GB2383689A

GB2383689A - Antenna assembly

Info

Publication number: GB2383689A
Application number: GB0126724A
Authority: GB
Inventors: William Hislop Dobbie
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-07
Filing date: 2001-11-07
Publication date: 2003-07-02
Also published as: GB0126724D0

Abstract

An assembly of 4 or more electronically steerable flat plate or similar antennas are arranged to allow narrow beams to be pointed over 360 degrees azimuthally and over a limited vertical arc. The beams from adjacent antennas pointing closely enough to the required direction can be combined to increase the overall gain by switching between antennas and controlling the pointing of the beams. In the preferred embodiment an array of rectangular (or similar) antennas (9) are arranged around the inside of a cylindrical enclosure (8) with a vertical axis. The resulting combined shape can be higher than it is wide. The space enclosed by the antennas is used for a tranceiver, circuitry for processing or a motor and gearing. Alternative embodiments could use two or more different shaped antennas which can have curved surfaces or 2 vertically stacked layers of antennas without combining the outputs. The antenna assembly may be used at a node of a communications network, to maintain links between nodes by steering the beam.

Description

MESH ANTENNA ASSEMBLY This invention relates to radio antennas for point to point communications and particularly for broadband fixed wireless access networks using a mesh configuration.

Until recently most systems have connected an optical fibre or coax core network to a base station which then interconnects with the end users via radio links. In many cases the base stations use omni-directional or sectorised transmit and receive antennas and the end user is equipped with a directional antenna. A directional antenna can also be interconnected with a smaller base station to implement a relay to feed other end users that are either out of range or behind an obstruction such as a building.

Alternatively, the base station can consist of a cluster of directional antennas each used for a point to point link to an end user or a relay equipped with one or more fixed directional antennas. This means that the amplifiers used at the base station can be lower power. Spectrum efficiency is also significantly improved.

This approach has recently been extended by the use of relays (normally termed nodes) with steerable directional antennas. This means that an end user can be served via a series of point to point links between nodes.

Providing there are enough nodes it is possible to re-route the users data in the event of a temporary or permanent failure of an intermediate node. The connection to the core network can use one or more nodes similar to those on customer's premises and they need not be c-located as shown on figure 1 so there is not longer a base station as such. The resulting configuration (termed a mesh network) is illustrated in International Patent Specification W098/27694.

If a new node is to be connected to the mesh or if a node fails or is no longer required it is necessary to align the directional antennas on the new node and re-align those on a number of other nodes in the mesh. This process is automated in order to avoid the need for a series of engineering visits. A remote controller is used (sometimes in conjunction with local sensors) to decide where to point the steerable antennas.

It is desirable for the antenna array which determines the minimum size of the node to be as small as possible to reduce wind loading, ease installation problems and minimise safety concerns. Reducing size will also help make the appearance acceptable to customers, increasing take-up of the fixed wireless access services that are enabled.

One way to implement a steerable antenna is described in International Patent Application WO 99/65162. An array of 32 directional horn antennas covering a 360 degree azimutal plane is provided. The feeds to the antennas are switched on when required allowing the antenna pointing most closely towards the required direction to be used. Links can be set up in a number of

directions by the use of time division multiplexing techniques. The resulting array is relatively large because each fixed antenna is large and only one is used at any time.

Flat plate techniques can also be used to implement an electronically steerable antenna with up to +/-60 degrees of pointing away from the normal to the plane of the antenna. The flat plate consists of a number of printed, etched, machined or other radiative elements plus a means of changing the phase of the signals so that the resulting combined beam can be steered.

However the gain of the antenna reduces as the angle of pointing increases because the surface area pointing in the direction of the beam is reduced.

This makes it necessary to increase the surface area of the antenna by increasing the width to maintain an acceptable azimutal gain for large angles of pointing. It would be possible to produce an antenna array that can be electronically steered over 360 degrees using three rectangular flat plate antennas at 120 degrees to each other. However, if the antennas were arranged on a single layer round a common vertical axis the diameter of a cylindrical enclosure used to cover the array would be relatively large and the resulting shape would be considered objectionable by many users.

An alternative is to use a number of physically steerable antennas, as described in International Patent Application WO 99/65105. Each antenna is arranged to sweep over a 360 degree azimutal plane and this means that they would normally be stacked vertically and rotate around a common vertical axis. However, the resulting node is still relatively large.

