Abstract
An antenna feeding network for a multi-radiator base station antenna and an antenna arrangement comprising such a feeding network is provided. The feeding network comprises substantially air filled feeding lines and a coaxial connector for an antenna feeder cable, the connector being connected to at least one of the coaxial lines. The substantially air filled feeding lines each have a central inner conductor and an elongated outer conductor surrounding the central inner conductor. The coaxial connector comprises a body having an attachment portion, the attachment portion being attached to, and arranged in abutment with, a portion of at least one outer conductor such that the body connects electrically and mechanically with the outer conductors of the feeding lines.
Claims
1. An antenna feeding network for a multi-radiator base station antenna, said feeding network comprising: feeding lines, each having a first conductor and a second conductor surrounding the first conductor, the first and second conductor running in parallel and separated substantially by air; a coaxial connector for an antenna feeder cable, said connector being connected to at least one of said feeding lines; wherein said coaxial connector comprises a body having an attachment portion arranged to extend in parallel and in abutment with a longitudinally extending portion of at least one second conductor, said attachment portion being attached to said longitudinally extending portion, whereby said body connects electrically with said second conductor.
2. The antenna feeding network according to claim 1, wherein the second conductor is wider than the first conductor.
3. The antenna feeding network according to claim 1, wherein said attachment portion is attached to said longitudinally extending portion by means of screws or bolts extending perpendicularly relative said longitudinally extending portion.
4. The antenna feeding network according to claim 1, wherein said coaxial connector comprises a central pin connected to a primary first conductor, namely one of the first conductors of said feeding lines.
5. The antenna feeding network according to claim 3, wherein an end portion of said central pin and an end portion of a primary first conductor, are each provided with an engaging portion configured to engage with each other, wherein one of said engaging portions is in the form of a cavity and the other is in the form of a protrusion.
6. The antenna feeding network according to claim 3, wherein said central pin is galvanically connected to said primary first conductor, and wherein said primary conductor is indirectly interconnected with at least one further first conductor of said first conductors to provide a capacitive and/or inductive connection there between.
7. The antenna feeding network according to claim 6, further comprising at least one connector device configured to indirectly interconnect said primary first conductor and said at least one further first conductor.
8. The antenna feeding network according to claim 7, comprising at least one insulating layer, wherein the insulating layer is arranged on the connector device or on said primary first conductor or on the at least one further first conductor thereby indirectly connecting said first conductor to said at least one further first conductor.
9. The antenna feeding network according to claim 3, further comprising a DC grounded stub or a coil connected between said central pin and said body.
10. The antenna feeding network according to claim 4, further comprising a DC grounded stub or a coil connected between at least one first conductor and at least one second conductor.
11. The antenna feeding network according to claim 4, wherein said central pin is galvanically connected to said primary first conductor, the antenna feeding network further comprising: a grounding device connected between at least one first conductor and at least one second conductor; a connector device indirectly interconnecting said primary first conductor with at least one further first conductor of said first conductors to provide a capacitive and/or inductive connection there between, wherein the connector device is connected to the primary first conductor at a location between the central pin and the grounding device such that a quarter wave stub is formed between the connector device and the grounding device.
12. The antenna feeding network according to claim 4, wherein said central pin is galvanically connected to said primary first conductor, the antenna feeding network further comprising: a screw used to galvanically connect at least one first conductor and at least one second conductor thereby DC grounding said first conductor; a connector device indirectly interconnecting said primary first conductor with at least one further first conductor of said first conductors to provide a capacitive and/or inductive connection there between, wherein the connector device is connected to the primary first conductor at a location between the central pin and the screw such that a quarter wave stub is formed between the connector device and the screw.
13. The antenna feeding network according to claim 4, wherein said central pin is galvanically connected to said primary first conductor, the antenna feeding network further comprising: a connector device galvanically interconnecting said primary first conductor with at least one further first conductor of said first conductors, a grounding device connected between one of said at least one further first conductors and at least one second conductor.
