy mechanism to achieve the required stiffness to hold the antenna steady.

Furthermore, a problem is encountered when tracking a geosynchronous satellite through zenith, since it is not normally possible to provide elevation axis adjustment from 0 to 180 degrees. This keyhole problem means that as the antenna is positioned looking -,)-directly up, to look backwards over itself it must rapidly rotate through azimuth and polarisation before being able to descend down the other side.

To provide larger bandwidth, larger reflectors are needed. With these, wind-induced loads increase but the radiated beam width also becomes smaller, which increases the need for a stiff antenna positioner. The use of higher frequency transmission and receivers also results in a narrower beam width, again increasing the need for a stiff antenna positioner.

The present invention arose in a bid to provide an improved mount for a satellite that is lightweight yet stiff and that allows for rapid traversing to track a satellite through zenith.

According to the present invention in a first aspect, there is provided a mount for a satellite antenna, comprising respective components rotatable about an azimuth axis, a central axis at an oblique angle to the azimuth axis, and a polarisation axis at an oblique angle to the central axis.

Preferably, the central axis is at an angle 0 to the azimuth axis and the polarisation axis is at an angle of 90-0 to the central axis.

Preferably, the mount comprises a base, which comprises a lower section and an upper section, and an antenna support, wherein the lower section of the base is adapted to rotate about the azimuth axis, the upper section of the base is adapted to rotate relative to the lower section of the base about the central axis and the support is adapted to rotate relative to the upper section of the base about the polarisation axis.

According to the present invention in a second aspect, there is provided a method of causing a satellite antenna, which is mounted on the mount of the first aspect, to track a satellite, comprising simultaneously or sequentially adjusting the mount about the axes, thereby causing the satellite antenna to track across an arc of sky.

According to the present invention in a further aspect, there is provided a mount for a satellite antenna comprising components arranged to rotate relative to each other about three axes, an azimuth axis, a central axis and a polarisation axis, wherein the mount is rotatable about each axis, and the central axis is oblique to both the azimuth and polarisation axes.

Since in embodiments of the invention, the bearing surfaces have relatively large diameters, the niount has a high stiffness. The bearing surfaces may be provided with any suitable bearing type, niost preferably wire type roller hearings.

Gears, belts, chains, levers, direct drive components or similar for each axis may be mounted adjacent to the large diameter bearing surfaces.

The angled central axis spreads the loads between the bearings and drive mechanism allowing it to be smaller and lighter than with conventional mounts.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a side view of the mount according to a first embodiment, with a satellite dish attached and the dish at 90 degrees to the ground; Figure 2 shows a side view of the mount of Figure 1, with a satellite dish attached and the dish at. 45 degrees to the ground; Figure 3 shows a side view of the mount of Figure 1, with the polarization axis at 45 degrees to the ground; Figure 4 shows a side view of the mount according to a second embodiment, with a satellite dish attached and the dish at 90 degrees to the ground; and Figure 5 shows a previously proposed mount.

A nlount 1, shown in Figures 1 to 3, comprises a base, which comprises a lower section 2 and an upper section 3, and an antenna support 4, wherein the lower section 2 of the base is adapted to rotate about a first azimuth axis (axis A), the upper section 3 of the base is adapted to rotate relative to the lower section 2 of the base about a second central axis (axis B and the support 4 is adapted to rotate relative to the upper section 3 of the base about a third polarisation axis (axis C), and wherein the second axis is oblique to both the first and third axes.

It will be seen that the orientation of the first axis relative to the second axis is fixed and the orientation of the second axis relative to the third axis is fixed. The first and third axes may be brought into and out of axial alignment by rotation of the mount about the second axis. When the first and third axes are aligned, the second axis, at the point of rotation, is collinear with the first and third axes. The mount may be rotated about all three axes simultaneously or independently.

The lower section 2 of the base comprises a lower face 6 and an upper face 7 that are joined by a continuous sidewall 8. The lower section 2 further comprises a pedestal 9 that allows for rotation of the lower section 2 about the first axis. The lower face 6 is substantially planar and is slidably supported on the pedestal 9, which lies parallel to the lower face 6. Any suitable bearing arrangement may be provided to allow for rotation of the power section relative to the pedestal, most preferably a wire type roller bearing is used.

