Antenna system and method of manufacturing said system

Abstract: An antenna system comprises at least two dipole antennas (6) constituting an antenna module and is placed above and parallel with a common, artificial ground plane (5) in the form of an electrically conducting plate, for instance the bottom of a metal box (2). The dipoles (7) and the feed lines (8, 9, 10, 11) are designed as air dielectric strip-lines and are configured in one piece of a homogeneous material and extend mechanically and electrically in an uninterrupted manner from the dipoles to the antenna connector. The parts configured in one piece are produced by punching out sheet metal, and after suitable bending the parts are inserted in corresponding openings (16) in the ground plane (5).

Description: Background of the invention The invention relates to an antenna system as defined in the preamble of claim 1 and a method of manufacturing said system as defined in the preamble of claim 5. For instance, such antennas are used as base station antennas, i.e. the antenna system is placed in a mast and is coupled to a transmitter-receiver system via a coaxial cable. The frequency range is normally in the range of 450-900 MHz, but the antenna system can also be used in other frequency ranges. Many known antenna systems of this type are built up of individual parts by welding, soldering or screwing together the antenna parts, the feed line parts, etc. In this manner an antenna with the required electrical qualities is obtained. However, the production costs are comparatively high, as all individual parts must have precise dimensions after the assembly operations due to the comparatively high frequency range for which the antenna system is to be used. Moreover, the numerous assemblies are time-consuming and require qualified and well-educated staff in the production. Besides, an antenna construction of this type does not have optimum electrical qualities, because the many assemblies cause discontinuity in the materials used resulting in varying electrical qualities at high frequencies. Consequently, assemblies made by soldering or screwing may result in various unwanted signal components in the antenna signal. DE-A-2 325 704 discloses an antenna system comprising at least two dipole antennas constituting an antenna module and placed above and parallel to a common, ground plane in the form of an electrically conducting plate. Further feed lines designed as wave guides with air dielectric from the dipoles to a common feeding point are used and the dipoles are carried by legs which form part of the feed lines, in which the feed lines from each dipole to the common point and one dipole arm in each dipole are configured mechanically and electrically in one piece of homogeneous material. Advantages of the invention The antenna system according to the invention and with the features as defined and characterized in claim 1 has the advantage that the parts are fixed, placed correctly and at a well-defined distance from the ground plane at once. The fixing is usually carried out by soldering or welding on the back of the ground plane, i.e. the side turning away from the active antenna parts. In this manner changes on the antenna side of the ground plane are avoided. The antenna according to the invention is preferably produced in such a manner that the parts which are to be fixed to the ground plane, being a metal plate or an open sheet metal box, are constructed with areas with reduced dimensions to be placed directly in corresponding openings in the ground plane. In order to position the dipole legs correctly to each other, especially when using long dipole legs, a holder of dielectric material as stated in claim 2 could be used. Various methods, such as casting, for instance die casting, or punching out sheet metal and subsequent bending, can be applied for the production of the homogeneous antenna with feed lines etc. By manufacturing the antenna system according to the invention as defined and characterized in claim 5, a rational production is achieved at heavily reduced production costs compared with the traditional method. The punching or cutting can be carried out either in one step using a punching or cutting tool corresponding to an antenna module, or by using a programmable machine tool for current or stepwise cutting or punching. The first punching method is particularly applicable for the manufacture of many identical antenna modules, whereas the latter method renders the manufacture of antennas of almost any type or size possible by controlling a programmable machine tool. In many antenna systems it will be possible that the common feeding point is an antenna connector, so that the assembly between the antenna connector and the feed line of the antenna is the only mechanical assembly of the antenna. If the antenna system is made up of a number of antenna modules, it will be possible to couple these antenna modules with at least one additional feed line produced in the same way as the rest of the antenna, and which can either be configured in one piece with the antenna system according to the invention, or be coupled together with the antenna system in a generally known manner. As the two arms of each dipole must be electrically isolated from each other, areas can be punched or made during the punching of the antenna parts, in which area a dielectric holder can be placed, so that the parts are placed correctly relative to each other during the building up of the antenna. These holders can remain in the antenna parts to continuously ensure that the parts are positioned correctly in relation to each other, so that increased mechanical stability of the antenna parts is obtained. The drawing In the following the invention will be explained in further detail with reference to the drawing, in which fig. 1a shows an antenna system with two pairs of dipoles according to a first embodiment of the invention, fig. 1b shows the same antenna system as in fig. 1a, but as an exploded view, fig. 2 shows the antenna in fig. 1 with feed lines as a plane item before the bending and mounting operation, fig. 3 shows an antenna system with one pair of dipoles according to another embodiment of the invention, and fig. 4 shows in principle how an antenna system with four pairs of dipoles (antenna modules) can be built up according to the invention. Description of embodiment examples The antenna system 1 in fig. 1 comprises a metal box 2, the bottom 5 of which is an artificial electrical ground plane for four antennas 3 each consisting of a dipole antenna 6. The dipole antennas 6 are placed in parallel pairs opposite each other and form an antenna module 40, so that the antenna system comprises two antenna modules. Via the feed lines 8, 9, 10, 11, which are designed as so-called "strip-line" feeders, the dipole antennas 6 are connected to a common antenna connector 4 by means of a screw 12 or a similar fixing. The antenna connector 4 is placed in an opening 15 in the ground plane 5. In the usual manner each dipole antenna is provided with two arms 7, 7' carried by legs 17 and 17', respectively. The box 2 can be open as shown or closed with a not shown radome or the like of non-electrically conducting material, which prevents precipitation from penetrating into the antenna system and moreover reduces a possible windload on the antenna system. The active part of the antennas including the feed lines are made as shown in fig. 2 by punching or cutting in a plane item 20, which for instance is a 3 mm thick plate of AlMg 3 or a similar material suited for the purpose. Fig. 2 shows that after the punching or cutting operation the parts 7, 8, 9, 10, 11, 17 are configured in one piece. After appropriate bending along the bending lines 19 the active part shown in fig. lb appears except the dipoles 7' and the matching legs 17', which are punched or cut out separately, either as shown in fig. 2 or of a separate plate. In order to position the dipole arms 7 and 7' correctly relative to each other and to get the correct distance between the feed line 8 and the leg 17', appropriate punchings 14 can be made, for instance circular punchings, in which a holder 13 of a dielectric material, for instance a synthetic material, can be inserted. In the end pointing away from the dipoles 7, 7' all the legs 17, 17' have sharp-edged cut-offs 18 with well-defined dimensions, so that this end of the antenna legs 17, 17' fits precisely into corresponding punched openings 16 in the electrical ground plane 5 constituted by the bottom of the box 2, so that the entire antenna with feed lines 3 can be inserted at a time as shown in fig. lb. The parts are fixed by welding or soldering on the back of the box 2. In this way the transmission lines 9, 10, 11 will run in a fixed well-defined distance from the ground plane 5, see figs. la and 1b. By means of a screw 12 or a similar means the feed line 11 is mechanically and electrically fixed to the centre conductor of a coaxial connector 4, so that the feed line is positioned in correct distance from the ground plane. The box 2 comprising the ground plane 5 is made by cutting and bending a suitable metal sheet, for instance a 2 mm AlMg 3 plate, where the corners are welded together on the outside after bending. Fig. 3 shows another embodiment of an antenna system according to the invention, viz. an antenna system 21 comprising one antenna module placed in a corresponding box 22, the bottom 25 of which constitutes the electrical ground plane. Fig. 4 shows in principle how four antenna modules 40 are coupled together in a not shown box on a not shown ground plane. The antenna modules are coupled together in pairs and the common feed line 11 extending from here is coupled to the antenna connector 4 via an additional feed line 28. As explained previously the parts can be configured in one piece, but the additional feed line 28 can also be coupled together with the feed lines 11 at the marked corner assemblies 30. In the same way antennas with any number of modules can be built up applying the above design and method.

