Patent Grant
11018424
The invention relates to the field of multi-radiator antennas comprising a feeding network having at least one coaxial line.
Multi-radiator antennas are frequently used in for example cellular networks. Such multi-radiator antennas comprise a number of radiating antenna elements for example in the form of dipoles for sending or receiving signals, an antenna feeding network and an electrically conductive reflector. The antenna feeding network distributes the signal from a common coaxial connector to the radiators when the antenna is transmitting and combines the signals from the radiators and feeds them to the coaxial connector when receiving. A possible implementation of such a feeding network is shown in
In such a network, if the splitters/combiners consist of one junction between e.g. 3 different 50 ohm lines, impedance match would not be maintained, and the impedance seen from each port would be 25 ohm instead of 50 ohm. Therefore the splitter/combiner usually also includes an impedance transformation circuit which maintains 50 ohm impedance at all ports.
A person skilled in the art would recognize that the feeding is fully reciprocal in the sense that transmission and reception can be treated in the same way, and to simply the description of this invention only the transmission case is described below.
The antenna feeding network may comprise a plurality of coaxial lines being substantially air filled, each coaxial line comprising a central inner conductor at least partly surrounded by an outer conductor with insulating air in between. The coaxial lines and the reflector may be formed integrally with each other in the sense that the outer conductors and the reflector are formed in one piece.
In a multi radiator antenna, the radiators may be positioned in a vertical column. During installation or tuning, the tilt angle may be adjusted. This may either be done physically, i.e. by mechanically tilting the complete antenna, or alternatively electrically by adjusting the electrical tilt angle. The antenna electrical tilt angle is determined by the relative phases of the signals radiating from the radiators. The relative phases can be fixed giving the antenna a predetermined tilt angle, or the relative phases can be variable if a variable tilt angle is required.
A phase shifting arrangement may be achieved using one or more dielectric elements which co-operate with one or more conductors. The phase shift may be adjusted by moving the dielectric element(s) relative the conductors. In the case of a substantially air filled coaxial line, dielectric element(s) can be arranged inside the coaxial line(s). It is a known physical property that introducing a material with higher permittivity than air in a substantially air filled coaxial line will reduce the phase velocity of a signal propagating along that transmission line. This can also be perceived as delaying the signal or introducing a phase lag compared to a coaxial line that has no dielectric material between the inner and outer conductors. The phase shift is achieved by moving the dielectric element that is located between the inner conductor and the outer conductor of the coaxial line. If the dielectric element is moved in such a way that the outer conductor will be more filled with dielectric material, the phase shift will increase.
Tilt angle in variable tilt antennas is often monitored by having e.g. a scale stick protruding through the bottom of the antenna, or from a motor unit attached to the antenna. A disadvantage with such a scale stick is that an opening is required in the environmental protection of the antenna or the motor unit. The scale stick can also easily be damaged, and might be impacted by ice building on the antenna.
WO 2009/041796 discloses an antenna arrangement having an adjustable differential phase shifter including a movable dielectric part arranged inside outer conductors of the coaxial lines. One disadvantage with this and other known arrangements is that it may be difficult to determine the actual electrical tilt achieved by moving the dielectric part(s).
An object of the present invention is to provide an improved multi radiator antenna, which may at least partly solve or improve on the disadvantages of the prior art described above.
These and other objects are achieved by the present invention by means of a multi radiator antenna according to the independent claim.
According to the invention, a multi-radiator base station antenna is provided. The multi radiator antenna comprises an electrically conductive reflector, at least two radiating elements arranged on said reflector, a feeding network connected to the radiating elements, and a protective cover. The feeding network comprises a plurality of conductors for distributing signals to the radiators. The feeding network has means for adjusting relative phases of said signals in order to adjust a direction of the antenna main lobe of said multi-radiator base station antenna. The means for adjusting is provided with, or is connected to, an indicating portion or element configured to provide a visual indication of said direction. The protective cover is provided with an at least partially transparent wall portion arranged such that said indicating portion or element is visible there through. The protective cover may be arranged to protect the feeding network.