The first axis is perpendicular to the lower face 6. In use, the base is arranged such that the lower face 6 lies substantially parallel to the ground or other support with the first axis thereby extending substantially perpendicular to the ground. The upper face 7 is oblique to the lower face 6 and is substantially planar. The upper face 7 is provided, in preferred embodiments, at an angle of 45 degrees relative to the lower face 6. The second axis extends perpendicular to the upper face 7 and at an angle of 45 degrees to the first axis.

The pedestal 9 may be located directly on the ground; alternatively the pedestal 9 may be positioned on top of a transit case, a tripod or similar, or on a combination of a transit case and a tripod or similar. Any such support may be provided with self-levelling feet (not shown) or similar that will allow the first axis of the mount to be perpendicular to the surface of the earth (vertical) when the antenna is used in an area that has uneven or sloped ground.

The upper section 3 of the base comprises a lower face 10 and an upper face 11 that are joined by a continuous sidewall 12. The lower face 10 is substantially planar and is parallel to, and slidably supported on, the upper face 7 of the lower section 2. The second axis is perpendicular to the lower face 10. The upper face 11 is oblique to the lower face 10 and is substantially planar. The upper face 11 is provided at an angle of 45 degrees relative to the lower face 6. The third axis extends perpendicular to the upper face 11 and at an angle of 45 degrees to the second axis.

The contact area of the upper face 7 of the lower section 2 and the lower face 10 of the upper section 3 is circular. The upper face 7 and the lower face 10 provide a pair of bearing surfaces that rotably slide against each other when the upper and lower sections of the base 2, 3 are rotated relative to each other about the second axis. Any form of bearing may be provided to facilitate the sliding with the bearing located between the bearing surfaces. Most preferably a wire type roller bearing is used. Alternatively, the bearing surfaces may be in direct sliding contact to provide a sliding bush.

The antenna support 4 is rotatably mounted to the upper face 11 of the upper section 3 and is adapted to support a satellite dish 5. Any suitable bearing arrangement niay be provided to allow for rotation of the satellite dish relative to the upper section, most preferably a roller type bearing is used. The support 4 lies parallel to the upper face 11 and is rotatable relative to the upper section 3 about the third axis, which extends perpendicular to the support 4 and to the upper face 11. The satellite dish is fixed to the support 4 so that it lies perpendicular to the support and rotation of the support about the third axis results in rotation of the dish 5 about the third axis.

The upper and lower sections of the base are substantially hollow and house a drive mechanism for rotation of the mount I about the first, second and third axes. In alternative arrangements, the drive mechanism may he located on the outside of the mount. The drive mechanism comprises gears and actuators. The gears being provided adjacent to, or in the vicinity of the planar surfaces that provide slidable contact between each of the components of the mount. The drive mechanism is most preferably electrically actuated although it may be manually actuated. Electrical actuation is effected by electric motors and optionally gearboxes, and manual actuation is effected by hand wheels or similar, as known within the art. A control system is provided to send control signals to the electrical actuators when the mount is electrically actuated. The control system allows for automatic adjustment of the mount, manual adjustment of the mount or a combination of automatic and manual adjustments. The control system may comprise a personal computer, dedicated controller or similar. The drive mechanism allows for the mount to be rotated about the three axes simultaneously or about each of the axes independently. The drive mechanism further allows the components of the mount to be locked relative to each other in any desired angular orientation.

The base and antenna support 4 are produced from carbon fibre although may be made from any suitable alternative materials. The components of the mount are secured together using mechanical fastenings that are provided within the mount. The mount is scalable to accommodate a range of different sized satellite antennas with the planar contact surfaces of the components providing large diameter bearing surfaces relative to antenna

size when compared to prior art mounts.

Whilst in the present embodiment the second axis is provided at an angle of 45 degrees relative to each of the first and third axis (by virtue of the relative orientation of the upper and lower faces of each of the upper and lower sections), it should be appreciated that the invention is not limited to such an arrangement; the angle may be any angle. It may lie, for example, within the range of 30 to 60 degrees or within the range of 40 to 50 degrees, to the azimuth axis, or be different to this.

