This invention relates to array antennas and in a preferred embodiment, to multipolar arrays.
Array antennas, having a plurality of radiating elements, are increasingly used in adaptive and/or multibeam applications. They are expected to be an important element of future broadband wireless solutions since such antennas enable significant capacity gains to be produced, for example, using accurate beam steering and beam forming.
However, since the amplitude and phase weights of the array elements need to be accurately controlled in order to generate the desired beam patterns, the feed networks of such antennas are complex which means that the antennas are generally expensive to produce. In addition, they generally require multiple rows and columns, resulting in large structures with many piece parts, which are heavy.
With increasing use of such antennas it will become necessary to reduce complexity of manufacture in order achieve a reduction in cost. In order to allow easy mounting of such antennas and to reduce the cost of installation, it is also desirable to reduce the weight of such antennas.
Hitherto, antennas of this type have typically been formed using discrete dipole antennas mounted adjacent a planar reflector. The feed to each antenna has been achieved using a network of coaxial cables. Alternative structures also exist which employ microstrip patch elements and microstrip feed networks.
In a first aspect, the invention provides an antenna comprising an electrically conductive tube, an electrically conductive outer surface covering a front face and at least part of the two adjacent side faces of the tube, a feed layer located between the tube and the outer surface and arranged to carry electrically conductive tracks, and dielectric material located between the tube and the feed layer and between the outer surface and the feed layer, the antenna further comprising a plurality of radiating elements formed as slots defined by areas of non-conductivity in the front face of the outer surface and in the tube which are in registry with one another and respective conductive tracks defined on the feed layer which are generally in registry with the slots.
The components may, for example be made from plastics mouldings with an electrically conductive coating. This provides a very lightweight structure.
It will be noted that the feed layer is sandwiched between two conductive components which forms a triplate, type feed network. This obviates the need for complex and heavy feed networks using coaxial cables.
By arranging a plurality of the tubes side by side, a further set of radiating elements may be provided so that an array may be made up in a modular fashion using as many tubes as are required. The tubes may share the common parts of the outer surface as described below.
By varying the orientation of the slots, it is possible to achieve different polarisations and/or multiple polarisations from the same antenna. This is described in detail below.
In a preferred embodiment, slots are oriented at plus and minus 45 degrees and are interspersed so that the array provides plus and minus 45 degree polarised radiation.
With suitable choices of plastics, the antenna may be constructed without a radome; further reducing cost and weight.
The outer surface may have a curved profile. This typically increases strength of the tube and may be used also to further tailor the spatial variation of the antenna pattern. This structure also has the advantage that it need not be necessary to turn the feed layer through sharp corners.
In a second aspect, the invention provides a multibeam antenna comprising a generally cylindrical electrically conductive outer layer, a plurality of electrically conductive tubes arranged around the central axis of the cylinder, an electrically conductive inner cylindrical layer forming the outermost wall of each tube, and a feed layer located between the inner and outer layers and arranged to carry electrically conductive tracks, and dielectric material located between the outer layer and the feed layer and between the inner layer and the feed layer, the antenna further comprising a plurality of radiating elements formed as slots defined by areas of non-conductivity in the outer layer and in the inner layer which are in registry with one another and respective conductive tracks defined on the feed layer which are generally in registry with the slots, whereby each tube generally corresponds to a single respective beam of the antenna.
This arrangement has particular application in cellular networks such as cellular telephone networks. The tubes may be arranged singly or in multiple arrays to provide, for example, three beams spaced generally equally around the cylinder. This provides a particularly effective and economical antenna.
In a third aspect, the invention provides an antenna component comprising an electrically conductive tube, an electrically conductive outer surface covering a front face and at least part of the two adjacent side faces of the tube, a feed layer located between the tube and the outer surface and arranged to carry electrically conductive tracks, and dielectric material located between the tube and the feed layer and between the outer surface and the feed layer, the antenna further comprising a radiating element formed as a slot defined by areas of non-conductivity in the front face of the outer surface and in the tube which are in registry with one another, the slot being energized in use by a conductive track defined on the feed layer which is generally in registry with the slots.
This module, may be used as a building block for the antennas of the other aspects. With a baffle at one or both ends, it forms a single cavity-backed slot component. Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
With reference to
An electrically conductive outer surface 4 formed, for example, from metal film or metallized plastic spreads across the front, covering the front faces of the tubes 2. This component is ribbed and has ribs 6 extending rearwardly between the tubes 2.
A feed layer 8 typically formed from flexible film such as mylar, extends between the outer surface 4 and the tubes 2. This film contains conductive stripline elements which excite the radiating slots and also form a feed network as described below.
In a further alternative embodiment (not shown), the outer surface 4 of
In both cases, edge connectors 12, 12-1 are formed at the rear end of the array to allow connection to the feed layer and also to allow grounding of the tubes 2, 2-1 and front surface 4, 4-1.
