Patent Application
20070080884
The invention relates to a feed network, and/or an antenna having at least one antenna element and a feed network according to the precharacterizing clause of claim 1.
Antenna arrays, using dipole antenna elements by way of example, are disclosed as being known from, for example, DE 197 22 742 A, DE 106 27 015 A or, for example, EP 1 057 224 B1. The use of so-called patch antenna elements is likewise also known, which can be installed, like the dipole antenna elements mentioned above, in, for example, the base station of a stationary mobile radio antenna installation.
The antenna arrays with an associated antenna element are fed using a large number of coaxial cables. This coaxial cable technique is expensive owing to the connecting junctions. In this case, it is always necessary to ensure that the electrical contacts are made correctly and that they also withstand electromechanical and thermal stresses.
However, feed systems using stripline technology are also known instead of a coaxial feed system, for example from EP 0 994 524 B1 or from U.S. Pat No. 6,697,029 B2. In the case of feeds such as these, the line which leads to the antenna element is firmly connected to the feed network. In this case, U.S. Pat No. 6,697,029 B2 provides for the stripline feed system, which is composed of a stamped metal sheet, to be arranged above the reflector, using air as the dielectric, and to be firmly connected to a bracket structure, which is then attached to a cruciform dipole by means of screws. In contrast, EP 0 994 524 B1 provides for the feed bracket, which is connected to the feed system that is designed for using stripline technology to be capacitively coupled to a cruciform dipole, rather than electrically conductively.
However, these structures also lead to problems, because relatively large antenna structures also require comparatively tight manufacturing tolerances. Shock effects or vibration can lead to forces being introduced to the connection between the feed line and the antenna element. Bending of the ground plane (reflector) while the distance from the stripline is constant likewise produces movements and tensile or compressive changes in the longitudinal direction of the line.
In addition, thermal strain with a feed technique such as this will lead to movements and mechanical stresses. Deformation could occur and, in the end, fractures as well. These would also correspondingly disadvantageously affect the electrical characteristics, in some circumstances even leading to total failure, so that this feed technique does not in practice represent a real alternative to coaxial conductor feed technology.
One object of the present invention is thus to overcome the disadvantages according to the prior art and to provide an improved feed system, in particular an antenna with at least one antenna element device and an associated feed network for this purpose, which can be constructed at low cost and avoids the disadvantages according to the prior art.
According to the invention, the object is achieved on the basis of the features specified in claim 1. Advantageous refinements of the invention are specified in the dependent claims.
According to the invention, a feed system is now proposed which is largely independent in terms of mechanical and thermal influences, and which allows improved electrical contact conditions, with a simple design overall.
Specifically, according to the invention, a capacitive, flat line coupling is proposed, using stripline technology. The feed network in this case has a coupling surface, with a coupled line being positioned parallel to it and having a second flat coupling surface. This second coupling surface is connected to a downstream feed or supply to an electrical appliance, in particular to an antenna element of an antenna or a mobile radio antenna, to be precise avoiding solder points or other contact points, and forming a continuous coupled line. The feed or supply that has been mentioned for the downstream electrical appliance or, in particular, the antenna element or a downstream antenna element device, is in this case part of this antenna element device. In other words, in particular, a corresponding antenna element device with this coupling device that has been mentioned can be mounted directly on a reflector, producing the desired capacitive inner conductor coupling, while avoiding contact points or solder points. The ground current of the feed network preferably, for the purposes of the invention, passes via the reflector, with the ground current then being able to flow onward via a contact point to the antenna point to the antenna element structure.
The stripline may in this case be designed to be unbalanced, that is to say using a ground plane and one conductor. The stripline may, however, also just as well be designed to be balanced, specifically using one conductor which is arranged between two ground planes.
The coupling surface of the feed network is preferably positioned in such a way as to avoid a solid dielectric, in other words using air as the dielectric. The two coupling surfaces can be positioned in the desired correct relative position with respect to one another only by means of a dielectric holding or bracket device.
In contrast to the implementation explained above, the feed network may, however, also be designed to be in the form of a substrate, for example a continuous substrate, on one side, in which case the substrate may be in the form of a printed circuit. In other words, a ground plane which forms a reflector can be provided on the opposite side of the substrate or of the printed circuit. Further modifications are possible.
