AN ANTENNA ARRANGEMENT, A RADIATING ELEMENT AND A METHOD OF MANUFACTURING THE RADIATING ELEMENT

Abstract

An antenna arrangement comprising an antenna feeding network, an electrically conductive reflector and at least one radiating element arranged on said reflector is provided. The radiating element a first part made of a first metallic material and a second part being provided in the lower part of the radiating element for connecting the radiating element to the reflector; wherein the second part is made of a second metallic material being different than the first metallic material. There is also provided a radiating element and a method of manufacturing the radiating element.

Claims

1. An antenna arrangement comprising an antenna feeding network, an electrically conductive reflector and at least one radiating element arranged on said reflector, the radiating element having a first part comprising radiating parts forming a dipole, and a balun part; said first part being made of a first metallic material; and a second part made of a second metallic material being different than the first metallic material, said second part being provided in the lower part (6f) of the radiating element for connecting the radiating element to the reflector.

2. The antenna arrangement according to claim 1 wherein the second metallic material has less creep than the first metallic material.

3. The antenna arrangement according to claim 1 wherein the second part is made as an insert element in the bottom part (6f) of the balun part.

4. The antenna arrangement according to claim 1 wherein the first metallic material has a lower melting temperature than the second metallic material.

5. The antenna arrangement according to claim 1 wherein the first metallic material is a zinc-based material and the second metallic material is an aluminium-based material or a brass-based material.

6. The antenna arrangement according to claim 3 wherein the insert element is galvanically connected to the bottom part of the balun part or capacitively connected to the bottom part of the balun part.

7. The antenna arrangement according to claim 3, wherein the radiating element is attached to the reflector by using tightening means passing through a hole of the insert element.

8. The antenna arrangement according to claim 3 wherein the insert element includes at least one groove and/or at least one protrusion.

9. The antenna arrangement according to claim 7 further comprises a metal-based washer including a central hole, the washer being placed in-between the insert element and the reflector allowing the screw holding the radiating element to the reflector to pass through the hole of the insert element and the hole of the washer.

10. The antenna arrangement according to claim 9 wherein the metal-based washer is made in a metallic material which is harder than the metallic material of the reflector.

11. The antenna arrangement according to claim 9 wherein the metal-based washer is made in a metallic material which is harder than the second metallic material of the radiating element.

12. A radiating element for an antenna arrangement comprising an antenna feeding network and an electrically conductive reflector; the radiating element having a first part comprising radiating parts forming a dipole and a balun part; said first part being made of a first metallic material; a second part being provided in the lower part of the radiating element for connecting the radiating element to the reflector; wherein the second part is made of a second metallic material being different than the first metallic material.

13. The radiating element according to claim 12 wherein the second metallic material has less creep than the first metallic material.

14. The radiating element according to claim 12 wherein the second part is made as an insert element in the bottom part of the balun part.

15. The radiating element according to claim 12 wherein the first metallic material has a lower melting temperature than the second metallic material.

16. The radiating element according to claim 12 wherein the first metallic material is a zinc-based material and the second metallic material is an aluminium-based material or a brass-based material.

17. The radiating element according to claim 14 wherein the insert element is galvanically connected to the bottom part of the balun part or capacitively connected to the bottom part of the balun part.

18. The radiating element according to claim 14, is configured to be attached to the reflector using tightening means passing through a hole of the insert element.

19. The radiating element according to claim 14 wherein the insert element includes at least one groove and/or at least one protrusion.

20. A method of die casting a radiating element for an antenna arrangement comprising: placing an insert element in a die cast mold cavity representing the radiating element; forcing a first metallic material, in molten form, under high pressure into the mold cavity; wherein the insert element is made of a second metallic material being different than the first metallic material.

21. The method according to claim 20 wherein the second metallic material has less creep than the first metallic material.

22. The method according to claim 20 wherein the first metallic material is a zinc-based material and the second metallic material is an aluminium-based material or a brass-based material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which:

[0038] FIG. 1 schematically illustrates a feeding network of an antenna arrangement;

[0039] FIG. 2 illustrates a perspective view of a prior art antenna arrangement;

[0040] FIG. 3 illustrates a perspective view of a portion of the antenna arrangement including three radiating elements;

[0041] FIG. 4 illustrates a cross view of a section of one radiating element on a reflector of the portion of FIG. 3.

[0042] FIG. 5A illustrates a cross view of a section of a radiating element connected to a reflector, according to an aspect of the present invention.

[0043] FIG. 5B illustrates a cross view of a section of a radiating element connected to a reflector, according to another aspect of the present invention,

[0044] FIG. 6A illustrates and example of an insert element suitable for use in the radiating element according to the present invention.

[0045] FIG. 6B illustrates and example of a brass washer suitable for use in the antenna arrangement according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0046] 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. Each radiating element 6 comprises radiating parts in the form of dipoles.