14. The antenna feeding network according to claim 9, wherein said DC grounded stub is grounded to a reflector by a grounding device, wherein an end portion of said stub and an end portion of said grounding device are each provided with an engaging portion configured to engage with each other, wherein one of said engaging portions is in the form of a cavity and the other is in the form of a protrusion.
15. The antenna feeding network according to claim 1, wherein said longitudinally extending portion is formed by at least one bottom or top portion of said second conductors.
16. The antenna feeding network according to claim 1, wherein said longitudinally extending portion is formed by at least one side wall portion of said second conductors.
17. The antenna feeding network according to claim 4, further comprising a RF grounded stub or coil indirectly connected between said central pin and said body.
18. The antenna feeding network according to claim 5, further comprising a RF grounded stub or coil indirectly connected between said first conductor and a second conductor surrounding said first conductor.
19. The antenna feeding network according to claim 18, wherein said RF grounded stub is indirectly connected to at least one of said second conductors by a grounding device, wherein an end portion of said stub and an end portion of said grounding device are each provided with an engaging portion configured to engage with each other, wherein one of said engaging portions is in the form of a cavity and the other is in the form of a protrusion.
20. The antenna feeding network according to claim 19, said grounding device is mechanically attached to the second conductor with a screw and is electrically isolated from the second conductor by an isolating film or layer between the grounding device and the second conductor and an isolating bushing surrounding a portion of the screw protruding through the second conductor.
21. The antenna feeding network according to claim 11, further comprising a circuitry connected to the grounding device, said circuitry being arranged to separate DC voltage and a communication signal.
22. The antenna feeding network according to claim 11, wherein a gas discharge tube is connected between the grounding device and the second conductor.
23. An antenna arrangement comprising: an antenna feeding network having: feeding lines, each having a first conductor and a second conductor surrounding the first conductor, the first and second conductor running in parallel and separated substantially by air; a coaxial connector for an antenna feeder cable, said connector being connected to at least one of said feeding lines; wherein said coaxial connector comprises a body having an attachment portion arranged to extend in parallel and in abutment with a longitudinally extending portion of at least one second conductor, said attachment portion being attached to said longitudinally extending portion, whereby said body connects electrically with said second conductors; and a reflector extending in parallel with said feeding lines.
24. The antenna arrangement according to claim 23, wherein said reflector is integrally formed with the feeding lines.
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 schematically illustrates a multi-radiator antenna arrangement;
(3) FIG. 2 shows a prior art antenna feeding network where the coaxial connector is attached to a bottom plate;
(4) FIG. 3 shows a view from the rear side of parts of an antenna feeding network according to an embodiment of the first aspect of the invention;
(5) FIG. 4 shows a view from the reflector side of an antenna feeding network according to an embodiment of the first aspect of the invention;
(6) FIG. 5 shows a view from the rear side of the embodiment in FIG. 4;
(7) FIG. 6 shows a cross section side view of the embodiment in FIGS. 4 and 5 where DC-grounding of the inner conductor is illustrated;
(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 a view from the rear side of a feeding network according to an alternative embodiment of the first aspect of the invention; and
(10) FIG. 9 shows a cross section view of parts of an antenna feeding network according to an embodiment of the first aspect of the invention where the DC grounding has been replaced with a RF grounding.
DETAILED DESCRIPTION
(11) FIG. 1 schematically illustrates an antenna arrangement 1 comprising an antenna feeding network 2, an electrically conductive reflector 4, which is shown schematically in FIG. 1, and a plurality of radiating elements 6. The radiating elements 6 may be dipoles.
(12) The antenna feeding network 2 connects a coaxial connector 10 to the plurality of radiating elements 6 via a plurality of lines 14, 15, which may be coaxial lines, which are schematically illustrated in FIG. 1. The signal to/from the connector 10 is split/combined using, in this example, three stages of splitters/combiners 12.