Claims: Antenna system comprising at least two dipole antennas (6) constituting an antenna module (40) and placed above and parallel to a common ground plane (5, 25), which is formed by the bottom of a box (2, 22) of an electrically conducting material, feed lines (8, 9, 10, 11) designed as wave guides with air dielectric from the dipoles to a common feeding point (4) and where the dipoles are carried by legs (17) which can form part of the feed lines, that the feed lines from each dipole (6) to the common point (4) and at least one dipole arm (7) in each dipole and possibly a matching leg (17) are configured mechanically and electrically in one piece of a homogeneous material, and that the legs (17, 17') of each dipole have an area (18) with reduced width or thickness in the end pointing away from the dipoles, characterized in that the side opposite the bottom is open or of a non-electrically conducting material and in that through-going openings (16) are provided in the ground plane corresponding to the reduced width or thickness of the dipole legs (17, 17'). Antenna system according to claim 1, characterized in that at least one of the dipole legs (17') in each dipole (6) is positioned and fixed in relation to the feed line (8) by means of at least one holder (13) of dielectric material. Antenna system according to claim 1, characterized in that the common feeding point is an antenna connector (4), to which a feed line is secured both mechanically and electrically. Antenna system according to claim 1 or 2, characterized in that it comprises a number of antenna modules (40) configured in one piece and coupled together by means of at least one additional feed line (28) and is placed in a common ground plane. Method of manufacturing an antenna module for an antenna system according to claim 1, where the antenna system is made up of active antennas with matching feed lines and a common ground plane, wherein a part of the antenna modules are punched or cut out of sheet metal (30) of electrically conducting material and wherein a part is bent in previously defined points and secured by welding or soldering to an electrically conducting plate constituting a ground plane for the antenna characterized in that through-going holes (16) are made in the ground plane, and preferably as square holes, and that the legs of each dipole are punched or cut out in such a manner that there are areas (18) with reduced width or thickness corresponding to the preferably square holes, and that the soldering or the welding is made on the back of the ground plane. Method according to claim 5, characterized in that during the punching or cutting out of the antenna parts, areas (14) are formed in parts which are to be positioned in relation to each other, and that holders (13) are inserted in these areas, preferably before the parts are secured to the ground plane.

Inventors: FUNDER TORBEN, FUNDER, TORBEN
Applicants: CELWAVE R F A S, CELWAVE R.F. A/S
Application year: 1993
Main classification: H01Q21
IPC codes: H01Q21