GB2398171A - Antenna and mounting apparatus for an antenna - Google Patents

Abstract

Apparatus for mounting a directional antenna upon a support structure is disclosed. The purpose of the apparatus is keep the antenna pointing in a fixed direction when it is mounted on a movable support, such as a boat (10) at anchor. The apparatus comprises a controller (32) and a rotator (22) upon which an antenna (20) can be mounted. The rotator (22) is operable by the controller to rotate the antenna to a preferred alignment direction. A sensor (36) provides to the controller a direction signal indicative of an alignment direction of the support structure. The controller is responsive to the direction signal to cause the rotator to rotate an antenna mounted on it to attempt to maintain its alignment direction constant upon rotation of the support structure.

Description

1 2398171 Antenna and mounting apparatus for an antenna This invention

relates to an antenna and mounting apparatus for an antenna. It has particular application for use with an antenna for receiving broadcasts, such as television broadcasts, on a constrained moving object, such as a boat at anchor.

When a directional antenna is used to receive a signal, such as a television signal, from a fixed location, the antenna must be disposed with its direction of sensitivity directed towards the signal source. When an antenna is mounted on a fixed structure, such as a building, it need be aligned just once upon installation, and subsequent re-alignment is necessary only if the antenna is dislodged or if the signal source is moved.

However, significant problems arise if an antenna is to be mounted on a moving object such as a land vehicle or a boat. On a freely-moving object, such as a motor car or a boat under way, the problems are particularly severe. It is common to mitigate the problem through use of an omnidirectional antenna. However, this is not a particularly satisfactory solution because these antennas have low gain and the quality of the received signal is often poor. This is especially so when the signals are UHF television signals, which are susceptible to reflection from structures giving rise to multi-path distortion that is manifest as "ghosting" in the television picture. Other systems have been proposed which make use of multiple antennas and beam-steering techniques to track the signal source actively. However, such systems are difficult to implement and are costly. Some proposals have been made to use the global positioning system to monitor the position of the receiving antenna and compute the direction of optimal sensitivity to receive signals from a pre-selected transmitter. Such systems require that the user have access to a database of the locations of transmitters, which is not always readily available.

The present inventor has realised that a particular problem of lesser complexity is connected with reception of a signal in a boat at anchor (or moored by the bow), or other situations in which movement is limited. The characteristic of a boat at anchor is that its general position does not change. However, the boat will always tend to pivot so that its bow faces the wind. As such pivoting movement occurs, the alignment of a directional antenna will be lost, but only in a predictable manner. It is through this realisation that the inventor has arrived at technologically simple apparatus for use in receiving signals on platforms with this restricted type of movement.

From a first aspect, this invention provides apparatus for mounting a directional antenna upon a support structure comprising a controller; a rotator upon which an antenna can be mounted, the rotator being operable by the controller to rotate the antenna to a preferred alignment direction; a sensor operative to provide to the controller a direction signal indicative of an alignment direction of the support structure; in which the controller is responsive to the direction signal to cause the rotator to rotate the antenna to attempt to maintain its alignment direction constant upon rotation of the support structure.

This arrangement is sufficient to maintain the antenna in correct alignment on a platform that is subject to free rotational movement but minimal translation movement.

This movement characteristic is typical of a boat at anchor.

Apparatus embodying the invention most preferably allows initial setting of the alignment of the antenna, either manually or through the use of user controls. In such embodiments, once a satisfactory alignment has been achieved, the apparatus then operates to maintain that alignment automatically. For example, a remote control unit may be provided that has controls to enable a user to aim the antenna. Once the user is satisfied with the signal reception, a further control is operated that locks its direction.

The apparatus may operate incrementally, moving the rotator in response to each movement of the boat. Alternatively, or in addition, it may calculate the desired orientation of the antenna, and periodically drive the rotator to a position to achieve that desired orientation.

In a particularly convenient arrangement, the sensor may include a compass, for example an electronic compass such as a fluxgate compas. Such devices are in widespread use as direction sensors and the technology for providing robust marine fluxgate devices is well understood. Moreover, many boats already have a fluxgate device installed for generating signals for use with navigation equipment. A sensor in apparatus embodying the invention may use a signal from such installed navigation equipment. In embodiments that include a compass, initial setting of the direction of the antenna may be by way of specification of a compass bearing in which the antenna should point. Such a bearing may be specified by way of a digital control or by a rotary control that represents compass directions.

