Calibration device for a switchable antenna array and corresponding operating method

The invention relates to a calibration device for an antenna array according to the preamble of claim 1.

A generic antenna array (group antenna) usually comprises a plurality of primary radiators, but at least two radiators arranged side by side and one above the other, so that a two-dimensional array arrangement results. These antenna arrays, also known as "smart antennas", are also used, for example, in the military field for tracking targets (radar). These antennas have, however, recently also been used in mobile communications, in particular in the frequency ranges 800 MHz to 1000 MHz or 1700 MHz to 2200 MHz.

The development of new primary beam systems has now also made possible the construction of dual-polarized antenna arrays, in particular with a polarization orientation of + 45 ° and -45 °, respectively, relative to the horizontal or vertical.

Antenna arrays of this kind, whether they are basically dual-polarized or consist of simply polarized emitters, can be used to determine the direction of the incoming signal. At the same time, however, by appropriate adjustment of the phase position of the transmitting signals fed into the individual columns, the radiation direction can also be changed, ie, selective beam shaping takes place.

This orientation of the antenna in different horizontal directions is effected, for example, by means of a beam-forming-network. Such a beam shaping network can, for example, consist of a so-called butler matrix, which has, for example, four inputs and four outputs. Depending on the connected input, the network produces a different but firm phase relationship between the radiators in the individual dipole series. Such an antenna configuration with a butler matrix has, for example, been disclosed in US Pat. No. 6,351,243.

The antenna array which is known from the abovementioned US patent has, for example, four columns extending in the vertical direction and adjacent to one another in the horizontal direction, into which in each case four radiators or radiator devices are accommodated one above the other. The four inputs for the radiators arranged in a column (hereinafter also referred to as column inputs in some cases) are connected to the four outputs of an upstream butler matrix. The butler matrix has, for example, four inputs. This upstream beam shaping network in the form of the butler matrix produces a different but fixed phase relationship between the radiators in the four columns, depending on the connected input, that is, depending on which of the four inputs the connecting cable is connected to. Thereby four different orientations of the main beam direction and thus of the main beam are determined. In other words, the main beam direction can be set in a different angular position in a horizontal plane. In addition, the antenna array can, of course, in principle also be provided with a down-tilt device in order, in addition, to change the lowering angle of the main beam direction and thus of the main lobe.

In principle, however, there are two major problems with such antenna arrays using correspondingly arranged beam shaping networks, for example in the form of a butler matrix. On the one hand, an adjustment of the main beam direction in the azimuth direction is possible only in the predetermined steps, which is predetermined by different wiring according to the number of inputs. In the case of a butler matrix, for example with four inputs and four outputs, only four different azimuth angles can be set on the antenna array.

In addition, there is a special problem in the connection of a butler matrix for the purpose of setting-up in that a calibration is quite complicated. Because the phase position is non-uniform according to the butler matrix. In addition, a plurality of primary radiators of the antenna receive a part of the signal, independently of which input of the butler matrix is ​​switched.

From EP-A-0 877 444, a generic calibration device for an antenna array is known to be known, with inputs being assigned to the emitters, to which a beam shaping network is connected. The outputs of the beam shaping network are in each case connected to an assigned input of the antenna array, via which the radiators provided in a column are fed. In the beam shaping network, a different phase relationship is produced between the radiators arranged in the individual columns, depending on the input that is wired, in order to achieve a different beam direction, at least two inputs being fed via a common or separate feed cable. The calibration device further comprises probes which are arranged in the field of the radiators, as well as a matching device which is assigned to the outputs of the beam shaping network and by means of which the phase position for the incoming radiation limit of feedable signals can be adjusted and / or changed.

Finally, an antenna array with a beam-shaping network (butler matrix) and a matching device, which is arranged upstream of the inputs of the beam-shaping network, is also known from WO-A-0 156 186. The matching device is not yet part of a calibration device, but rather is used by an adaptive control for additional beam shaping.

It is an object of the present invention to provide a calibration device for a switchable antenna array, in particular for an antenna array with an upstream beamforming network, for example in the form of a butler matrix, such that the improved calibration makes the antenna array in the azimuth direction possible An even greater number of different angles with respect to the beam direction. It is also an object of the invention to provide a corresponding operating method for the operation of a corresponding antenna array.

