Antenna feeding network

Abstract

An antenna feeding network for a multi-radiator antenna. The feeding network comprises at least one substantially air filled coaxial line, each comprising a central inner conductor, an elongated outer conductor surrounding the central inner conductor, and an elongated rail element slideably movably arranged inside the outer conductor. The rail element is longitudinally movable in relation to at least the outer conductor.

Claims

1. An antenna feeding network for a multi-radiator antenna, said feeding network comprising at least one substantially air filled coaxial line, each coaxial line comprising: a central inner conductor; an elongated outer conductor surrounding the central inner conductor; and an elongated rail element slidably arranged inside the outer conductor, said rail element being longitudinally movable in relation to said conductors, wherein at least one elongated rail element is provided with at least two dielectric elements being attached thereto.

2. The antenna feeding network according to claim 1, wherein at least one coaxial line further comprises at least one support element configured to support said central inner conductor, said support element being arranged between said inner and outer conductors.

3. The antenna feeding network according to claim 1, wherein said at least two dielectric elements are configured to co-operate with the at least one coaxial line to provide a phase shifting arrangement.

4. The antenna feeding network according to claim 1, wherein said at least two dielectric elements have a U-shaped profile such as to partly surround the inner conductor of said at least one coaxial line and to at least partly fill out the cavity between the inner and outer conductors of said at least one coaxial line.

5. The antenna feeding network according to claim 1, wherein said outer conductor is provided with guiding means configured to guide the rail element inside the outer conductor.

6. The antenna feeding network according to claim 5, wherein said guiding means comprises at least one longitudinally extending protrusion provided on the inside of said outer conductor.

7. The antenna feeding network according to claim 1 comprising a plurality of said coaxial lines and means for moving at least two rail elements of said coaxial lines simultaneously at different speed.

8. The antenna feeding network according to claim 7, wherein said means for moving comprises a longitudinally extending rod and at least first and second connecting elements, each being mechanically connected to respective at least first and second rail elements of said at least two rail elements, wherein each connecting element is provided with an internally threaded portion, said threaded portions being configured to co-operate with corresponding threaded segments of said rod, wherein said threaded segments have different pitch such that said first connecting element and first rail element moves at a different speed than said second connecting element and second rail element when said rod is rotated.

9. The antenna feeding network according to claim 8, wherein said means for moving comprises at least one electric motor arranged to rotate said longitudinally extending rod and means for electrically controlling said electric motor from a distance.

10. The antenna feeding network according to claim 2, wherein said support element is configured to position the inner conductor relative the outer conductor.

11. The antenna feeding network according to claim 1 further comprising at least one holding element configured to attach said inner conductor to said outer conductor.

12. The antenna feeding network according to claim 1, wherein said outer conductor are configured to form a cavity around the inner conductor.

13. The antenna feeding network according to claim 1, comprising at least two substantially air filled coaxial lines formed using a common elongated compartment, said elongated compartment being defined by walls forming outer conductors which surround at least two central inner conductors arranged consecutively within the compartment, wherein a common elongated rail element is slidably arranged within the compartment, and is provided with at least two dielectric elements, each being configured to co-operate with a corresponding inner conductor of the at least two coaxial lines formed in the common compartment to form at least two phase shifting arrangements.

14. The antenna feeding network according to claim 1, comprising at least two substantially air filled coaxial lines, wherein the inner conductors of at least two of said coaxial lines are interconnected by means of a connector device.

15. A multi radiator antenna comprising an electrically conductive reflector, at least one radiating element arranged on said reflector and an antenna feeding network, said radiating elements being connected to said antenna feeding network, and said antenna feeding network comprising at least one substantially air filled coaxial line, each coaxial line comprising: a central inner conductor; an elongated outer conductor surrounding the central inner conductor; and an elongated rail element slidably arranged inside the outer conductor, said rail element being longitudinally movable in relation to said conductors, wherein at least one elongated rail element is provided with at least two dielectric elements being attached thereto.

16. The multi radiator antenna of claim 15, wherein at least one coaxial line further comprises at least one support element configured to support said central inner conductor, said support element being arranged between said inner and outer conductors.

17. The multi radiator antenna of claim 15, wherein said at least two dielectric elements are configured to co-operate with the at least one coaxial line to provide a phase shifting arrangement.

18. The multi radiator antenna of claim 15, wherein said at least two dielectric elements have a U-shaped profile such as to partly surround the inner conductor of said at least one coaxial line and to at least partly fill out the cavity between the inner and outer conductors of said at least one coaxial line.