[0047] The antenna feeding network 2 connects a coaxial connector 10 to the plurality of radiating elements 6 via a plurality of lines or conductors 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.

[0048] The antenna feeding network shown is used for feeding single polarisation radiating elements. In case dual polarisation radiating elements are used, the feeding network will be duplicated for the second polarisation.

[0049] Turning now to FIG. 2, which illustrates a 3D perspective view of the antenna arrangement 1 comprising the feeding network 2, the electrically conductive reflector 4 and the radiating elements 6. Here, the antenna arrangement 1 is shown comprising 24 radiating elements. It should be noted that the antenna arrangement according to the present invention is not restricted to any particular number of radiating elements 6.

[0050] The electrically conductive reflector 4 comprises a front side, where the radiating elements 6 are mounted and a back side (not shown).

[0051] FIG. 3 depicts a perspective view of a portion of the antenna arrangement 1 of FIG. 2 including three radiating elements 6. FIG. 3 also shows two coaxial lines 20, each comprising a central inner conductor 14, an elongated outer conductor 15 forming a cavity or compartment around the central inner conductor 14. The outer conductors 15 have rectangular cross sections and are formed integrally and in parallel to form a self-supporting structure. The wall which separates the coaxial lines 20, constitute vertical parts of the outer conductors 15. The outer conductors 15 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 17 and the back side 19 of the reflector, respectively.

[0052] Although the inner conductors 14 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. In addition, the embodiments herein are not restricted to any particular number of conductors and coaxial lines, radiating elements, etc.

[0053] In FIG. 3, not all longitudinal channels or outer conductors are illustrated with inner conductors. It is however clear that they may comprise such inner conductors.

[0054] Each of the radiating elements 6 is configured to be electrically connected to at least one of the inner conductors 14 via, e.g. coupling element(s) (not shown).

[0055] As shown in FIG. 3, each radiating element 6 comprises a first part composed of four identical radiating parts 6a-6d forming a dipole and the balun 6e. Note that the radiating element 6 may include fewer than four or more than 4 radiating parts.

[0056] The radiating parts 6a-6d extend essentially in a plane parallel with the antenna reflector 4. The radiating parts 6a-6d are fed using the balun 6e, which also forms a mechanical support for the radiating parts 6a-6d. The balun 6e comprises a body part 6e′ and at least one inner conductor 24 (see FIG. 4) which may be positioned in the centre of a cylindrical hole in the body part. The body part 6e′ is connected to the outer conductor 15 and to the antenna reflector 4. The connection between said at least one balun inner conductor 24 and the feeding network coaxial line inner conductor 14 may be galvanic or indirect. An indirect connection may be either capacitive, inductive or a combination thereof and can be achieved by providing a thin insulating layer on at least the free end portion of the coupling element. The thin insulating layer could be provided by applying a thin layer of a polymer material, or by having a thin oxide layer, or by some other provisions applying an isolating layer. The insulating layer may have thickness of less than 50 μm, such as from 1 μm to 20 μm, such as from 5 μm to 15 μm, such as from 8 μm to 12 μm.

[0057] Referring to FIG. 4, there is illustrated a cross sectional view of a section of one of the radiating elements 6 shown in FIG. 3. The first part is here shown including only two radiating parts 6a-6b and the balun 6e. The cross section is cut-through the radiating element 6 and the inner conductors 14. The balun 6e and the balun body 6e″are also schematically depicted.

[0058] The radiating element 6 may be mechanically fixed to the reflector 4 using tightening means 3, such as a screw as shown in the Figure. Any suitable tightening means or fastener may be used. The screw presses the lower part 6f of the radiating element 6, which is also the balun bottom side, against the reflector 4 which also acts as the feeding network outer conductor. Thus, a galvanic connection may be established between the bottom side of balun outer conductor and the reflector and at the same time with the feeding network outer conductor.

[0059] According to the present invention, and with reference to FIG. 5A, the radiating element 6 further comprises a second part 7 in the bottom/lower part 6f of the balun 6e or balun body 6e″. The second part 7 is provided in the lower part 6f of the radiating element 6 for connecting the radiating element 6 to the reflector by means of the screw or any suitable tightening means 3 or fastener.

[0060] Further, and according to the present invention, the first part of the radiating element 6 (forming the radiating parts and the balun) is made of a first metallic material, whereas the second part is made of a second metallic material being different from the first metallic material. The second part may be made as an insert element 7 in the bottom part 6f of the balun 6e.

[0061] Thus, the radiating element 6 is a combination of two different metallic materials exhibiting different properties in terms of creep and melting temperature. The second metallic material having less creep than the first metallic material. The first metallic material having a lower melting temperature than the second metallic material.

[0062] According to an embodiment of the present invention, the first metallic material of the first part is a zinc-based material and the second metallic material of the second part 7 is an aluminium-based material. Tests have shown that having a radiating element composed of a first part made of zinc and a second part 7 (or insert element) made of aluminium or silver-plated brass, the performance in terms of throughput and/or coverage is not degraded. Such a radiating element has similar performance as a radiating element manufactured only in aluminum. But the radiating element according to the present invention is less costly, easier to manufacture and does not require machining.