The object is achieved according to the invention with respect to the calibration device according to the features indicated in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

It must be said to be quite surprising that with a beam shaping network known per se, for example in the form of a butler matrix, it has now become possible independently of the four different inputs, which are predetermined, by means of which the antenna is adjusted in four azimuth directions at four different emission angles Can additionally set the antenna array in the azimuth direction in additional angular orientations. According to the invention, this is possible in that at least one input of the beam-shaping network, for example in the form of the butler matrix, but preferably at least two inputs of this network are fed in a correspondingly balanced and calibrated phase position, whereby it is possible according to the invention that, for example, intermediate cobes are generated. Thus, radiation directions of the antenna array can also be set at additional intermediate angles opposite the predetermined main angles.

According to the invention, however, this is only possible if a phase adjustment for the radiators which have been supplied via the butler matrix has previously been carried out, so that the individual lobes are phase-added during the wiring of, for example, two inputs. In other words, a calibration of the feed lines to the antennas is provided in accordance with the invention in order to ensure that the signals present there are phase-matched at the outputs of the beam-shaping network, for example in the form of the butler matrix.

This is preferably realized by the fact that at least at least the phases arranged in some columns of the antenna array can be shifted in front of the inputs of the beam shaping network, for example in the form of the butler matrix, in such a way that the excited radiators are simultaneously connected to a plurality of inputs for obtaining a desired Pivoting of the lobes can be controlled accordingly.

In the case of a 4 × 4 antenna array with four columns and in each case four emitters or beam groups, the phase positions of all the emitters are preferably simultaneously shifted accordingly.

Preferably, the calibration of the phase position can be performed by phase adjusters which are connected to the corresponding inputs of the butler matrix. Alternatively, this can also be carried out by using upstream auxiliary lines to the butler matrix, which must be selected in a suitable length in order to realize the desired phase adjustment.

Furthermore, it has proved to be advantageous to place corresponding probes on the antenna array itself, via which corresponding calibration signals can be intercepted in order to carry out the phase matching by means of a calibration network.

Finally, a further improvement can also be achieved by the fact that the combination network contains loss-bearing components. These components contribute to a reduction in resonances.

Although the phase position of the transmission from the input of the individual columns or of the antenna inputs is preferably of the same magnitude, however, in practice the phase position (or the group delay) to the ideal phase position exhibits more or less severe tolerance-induced deviations. The ideal phase position is given by the fact that the phase is identical for all paths, also with respect to the beam shaping. The more or less strongly tolerance-induced deviations are additive as an offset or also frequency-dependent by different frequency ranges. According to the invention, it is proposed here to measure the deviations over all transmission paths preferably on the path from the input antenna array or beam shaping network to the probe output or input to probe outputs and preferably over the entire operating frequency range (for example during the production of the antenna). In the case of the use of coupling devices, the transmission paths are preferably measured on the path from the input antenna array or beam shaping network to the coupling output or coupling outputs. These determined data can then be stored in a data record. These data, stored in a suitable form, for example in a data set, can then be made available to a transmitting device or the base station, in order then to be taken into account for the electronic generation of the phase position of the individual signals. It is particularly advantageous, for example, to assign this data or the data set mentioned with the corresponding data to a serial number of the antenna.

The invention is explained in more detail below with reference to exemplary embodiments. In this context,<dl id="dl0001"><dt>FIG. 1:</dt><dd>5 shows a schematic plan view of an antenna array according to the invention with probes shown for a calibration device;</dd><dt>FIG. 2:</dt><dd>2 shows a schematic, preferably vertical cross section, along a vertical plane through a column of the antenna array shown in FIG. 1; FIG.</dd><dt>FIG. 3:</dt><dd>4 is a representation of four typical horizontal diagrams generated by a group antenna by means of a butler matrix;</dd><dt>FIG. 4:</dt><dd>4 is a diagram for explaining the phase relationship between the radiators in the individual columns before performing a calibration;</dd><dt>FIG. 5:</dt><dd>4 shows a representation corresponding to FIG. 4 after carrying out the calibration; FIG.</dd><dt>FIG. 6:</dt><dd>FIG. 3 is a representation corresponding to FIG. 3 of typical horizontal diagrams of the antenna array, which shows that additional intermediate lobes can be produced according to the invention;</dd><dt>FIG. 7:</dt><dd>A calibration device having a combination network using coupling means;</dd><dt>FIG. 8:</dt><dd>7 is an expanded calibration device for an antenna with two polarizations, which are aligned, for example, in + 45 ° and -45 ° with respect to the horizontal; FIG. and</dd><dt>FIG. 9:</dt><dd>A representation of a calibration device corresponding to FIG. 7, but not by means of coupling devices, but of probes (which can be installed at home on an antenna array).</dd></dl>