(13) FIG. 2 shows a prior art antenna feeding network 2 comprising an electrically conductive reflector 4 and a substantially air filled coaxial line formed by an outer conductor 15 and an inner conductor 14. The outer conductor 15 are integrally formed with the reflector 4. A coaxial connector 10 is mechanically attached to a bottom plate 3, which in turn is attached to end portions of the reflector/outer conductors. The coaxial connector 10 is electrically connected to the inner and outer conductors via a separate coaxial cable 5. At an end of the separate coaxial cable, its outer line is connected to the outer conductor 15 using a connection piece 7, and its inner line is connected to the inner conductor 14 in a groove 8.
(14) FIG. 3 shows a view from the rear side of parts of an antenna feeding network according to an embodiment of the first aspect of the invention. The rear side in this context refers to the side of the antenna feeding network opposite to the (reflector) front side on which radiating elements (not shown) are mounted. The antenna feeding network comprises outer conductors 15a-c which together with inner conductors arranged therein (not shown) form air filled coaxial lines. The outer conductors 15a-c have square cross sections and are formed integrally and in parallel to form a self-supporting structure. The outer conductors 15a-c are formed integrally with the reflector 4 in the sense that the upper and lower walls of the outer conductors are formed by the front side and the back side of the reflector, respectively. A coaxial connector 10 is shown which comprises a body or outer connector 11 which is provided with an attachment portion 11a. The attachment portion 11a is arranged to extend in parallel and in abutment with a longitudinally extending portion of the outer conductors/reflector, i.e. the portion of the reflector or outer conductors which is, as seen in the figure, arranged directly below the attachment portion. The attachment portion 11a is attached to the longitudinally extending portion of the reflector 4 by means of for example screws or bolts (not shown) in the holes illustrated in the figure. Electrical connection between the body of the coaxial connector and the reflector/outer conductors is achieved through direct contact between the attachment portion and the reflector. A mechanically stable attachment of the coaxial connector may be achieved due to the large area of contact between the attachment portion and the reflector.
(15) FIG. 4 shows a view from the front side 17 of the reflector of an antenna feeding network according to an embodiment of the first aspect of the invention. The front side in this context refers to the side of the antenna feeding network on which the front of the reflector and the radiating elements (not shown) are disposed. The reflector is integrally formed with the outer conductors in the same manner as described above with reference to FIG. 3, but may in other embodiments be a separate component. A coaxial connector 10 is shown which comprises a body or outer connector 11 which is provided with an attachment portion 11a. The attachment portion 11a extends in parallel with, and in abutment with, a longitudinally extending portion of the outer conductors. The attachment portion 11a is attached to the longitudinally extending portion by means of screws 9 extending in perpendicular relative the front side 17 of reflector. Since the screws are spaced apart both in the longitudinal and in the lateral direction, it is ensured that a consistent electrical connection is achieved between the attachment portion and the outer conductors, even if the coaxial connector is subject to mechanical forces in different directions.
(16) FIG. 5 shows a view from the rear side of the same embodiment shown in FIG. 4. In this figure, part of the rear side of the reflector is removed to illustrate the internal components of the antenna feeding network. A central pin 13 of the coaxial connector 10 extends through the body 11 and connects with a first central inner conductor 14a arranged inside an outer conductor to form a first coaxial line. The interconnection between the central pin and the first central inner conductor is shown in more detail in FIG. 6. The first central inner conductor 14a is interconnected to a second central inner conductor 14b using a connector device 16 extending between the two coaxial lines. The first central inner conductor 14a is connected to the reflector (and consequently also to the outer conductors 15a, 15b) using a quarter wave stub 18 which is grounded to the reflector by grounding device 18a. The quarter wave stub 18 is configured to provide a DC ground for the inner conductor 14a.
(17) In the embodiment in FIG. 5, the quarter wave stub 18 and the first central inner conductor 14a are both formed by a rod shaped conductor, where the portion of the conductor between the central pin 13 and the connector device forms the first central inner conductor 14a, while the portion of the conductor between the connector device 16 and the grounding device 18a forms the quarter wave stub 18. The grounding device 18a may also be considered a part of the quarter wave stub. In embodiments, the connector device 16 may be configured to provide an indirect interconnection between the first central inner conductor 14a and the second central inner conductor 14b. The indirect interconnection may be achieved using at least one insulating layer (not shown) arranged in between the conductive material of the connector device and the conductive material of the inner conductors.