19. The multi radiator antenna of claim 15, wherein said outer conductor is provided with guiding means configured to guide the rail element inside the outer conductor.

20. The multi radiator antenna of claim 19, wherein said guiding means comprises at least one longitudinally extending protrusion provided on the inside of said outer conductor.

21. The multi radiator antenna of claim 15, comprising a plurality of said coaxial lines and means for moving at least two rail elements of said coaxial lines simultaneously at different speed.

22. The multi radiator antenna of claim 21, wherein said means for moving comprises a longitudinally extending rod and at least first and second connecting elements, each being mechanically connected to respective at least first and second rail elements of said at least two rail elements, wherein each connecting element is provided with an internally threaded portion, said threaded portions being configured to co-operate with corresponding threaded segments of said rod, wherein said threaded segments have different pitch such that said first connecting element and first rail element moves at a different speed than said second connecting element and second rail element when said rod is rotated.

23. The multi radiator antenna of claim 22, wherein said means for moving comprises at least one electric motor arranged to rotate said longitudinally extending rod and means for electrically controlling said electric motor from a distance.

24. A method for manufacturing a substantially air filled coaxial line for a multi-radiator base station antenna feeding network, said method comprising: providing a central inner conductor, an elongated outer conductor, providing an elongated rail element adapted to be slidably movable inside the outer conductor, providing at least two dielectric elements; and attaching said dielectric elements to said elongated rail element, arranging said central inner conductor on said elongated rail element, sliding said elongated rail element with said inner conductor arranged thereon into said outer conductor such that said outer conductor together with said inner conductor form a substantially air filled coaxial line.

25. The multi radiator antenna of claim 15, further comprising at least one holding element configured to attach said inner conductor to said outer conductor.

26. The multi radiator antenna of claim 15, comprising at least two substantially air filled coaxial lines formed using a common elongated compartment, said elongated compartment being defined by walls forming outer conductors which surround at least two central inner conductors arranged consecutively within the compartment, wherein a common elongated rail element is slidably arranged within the compartment, and is provided with at least two dielectric elements, each being configured to co-operate with a corresponding inner conductor of the at least two coaxial lines formed in the common compartment to form at least two phase shifting arrangements.

27. The multi radiator antenna of claim 15, comprising at least two substantially air filled coaxial lines, wherein the inner conductors of at least two of said coaxial lines are interconnected by means of a connector device.

28. The multi radiator antenna of claim 24, wherein said support element is configured to position the inner conductor relative the outer conductor.

29. The method according to claim 24, wherein said arranging comprises arranging said central inner conductor on said elongated rail element at a distance therefrom using at least one support element.

30. The method according to claim 24 further comprising: providing at least one holding element; and after said step of sliding, attaching said inner conductor to said outer conductor by means of said holding element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described in more detail with reference to the appended drawings, which show presently preferred embodiments of the invention, wherein:

(2) FIG. 1 shows a schematic view of an antenna feeding network for a multi radiator antenna;

(3) FIG. 2 shows a cross section view of a prior art coaxial line;

(4) FIG. 3 shows a schematic cross section view of a prior art multi-radiator antenna, where the outer conductors of the coaxial lines combine to form a reflector for the radiators;

(5) FIG. 4 shows a detail view of an antenna feeding network according to an embodiment of the first aspect of the invention;

(6) FIG. 5 shows a view of a multi radiator antenna according to an embodiment of the second aspect of the invention;

(7) FIG. 6 shows parts of an antenna feeding network according to an embodiment of the first aspect of the invention;

(8) FIG. 7 shows a cross section view of an antenna feeding network according to an embodiment of the first aspect of the invention;

(9) FIG. 8 shows means for moving two rail elements in an antenna feeding network according to an embodiment of the first aspect of the invention in a partial cross section view from the side; and

(10) FIG. 9 shows a schematic view of an antenna feeding network according to an embodiment of the first aspect of the invention.

DETAILED DESCRIPTION

(11) FIG. 1 schematically illustrates an antenna arrangement 1 comprising an antenna feeding network 1, an electrically conductive reflector, which is shown schematically in FIG. 1, and a plurality of radiating elements 14. The radiating elements 14 may be dipoles. The antenna feeding network 1 connects a coaxial connector 15 to the plurality of radiating elements 14 via a plurality of lines which may be coaxial lines, which are schematically illustrated in FIG. 1. The signal to/from the connector 15 is split/combined using, in this example, three stages of splitters/combiners 16.