According to the invention there is provided an assembly of electronically steerable flat plate or similar antennas arranged to allow narrow beams to be pointed over 360 degrees azimuthally and over a limited vertical arc. The beams from adjacent antennas pointing closely enough to the required direction can be combined to increase the overall gain. The antennas may use printed, etched, machined or other radiative elements to achieve the beam steering according to any suitable processing technique.

In a preferred embodiment an array of rectangular (or similar) antennas are arranged round the inside of a cylindrical enclosure with a vertical axis. The number of antennas is ideally greater than four to maximise the width of the combined shape formed by the antennas pointing in the required direction for a particular radius drum. The width of the resulting shape determines the azimutal beam width and it must be large enough to give the gain needed to achieve a spectrally efficient mesh network. The resulting combined rectangular shape can be made higher than it is wide to increase the overall gain without increasing the width beyond the minimum requirement. This means that the beam is narrower vertically than azimuthally but this is acceptable as the beam can be pointed vertically In an alternative embodiment, all of the antennas are rectangular in shape and much wider than they are high. Two antennas are mounted back to back.

A stack of such pairs of antennas are arranged in an evenly spaced spiral configuration where the centre of each pair of antennas lies on a common

vertical axis. By combining the beams that can point most closely to the required direction it is possible to present a near uniform pattern in all azimutal directions.

In some of the other embodiments to be described two or more types of antenna with different size and shape are used. The smaller secondary antennas are used to increase the total area presented azimuthally while maximising the amount of space for processing circuitry enclosed by the antennas. The surface of the antennas can also be shaped to maximise the area presented azimuthally.

In alternative embodiments, four or more secondary antennas are mounted behind a primary antenna and arranged in two or more layers so that the coverage patterns interleave while allowing maximum space for processing circuitry behind the antennas.

In two simpler embodiments two or more similarly shaped antennas are arranged on two or more vertically stacked layers with the beams interleaved.

Because four or more antennas are used, each one is able to steer over a smaller azimutal angle than for the case with three steerable antennas on a single layer and so the width of each antenna can be less. This makes it possible to arrange the antennas in a cylindrical shape that is taller than it is wide. This approach can be used to implement an array in an enclosure with such a shape without combining the beams from adjacent antennas.

The resulting mesh antenna array would normally be covered by a fixed enclosure that does not attenuate radio signals excessively in all cases. This can be shaped to minimise wind loading and to improve the appearance. The node can be mounted on a pole with a cable or cables inside it to feed signals to the indoor equipment and provide power. The complete node can be arranged to rotate around the axis of the pole using an internal motor and gearing to maximise the gain of one or more beam for embodiments where the gain is not uniform for all azimutal angles. In cases where there are two or more layers a layer can be arranged to rotate relative to the other layers.

Eight specific embodiments of the invention will now be described by way of example only with reference to the accompanying figures in which: Figure 1 illustrates a mesh network of the type that this invention is intended to work with.

Figure 2 and 3 are plan and elevation views of a mesh antenna assembly according to a first embodiment of the invention.

Figure 4 and 5 are plan and elevation views of a mesh antenna assembly according to a second embodiment of the invention.

Figure 6 and 7 are plan and elevation views of a mesh antenna assembly according to a third embodiment of the invention..

Figure 8 and 9 are plan and elevation views of a mesh antenna assembly according to a fourth embodiment of the invention.

Figure 10 and 11 are plan and elevation views of a mesh antenna assembly according to a fifth embodiment of the invention.

Figure 12 and 13 are plan and elevation views of a mesh antenna assembly according to a sixth embodiment of the invention.

Figure 14 and 15 are plan and elevation views of a mesh antenna assembly according to a seventh embodiment of the invention.

Figure 16 and 17 are plan and elevation views of a mesh antenna assembly according to an eighth embodiment of the invention.

Figure 1, which is based on a figure from International Patent Specification W098/27694, shows a simple example of a network of the kind that the present invention is intended for use. In the example shown, there are thirteen users each associated with a node (2). Each node (2) has a radio tranceiver unit that is able to transmit and receive high frequency radio signals, for example between 5GHz and 120GHz. The transceiver unit of each node (2) is in contact with several other similar units at other respective nodes (2) by direct line-of-sight wireless links (3). The nodes (2) of network (1) can communicate with each other either directly, or by way of other nodes if necessary to avoid buildings (4) or other obstructions which block direct lineof-sight connection between particular nodes (2) or to overcome the limited range of transmitters working at these frequencies. A message from any one node (2) to any other node (2) will typically traverse several links (3) across the network. Interconnect links (5) are used to connect nodes (2) in the network to a trunk network (6).

