DUAL POLARISED PLANAR ANTENNA, BASE STATION AND METHOD OF MANUFACTURE

Abstract

A dual polarised planar antenna (10) comprising first (12) and second (13) antenna elements having respective orthogonal polarisations, the antenna elements (12, 13) being arranged in a back-to-back configuration and fed directly by respective first and second antenna feeds (15), wherein the dual polarised planar antenna (10) further comprises a parasitic element (14) arranged between the antenna elements (12, 13) such that in-use the antenna feeds (15) are decoupled. Particularly suited to low profile antennas and compact antenna base stations. Also relates to a method of manufacture.

Claims

1. A dual polarised planar antenna comprising first and second antenna elements having respective orthogonal polarisations, the antenna elements being arranged in a back-to-back configuration and fed directly by respective first and second antenna feeds, wherein the dual polarised planar antenna further comprises a parasitic element arranged between the antenna elements, such that in-use the antenna feeds are decoupled.

2. The dual polarised planar antenna of claim 1, wherein the parasitic element is sandwiched between the antenna elements.

3. The dual polarised planar antenna of claim 1, wherein the parasitic element consists of a single substantially annular parasitic element.

4. The dual polarised planar antenna of any one of claim 1, wherein the antenna elements are planar antenna elements.

5. The dual polarised planar antenna of claim 4, wherein the antenna elements are printed circuit board antennas.

6. The dual polarised planar antenna of any one of claim 4, wherein each of the antenna elements comprises a dipole antenna.

7. The dual polarised planar antenna of claim 6, wherein the dipole antennas have orthogonal radiating arms.

8. The dual polarised planar antenna of claim 4, wherein the antenna elements further comprise parasitic radiating elements.

9. The dual polarised planar antenna of claim 4, wherein each planar antenna element comprises a dog-leg feed.

10. The dual polarised planar antenna of claim 9, wherein the parasitic element is arranged between the dog-leg feeds.

11. The dual polarised planar antenna of claim 1, further comprising a main antenna back plate arranged adjacent the antenna elements.

12. The dual polarised planar antenna of claim 11, wherein the main antenna back plate comprises a centre plate and two angled wing plates.

13. The dual polarised planar antenna of claim 12, wherein the wing plates are angled at 150 degrees to the centre plate.

14. The dual polarised planar antenna of claim 11, further comprising an intermediate back plate arranged between the main antenna back plate and the antenna elements.

15. The dual polarised planar antenna of claim 1, mounted upon a vehicle.

16. A base station antenna, comprising a plurality of the dual polarised planar antennas of claim 11, the dual polarised planar antennas being arranged in a substantially equidistant distributed array around a central axis, such that in-use the dual polarised planar antennas provide combined dual-polarised omnidirectional performance directed away from the central axis.

17. The base station antenna of claim 16, further comprising powering means for powering the dual polarised planar antennas in-phase with each other.

18. Use of a parasitic element to decouple antenna feeds of respective back-to-back antenna elements having orthogonal linear polarisations.

19. The use of claim 18, wherein the parasitic element consists of a single substantially annular parasitic element.

20. A method of manufacturing a dual polarised planar antenna, comprising the steps of: a) Arranging first and second antenna elements having orthogonal linear polarisations in a back-to-back configuration; b) Providing respective first and second antenna feeds as direct feeds to the antenna elements; and then c) Arranging a parasitic element between the antenna elements; such that in-use the antenna feeds are decoupled.

21. The method of claim 20, wherein the parasitic element consists of a single substantially annular parasitic element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0023] FIG. 1a illustrates in cutaway plan view an embodiment of a dual polarised planar antenna with a parasitic element;

[0024] FIG. 1b illustrates in cutaway plan view the arrangement of the parasitic element in FIG. 1a;

[0025] FIG. 2a illustrates in perspective view an embodiment of a base station antenna; and

[0026] FIG. 2b illustrates in plan view the base station antenna of FIG. 2a.

DETAILED DESCRIPTION

[0027] FIG. 1a illustrates in cutaway plan view an embodiment of a dual polarised antenna 10. The dual polarised antenna 10 is a planar antenna comprising a square printed circuit board 11. A first dipole antenna 12 is printed on one side of circuit board 11. A second dipole antenna 13 is printed on an opposing side of circuit board 11. Each dipole (12, 13) is 116 mm in length, measured linearly between the outer periphery of the radiating arms. The figure shows the circuit board 11 being semi-transparent for indicative purposes only. The dipole antennas (12, 13) are shown as having 90 degree relative rotation about a central axis perpendicular to the circuit board 11. This achieves respective orthogonal linear polarisations. At the centre of the dipoles (12, 13) are respective dog leg feeds 15. The feeds 15 are directly connected to the radiating elements of the dipoles (12, 13). Between the feeds 15 there is a parasitic element 14. The parasitic element is annular having a 11 mm diameter and is formed from metal. Additional radiators 16 are also present on both opposing sides of the circuit board 11. The additional radiators 16 have a length of 30 mm. The multi-sectored element array has two distinct isolated radiating elements providing an overall multi-channel performance.