In contrast, in the case of the previous coaxial feed networks, the coaxial lines that were used or the feed lines normally had to be laid in loops using stripline technology in order to allow them to absorb movements, so that no mechanical stresses are introduced to the connecting points or solder points. However, a stripline according to the prior art also did not, until now, allow any deformation in the direction of its plane.
According to the invention, the electrical appliance is now preferably coupled to the feed network in the form of an antenna element or in the form of an antenna element device of an antenna, such that no movement and no mechanical forces either can occur in the direction parallel to the ground plane on the feed line, for example, of the dipole antenna element. In the case of the coupling device according to the invention, the line which is coupled to the feed network can be moved relative to the feed network. For example, a movement of 1 mm at a frequency of 960 MHz results in a phase shift of only about 1.2°. A phase error such as this of one antenna element has only negligible effects on the polar diagram. The effect of a phase shift of the impedance of 2.4° occurring on the feed network when the dipole impedance is connected as well is also within the normal range of tolerances, and is negligible.
In contrast, if a feed line were to be pulled away from the dipole foot (ground plane) of the dipole in the case of the prior art, this would result in a major change in the characteristic impedance, and thus a different transformation. Overall, this would influence the matching of the entire antenna.
If it is remembered that the greatest thermal strains always occur in the direction of the greatest strain of a structure, this means in this application that, for example, a thermal change results in a detectable length strain of the stripline, which is normally laid longitudinally, of the feed network. If a corresponding coupling point of an antenna element were now to be firmly connected here, this would lead to considerable thermal stress on the connecting point or solder point. In contrast, according to the invention, quite specific capacitive coupling is provided in a specific refinement and arrangement in order to allow a change in the position and/or length of the feed network, which is in the form of a stripline, caused by vibration, shock or thermal loads, rather than suppressing such changes, to be precise in the sense of a relative movement with respect to a coupling section, which cannot also be moved, of the coupled line which, for example, is integrally or conductively connected to the downstream electrical appliance, in particular to the antenna element or antenna element device of an antenna of a mobile radio base station. The disadvantageous position or length change which was found in the prior art can thus no longer cause any relevant influence according to the invention.
In summary, the solution according to the invention has the following advantages:
The schematic exemplary embodiment illustrated in
The illustrated exemplary embodiment uses a dual-polarized antenna element device 1, which can transmit and/or receive on two mutually perpendicular polarization planes, with the two polarization planes passing through the corner points of the antenna element device 1, which is square when viewed in plan view, that is to say quasi-diagonally with respect to it. This antenna element device is so-called vector dipole, as is known, in principle, from EP 1 057 224 B1. From the electrical point of view, this is a cruciform antenna element, which radiates on the two mutually perpendicular polarization planes that have been mentioned. Reference should therefore be made to this prior publication for further details relating to its design and method of operation.
The antenna element device is located in front of a reflector 7 which, when positioned normally, is arranged such that it runs vertically or runs approximately vertically so that the antenna element devices 1 which have been mentioned are located one above the other in a vertically running column. The reflector 7 can be provided, for example, with boundary or longitudinal webs 9 on its left-hand and right-hand boundary areas, at the outermost edge or offset more toward the center, which can run transversely that is to say they can run at an angle or at right angles to the plane of the reflector 7.
In the illustrated exemplary embodiment, one feed network 13 is used for each polarization and comprises a stripline 13a, which is also referred to, for short, as a feed stripline 13a.
This stripline 13a is arranged in front of the electrically conductive reflector 7, without any electrically conductive contact with it. The stripline 13a could be arranged directly on the surface of the reflector 7 only if the reflector 7 were provided on its side to which the antenna element device 1 is fitted and which is composed of electrically non-conductive material, or is provided with an electrically non-conductive surface (when the conductive surface is formed, for example, on the rear face or lower face of the reflector). In this case, the feed network can preferably be formed on a printed circuit, in which case the ground plane which forms the reflector can then be formed on the non-conductive substrate on the opposite face to a feed network.