FIG. 1 shows, in schematic plan view, an antenna array 1 which, for example, comprises a plurality of dual-polarized radiators or radiating elements 3 arranged in front of a reflector 5. On the vertical longitudinal sides, an edge limiter 5 'belonging to the reflector 5 can be provided on the reflector 5, for example, which is arranged angularly to right-angled relative to the plane of the reflector plate. These reflector edge boundaries 5 'are often placed slightly obliquely outwards in the radiation direction.

In the exemplary embodiment shown, the antenna array shows four columns 7 which are arranged vertically, with four radiators or radiator groups 3 being arranged one above the other in each column in the exemplary embodiment shown.

In the antenna array according to FIGS. 1 and 2, four columns 7 are provided in which the four radiators or radiator groups 3 are positioned one above the other in the vertical direction. The individual radiators or radiator groups 3 need not necessarily be arranged at the same height in the individual columns. Preferably, for example, the radiators or radiator groups 3 can be arranged in offset in each case two adjacent columns 7 by half the vertical distance between two adjacent radiators. To this end, a representation is shown in the schematic plan view in FIG. 1, in which the radiators or radiator groups 3 in adjacent columns each lie on the same height line.

In the case of a dual-polarized antenna indicated in FIGS. 1 and 2, the radiators 3 can, for example, consist of cruciform dipole radiators or dipole squares. Dual-polarized dipole emitters 3 'are particularly suitable, as are known, for example, from WO 00/39894. Reference is made to the disclosure content of this prior publication in its entirety and is incorporated into the content of this application.

Finally, a beam shaping network 17 is also provided in FIG. 1, which has, for example, four inputs 19 and four outputs 21. The four outputs of the beam shaping network 17 are connected to the four inputs 15 of the antenna array. The number of outputs N may deviate from the number of inputs n, ie in particular the number of outputs N can be greater than the number of inputs n. In such a beam shaping network 17, a supply cable 23 is then connected, for example, to one of the inputs 19, All the outputs 21 are fed accordingly. For example, when the feed cable 23 is connected to the first input 19.1 of the beam-shaping network 17, a horizontal radiator alignment 16.1 with, for example, -45 ° to the left can be effected, as can be seen from the schematic diagram according to FIG. If, for example, the supply cable 23 is connected to the right-hand terminal 19.4, a corresponding alignment 16.4 of the main lobe 16 of the radiation field of the antenna array is effected to an angle of + 45 ° to the right. Correspondingly, when the supply cable 23 is connected to the connection 19.2 or the connection 19.3, the antenna array can be operated in such a way that, for example, a pivoting 16.2, 16.3 is effected by 15 ° to the left or to the right against the vertical plane of symmetry of the antenna array In different azimuth directions.

For this reason, it is customary in such a beam shaping network 17 to provide a corresponding number of inputs for different azimuthal angular orientations of the main antenna 16 of the antenna array, the number of outputs generally corresponding to the number of columns of the antenna array. In this case, each input is connected to a plurality of outputs, as a rule each input is connected to all outputs of the beam shaping network 17.

The beam shaping network 17 can, for example, be a known butler matrix 17 ', the four inputs 19.1, 19.2, 19.3 and 19.4 of which are connected in each case to all the outputs 21.1, 21.2, 21.3 and 21.4 3.

