Antenna and a method of operating it

Abstract

An antenna with a radiation emitter/receiver, a base and a mount system capable of rotating the radiation emitter/receiver in relation to the base around at least three axes, where a controller may ensure that the emitter/receiver is directed in a first direction in relation to the base while portions of the mount system rotate so as to prevent bearings of the mount system to deteriorate.

Claims

1. An antenna, comprising: a radiation emitting/receiving element configured to emit radiation along a first direction and/or receive radiation from the first direction, a base, a mount system, the radiation emitting/receiving element and the base connected to the mount system, where the mount system comprises at least a first mount part and a second mount part, a first drive configured to rotate the first mount part in relation to the base around a first axis, a second drive configured to rotate the second mount part in relation to the first mount part around a second axis, a third drive configured to rotate the radiation emitting/receiving element in relation to the second mount part around a third axis, and a controller configured to control the first, second and third drives, wherein the controller is configured to: maintain a predetermined relative direction between the base and the first direction while operating at least one of the drives to rotate at least two of: the first mount part at least 2 degrees around the first axis in relation to the base, the second mount part at least 2 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element at least 2 degrees around the third axis in relation to the second mount part.

2. An antenna according to claim 1, wherein the controller is configured to, while maintaining the predetermined relative direction between the base and the first direction, rotate all of: the first mount part at least 2 degrees around the first axis in relation to the base, the second mount part at least 2 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element at least 2 degrees around the third axis in relation to the second mount part.

3. An antenna according to claim 1, wherein the controller is configured to rotate the at least 2 degrees over a period of time exceeding 2 seconds.

4. An antenna according to claim 1, wherein the controller is configured to rotate the at least 2 degrees over a period of time being 2 days or less.

5. An antenna according to claim 1, wherein the controller is configured to maintain the predetermined relative direction within 1 degree.

6. An antenna according claim 1, wherein the controller is configured to cyclically rotate the at least two of the drives, within extreme angular positions positioned, around the respective axis, more than 2 degrees apart.

7. A method of operating an antenna comprising a base, a radiation emitting/receiving element receiving radiation from and/or emitting radiation toward a first direction, and a mount system connecting the radiation emitting/receiving element to the base via at least a first mount part and a second mount part and enabling the radiation emitting/receiving element to be rotated in relation to the base around three or more axes, the method comprising: maintaining the radiation emitting/receiving element directed, in relation to the base, in a predetermined direction while rotating at least two of: the first mount part at least 2 degrees in relation to the base, the second mount part at least 2 degrees in relation to the emitting/receiving element, and the first mount part of at least 2 degrees in relation to the second mount part.

8. A method according to claim 7, wherein the maintaining step comprises maintaining the radiation emitting/receiving element directed, in relation to the base, in the predetermined direction while rotating the first mount part at least 2 degrees in relation to the base, the second mount part at least 2 degrees in relation to the emitting/receiving element and the first mount part at least 2 degrees in relation to the second mount part.

9. A method according to claim 7, wherein the maintaining step comprises maintaining the radiation emitting/receiving element directed, in relation to the base, in the predetermined direction within 1 degree.

10. A method according to claim 7, wherein the maintaining step comprises cyclically rotating the first mount part in relation to the base and the second mount part in relation to the radiation emitting/receiving element within extreme angular positions positioned, around the respective axis, more than 2 degrees apart.

11. A method of operating an antenna mounted on to a structure tilting with respect to a vertical axis and the tilting having an amplitude of no more than 3 degrees, the antenna comprising a radiation emitting/receiving element receiving radiation from and/or emitting radiation toward a predetermined direction, and a mount system connecting the radiation emitting/receiving element to the structure via at least a first mount part and a second mount part and enabling the radiation emitting/receiving element to be rotated in relation to the structure around three or more axes, the method comprising: rotating the first mount part at least 5 degrees around a first axis in relation to the structure, rotating second mount part at least 5 degrees around a second axis in relation to the first mount part, and rotating the radiation emitting/receiving element at least 5 degrees around a third axis in relation to the second mount part, wherein angles of rotation, of the rotating around the first axis, the second axis, and the third axis, are each larger than the amplitude of the tilting of the structure with respect to the vertical axis.