Put differently, the antenna feeding network may be provided with means for adjusting the phase in at least one of said plurality of conductors, in order to adjust the relative phase of at least two signals, thereby adjusting the electrical tilt angle in a multi-radiator base station. The means for adjusting may be provided with an indicating portion or element configured to provide a visual indication of the electrical tilt angle. Alternatively, the indicating portion or element may be a separate part which is attached or connected to (but separate from) the means for adjusting.
The protective cover may be arranged to surround or cover at least parts of the antenna feeding network. For example, the protective cover may cover or protect the rear side of the antenna feeding network, while the front side may be covered or protected by the reflector. In other embodiments the protective cover may surround or cover not only the antenna feeding network, but also at least parts of the reflector and/or the radiators. The protective cover may be formed by two or more cover portions. It is understood that the at least partially transparent wall portion may be located at any part of the protective cover or portions thereof as long as the indicating portion or element is visible there through.
The invention is based on the insight that an accurate indication of the actual direction of the antenna main lobe or the actual electrical tilt angle may be provided to the user of the antenna by providing the means for adjusting relative phases in the internal antenna feeding network with an indicating portion or element which is visible through a transparent wall portion of the protective cover which surrounds or protects the feeding network. By providing the already existing protective cover with a transparent wall portion which makes the indicating portion visible from the exterior of the antenna feeding network, a compact solution is achieved which does not add to the size of the antenna. The invention is further based on the insight that a robust and reliable antenna may be achieved by providing the indicating portion inside the protective cover.
It is understood that the directions referred to in this application relate to a multi-radiator base station antenna where a plurality of coaxial lines are arranged side by side in parallel to each other and also in parallel with a reflector on which the radiating elements are arranged. Longitudinally in this context refers to the lengthwise direction of the coaxial lines, and sideways refers to a direction perpendicular to the lengthwise direction of the coaxial lines. It is also understood that the term encircle used herein refers in general to completely surrounding an object, and is not limited to a circular surrounding shape. It is furthermore understood that the rear side of the antenna feeding network refers to the side which is opposite the reflector side, which reflector side is provided with the radiating elements.
In embodiments, the plurality of conductors of said feeding network are configured as substantially air filled coaxial lines, each comprising a central inner conductor and an elongated outer conductor substantially surrounding the central inner conductor. Such substantially air filled coaxial lines have the advantage that low losses in the feeding network may be achieved. In other words, the feeding network comprises a plurality of substantially air filled coaxial lines, each comprising an inner conductor centrally arranged in an elongated outer conductor with air in-between, where each central inner conductor is at least partly surrounded by the corresponding outer conductor. The central inner conductor(s) may be substantially surrounded by the corresponding outer conductor in the sense that one or more openings are provided in the outer conductor, which may be small openings with limited extension in the longitudinal direction of the coaxial line, provided for example to allow electrical connection(s) to the inner conductor. In embodiments, the central inner conductor(s) may be encircled or completely surrounded by the outer conductor in the sense that the outer conductor forms a closed loop around the inner conductor as seen in a cross section perpendicular to the longitudinal direction of the coaxial line. The air between the conductors replaces the dielectric often found in coaxial cables between the inner and outer conductor. The outer conductor may in embodiments be a tube-shaped element having a square cross section. It is understood that the term substantially air filled is used to describe that the coaxial line may not be provided solely with air in between the outer and inner conductors. In embodiments described below, the antenna feeding network may be provided with further components inside the outer conductor such as an elongated rail element and dielectric elements which also occupies part of the space inside the outer conductor which would otherwise be filled with air. The coaxial line is thus substantially, but not completely air filled in these embodiments.
