Patent Application
20050206575
The present invention relates to a dual polarisation antenna.
A conventional dual polarisation antenna is described in U.S. Pat. No. 6,072,439. A pair of side walls are arranged on opposite sides of a line of six crossed-dipole radiating elements. In one embodiment the side walls are C-shaped in cross-section and have edges which create a diffraction pattern that increases the beamwidth by approximately ten degrees compared to similar antennas with no side walls. In another embodiment the side walls are L-shaped in cross-section and narrow the 3 dB beamwidth of the antenna compared to similar antennas with no sidewalls. A single parasitic isolation element is located midway along the length of the line of dipole radiating elements.
An alternative antenna arrangement is described in U.S. Pat. No. 5,952,983. A line of three cross-dipole radiating elements is provided, with a parasitic element between two of the radiating elements. In one arrangement, the parasitic element is inserted into a groove formed along the top edge of a non-conducting support which extends transversely across the array and is attached to the back plane. In another arrangement, the parasitic element is supported and elevated by pairs of rod supports.
In U.S. Pat. No. 5,940,044, isolation elements in the form of isolation plates of conductive material are disposed between each dipole sub-array. The isolation plates are connected to the back plate by suitable fasteners.
Various different isolation devices are described in U.S. Pat. No. 6,028,653, including isolation trees or bars arranged between bow tie radiating assemblies; isolation rails arranged alongside bow tie assemblies; rods or wires arranged in or on a radome that covers the bow tie assemblies; isolation strips arranged between a positive and negative arm of a dipole of a bow tie assembly; or a combination of one or more of the above.
An object of the invention is to provide an alternative antenna construction incorporating side walls and one or more isolating elements.
The present invention provides a dual polarisation antenna comprising:
The invention provides an alternative method of supporting the isolating element(s). In contrast to the prior art discussed above, which uses the back plane to support the isolating element(s), we use the side walls to fully or at least partially support the isolating element(s).
The side walls modify the beam width of the antenna (compared to a similar antenna with no side walls), and the isolating element(s) improve isolation between the two polarisation ports of the antenna.
By using the side walls to support the isolating element(s) we reduce the number of parts compared to U.S. Pat. No. 5,952,983, which requires separate members to support the isolating element.
There may be a continuous conductive connection between the isolating element and the side wall(s). For instance the isolating element may be soldered to one or both of the side walls, or the isolating element and its supporting side wall(s) may be formed integrally from a single piece of conductive material. However a problem with a conductive connection is that in some circumstances, intermodulation distortion may occur at the joint between the element and its supporting side wall(s). Therefore in some embodiments an insulating element is arranged between an isolating element and its supporting side wall. The insulating element may be a strip of tape, or may be an element such as a rivet which passes through a hole in the supporting side wall.
Preferably, the antenna comprises:
This provides a more symmetrical arrangement than the arrangement in U.S. Pat. No. 6,072,439. We have found that this added symmetry improves isolation between the two polarisation ports of the antenna.
At a minimum (that is, in the case where only two radiating elements are provided) only three isolating elements are required—one between the radiating elements and one at each end. In the more general case, (that is, where n radiators are provided) n+1 isolating elements will typically be provided (although in some arrangements only n−1 may be required, with the isolating elements at each end omitted).
Typically the radiating elements are arranged in front of a planar reflector. The isolating elements may be partially supported by the reflector (either directly or via an insulating element), or may be fully supported by one or both of the side walls.
The isolating elements may be supported by one of the side walls only. In this case, the element is typically formed as a substantially rectangular tab. The element is preferably directed inwardly: that is, the element subtends an angle of less than 180 degrees with the inner face of its supporting side wall.
Alternatively, the isolating elements(s) may be supported by both side walls.
In one embodiment at least one of the isolating element(s) comprises a rod with a substantially circular cross-section. In another embodiment at least one of the isolating element(s) comprises a wall, which may be connected to the back reflector as well as the two side walls. In another embodiment at least one of the isolating element(s) comprises a strip which is substantially rectangular in cross-section.
In one embodiment the isolating element is formed with a ridge or trough between the two side walls. Preferably the ridge or trough is formed by bending a strip of metal.
The radiating elements may be dipoles, as in U.S. Pat. No. 5,952,983. However, a problem with using dipoles is that they are relatively tall, and therefore the isolating element(s) need(s) to be mounted some distance away from the back reflector. For this reason, in U.S. Pat. No. 5,952,983 the isolating rods are mounted on rod supports. Therefore preferably the radiating elements are patches. Patches generally have a lower profile than dipoles, thus enabling the isolating element(s) to be supported by a side wall at a lower position.
Typically the side walls are substantially continuous (that is—with no slots or holes formed in them).
Typically the side walls are postioned to influence the azimuthal beamwidth of the antenna, for instance to provide an azimuthal beamwidth of 65 degrees.
Typically a plurality of radiating elements are provided, for instance eight. One or more phase shifters may be provided to generate relative phase differences between the elements, for instance to control beam downtilt in a cellular communication system which communicates with mobile devices.
The isolating element(s) may be placed between adjacent radiating elements, and/or aligned with respective radiating elements.
Three embodiments of the invention will now be described with reference to the accompanying drawings, in which:
a is a plan view of the patch tray assembly.
Referring to the first embodiment shown in
Referring to
The side walls 11,12 each support eight rectangular tabs which are each aligned with the centre of a respective patch radiating element. Two of the tabs 40,41 are shown in cross-section in
Eight additional isolating elements are suspended between the side walls 11,12. One of the elements is shown in detail in
In an alternative embodiment (not shown) the cylindrical rods may be replaced by flat strips with a planar surface lying parallel with the reflector 10. These strips may be welded to the side walls 11,12 or insulated from the side walls by insulating elements.
An alternative patch tray assembly is shown in
Prior to folding to form the reflector 10 and side walls 11,12, the aluminium sheet is powder coated with an electrically insulating layer 60 shown in
In an alternative arrangement (not shown), powder coating of the reflector 10 and side walls 11,12 may not be necessary.
An alternative isolating element is shown in
In an alternative arrangement (not shown), the strip 70 may be bent downwardly to form a trough at its central point.
The antenna is mounted vertically in use at a cellular telecommunication base station. The patch radiating elements transmit and receive signals at +45 degrees and −45 degrees polarisation which are fed to/from the antenna via respective polarisation ports (not shown). The −3 dB beamwidth of the antenna is reduced to approximately 65 degrees by the side walls 11,12. The antenna typically works in a cellular telecommunication band such as 1710-1880 MHz, 1750-1990 MHz or 1900-2170 MHz, but could be reasonably expected to work anywhere between 400 and 3000 MHz.
Isolation between the different polarisation ports is improved by the isolating elements positioned between the radiating elements and by the tabs mounted on the side walls. It has also been found that isolation is improved in some cases by including isolating elements at the top and bottom of the array—that is, by including the rod 14 and end wall 13 shown in
As shown in
We have found that the gap between the side walls 52,53 of the isolating element 50 and the side walls 11,12 of the tray is particularly critical to the operation of the antenna. This spacing can be accurately controlled by suitable selection of the thickness of the powder layer 60 and tape 61,62. We have found that the rods in the first embodiment do not need to be so close to the side walls, so can be spaced further away by the insulating bushes 42,43. The arrangement of
Where in the foregoing description reference has been made to integers or components having known equivalents then such equivalents are herein incorporated as if individually set forth.
Although this invention has been described by way of example it is to be appreciated that improvements and/or modifications may be made thereto without departing from the scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 509097 | Dec 2000 | NZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NZ01/00293 | 12/20/2001 | WO | 12/27/2004 |