By providing the second (central) axis at an angle of 45 degrees relative to each of the first (azimuth) and third (polarisation) axes, and arranging the first (azimuth) axis so that it is vertical (perpendicular to the earth's surface), the mount allows a satellite to be tracked through 180 degrees in elevation. No rapid combined azimuth and polarisation traverse is required since by controlled simultaneous or sequential rotation of the components about the three axes, the mount can be used to track a satellite through an arc 01180 degrees whilst maintaining the orientation of the satellite antenna relative to the satellite throughout the arc. This tracking operation may be controlled by the control system.

The mount geometry is capable of moving from 0 to 180° in elevation without having to do a rapid combined azimuth and polarisation traverse if the centre axis is positioned in line with the long axis of the lissajous figure described by the movement of the satellite it is tracking Figures 1 and 2 show the mount arranged with the azimuth axis vertical. In Figure 1 the satellite dish 5 is positioned looking directly up (at zenith) and in Figure 2 the satellite dish 5 is positioned looking at an angle of 45 degrees to zenith. The change in the direction of the dish is effected by rotation of the mount about the central axis by an angle of 90 degrees. Rotation of the mount about the central axis by a further 90 degrees will result in the dish 5 being positioned to look at an angle of 90 degrees to zenith (parallel to the ground). It follows that with the same rotation from zenith in the opposite direction, the dish may look through an arc of 180 degrees by rotation of the mount about the central axis.

However, the rotation of the mount about the central axis clearly also has an effect on azimuth and polarisation. Thus, in order to scan a satellite traversing across the skies, the mount during rotation about the central axis is also rotated about the azimuth and polarisation axes.

Alternatively, adjustment may first be made about the central axis, then the other axes (preferably, first central, then azimuth and then polarisation).

With the angle of the central axis provided at an angle of greater than 45 degrees to each of the azimuth and polarisation axes the mount may be affanged to track a satellite through arcs of greater than 180 degrees.

If the mount is manually adjusted, since the central axis results in movement in azimuth and polarisation, the central axis will likely he adjusted first, followed by azimuth and then polarisation. The control system and drive unit are effective to convert between the mount axis geometry and traditional mount geometry.

A mount 101 according to an alternative embodiment is shown in Figure 4, the mount 101 is identical in function to the first embodiment and differs only in the shape of the upper and lower sections 102, 103 of the base. In the second embodiment the base is substantially cylindrical, when the first and third axes are brought into axial alignment (as shown). The contact area of the upper face 107 of the lower section 102 and the lower face 110 of the upper section 103 is then elliptical rather than circular. This, however, then means that when rotated about the centre axis, the part 103 protrudes' beyond the part 102 due to their being elliptical. In the embodiment of Figures 1 to 3, however, since the contact faces are circular this protrusion does not occur.

Embodiments of the invention have significant advantages over other types of antenna mounts by distributing the wind loads through the mount structure in such a way as to reduce the antenna movement and also reduce the size of the drive mechanism needed to move the antenna, resulting in a lighter weight mount that is able to be used to give equivalent strength and stiffness to other geonletly antenna mounts. Furthermore, the geometry of the mount allows a satellite to be tracked though a large angle without requiring a rapid traverse in polarisation and azimuth.

The above description is of two specific preferred embodiments of the present invention, however, it will be appreciated that many modifications to the preferred embodiments may be possible which are within the scope of the present invention as defmed by the appended claims. For example the described components of the mount may be substituted with any alternative components that are arranged to rotate relative to each other about an azimuth axis, a central axis and a polarisation axis, with the mount rotatable about each axis, and the central axis oblique to both the azimuth and polarisation axes.

It should be noted that central' in terms of the central axis does not necessarily imply that this axis lies midway between the azimuth and polarisation axes. It simply means that this axis lies between those axes.