In embodiments, the means for adjusting relative phases of said signals is configured to adjust the antenna main beam angle in the elevation plane. In these embodiments, the indicating portion may be configured to provide a visual indication of the electrical tilt in the elevation plane.
In embodiments, the at least partially transparent wall portion comprises a scale, wherein said indicating portion is configured to form an indicator co-acting with said scale to indicate said position. Put differently, the at least partially transparent wall portion and/or a wall portion of the protective cover being adjacent the at least partially transparent wall portion is provided with a scale, i.e. a graded or scaled reference portion on which, due to its location adjacent the indicating portion, a position of the indicating portion may be read visually. This embodiment is advantageous since a purely mechanical solution of determining the position of the indicating portion may be achieved, which may be reliable. The indicating portion may be slidably arranged relative the scale.
In embodiments, the means for adjusting comprises at least one dielectric element, each being configured to co-operate with at least one of said conductors to provide a phase shifting arrangement. In the case where the conductors are substantially air filled coaxial lines, each dielectric element is arranged inside one of the outer conductors and at least partly fills the space between the outer and inner conductors. The at least one dielectric element may have a U-shaped profile such as to partly surround the inner conductor in order to at least partly fill out the cavity between the inner and outer conductors.
In embodiments, the means for adjusting comprises displacement means configured to displace said at least one dielectric element and said indicating portion. The displacement means may comprise an at least partly threaded rod which extends longitudinally, where the dielectric element and the indicating portion are provided with, or attached to, a corresponding connecting element having an internally threaded portion arranged to move in the longitudinal direction of the antenna when the rod is rotated. The displacement means may comprise a manual actuating arrangement configured to actuate said displacement means, which actuating arrangement may comprise a handle or knob, which may be arranged to rotate the above mentioned rod. Alternatively, the displacement means comprises an electrical actuating arrangement configured to actuate the displacement means, and optionally means for controlling said electrical actuating arrangement from a distance. The electrical actuating arrangement may comprise at least one electric motor, which may be arranged to rotate the above mentioned rod. These embodiments are advantageous since a simple and reliable arrangement, which may displace or move the dielectric elements accurately, is achieved.
In embodiments where the conductors are substantially air filled coaxial lines, the antenna may further comprise at least one elongated rail element, each being slideably arranged inside an outer conductor of said coaxial lines, said rail element being longitudinally movable in relation to said outer conductor. The elongated rail element may be described as a bar-shaped element, i.e. an element which is substantially longer than wide, which is also wider than thick. The means for adjusting may further comprise at least one connecting element connected to the rail element of at least one of said coaxial lines, said connecting element being provided with said indicating portion, and wherein each of said at least one dielectric element is configured to co-operate with a corresponding coaxial line by being attached to an elongated rail element arranged therein. The outer conductor may be provided with at least one longitudinally extending slot, and wherein said connecting element is connected to the rail element through said slot. In embodiments where the means for adjusting comprises displacement means in the form of an at least partly threaded and longitudinally extending rod, each connecting element is provided with an internally threaded portion, the internally threaded portions being configured to co-operate with corresponding (externally) threaded segments or portions of the rod.
In embodiments, means for adjusting is configured to achieve more phase shift in one coaxial line than in another, i.e. to control the relative phases, in order to control the electrical antenna tilt angle. This may be achieved by having dielectric elements of different sizes, and/or by moving the rails and corresponding dielectric elements at different relative speeds, and/or by using dielectric elements with different dielectric constants. In such an embodiment, the means for adjusting may be configured to move at least two rail elements of the coaxial lines simultaneously at different speeds. Because the rail elements and the dielectric elements attached thereto move at different speed, and/or because the dielectric elements are of different sizes and/or have different dielectric constant, more phase shift will be achieved in at least one of the coaxial lines than in at least one other of the coaxial lines. In embodiments where the means for adjusting comprises displacement means in the form of an at least partly threaded and longitudinally extending rod, the means for adjusting may further comprise at least first and second connecting elements, each connecting element being connected to a corresponding separate rail element, each connecting element being provided with an internally threaded portion, the internally threaded portions being configured to co-operate with corresponding (externally) threaded segments or portions of the rod, wherein the threaded segments or portions of the rod have different pitch from each other such that the first and second connecting elements move at different speed when the rod is rotated. In other words, the internally threaded portion of the first connecting element has a first pitch and is engaged with a first threaded segment on the rod having the first pitch, and the internally threaded portion of the second connecting element has a second pitch, which is different from the first pitch, and is engaged with a second threaded segment on the rod having the second pitch.