If, however, it is desired, in a beam-shaping network 17, for example in the form of a butler matrix 17 ', which basically allows the different settings of the main beam direction 16 according to FIG. 3, that the main beam direction is still adjustable to other azimuth angular positions Not realizable. For the connection of the feed cable 23 with one of the inputs 19.1 to 19.4 can only be used to achieve an orientation of the main beam direction in accordance with FIG.

3, it is now necessary to connect the feed cable 23 via a branching or summing station 26 not only with an input, but also at least to the input of the output cable Two inputs or several of the inputs 19.1 to 19.4.

However, this alone would not lead to a useful result. It has been found that a corresponding generation of further intermediate lobes in the "gaps" in the diagram according to FIG. 3 is only possible if a corresponding phase adjustment is first performed before the butler matrix, ie, before the beam shaping network 17, So that the individual lobes can be added correctly.

For this purpose, a calibration of the butler matrix and the connected antenna array must first be carried out. This first requires the phase sequence at the outputs 21.1 to 21.4 of the beam shaping network 17 to be measured preferably in the form of the butler matrix 17 ', specifically as a function of a feed of the feed signal once via the input 19.1, 19.2, 19.3 and 19.4 of the butler matrix 17 '. Depending on the input 19.1 to 19.4, the beam-shaping network 17 produces different radiation diagrams in the form of the butler matrix 17 'because of the different phases of the dipoles or dipole series, that is the radiators 3, 3'. For example, in the vertical arrangement of radiators 3, 3 ', four different horizontal diagrams are generated in the four columns 7. The phase relationships of the radiators in the individual columns are shown in the diagram according to FIG. 4.

In the diagram according to FIG. 4, the four outputs 21.1 to 21.4 are reproduced below with the Roman numerals I to IV. The relative phase relationships and / or phase differences (eg in degrees) are respectively fixed on the Y axis. The measurement curves shown in the diagram according to FIG. 4 then result in the form of four lines.

In the case of the dual-polarized antennas described by way of example, using dual-polarized radiators 3 ', for example, a phase jump of for example 180 ° between the primary radiators 3, 3' of the different polarizations can occur.

In order now to perform a phase adjustment for all the inputs 19.1 to 19.4 of the beam shaping network 17, for example in the form of the butler matrix 17 ', the measurement curves (straight lines) shown in FIG. 4 must be changed in their position according to the arrow representation 28 in such a way that the two upper, Measuring curves in the form of straight lines 30 and 32 with the two measuring curves 34 and 36 which lie deeper and steeper in FIG. 4 at a common point of intersection X, as is shown in FIG.

In other words, a corresponding phase adjustment must now be made, for example, by means of suitable phase adjusters in the exemplary embodiment shown, either with respect to the inputs 19.1 and 19.4 or with respect to the inputs 19.2 and 19.3, in order to obtain a common intersection point according to FIG. This can be done, for example, in accordance with the illustration according to FIG. 1 by phase adjusting elements 37, which are connected upstream of the inputs 19.1 to 19.4 of the butler matrix 17 ', so that inputs A to D for the overall circuit result. Instead of the phase adjusting elements 37 shown in FIG. 1, corresponding additional cable lengths can be provided at the individual inputs 19.1 to 19.4, the length of the cables being dimensioned such that the desired phase shifting is effected.

After performing such a phase adjustment, intermediate lobes 116 can now be generated, as shown, for example, in the case of the input 19.1 and 19.2 or 19.2 and 19.3 and 19.3 and 19.3 and 19.4, respectively, as is shown in the diagram according to FIG. All inputs are preferably supplied with the same power.

The desired calibration described above can now be carried out by an arrangement according to the invention with a very small number of probes or coupling devices. In the prior art, such calibration devices are placed at the input of the beam shaping network. On the contrary, it is proposed within the scope of the present invention to perform the decoupling directly at the individual columns. This provides a better accuracy, since the tolerances of the butler matrix are already calibrated out, but a reduction in the number of required coupling devices is also possible.

FIG. 7 now shows the device for the phase matching of the leads, that is, for performing a phase calibration. The phase adjustment for the intermediate lobes 116 is carried out with the phase adjusting elements from the butler matrix 17 ', so that these can be used by combinations of the inputs A and B, C and C or D sensibly and without further measures on the antenna feed lines .