[0028] FIG. 1b illustrates in cutaway plan view the dual polarised planar antenna 10 of FIG. 1a, zoomed to depict the arrangement of the parasitic element 14. The dog leg feeds 15a and 15b of the first and second dipole antennas (12, 13) are shown adjacent each other, but rotated 90 degrees to each other. The dog legs 15a and 15b can therefore be interfaced with separately at locations 17a and 17b respectively. The annular parasitic element 14 is shown sandwiched between the feeds 15a and 15b to mitigate coupling.

[0029] In use the dual polarised planar antenna 10 is fed using dog leg feeds 15a and 15b. The orthogonal spatial orientations of dipoles 12 and 13 results in the transmitted radiation from each dipole (12, 13) having a different linear polarisation. Radiation that would normally electromagnetically couple between the feeds 15a and 15b is absorbed by the parasitic element 14. This allows for two channels of simultaneous transmission whilst minimising artefacts of a signal transmitted from one dipole (12, 13) antenna coupling across to the transmission from the other (13, 12). A similar benefit is achieved from the dipole antennas (12, 13) are operated in receive.

[0030] FIG. 2a illustrates in perspective view dual polarised planar antennas 10 arranged as a base station around a central axis ‘A’. A total of three planar antennas 10 are shown positioned adjacent respective main back plates 20. Intermediate each main back plate 20 is an intermediate back plate 24. Each planar antenna and respective main 20 and intermediate 24 back plates are fixed relative to each other using non-conductive pillar mounts 25. The distance between an antenna 10 and its respective main back plate 20 is 120 mm. The distance between an antenna 10 and its respective intermediate back plate 20 is 40 mm. The intermediate back plate 24 measures 90 mm x×90 mm and is spatially smaller than the main back plate 20. The main back plates 20 comprise a central plate 21 and two wing plates 22a and 22b. The total width of each main back plate is 260 mm, measured between the respective ends of the wing plates 22a and 22b. The central plate 21 is parallel to the respective planar antenna 10, whereas the wing plates 22 are angled thereto. All the back plates (20, 24) are formed from metal.

[0031] FIG. 2b further illustrates the base station shown in FIG. 2a in plan view. The dual polarised planar antennas 10 are shown adjacent their respective main back plates 20, forming a total of three directional antennas. The main back plates 20 are able to abut each other to form a spatially compact base station, owing to the angling of the wing plates 22. The wing plates 22 in this embodiment are angled relative to the central plate 21 by 150 degrees. The base station therefore comprises an array of directional antennas that radiate away from the central axis ‘A’ in a combined omnidirectional manner.

[0032] In use each dual polarised antenna 10 transmits from both its respective dipole antennas (12, 13), each dipole antenna (12, 13) transmitting with a different linear polarisation. Radiation transmitted towards the main back plate 20 and intermediate back plate 24 is reflected, giving each dipole antenna a directional radiation pattern. The distances between the main back plate 20 and intermediate back plate 24 can be configured for particular frequencies (for instance the intermediate back plate 24 may be used to define cavity back plate for higher frequencies than the main back plate 20. The radiation patterns from each dual polarised antenna 10 with respective back plates (20, 24) can be configured to overlap to provide high gain omnidirectional performance radiating away from central axis A. This provides a high gain omnidirectional base station simultaneously operable at two orthogonal polarisations, with a compact design. The described base station may operate at frequencies between 600 MHz and 3.4 GHz, but with an overall diameter of approximately 160 mm.

[0033] Whilst the embodiments show printed dipole antennas, this is not intended to be limiting. Other antenna designs can be configured in a back-to-back arrangement and operated with two polarisations if a parasitic element is arranged between the antenna feeds. In addition, a base station may be designed with an alternative number of antenna elements if the wing plates of the main back plates are angled differently. The dual polarised antennas may be operated in phase, but may additionally be used to provide angular diversity to the base station. A plurality of base station antennas may be attached together so as to provide increased bandwidth. For instance a first base station antenna may be used for covering 2G, 3G and 4G frequencies, with a second base station antenna attached to the first base station antenna, optionally providing additional 5G frequency coverage. The base station antennas may be vertically mounted to each other so as to not obstruct their respective omnidirectional performances.