As will be described in more detail below, the conductive surfaces of the front surface 4 and the tubes 2 are interrupted to create non-conductive slots. Typically, a T bar radiator is formed at the same position in the feed network. This construction therefore provides a cavity backed, slot radiating element and a triplate (i.e. stripline tracks between ground plates) feed network along the ribs, 6, 6-1. This provides particularly compact construction. Furthermore, when made of plastics material, the antenna is both light and resistant to water ingress and corrosion. Thus the antenna need not be provided with a separate radome. However as described below, some embodiments may have slots passing entirely through the components (rather than merely having the conductive surface removed) and thus a separate radome may be desirable in those cases to avoid water ingress.
With reference to
The figure shows slots in adjacent columns have slots of the same orientation in each row of the array. An alternative arrangement is to ensure that the adjacent slots of adjacent tubes are at different polarisation angles, for example, by alternating the slot orientation along a row i.e. across the tubes. This might reduce coupling between adjacent slots.
The feed network terminates in a T bar located in each respective slot, which matches the feed network to the slot and also excites it causing it to radiate. The slots are formed by removing metallization or forming an aperture through the entire material of the tubes and front face. It will be noted that the slots 18 are oriented in different directions. In this case the directions are plus and minus 45 degrees in relation to the axis of each of the tubes 2. These orientations allow the antenna array to operate in a dual polar mode and it will be noted that the feed networks for each of the alternately oriented slots pass along opposite sides of the tubes 2. This separation of the feed networks is not essential but aids layout of the feed network and makes best use of the available space.
It will be appreciated that the array shown may extend in any direction by extending the length of the tubes 2 and/or by adding additional tubes and that angles other than 45 degrees may be selected for the slots for different desired polarisation angles and that the polarisation angles need not be orthogonal.
As the height of the array increases, additional branches of the feed network are required. The space for this may readily be accommodated simply by extending the rib 6 further back into the plane of the page as drawn.
Typically the horizontal spacing between slots is λ/2 where λ is the designed operating wavelength of the antenna. Also, the typical vertical spacing between slots of the same orientation is approximately 0.8λ. Thus in the embodiment shown, with alternating orientations of slots, each of the cavities behind the slots is approximately λ/2 wide by 0.4λ high. The cavity depth is approximately λ/4. Optionally, baffles 20 may be inserted across the tubes in order to reduce coupling between the slots and T bar elements of differing polarisations.
It will be noted that the spacing of the slots may vary. For example, the array may be arranged for scanning of beams in the vertical plane. In that case, a horizontal spacing of about 0.8λ and a vertical spacing of about λ/2 would be desirable. This may be achieved by rotating the array through 90 degrees; so having the tubes running horizontally, or alternatively by making the tubes wider (to achieve the wider horizontal spacing) and decreasing the spacing between slots in each tube. It will be appreciated that many other variations are possible and will generally be dictated by the desired beam patterns and adjustability requirements of the antenna.
In this preferred embodiment, the slots also have a “dog bone” configuration with wider portions at the ends of the slots. This allows better control of the resonant frequency whilst keeping the physical slot length shorter than otherwise would be the case. It is anticipated that without the dog bone configuration, these slots lengths would approach λ/2. This length may, for example, be reduced to 0.45λ with the use of the dog bone configuration; thereby improving the space efficiency of the antenna.
Considering again the arrangement of
It will be noted that the cavities behind the slots are offset from the vertical axis. Thus this arrangement may be constructed, for example, by forming each cavity as a separate unit and assembling the array from separate cavities and weaving the feed layer between the cavities. Alternatively, each tube may be formed as a stepped arrangement with each alternate cavity offset to one side or the other. The term ‘tube’ as used in the present application is intended to encompass such a stepped arrangement.
Other configurations are within the scope of this invention.
The slot width is approximately 0.7λ which is about 1 cm at 2GHz. As will be seen, a 10 dB return loss for the two slots occurs in the band 1.83 to 2.01 GHz and 1.86 to 2 GHz respectively. Mutual coupling between the slots is less than −20 dB. Tuning of the length of the slots, the width of the dog bones, the width and length of the T bar and the positioning of the T bar may be used to adjust the performance of the antenna. Arrangements other than T-bars may also be used. Furthermore, a baffle as described above, has been inserted between the two slots in order to reduce coupling therebetween.
Thus the array described above may be used in single columns or multiple columns to provide a static beam of well defined shape and direction (with a static feed network) or a steerable and adaptive beam of variable beam shape and/or direction depending on the phase and gain of the feed network fed to each of the slot radiators.
In an alternative embodiment as shown in
Slots are formed through both the cylinders in the same way as described above and are shown in
With particular reference to
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Number | Date | Country | |
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20070057859 A1 | Mar 2007 | US |