12. A method according to claim 11, wherein the rotating step comprises, while: the first mount part rotates at least 5 degrees around the first axis in relation to the structure, the second mount part rotates at least 5 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element rotates at least 5 degrees around the third axis in relation to the second mount part, directing the radiation emitting/receiving element toward a predetermined direction being more than 5 degrees away from a horizontal direction and a vertical direction.

13. A method according to claim 11, wherein the rotating step comprises, while: the first mount part rotates at least 5 degrees around the first axis in relation to the structure, the second mount part rotates at least 5 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element rotates at least 5 degrees around the third axis in relation to the second mount part, altering the predetermined direction from a first direction to a second direction, the first and second directions being at least 5 degrees from a horizontal and a vertical direction, and a smallest angle between the first and second directions being at least 5 degrees.

14. A method according to claim 11, wherein the altering step comprises: the first mount part rotates at least 5 degrees around the first axis in relation to the structure, the second mount part rotates at least 5 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element rotates at least 5 degrees around the third axis in relation to the second mount part, during a period of time where the amplitude is no more than 3 degrees.

15. An antenna, comprising: a radiation emitting/receiving element configured to emit radiation along a first direction and/or receive radiation from the first direction, a base, a mount system, the radiation emitting/receiving element and the base connected to the mount system, where the mount system comprises at least a first and a second mount part, a first drive configured to rotate the first mount part in relation to the base around a first axis, a second drive configured to rotate the second mount part in relation to the first mount part around a second axis, a third drive configured to rotate the radiation emitting/receiving element in relation to the second mount part around a third axis, and a controller configured to control the first, second and third drives, wherein the controller is configured to, while maintaining a predetermined relative direction between the base and the first direction, operate the first drive, the second drive, and the third drive to rotate all of the first mount part at least 2 degrees around the first axis in relation to the base, the second mount part at least 2 degrees around the second axis in relation to the first mount part, and the radiation emitting/receiving element at least 2 degrees around the third axis in relation to the second mount part.

Description

(1) In the following, preferred embodiments will be described with reference to the drawings, wherein:

(2) FIG. 1 illustrates the movement of a ship at sea,

(3) FIG. 2 illustrates a number of 3-axis set-ups and

(4) FIG. 3 illustrates 3-axis and 4-axis setups.

(5) In FIG. 1, the typical movements of a ship at sea are illustrated. In the following, a ship is used for illustrating the principle of the invention, even though the exact same solution may be useful also for antennas mounted on vehicles, airplanes or the like.

(6) In general, the angular movement of a ship is a yaw, which alters the ships overall heading, a roll, which is a rotation around the longitudinal axis of the ship, and a pitch, which is a rotation around an axis perpendicular to the longitudinal axis and parallel to the deck of the ship.

(7) To counteract such movements, the antenna is able to compensate for these movements of the base and keep the emitting/receiving element pointing in a fixed direction, such as toward a satellite or the like.

(8) In this context, the actual antenna may be based on any principle. Usually, the antennas for this application are directed and often highly directed and thus comprise a disc, usually a parabolic disc, which is configured to collimate radiation output from the antenna and/or to focus radiation received on to a receiver. Often, the present set-ups are used for communicating with satellites.

(9) The collimating/focusing disc may be replaced by an antenna array which to a certain degree is also able to direct/detect radiation.

(10) As explained above, an antenna mounted to the ship needs only rotation around two (non-parallel) axes in order to direct the antenna toward any object around the ship, such as a satellite, but due to the gimball lock problem, rotation around at least three axes is desired.

(11) Mount systems with three axis rotation are obtained in a number of manners. In FIG. 2, three types of three-axis set-ups (a), (b), and (c) are illustrated. In FIG. 2, the axes are illustrated but not the antenna, the base at which the mount systems are fastened to the e.g. ship, the elements rotated around the axes and the drives causing the rotation.

(12) In FIG. 3, further set-ups are illustrated where set-ups (a), (b), (c), and (d) are three-axis set-ups. Naturally, also set-ups with more axes are known. In FIG. 3 (e) an example of a four-axis set-up is seen.

(13) In general, rotation around an axis may be performed using an actuator, such as a linear actuator, which may be based on electrics or hydraulics, a motor, such as a stepper motor, an electrical motor, a brush-less motor, or the like.