Each node (2) is provided with an antenna assembly capable of supporting all of the links (3) associated with that node (2). To allow reconfiguration of the network as nodes (2) are added or removed or to allow for new obstructions (4) the nodes are provided with the capability to adjust the directions of the antennas so that links (3) can be set up in any azimutal direction. In one arrangement discussed in the prior art reference W098/27694, an array of fixed antennas is provided, the appropriate antenna or antennas for each link (3) being switched in as required. Such an arrangement requires a much larger number of antennas to be provided at each node than are actually needed at any one time, significantly increasing the size, bulk and capital cost of the node installation. In alternative arrangements a smaller number of independently steerable antennas are provided. The steering may be electrical (that is, by controlling the electrical characteristics of the antenna to control the effective boresight direction) or by physical movement of the antenna. Different nodes (2) can use different types of antenna assembly.

To obtain optimum use of the radio spectrum and minimise the amount of equipment required at each node, the antennas at a given node may share a

single tranceiver, using any known multiplexing technique to serve all the links (3) from the one node (2).

Figures 2 and 3 show schematically an antenna assembly (7) according to the invention, for use at one or more of the nodes (2) of such a network. Figure 2 is an elevation and figure 3 is a plan view. Both figures (and all the others that follow) show the antennas only. The tranceiver and all necessary processing equipment plus motors etc. would be fitted within the area enclosed by the antennas where possible. Otherwise they would be fitted above or below the antenna array.

A possible enclosure (8) is provided to protect the components within from the weather. It would normally be shaped to provide an aesthetically attractive appearance. The enclosure (8) which is shown dotted in all cases is as near transparent to radio waves as possible. In this embodiment the enclosure is cylindrical with a vertical axis and the edges are rounded but other shapes could be used. The complete node can be secured to a building or other structure by any suitable means, from which it may also obtain its power supply. Signals for processing by the user terminal (normally within the building or structure) or generated by it or any user equipment that it is connected to can be carried over any suitable wired or wireless network.

In this embodiment an array of electronically steerable rectangular flat plate (or similar) antennas (9) are evenly spaced round the vertical axis. Processing (not shown) is provided to enable the beams to be steered azimuthally and vertically and to allow the beams from adjacent antennas pointing closely enough to the required direction to be combined to increase the overall gain.

Ten antennas (9) are shown however this is not to be taken as limitative. The radius of the circle enclosing the antennas and the number of antennas (9) is selected to allow the width of the resulting shape formed by the active antennas pointing in the required direction to be set to a particular value. The height of the antennas (9) is set to achieve the required overall gain. The height of the overall shape can be greater than the width. In this embodiment the beams from three or four antennas (9) would normally be combined to form a beam pointing in any direction azimuthally and over a limited vertical arc allowing for nodes (2) to be interconnected even if they are at different heights above sea level. It is believed that +/-20 degrees would be sufficient but this should not be taken at limitative.

The information required to point the beams so that links (3) can be set up between nodes (2) by remote control can be delivered to node (2) initially via a separate network such as the public switched telephone network (PSTN) connected via the interface with the user terminal. A node (2) can include a means of determining its orientation. It can also include a means of searching for active nodes so that it can independently establish a connection with the central network controller. Once an initial connection is made with the central network controller the pointing information can be delivered via the mesh network (1) however knowledge about other visible nodes may also be used.

A node (2) can also include a means of optimising the antenna pointing to maximise the performance for any link (3). Node (2) can include a motor plus gearing (not shown) allowing the antenna assembly (7) to physically rotate around the vertical axis so that the gain can be maximised for one or more links (3) where there is high attenuation. This would only normally be necessary for this embodiment (and several others described below) if the number of antennas (9) used was low which could make the gain higher in some directions than others.

The alternative embodiments described below can be similar to the first embodiment in most respects. The main differences are identified in each case.

Figures 4 and 5 show schematically an alternative antenna assembly (7) according to the invention. Figure 4 is an elevation and figure 5 is a plan view.