(12) FIG. 2 shows a cross section view of a prior art coaxial line 3, where the outer conductor 5 is formed as a square cross section tube, and the inner conductor 4 is supported by dielectric support means 7.

(13) FIG. 3 shows a schematic cross section view of a prior art multi-radiator antenna, having an antenna feeding network comprising a plurality of coaxial lines, each having an outer conductor with a substantially square cross section and an inner conductor 4 arranged in the outer conductor. The antenna feeding network is of the open type, i.e. each of the coaxial lines is provided with a longitudinally extending opening 17 along one side of the outer conductor, in this case along the bottom of the outer conductor. The antenna further comprises a reflector 17 which is formed by upper outer surfaces of the outer conductors of the coaxial lines, and radiators/dipoles 14 arranged in parallel (only one is seen in the figure) on the reflector. The antenna feeding network and the reflector form a self-supporting structure.

(14) FIG. 4 shows a detail view of an antenna feeding network according to an embodiment of the first aspect of the invention. The feeding network comprises a plurality of parallel coaxial lines. The figure shows two coaxial lines 3a, 3b which each comprise a central inner conductor 4a, 4b, an elongated outer conductor 5a, 5b forming a cavity or compartment around the central inner conductor, and an elongated rail element 6a, 6b slidably arranged inside the outer conductor. The outer conductors 5a, 5b have square cross sections and are formed integrally and in parallel to form a self-supporting structure. The wall which separates the coaxial lines 3a, 3b constitute vertical parts of the outer conductors 5a, 5b of both lines. The rail elements 6a, 6b are longitudinally movable relative the outer conductors. In the figure is illustrated a support element 7 which is arranged between the rail element 6b and the inner conductor 4b, and also between the inner and outer conductors. Furthermore, the coaxial line 3a is provided with a dielectric element 8 which is attached to the elongated rail element 6a and is configured to co-operate with the coaxial line 3a. The dielectric element 8 has a U-shaped cross section and is arranged around the inner conductor 4a such that it partially surrounds the inner conductor from below and fills most of the cavity between the conductors. Arranging the dielectric element 8 in the cavity between the inner and outer conductor forms a phase shifting device arranged to adjust the phase of signals in coaxial line 3a. Since the dielectric element 8 is attached to the rail element 6b, the phase may be adjusted by moving or sliding the rail element longitudinally 6a until the desired position and phase shift is achieved.

(15) FIG. 5 shows a view of a multi radiator antenna according to an embodiment of the second aspect of the invention. The antenna 2 comprises an antenna feeding network 1, a reflector 17 and three radiating elements or dipoles 14a-c arranged on the reflector. The antenna feeding network is provided with coaxial lines 3a, 3b having central inner conductors 4a, 4b and outer conductors 5a, 5b. The description above with reference to FIG. 4 also applies to this feeding network, although no rail elements are shown in FIG. 5. In this figure, it is illustrated how the coaxial lines are integrally formed with the reflector in the sense that the reflector 17 is formed by the upper walls of the outer conductors. Each outer conductor is formed by the walls defining an elongated compartment, the walls being made in a conductive material such as aluminum. The inner conductors and the rail elements are thus arranged in elongated compartments. Although only two of the compartments are provided with inner conductors in FIG. 5, it is realized that one or a plurality of the shown compartments may also be provided inner conductors to form coaxial lines. It is further realized that the number of inner conductors (two) and number of radiators (three) shown are only for illustrative purposes, and that further inner conductors may be used to provide a splitting/combing antenna feeding network of the type shown in FIG. 1. Outer conductors of the antenna feeding network 1 are provided with openings 22. The openings 22 have an elongated shape in the lateral direction and are solely provided to allow electrical interconnection between inner conductors. The openings are thus of quite short extension in the longitudinal direction. The outer conductors thus substantially surround the inner conductors, and the antenna feeding network may be described as a substantially closed type of antenna feeding network.