(18) Although the first and second inner conductors 14a, 14b are illustrated as neighbouring inner conductors they may actually be further apart thus having one or more coaxial lines, or empty cavities or compartments, in between.
(19) Although the invention is illustrated with two neighbouring inner conductors 14a, 14b it falls within the scope to have a connector device 16 than can bridge two or even more inner conductors. Such a connector device (not shown) may thus be designed so that it extends over a plurality of coaxial lines between two inner conductors or over empty cavities or compartments. Such a connector device (not shown) may also be used to connect three or more inner conductors.
(20) FIG. 6 shows a cross section side view of the embodiment shown in FIGS. 4 and 5. The cross section is seen through the center pin of the coaxial connector 10, the first central inner conductor 14a and the quarter wave stub 18. The central pin 13 is provided with an engaging portion in the form of a rod-shaped protrusion 13a extending axially from its end, and which is arranged inside a corresponding engaging portion in the form of an axially extending cavity 14a in a first end of the first central inner conductor 14a. Thereby, an electrical connection between the central pin 13 and the inner conductor 14a is achieved. The rod-shaped protrusion 13a is attached in the cavity 14a by means of for example soldering or electrically conductive glue to provide a galvanic connection there between. The end of the quarter wave stub 18 (being opposite the connector device 16) is provided with an engaging portion in the form of a rod-shaped protrusion 18 extending axially, and which is arranged inside a corresponding engaging portion in the form of a cavity 18a in the grounding device 18a. The rod-shaped protrusion 18 is attached in the cavity 18a by means of for example soldering or electrically conductive glue to provide a galvanic connection there between. The grounding device is attached to the outer conductor using a screw inserted from the front side of the reflector (from beneath as seen in the figure). In the figure, it is also illustrated that the connector device 16 may be inserted from the front side through an opening in the outer conductor/reflector. The quarter wave stub 18 and the grounding device 18a provides a DC ground for the central pin 13 (since the central pin and the first inner conductor 14a are galvanically interconnected). As described above however, the first central inner conductor may be indirectly interconnected with at least the second central inner conductor. Thus, at least parts of the antenna feeding network may be indirectly coupled.
(21) In FIG. 7, a cross section view of an antenna feeding network according to an embodiment of the first aspect of the invention is shown. This embodiment is similar to the embodiment shown in FIGS. 4-6, but the coaxial connector is not visible in the shown cross section, which is cut at right angle through the antenna feeding network close to the connector device 16. The connector device is arranged in an opening 21 in the reflector 4. The connector device 16 is clipped or snapped onto the first inner conductor 14a and the second inner conductor 14b. The connection between the first inner conductor 14a and the second inner conductor 14b is electrically indirect, which means that it is either capacitive, inductive or a combination thereof. This is achieved by providing a thin insulating layer of a polymer material or some other insulating material (e.g. a non-conducting oxide) on the connector device 16. The insulating layer may have a thickness of 1 m to 20 m, such as from 5 m to 15 m, such as from 8 m to 12 m, or may have a thickness of 1 m to 5 m. The insulating layer may cover the entire outer surface of the connector device 16, or at least the portions 22, 22 of the connector device 16 that engage the first and second inner conductors 14a, 14b. The insulating layer may alternatively be applied to the inner conductors 14a, 14b on at least to the portions of the inner conductors being close to fingers 22, 22, or on both the connector device and the inner conductors.