The rotator may be configured for mounting upon a mast of a boat. Typically, the controller (or at least some of its components) will be configured for location within a cabin of a boat. While separate conductors may be provided to convey signals to the rotator, it is also possible that signals to control the rotator may be carried on a common conductor (for example, a coaxial cable) with signals from the antenna. Alternatively, the signals to control the rotator may be conveyed by a wireless link.

From a second aspect, this invention provides an antenna installation comprising an antenna mounted upon apparatus embodying the first aspect of the invention.

In such an installation, typically, the antenna is a directional antenna, for example for reception of UHF television signals, or other RF signals. Moreover, the support structure is, in typical embodiments, part of a boat.

An embodiment of the invention will now be described in detail, by way of example, and with reference to the accompanying drawings, in which: Figure l is a schematic diagram of an installation of a television reception antenna installed on a boat, the installation being an embodiment of the invention.

With reference to Figure 1, apparatus embodying the invention is installed on a boat 10.

As is common, the boat is moored by a rope 12 that extends from close to its bow and is secured to an anchor or to another fixed mooring location. The boat cannot move further than the slack in the rope 12 will allow. However, it will if any wind is blowing, or if the tide is flowing, the boat will tend to rotate around the mooring location such that the bow of the boat always faces into the wind or the tidal flow. (The invention could also be employed if the boat is moving relatively slowly, or if the transmitter is distant, such that the apparent position of the transmitter changes only slowly with time.) Now, consider a situation in which a directional antenna 20 is mounted on the boat 10 to receive signals from a transmitter. The antenna may be intended to receive television signals (e.g. UHF analog or digital terrestrial signals), radio signals, or any other transmitted RF signal. Since the antenna 20 is directional, it must be oriented in a direction that points it towards the transmitter. Typically, the distance from the boat to the transmitter is considerably greater that the distance that the boat is allowed to drift by its mooring. Therefore, drift of the boat will have little effect upon the direction in which the antenna 20 must point. On the other hand, rotation of the boat about its mooring can take place over a full 360 , so it can determine completely the direction in which the antenna 20 must point. Thus, to maintain the antenna 20 pointing in a direction towards the transmitter, it is sufficient to account for rotation of the boat about its mooring only.

Therefore, the embodiment of the invention mounts the antenna 20 upon a rotator 22.

Antenna rotators are already known to those skilled in this technology, so the rotator of this embodiment will be described only briefly. The rotator 22 includes a fixed part 26 that is secured to the boat 10, in this example, at the mast head, where it may receive the best signal. The antenna 20 itself is carried upon a movable part 24 of the rotator 22.

The movable part can be rotated by a motor, in plane that is as near as possible horizontal, through 360 . It is advantageous that the rotator can rotate continuously in either direction, but in some embodiments, rotation may be limited by the necessity to provide conductors to carry the signal from the antenna 20. Also mounted within the rotator 22 is an amplifier (not shown) for receiving and amplifying the signal from the antenna 20 The rotator 22 is controlled by a control unit 24 that supplies power and drive signals to the motor. A feed cable 30 extends from the rotator 22 to carry signals from the antenna to a controller 32 mounted in a safe place, for example, within a cabin of the boat. The feed cable 30 (in this embodiment) also carries power and control signals to the rotator 22, suitable filtering circuits being provided to separate the various signals on the feed cable. Alternatively, separate signal, control and power cables may be provided.

Thus, the controller 32 can send signals to the rotator 22 to rotate the antenna to point in any desired direction.

In order that the controller 32 can be made aware of the direction in which the boat is pointing, a compass module 36is provided, mounted in fixed relation to the hull of the boat. In this example, the compass module 36 includes a fluxgate compass, a type of electronic compass that is reliable and that has no moving parts. The compass module 36 provides the controller with a signal in which the instantaneous direction of the boat is encoded. The compass module 36 may, in addition, provide signals to navigation apparatus on the boat, this reducing the effective cost of providing apparatus of the invention.

The apparatus also comprises a user control unit 40. This is connected to the controller 32, either by way of a conductor or by a wireless link, such as a radio link. The minimum functionality that the user control unit provides will now be described.

First, the user control unit 40 provides direction controls that allow a user to direct the antenna in any direction that they choose. For example, these controls may include two pushbutton switches, one to signal to the controller to rotate the antenna clockwise, and the other to signal to the controller to rotate the antenna anti-clockwise. These allow a user to direct the antenna towards a transmitter from which signals are to be received.

Optionally, the user may be provided with feedback through a display that can generate an indication of the current compass bearing to which the antenna is pointing.