The mount can be used to position any type of antenna, such as reflector type antenna or flat panel type antenna that radiate directly from a dish without requiring a separate feedhorn. -10-

Claims

Claims 1. A mount for a satellite antenna, comprising an azimuth axis, a central axis at an oblique angle to the azimuth axis, and a polarisation axis at an oblique angle to the central axis.
2. A mount as claimed in Claim 1, wherein the central axis is at an angle 0 to the azimuth axis and the polarisation axis is at an angle of 90 -0 to the central axis.
3. A mount as claimed in Claim 1 or 2, comprising a base, which comprises a lower section and an upper section, and an antenna support, wherein the lower section of the base is adapted to rotate about the azimuth axis, the upper section of the base is adapted to rotate relative to the lower section of the base about the central axis and the support is adapted to rotate relative to the upper section of the base about the polarisation axis.
4. A mount as claimed in Claim3, wherein the base and support are arranged such that the azimuth and the polarisation axes may be brought into and out of axial alignment with one another.
5. A mount as claimed in Claim 3 or 4, wherein the base is arranged such that the upper section may be rotated relative to the lower section about the central axis by an angle of substantially 180 degrees.
6. A mount as claimed in any preceding claim, wherein the central axis is at an angle of between substantially 30 to 60 degrees to each of the azimuth and polansation axes.
7. A mount as claimed in any preceding claim, wherein the central axis is at an angle of between substantially 40 and 50 degrees to each of the azimuth and polarisation axes.
8. A mount as claimed in any preceding claim, wherein the central axis is at an angle -11-of substantially 45 degrees to each of the azimuth and polarisation axes.
9. A mount as claimed in any preceding claim, wherein the lower section of the base comprises a substantially planar upper face and the upper section of the base comprises a substantially planar lower face, the central axis extending perpendicular to each of the planar faces, and wherein the planar faces comprise a pair of bearing surfaces.
10. A mount as claimed in Claim 9, wherein the bearing surfaces are retained in direct sliding contact with each other so as to provide a sliding bush with the pair of bearing surfaces sliding against each other when the upper and lower sections of the base are rotated relative to each other about the central axis.
11. A mount as claimed in Claim 9, wherein there is a bearing mounted between the bearing surfaces with the bearing allowing for rotation of the upper and lower sections relative to each other about the central axis.
12. A mount as claimed in Claim 11, wherein the bearing is a wire type roller bearing.
13. A mount as claimed in any of Claims 9 to 12, wherein gears for each axis are mounted adjacent to, or in the vicinity of, the bearing surfaces.
14. A mount as claimed in any of Claims 9 to 13, wherein the planar faces are elliptical.
15. A mount as claimed in any of Claims 9 to 13, wherein the contact area of the planar faces is circular.
16. A mount as claimed in any preceding claim, wherein the base and the support are substantially hollow.
17. A mount as claimed in any preceding claim, wherein, in use, the azimuth axis is positioned generally perpendicular to the ground or a support surface.
18. A mount as claimed in any preceding claim, further comprising a drive mechanism arranged to provide rotation of the mount about the axes simultaneously and/or rotation of the mount about the axes independently.
19. A mount as claimed in Claim 18, wherein the drive mechanism is automatically or manually controlled.
20. A mount as claimed in any preceding claim in combination with a satellite antenna or a flat plate type antenna, wherein the antenna comprises a dish that is attached to the support, and wherein rotation of the support about the polarisation axis effects rotation of the dish about the polarisation axis.
21. A mount for a satellite antenna comprising components arranged to rotate relative to each other about three axes, an azimuth axis, a central axis and a polarisation axis, wherein the mount is rotatable about each axis, and the central axis is oblique to both the azimuth and polarisation axes.
22. A mount as claimed in Claim2 1, wherein the polarisation and azimuth axes are collinear, and the central axis, at the point of rotation, is also in line.
23. A mount as claimed in Claim 21 or22, wherein the central axis is at an angle of substantially 45 degrees to each of the polarisation and azimuth axes.
24. A mount as claimed in any preceding claim, wherein the adjustable components comprise faces rotating relative to each other about the respective axes.
25. A method of causing a satellite antenna mounted on a mount, as claimed in any of the claims, to track a satellite, comprising simultaneously or sequentially adjusting the mount about the axes, thereby causing the satellite antenna to track across an arc of sky.
26. A method as claimed in Claim25, comprising adjusting the components about the central axis first, then the polarisation axis, then the azimuth axis.
27. A mount substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.
28. A method of tracking a satellite substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.