[0063] In addition, tests have also shown that radiating elements, according to invention, exhibit good PIM performance i.e. −110 dBm and below and therefore the performance of the antenna including such radiating elements is not reduced. This is because high pressure, applied by the tightening means (e.g. a screw) or fastener, necessary to obtain low PIM is only applied to materials with low creep e.g. aluminium of which the insert element and the reflector are made of. The interface between the aluminium-made insert element (second part 7) of the radiating element and the zinc-made first part of the radiating element is not subject to high pressure, and hence creep will not occur. In addition, the low PIM performance of the radiating element does not deteriorate with time. As shown in FIG. 5A, the radiating element 6 is attached to the reflector 4 by means of a screw or tightening/fastening means 3 passing through the hole of the insert element 7.

[0064] Further, the good PIM performance is maintained even after accelerated life testing including temperature cycling, high and low temperature tests, humidity, salt spray and vibration.

[0065] Instead of aluminium, the insert element 7 or the second part 7 of the radiating element 6 may be made of brass or any other metal material which has good creep properties and thus may be advantageously used to make low PIM contacts between metal parts.

[0066] According to an embodiment, the insert element 7 may be galvanically connected to the bottom part of the balun part 6e or capacitively connected to the bottom part of the balun part 6e. The insert element 7 may be cylindrical but other forms could be used e.g. square or elliptical.

[0067] According to yet another embodiment and with reference to FIG. 5B, the antenna arrangement may be provided with a metal-based washer 9 including a central hole, the washer 9 being placed in-between the insert element 7 of the radiating element 6 and the reflector 4 allowing the tightening means 3 holding the radiating element 6 to the reflector 4 to pass through the hole of the insert element 7 and the hole of the washer 9. The washer 9 may be made in a metallic material which is harder than the metallic material of the reflector 4.

[0068] As an example, if the insert element 7 is made in aluminium and is to be attached/connected to an aluminium antenna reflector 4, it might be difficult to achieve a galvanic connection if the insert element 7 or the antenna reflector have acquired an isolating oxide layer. This is because aluminium is a rather soft metal. In this case, it may be advantageous to use a small washer of brass 9 or some other metal which is harder than aluminium between the radiating element 6 and the antenna reflector 4. An example of a washer 9 made of brass is shown in FIG. 6B. The washer 9 may be placed around the tightening means or screw holding the radiating element. If the washer 9 is in brass and in order to avoid oxidation corrosion, the washer 9 may be e.g. silver-plated. The bottom of the radiating element 6, or the antenna reflector 4, may be made to have a shape which helps to locate the washer 9 in its correct position.

[0069] According to another embodiment, the insert element 7 includes at least one groove 8 and/or at least one protrusion. A groove or a protrusion in a cylindrical surface of the insert element 7 may be used to better hold the insert element 7 into the radiating element. FIG. 6A shows a cylindrical insert element 7 with a groove 8. The insert element 7 may be a small part only located close to the mechanical interface between the radiating element 6 and the reflector 4, or it may be larger, and form the lower part of the balun 6e, or even form the whole balun 6e.

[0070] The shape of the insert element side connecting to the reflector 4 may be optimised to achieve best PIM performance. As an example, the surface contacting the reflector 4 may be reduced to a minimum to achieve a low PIM. The insert element 7 may have different types of surface treatments. For example, an insert element 7 made of brass may be silver-plated in order to avoid oxidation corrosion.

[0071] According to another embodiment, the insert element 7 is capacitively connected to the bottom part 6f of the balun part 6e or balun body. As an example, the insert element 7 may be capacitively connected to the zinc part of the radiating element 6 or the zinc part of the balun bottom part 6f of the radiating element 6.This may be achieved by anodizing the insert element 7 in order to get a thin isolating layer, but other types of isolating layers could also be used.

[0072] According to yet another aspect of the present invention, a method of manufacturing a radiating element by die casting is provided. As previously described, the radiating element is a combination of two different metallic materials having different properties. As an example, a radiating element made in zinc is combined with an insert element made in a metallic material with higher melting temperature than that of zinc, and hence with lower creep, such as aluminium or brass. The method of die casting comprises: placing the insert element (second metallic material) in the die cast mold cavity representing (the form of) the radiating element, before forcing zinc (first metallic material) in molten form under high pressure into it. Hence, the insert element will form an integral part together with the radiating element substantially manufactured in zinc. Additional details on the radiating element and the antenna arrangement comprising radiating elements according to the present invention have already been described and need not be repeated again.

[0073] 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 radiating parts/dipoles may be varied and also the shape of the radiating element 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. Further, the radiating elements may be connected to soft or semi-rigid coaxial cables. The scope of protection is determined by the appended patent claims.