One possible enclosure (8) is shown dotted. In this embodiment the antennas (10) are rectangular with the width much greater than the height. Two such antennas are mounted back to back so that they point in opposite directions.

A stack of such pairs of antennas (10) are arranged in an evenly spaced spiral configuration where the centre of each pair of antennas lies on a common vertical axis. By combining the beams that can point most closely to the required direction it is possible to maintain a near uniform overall shape in all azimutal directions. Twentyfour antennas (10) are shown however this is not to be taken as limitative. In this case it would not be necessary to provide a motor or gearing for physical steering. However, it would be necessary to provide space for other processing below the antenna array, as shown dotted.

Figures 6 and 7 show schematically an alternative antenna assembly (7) according to the invention. Figure 6 is an elevation and figure 7 is a plan view.

One possible enclosure (8) is shown dotted. A layer of electronically steerable primary antennas (11) are evenly spaced round a vertical axis. Two layers of electronically steerable secondary antennas (12) are mounted above and below the primary antennas and shaped to slope towards the vertical axis.

This allows the antenna array to be fitted into an enclosure with a circular azimutal cross-section and an oval or similar vertical cross-section, as shown on figure 7. This shape may be aesthetically attractive to some users. Ten primary antennas (11) and twenty secondary antennas (12) are shown however this is not to be taken as limitative. In this embodiment the beams from three or four primary antennas (11) and six or eight secondary antennas would normally be combined to form a beam pointing in any direction azimuthally and over a limited vertical arc.

Figures 8 and 9 show schematically an alternative antenna assembly (7) according to the invention. Figure 8 is an elevation and figure 9 is a plan view.

One possible enclosure (8) is shown dotted. A layer of circular electronically steerable primary antennas (11) are evenly spaced round a vertical axis. Two layers of electronically steerable secondary antennas (12) are mounted above and below the gaps between the primary antennas and shaped to slope towards the vertical axis. The secondary antennas have a shape similar to an arc of a circle This allows the antenna array to be fitted into a spherical

enclosure which may be aesthetically attractive to some users. Ten primary antennas (11) and twenty secondary antennas (12) are shown however this is not to be taken as limitative. In this embodiment the beams from one or two primary antennas (11) and two or four secondary antennas would normally be combined to form a beam pointing in any direction azimuthally and over a limited vertical arc.

Figures 10 and 11 show schematically an alternative antenna assembly (7) according to the invention. Figure 10 is an elevation and figure 11 is a plan view. One possible enclosure (8) is shown dotted. An array of electronically steerable rectangular flat plate (or similar) antennas (13) are evenly spaced round a vertical axis. The surface of the antennas (13) is shaped at the top and bottom to maximise the area presented azimuthally while fitting within a smaller enclosure. This allows the antenna array to be fitted into an enclosure with a circular azimuthal cross-section and an oval or similar vertical crosssection, as shown on figure 11. Five antennas (13) are shown however this is not to be taken as limitative. In this embodiment the beams from two or three antennas (13) would normally be combined to form a beam pointing in any direction azimuthally and over a limited vertical arc. The shape of the antennas (13) should also not to be taken as limitative. A layer of antennas shaped like the curved surface of an orange segment could for example be used to maximise the surface area of the antenna array intended for a spherical enclosure.

Figures 12 and 13 show schematically an alternative antenna assembly (7) according to the invention. Figure 12 is an elevation and figure 13 is a plan view. One possible enclosure (8) is shown dotted. A single electronically steerable primary antenna (14) is provided and two layers of electronically steerable secondary antennas (15) and (16) mounted behind it. The primary and secondary antennas are shaped to maximise the area presented azimuthally while fitting into a spherical enclosure. The secondary antennas (15) and (16) can be of different width to maximise the amount of space enclosed by the antenna array and allow the beams from the secondary antennas on the two layers to be interleaved. Four secondary antennas (15) and (16) on two layers are shown however this is not to be taken as limitative.

In this embodiment the gain of the primary antenna (14) would normally be greater than that of the secondary antennas (15) and (16) so a motor plus gearing would normally be used to physically steer the complete antenna array (7) to optimise the performance for one link (3). The beams from two adjacent antennas could be combined for some pointing angles. This approach could alternatively be used to implement a relatively simple antenna array where the beams from adjacent antennas are not combined.