In the illustrated exemplary embodiment, the two striplines 13a run symmetrically with respect to a vertical central plane of symmetry, parallel and at a distance from one another, although this is not shown in
The rest of the design will be described in more detail with reference to FIGS. 2 to 5. As can be seen, a coupled stripline 17 is arranged above part of the length of the feed striplines 13a, thus forming a capacitive coupling area 18. Both the coupled stripline 17 and the feed stripline 13a each have a coupling surface 13b and 17b, which in the illustrated exemplary embodiment are planar (flat) and are arranged a short distance one above the other. In the illustrated exemplary embodiment, the width of the coupled stripline 17 (
As can also be seen from
On at least one longitudinal face, the associated side web 21b or the base 21a projects beyond the adjacent longitudinal face 13c of the feed stripline 13a and is provided with a support, supporting foot or supporting strip 21e running to the surface 7a of the reflector 7, via which the receptacle or holder 21 is supported by the end lower face 21f of the support 21e on the upper face 7a of the reflector 7.
Two bracket or holding devices 27 are also used in the illustrated exemplary embodiment, whose upper limb 27a engages under the upper face 17c of the coupled feed stripline 13a, and whose lower limb 27b engages under the lower face 13e of the feed stripline 13a, with the inner faces, which point towards one another, of the upper and of the lower limb 27a, 27b preferably resting flat over their entire area on the upper face of the coupling surface 17b or the lower face 13e of the feed stripline 13a, respectively. The two limbs 27a, 27b are held and fixed in a prestressed manner via a clamping section 27c which is in the form of a part of a circle or is rather curved in the cross-sectional illustration.
In order that the limbs can rest thereon over their full area, the side webs 21b of the receptacle or holder 21 which have been mentioned each have interruptions 21e through which the upper limbs 27a of the clamping or holding device 27 project.
The detailed sectional illustration shown in
Opposite the free end of the coupled stripline 17 this merges into a connecting section 17d, which projects at the side at 90° in the illustrated exemplary embodiment. An appliance or antenna element line 17e is connected to the end of this connecting section 17d and is passed upward over more than 50%, in particular more than 70% or 80%, of the overall height of the antenna element device 1, and ends at the upper end in a feed section 17f which, in the illustrated exemplary embodiment, runs parallel to the reflector plane.
As can be seen from the described design, the entire coupled stripline 17 including its coupling surface 17b, the connecting section 17d which projects at right angles from it, the supporting section 17e which is adjacent to this, and the feed section 17f which runs upward comprises or is produced from an integral metal or an integral metal alloy, in particular a metal plate, for example by cutting and/or stamping and subsequent bending, folding and/or edging. The entire coupled stripline 17 therefore has no interruption over its entire profile and is not formed from two separate electrically conductive workpieces connected to one another by welding, soldering or in any other way. Consequently, this results in uniquely reproducible electrical conditions. Only at the end of the end section 17f is the stripline that is formed in this way soldered to the feed point of the antenna element structure that is provided there or formed integrally with the antenna element structure. The advantages according to the invention can also just as well be achieved by the coupled stripline 17 as explained above being produced, for example, rather than from a single metal strip or the like, but originally from a plurality of sections, that is to say at least two sections. At least in this case, the components, of which there would then be a plurality, would have to be firmly and conductively connected to one another, so that the coupled stripline 17 can once again be referred to as being continuous, particularly by means of a connection formed by techniques such as bonding, soldering or welding.
Once again in the form of an enlarged detailed illustration,
Merely for the sake of completeness, it should also be. mentioned that, at the transition from the connecting section 17d to the supporting section 17e, this supporting section 17e has a tapered section 17e′ in a small detail length.
If the position and/or length of the feed stripline 13a changes in its longitudinal direction as a result of vibration, mechanical or other deformation or influences, or else as a result of thermal influences, the overall design means that this stripline 13a can, if necessary, carry out a relative movement in its longitudinal direction with respect to the coupling surface 17b of the coupled stripline 17 without this leading in a mechanical or electrical sense to any adverse effect or detectable adverse effect.
In particular, the assembly process can be carried out without any soldering just by placing the isolating receptacle or holder 21 on the stripline network at the relevant points and then inserting the coupled stripline 17 into it and fixing it with the bracket and holding device 27, whose supporting section 17e represents a component of the antenna element device 1.
The section illustration shown in
In the exemplary embodiment shown in
This results in capacitive coupling 41 to a corresponding line section of an associated dipole half of an antenna element device which acts as a cruciform dipole.