(16) FIG. 6 shows parts of the antenna feeding network shown in FIG. 4. The support element 7 may be held in the desired axial position by being arranged in a circumferential recess or groove (not shown) of the inner conductor 4b. The support element has a circular through hole provided with a side opening, and is made from a flexible plastic material such that the inner conductor may be inserted into the through hole via the side opening, such that the inner conductor and the support element is engaged with each other as shown in the figure. The elongated dielectric element 8 on the other hand is attached to the rail element 6b (and thereby axially fixated). Thus, the support element(s) is axially fixated relative to the inner conductor, while the dielectric element(s) is axially fixated to the rail element. Prior to inserting the inner conductors, rail elements, support element(s) and dielectric element(s) into the outer conductors, the inner conductors and the support element are placed on top of the rail element, for example as illustrated in FIG. 6. Thereafter, the inner conductors, rail elements, support element(s) and dielectric element(s) are pushed into corresponding outer conductors as a single unit. Since the support element 7 is axially fixated to the inner conductor 4b, their relative positions are maintained after having been inserted into the corresponding outer conductor. After the inner conductors, rail elements, support element(s) and dielectric element(s) have been inserted into the outer conductors, each inner conductor is advantageously attached or fixated to the corresponding outer conductor, for example by means of at least one holding element. After the inner conductors have been attached or fixated, the rail elements may be moved back and forth independently of the inner conductors. It is understood that only axial portions of the inner conductors and rails are shown, and that at least one support element corresponding to that of inner conductor 4b may also be attached to inner conductor 4a, and that at least one rail dielectric element corresponding to element 8 may also be attached to the rail element 6a.

(17) The connector device 19 and the inner conductors 4a, 4b together form a splitter/combiner. When operating as a splitter, the inner conductor 4b is part of the incoming line, and the two ends of the inner conductor 4a are the two outputs of the splitter. The dielectric element 8 can be moved along the inner conductor 4a, which forms first and second coaxial output lines on opposite sides of the connector device 19 (together with an outer conductor which is not shown). The dielectric element thus has various positions along those coaxial output lines.

(18) We first consider the case when the dielectric element 8 is placed in a central position, equally filling the first and second output coaxial lines. When a signal is entered at the input coaxial line 4b, it will be divided between the first output coaxial line and the second output coaxial line, and the signals coming from the two output coaxial lines will be equal in phase. If the dielectric element 8 is moved in such a way that the first output coaxial line will be more filled with dielectric material than the second output coaxial line, the phase shift from the input to the first output will increase. At the same time the second output coaxial line will be less filled with dielectric, and the phase shift from the input to the second output will decrease. Hence, the phase at the first output will lag the phase at the second output. If the dielectric part is moved in the opposite direction, the phase of the first output will lead the phase of the second output. The splitter/combiner may thus be described as a differential phase shifter.

(19) FIG. 7 shows a detailed cross section view of the antenna feeding network shown in FIG. 4. In FIG. 7, it is clearly illustrated how the outer conductor is provided with guiding means configured to guide the rail element inside the outer conductor. The guiding means comprises one longitudinally extending protrusion or ridge 9a, 9b on each inner side wall of the outer conductor arranged at a distance from the bottom surface of the outer conductor corresponding to the thickness of the rail element 6b. The ridges extend in parallel along the whole or essentially the whole length of the outer conductor (in the depth direction as shown in the figure), such that the rail element is guided from below by the bottom surface 20 and from above by the ridges 9a, 9b.

(20) FIG. 8 shows means for moving two rail elements in an antenna feeding network according to an embodiment of the first aspect of the invention. The means for moving the two rail elements of the coaxial lines is configured to move the rail elements simultaneously at different speeds. The means for moving comprises a longitudinally extending rod 10 and at least first and second connecting elements 11, 12, each connecting element being provided with an internally threaded portion 11a, 11b, the internally threaded portions being configured to co-operate with corresponding (externally) threaded segments or portions 10a, 10b of the rod 10, wherein the threaded segment or portion 10a of the rod has a greater pitch than the other threaded segment or portion 10b, such that the first connecting element 11 moves at a greater speed than the second connecting element 12 when the rod is rotated. The connecting elements 11, 12 are connectable to respective rail elements (not shown in the figure) through elongated slots in the outer conductors. The rod may be rotated manually or using electric motors controlled by a controlling device such as micro-controller. When using electric motors, the rails, and hence the downtilt of the antenna, can be controlled remotely. The remote control can be achieved e.g. by connecting the motor and micro-controller to a cellular base station, or some other means for control. The means for moving two rail elements illustrated in FIG. 8 may be combined with two or more splitter/combiners of the differential phase shifting type illustrated in FIG. 6. Thus, the means for moving may be configured to move a rail element 6b and dielectric element 8 of a first splitter/combiner simultaneously and at a different speed than a rail element and dielectric of a second splitter/combiner. Such a combination including a plurality of differential phase shifters may be used in an antenna arrangement to provide a variable electrical tilt angle.