A rotary control may be provided, which a user can rotate to enter a compass bearing.

The rotary control is calibrated by way of aligning a mark on the control to markings surrounding it to indicate compass directions (with North uppermost). As just one of many alternatives, user controls may be provided that allow a user to specify a compass bearing as a number of degrees.

In addition, the control unit provides a "lock" control. When this control is first activated, the controller 32 continually samples the output of the compass module 36. If it detects that the direction of the boat has changed in a clockwise direction, it activates the rotator 22 to cause the antenna 20 to rotate by a similar amount in an anti-clockwise direction thereby maintaining the direction of the antenna 20 constant. A similar but opposite correction is made if the boat swings anti-clockwise. Thus, once locked onto the signal, the antenna continues to track it irrespective of changes in the direction in which the boat is oriented.

The direction of the antenna 20 can be maintained incrementally, as described above, or it can be maintained in an absolute manner. In the latter case, the rotator must be able to provide an indication of its instantaneous position to the controller 32. Upon activation of the lock control, the controller records the direction of the rotator 22 and of the boat, as recorded by the compass module 36. Thus, it can calculate the desired orientation of the antenna 20. The controller subsequently takes periodic samples from the compass module 36, and calculates the position of the rotator required to ensure that the antenna 20 is pointing in the desired orientation. If necessary, it then drives the rotator to the position required to achieve the desired orientation.

It may be that the controller 32 normally operates in the incremental manner described in the last-but-one preceding paragraph, and occasionally uses the absolute method to correct any cumulative errors in the orientation.

Claims (22)

1. Claims 1. Apparatus for mounting a directional antenna upon a support

   structure, the apparatus comprising a controller; a rotator upon which an antenna can be mounted, the rotator being operable by the controller to rotate the antenna to a preferred alignment direction; l O a sensor operative to provide to the controller a direction signal indicative of an alignment direction of the support structure; in which the controller is responsive to the direction signal to cause the rotator to rotate an antenna mounted on it to attempt to maintain its alignment direction constant upon rotation of the support structure.
2. 2. Apparatus according to claim I which allows initial setting of the alignment of the antenna.
3. 3. Apparatus according to claim 2 in which initial setting of the alignment is done either manually or through the use of user controls.
4. 4. Apparatus according to claim 2 or claim 3 in which once satisfactory alignment has been achieved manually, the apparatus then operates to maintain that alignment automatically.
5. 5. Apparatus according to any one of claims 2 to 4 further comprising a remote control unit that has controls to enable a user to aim the antenna and a further control which, when operated, that locks the direction of the antenna.
6. 6. Apparatus according to any preceding claim operative incrementally to move the rotator in response to each movement of the boat.
7. 7. Apparatus according to any preceding claim operative in an absolute mode to calculate the desired orientation of the antenna, and periodically drive the 5rotator to a position to achieve that desired orientation.
8. 8. Apparatus according to any preceding claim in which the sensor includes a fluxgate compass.
9. 9. Apparatus according to claim 8 in which initial setting of the direction of the antenna may be by way of specification of a compass bearing in which the 10antenna should point.
10. 10. Apparatus according to claim 9 in which the bearing may be specified by way of a digital control or by a rotary control that represents compass directions.
11. 11. Apparatus according to any preceding claim in which the sensor is configured to generate signals for use with navigation equipment.
12. 1512. Apparatus according to any one of claims I to 10 in which the sensor is incorporated within installed navigation equipment.
13. 13. Apparatus according to any preceding claim in which the rotator is configured for mounting upon a mast of a boat.
14. 14. Apparatus according to any preceding claim in which the controller, or at 20least some of its components, are configured for location within a cabin of a boat.
15. 15. Apparatus according to any preceding claim in which signals to control the rotator are carried on a common conductor (for example, a coaxial cable) with signals from the antenna.
16. 2516. Apparatus according to any one of claims 1 to 14 in which the signals to control the rotator are conveyed by a wireless link.
17. 17. A directional antenna upon a support structure substantially as described herein with reference to the drawings.
18. 18. An antenna installation comprising an antenna mounted upon apparatus according to any preceding claim.
19. 19. An antenna installation according to claim 18 in which the antenna is a directional antenna.
20. 20. An antenna installation according to claim 19 in which the antenna is suitable for example for reception of UHF television signals.
21. 21. An antenna installation according to any one of claims 18 to 20 in which the support structure is part of a boat.
22. 22. An antenna installation substantially as described herein with reference to the drawings.