The embodiments described above may be combined in any practically realizable way.
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:
The feeding network has means for adjusting (not shown) relative phases of said signals in order to adjust a direction of the antenna main lobe of said multi-radiator base station antenna. The means for adjusting is provided with an indicating portion 4 formed as a rounded protrusion having an indicating line or groove thereon. The indicating portion is configured to provide a visual indication of the electrical elevation tilt angle. The protective cover is provided with a transparent wall portion 5 through which the indicating portion 4 is visible. The transparent wall portion 5 is formed as a half-cylinder shaped protrusion in which the indicating portion 4 is movable in the longitudinal direction (up- and downwards as seen in the figure). The transparent wall portion 5 comprises a scale, wherein said indicating portion is configured to form an indicator co-acting with said scale to indicate said position. In other embodiments, a wall portion of the protective cover being adjacent the transparent wall portion is provided with a scale, i.e. a graded or scaled reference portion on which, due to its location adjacent the indicating portion, a position of the indicating portion may be read visually.
The rail elements 9a, 9b are longitudinally movable relative the outer conductors. Each coaxial line 6a, 6b is provided with a dielectric element 11a, 11b which is attached to the corresponding elongated rail element 9a, 9b and is configured to co-operate with the corresponding coaxial line 6a, 6b. The dielectric elements 11a, 11b both have a U-shaped cross section and are arranged around the respective inner conductor 7a, 7b such that it partially surrounds the inner conductor and fills most of the cavity between the conductors. Arranging the dielectric elements 11a, 11b in the cavity between the inner and outer conductor forms a phase shifting device arranged to adjust the phase of signals in coaxial line 6a, 6b. Since the dielectric elements 11a, 11b are each attached to a corresponding rail element 9a, 9b, the phase may be adjusted by moving or sliding the rail elements longitudinally until the desired position and phase shift is achieved. By varying the phase shift in the feeding network, it is possible to control the direction of the antenna main beam in the elevation angle; this is often referred to as controlling the antenna downtilt, or antenna tilt. The indicating portion 4 is formed as a portion of the connecting element 13. In other embodiments, the indicating portion 4 is a separate part or element which is connected to (but separate from) the connecting element 13.
The rail elements are moved or displaced using displacement means which comprises a threaded rod 12 which extends longitudinally (in the depth direction as seen in the figure) and a connecting element 13 which comprises a first arm portion 13a and a second arm portion 13b, each connected to a respective rail element 9a, 9b via respective attachment portions 13d, 13e. The connecting element is provided with an internally threaded portion 13c having pitch and dimensions adapted to co-operate with the threaded rod. The rail element is connected to dielectric elements 11a, 11b. Thus, when the rod 12 is rotated, the connecting element 13 and the thereto connected rail element 9a, 9b and consequently also the dielectric elements 11a, 11b move in the longitudinal direction, thus adjusting the phase shift of the coaxial lines. The rod may be rotated manually or using an electric motor controlled by a controlling device such as micro-controller. When using electric motors, the dielectric elements, and hence the downtilt of the antenna, can be controlled remotely. Remote control can be achieved e.g. by connecting the motor and micro-controller to a network control center, or a lap top computer, or some other means for control. Although only two of the outer conductors or channels are provided with inner conductors in
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 tilt angle range may be varied, 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.
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