(21) FIG. 9 shows a schematic cross section view of an antenna feeding network. The feeding network comprises eight coaxial lines. The figure shows four compartments 105a-105d formed in parallel in an integral self-supporting structure. The walls which separate the compartments constitute vertical parts of the outer conductors. In each of the first and second compartments 105a, 105b, a single inner conductor 104a, 104b is arranged, forming first and second coaxial lines together with the walls defining the compartment. In the compartment 105c, two inner conductors 104c1, 104c2 are arranged spaced apart from each other as seen in the longitudinal direction forming third and fourth coaxial lines using the walls defining compartment 105c as outer conductors. In the fourth compartment 105d, four inner conductors 104d1-104d4 are arranged spaced apart from each other as seen in the longitudinal direction forming fifth-eighth coaxial lines using the walls defining compartment 105d as outer conductors.

(22) The inner conductor 104a forms part of an incoming line 115. The inner conductor 104a of the first coaxial line is interconnected to the inner conductor 104b of the second coaxial line by means of a connector device 119a. Opposite ends of the inner conductor 104b of the second coaxial line are interconnected to the inner conductors 104c1 and 104c2, respectively, by means of connector devices 119b1 and 119b2. Opposite ends of the inner conductor 104c1 of the third coaxial line are interconnected to the inner conductors 104d1 and 104d2, respectively, by means of connector devices 119c1 and 119c2. The inner conductor 104c2 is connected to the inner conductors 104d3 and 104d4 by means of connector device 119c3 and 119c4 in the same manner. The connector devices 119a, 119b1-b2, 119c1-c3 may be of the same type shown in FIG. 6 and described above. Each of the inner conductors 104b, 104c and 104d may be considered to be a part of separate coaxial output lines on opposite sides of the corresponding connector device together with the outer conductors formed by the walls defining the respective surrounding compartment.

(23) The second, third and fourth compartments 105b-d are each provided with an elongated rail element 106b-d slidably arranged inside the corresponding compartment. The rail elements are longitudinally movable in the compartment. The rail element 106b in the second compartment is provided with a dielectric element 108b which is attached thereto such that the first and second coaxial lines form a splitter/combiner with differential phase shift as described above with reference to FIG. 6. The rail element 106c in the third compartment is provided with two dielectric elements 108c1, 108c2 which are attached thereto in a longitudinally spaced apart manner. The dielectric elements 108c1, 108c2 are configured to co-operate with a respective coaxial line formed with inner conductor 104c1, 104c2, such that the second coaxial line together with the third and fourth coaxial lines form two splitters/combiners with differential phase shift. In the same manner, the rail element 106d in the fourth compartment is provided with four dielectric elements 108d1-d4 which are attached thereto in a longitudinally spaced apart manner. The dielectric elements 108d1-d4 are configured to co-operate with a coaxial line formed with respective inner conductor 104d1-d4, such that the third and fourth coaxial lines together with the fifth-eighth coaxial lines form four splitters/combiners with differential phase shift. In other embodiments, the dielectric elements in the fourth compartment are omitted. The dielectric elements may be of the same type shown in FIG. 6 and described above.

(24) As shown schematically in the figure, the ends of the fourth-eighth coaxial lines are each connectable to a corresponding radiator/dipole, thus forming a multi radiator antenna. The upper side of the outer conductors (not visible in the shown cross section view) may form a reflector on which the radiators are arranged in the same manner as shown in FIG. 5 and described above.

(25) The embodiments shown in FIGS. 8 and 9 are advantageously combined to provide an antenna with electrically adjustable tilt. In such an embodiment, the means for moving are preferably configured to move the rail 106c (and the dielectric elements 108c1-c2) twice as fast/long as the rail 106d (and the dielectric elements 108d1-d4), and to move the rail 106b (and the dielectric element 108b) twice as fast/long as the rail 106c, i.e. four times as fast/long as the rail 106d.

(26) The text above describes one possible, but not limiting, embodiment of the invention. Other embodiments are possible, e.g. with other numbers of radiators such as 2, 4, 6, 10, 12, 14, 16, 18 etc. Embodiments with odd number of radiators are also possible.

(27) In such other implementations, the movement of the different rails will not be exactly twice or four times compared to that of the slowest moving rail.

(28) The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the number of coaxial lines may be varied, the number of radiators or dipoles may be varied, the number of coaxial lines provided with rail elements may be varied, the number of coaxial lines provided with dielectric elements and/or support elements may be varied, and the shape of the support element(s) and dielectric element(s) may be varied. Furthermore, the reflector does not necessarily need to be formed integrally with the coaxial lines, but may on the contrary be a separate element. The scope of protection is determined by the appended patent claims.