(22) The connector device 16 comprises a bridge portion 23 and two pairs of snap on fingers 22, 22. One of the two pairs of snap on fingers 22 is arranged close to one end of the bridge portion 23 and the other of the two pairs of snap on fingers 22 is arranged close to the other end of the bridge portion 23. The two pairs of snap on fingers 22, 22 may be connected to the bridge portion 23 via connecting portions configured such that the bridge portion 23 is distanced from the first and second inner conductors 14a, 14b. In other embodiments, the snap on fingers 22, 22 are connected directly to the bridge portion 23. The connecting portions, as well as the other portions of the connector device, are shaped to optimize the impedance matching of the splitter/combiner formed by the connector device and the coaxial lines. The shape, or preferably the diameter of the connecting inner conductors may also contribute to the matching of the splitter/combiner.
(23) As can be seen from FIG. 7, the vertical separating wall portion 24 is cut down to about two-thirds to three-quarters of its original height in the area of the opening 21 so that the connector device 16 does not protrude over the front side of the electrically conductive reflector 4. In other embodiments, the wall portion 24 is cut down all the way to the floor of the outer conductors. The remaining height of the wall portion is adapted together with the other components, such as the connector device to optimize the impedance match.
(24) In other embodiments (not shown in the figures), only one pair of snap on fingers is provided, for example the pair of snap on fingers 22 engaging the first inner conductor 14a providing an indirect connection, and to let the other end of the bridge portion 23 contact the second inner conductor 14b directly without insulating layer or coating. This direct connection can be provided by connecting the bridge portion 23 to inner conductor 14b by means of a screw connection, or by means of soldering, or by making the bridge portion an integral part of inner conductor 14b, or by some other means providing a direct connection.
(25) FIG. 8 shows a view from the rear side of an alternative embodiment where the coaxial connector 10 is directly connected to a first coaxial line. The central pin 13 and the first central inner conductor 14a are each provided with an engaging portion in the same way as described above with reference to the embodiment in FIGS. 5 and 6. The central pin 13 is galvanically connected to the first central inner conductor 14a and to the antenna feeding network. In this embodiment, DC-grounding is typically made in another position within the antenna feeding network.
(26) FIG. 9 shows a cross section side view of parts of an embodiment similar to that shown in FIGS. 4, 5 and 6, with the difference that the center pin is RF grounded instead of DC grounded. In the figure, only the end of the quarter wave stub 18, the grounding device 18b and the outer conductor is shown. The connection to the coaxial connector and to another inner conductor can be made in the same way as in FIGS. 5-6. The end of the quarter wave stub 18 (being opposite the connector device 16 as shown in FIGS. 5-6) is provided with an engaging portion in the form of a rod-shaped protrusion 18 extending axially, and which is arranged inside a corresponding engaging portion in the form of a cavity 18b in the grounding device 18b. The rod-shaped protrusion 18 is attached in the cavity 18b by means of for example soldering or electrically conductive glue to provide a galvanic connection there between. The grounding device is mechanically attached to the outer conductor using a screw 104 inserted from the front side of the reflector (from beneath as seen in the figure). The grounding device is electrically isolated from the outer conductor by means of an isolating film 101 or layer and an isolating bushing 100. The screw 104 is arranged through the bushing 100 which thereby isolates the screw from the outer conductor. The isolating film is arranged between the grounding device 18b and the inside surface of the outer conductor. The isolating film can be made in a polymer material such as Kapton, or it can be in the form of an oxide on one or both interfacing metal surfaces. In other embodiments, the isolating film can consist of a polymer layer deposited on one or both interfacing metal surfaces, i.e. on the grounding device 18b and/or on the inside surface of the outer conductor. The film or layer is kept thin and will together with the grounding device and the outer conductor act as a capacitor. An electrical wire 103 is soldered to the grounding device 102 and is arranged to connect the DC voltage and communication signal to the circuitry (not shown) arranged to separate the DC voltage from the communication signal, and demodulate the communication signal. The quarter wave stub 18 and the grounding device 18b together with the isolating layer 101 provide an RF ground for the central pin (ref. 13 in FIGS. 4-6). As described above, the first central inner conductor may advantageously be indirectly interconnected with at least the second central inner conductor. Thus, at least parts of the antenna feeding network may be indirectly coupled.
(27) 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 and the number of radiators/dipoles may be varied. Furthermore, the shape and placement of the coaxial connector 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.