Figures 14 and 15 show schematically an alternative antenna assembly (7) according to the invention. Figure 14 is an elevation and figure 15 is a plan view. One possible enclosure (8) is shown dotted. Two layers of electronically steerable antennas (17) are provided. Two corners of each antenna are rounded to allow the upper and lower edges of the enclosure to be rounded.

The antennas on each layer are evenly spaced round a vertical axis. The layers are arranged so that the beams can be interleaved. Six antennas (17)

are shown on two layers however this is not to be taken as limitative ! n this embodiment the beams from two antennas (17) could be combined. This approach could alternatively be used to implement a relatively simple antenna array where the beams from adjacent antennas are not combined. In that case the overall gain for each antenna could be increased to compensate by increasing the height.

Figures 16 and 17 show schematically an alternative antenna assembly (7) according to the invention. Figure 16 is an elevation and figure 17 is a plan view. One possible enclosure (8) allowing for processing etc. to be provided below the antennas is shown dotted. Two layers of electronically steerable antennas (18) are provided. Two antennas (18) are mounted back to back on each layer round a vertical axis. The layers are arranged so that the beams can be interleaved. This approach could also be used to implement a relatively simple antenna array where the beams from adjacent antennas are not combined. In that case the overall gain for each antenna could be increased to compensate by increasing the height. The complete antenna assembly (7) could be physically rotated around the axis to maximise the gain for a particular link (3) or to balance the performance of several links (3). It would be sufficient to allow for +/-90 degrees of rotation because the antennas are back to back. One of the layers of antennas could also be physically rotated by up to +/-45 degrees with respect to the other. Four antennas (18) are shown on two layers however this is not to be taken as limitative. The angles of rotation are also not to be taken as limitative

Claims

CLAIMS 1. An assembly of four or more electronically steerable flat plate or similar antennas in a single enclosure arranged to allow beams to be pointed in any azimutal direction by switching between antennas and controlling the pointing of the antennas under local or remote control.
2. An antenna assembly according to claim 1 where the beams from two or more separate electronically steerable antennas are combined to increase the overall gain in a particular direction.
3. An antenna assembly according to claim 1 or claim 2 where the beams are steered vertically as well as azimuthally.
4. An antenna assembly according to any preceding claim where the beams are steered azimuthally and vertically under local or remote control to maximise the received signal level independently for each link.
5. An antenna assembly according to any preceding claim where the height of the combined shape of the antennas pointing in any azimutal direction is greater than the width.
6. An antenna assembly according to any preceding claim where pairs of antennas pointing in opposite directions are arranged in a spiral configuration.
7. An antenna assembly according to any preceding claim consisting of primary and secondary antennas with different shapes arranged to maximise the surface area in all azimutal directions as well as the enclosed area while fitting into an enclosure with a circular azimutal cross section and a curved vertical cross section.
8. An antenna assembly according to any preceding claim where the complete assembly can be physically steered azimuthally under local or remote control to optimise the received signal level for one or more link.
9. An antenna assembly according to any preceding claim comprising a primary antenna with four or more secondary antennas fixed behind it.
10. An antenna assembly according to claim 9 where the secondary antennas are smaller than the primary antenna.
11. An antenna assembly according to claim 9 where the secondary antennas are in two or more layers with coverage patterns arranged to interleave.
12. An antenna assembly according to any preceding claim where the antennas are shaped at the top or bottom to maximise the surface area while fitting into an enclosure with a circular azimutal cross section and a curved vertical cross section.

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13. An antenna assembly according to any preceding claim where the surfaces of some or all of the antennas are shaped to increase the antenna area pointing in a particular direction or the amount of space enclosed by the antennas.
14. An antenna assembly according to any preceding claim where two or more antennas are arranged on each of two or more vertically stacked layers so that the coverage patterns interleave.
15. An antenna assembly according to any preceding claim where three similar antennas are arranged on each of two vertically stacked layers.
16. An antenna assembly according to any preceding claim where two similar antennas pointing in opposite directions are arranged on each of two vertically stacked layers where the layers are aligned at 90 degrees to each other.
17. An antenna assembly according to claim 15 or claim 16 where one complete layer of antennas is arranged to physically rotate around a substantially common axis with respect to the other layer.
18. An antenna assembly according to any preceding claim where the space enclosed by the antennas is used to accommodate a tranceiver, a multiplexer, circuitry for processing or a motor and gearing.

19 An antenna assembly substantially as herein described and illustrated in the accompanying drawings.