(14) Usually, the set-ups or mount systems have individual elements rotatable, relative to each other, around each axis. As an example, in FIG. 3 (a), an upright 14 is rotatable around an axis 16 in relation to a base 12 fastened to e.g. a ship. Another mount element 18 is rotatable around an axis 20 around another axis 20. The antenna (represented by its disc) 22 is rotatable around a third axis 24 in relation to the mount element 18.

(15) Thus, in total, the antenna 22 is rotatable around three axes 16, 20, 24, in relation to the base 12. In the set-up illustrated, the axis 16 is vertical and the axis 20 is horizontal, if the base/vessel is stable.

(16) The axis 16 is perpendicular to the axis 20 which again is perpendicular to the axis 24. These relative angles are defined by the mount elements 14 and 18 and may be selected as any angle between the pairs of axes. In some embodiments, the axis 20 may be directed 65 degrees in relation to the axis 16.

(17) Several use cases are seen in antennas of this type.

(18) If the antenna is fixed to a small vessel at sea, the vessel and thus the base will experience the movements illustrated in FIG. 1, whereby tracking of a satellite (geostationary or not) is usually performed by rotation around all three axes.

(19) If the antenna is instead fixed to a very large vessel or a stationary object, such as a ground station or a building, the tracking of a geostationary satellite may be quite simple as the satellite may, at least for extended periods of time, be at the same angle from the base. Thus, no rotation around the axes need take place. This then brings about the above problem with the bearings. In this situation, the invention relates to the rotation of the bearings none the less.

(20) In another use scenario, the antenna may be fixed to a large vessel or stationary object while tracking a non-geostationary satellite. In this situation, the satellite will travel along a well-defined path in relation to the vessel/object/base 12. This case will be described further below.

(21) Thus, in the two last use scenarios, as only two axes are required in order to direct the antenna 22 toward the satellite, one degree of freedom is available and may be used for allowing rotation around one or two of the axes while still directing the antenna 22 to the satellite.

(22) This rotation may both lubricate the bearings but may also prevent deformation of the bearings, which is often seen when bearings are stationary at the same rotational positionwith loadfor extended periods in time.

(23) Thus, the rotation may be slow or fast, periodic or stochastic, large or small, as long as the rotation moves e.g. a ball in a ball bearing more than a few degrees.

(24) The rotation amplitude around an axis preferably is at least 2 degrees and/or preferably takes place over more than 2 minutes, such as over more than an hour.

(25) The rotation may be a rotation in one direction around the axis or may be reciprocal. Thus the rotation may be performed over an extended period of time, where rotation takes place between two extreme angular positions around the axis. The rotation within these angular positions may be periodical or stochastic.

(26) The rotation may be quantified as an angular speed, such as one degree over 1 minute or more, such as 30 minutes or more, if desired.

(27) In many situations, the rotation takes place about at least 2 of the axes in order to both allow rotation around the axes and maintain the direction of the disc/antenna toward the antenna.

(28) In the last use scenario, two axes will usually be used for tracking the satellite. However, one axis may remain stationary and thus experience the bearing problem.

(29) In the set-up seen in FIG. 3(a), the element 18 is normally rotated (around axis 20) so as to keep the axis 24 horizontal. This has the advantage that the rotational (around the axis 20) relationship between the antenna 22 and the satellite is always the same, which is an advantage when polarized radiation is to be received/transmitted.

(30) Furthermore, with this limitation, the driving of the drives is simpler, as there is only a single solution to the equations defining the rotation of the drives.

(31) It is noted that this is the situation even when the satellite is not geostationary and/or where the antenna moves slowly in relation to the satellite and/or the earth.

(32) Thus, it is seen that when this antenna is positioned on a large vessel, an oilrig or a stationary object, there will be no or substantially no rotation around the axis 20, whereby the bearings in that respect have the above problem.

(33) In order to avoid this problem, rotation is now desired around also the axis 20. Naturally, this will rotate the disc around the axis or direction toward the satellite, but this may be compensated for by allowing a receiver/transmitter of the actual antenna 22 be rotatable in relation to the disc or at least in relation to the element 18 and around a symmetry axis of the disc.