At the outputs 21.1 and 21.4 (or 21.2 and 21.3) two couplers 111, which are as identical as possible, are now provided, each coupling out a small part of the respective signals. The decoupled signals are added in a combination network 27 (this is a "combiner", which is also abbreviated as "Comb." In the drawing). The result of the decoupling of the signals and the addition can be measured via an additional connection S at the combination network 27.

For the phase matching of the supply lines to the butler matrix 17 ', a suitable calibration signal, ie, a known signal, is now applied, for example, to the supply line for the input A, and the absolute phase is measured at the output S of the combination network (Comb). Now you can do this also for the leads to the inputs B, C and D.

If all the leads to the inputs A to D (electrical) are exactly the same length (and can otherwise be regarded as identical), the same absolute phase results at the output of the combination network, ie no phase difference occurs at the output S Switching of inputs A to D.

The fact that the same phase value is indicated for identical leads to the terminals A to D is made possible by the phase matching for the intermediate lobes 116 at the input, since by this measure the sum of the phases at the outputs 21.1 and 21.4 or 21.2 and 21.3 (that is to say at the outputs at which the couplers are seated) is always exactly twice the value of the point of intersection X of the four straight lines, as indicated in FIG. 5, relative to the inputs A to D.

7 that the couplers 111 are preferably connected between the respective output 21 and the respective input 15 of the assigned column 7 of the antenna array. In principle, the couplers must therefore be connected between the network accommodated in the butler matrix 17 'and at least one radiator 3, 3' in an allocated column 7 of the antenna array.

According to FIG. 8, it is shown how, for an antenna with two polarizations, eg + 45 ° and -45 °, the network can be combined for the phase matching of the feed lines. Such a combination is useful when, for example, the butler matrix can be realized together with the couplers and combination networks on a circuit board, since largely identical units (in each case couplers and combination networks) can be produced.

7 is achieved by combining the two outputs of the respective combination network 27 and 27 ', for example in the form of a combiner, with the inputs of a downstream second combination network 27 "likewise in the form of a combiner And to the common output S. The combination network 27 is thus used for determining the phase position on a radiating element with respect to the one polarization, the combination network 27 'being used for determining the phase position at a respective radiator for the other polarization.

For the sake of completeness, it is also mentioned in principle that it would be possible in principle to set the phase adjusters at the input of the beam shaping network 17, that is to say, for example, the butler matrix 17 ', in such a way that one can use a single coupler at the output of a respective matrix Phase independent of input A to D. In this case as well, the phase adjusters can consist of basically interconnectable line sections in order to change the phase position.

It is, of course, also possible to arrange one coupler 111, for example in the form of a directional coupler, on all four lines 35 in order to obtain even more measuring points for obtaining the straight line shown in the diagrams according to FIGS. 4 and 5.

Instead of the couplers 111 mentioned, however, it is also possible to use probes 11 which are, for example, of a pin-shaped design and preferably extend at a right angle from the plane of the reflector plate 5 and are assigned to a specific radiator 3. The probes 11 can preferably consist of capacitive coupling pins. However, they can also be formed from inductive coupling loops. In both cases, the probes 11 project from the reflector into the near field of the radiators. The mentioned probes 11 can also be used for dual-polarized radiators 3 ', since both polarizations can be measured. In FIG. 1, for example, one such probe 11 and 11b, shown in plan view, is assigned to the lowest radiators 3, 3 ', respectively, for the left and right columns. This probe is then used instead of the directional couplers 11 shown in FIGS. 7 and 8, in order to evaluate the signal measured therefrom in a combination network 27 and in the case of a dual-polarized antenna in a combination network 27 'and 27 ", a combination network 27 is shown , Which operates with two probes 11, ie 11a and 11b.

In principle, four probes, that is to say exactly as much probes as columns, can of course also be used here. In principle, the use of only one probe is also conceivable, in order to thereby determine the fixedly predetermined phase relationship of the radiators in the individual columns.

The combination networks are suitable for simple polarized antennas. They are basically also suitable for a dual-polarized antenna array. The use of probes 11 is particularly suitable here, since a single probe is sufficient to be assigned to a dual-polarized radiator arrangement 3, 3 ', since ultimately the desired partial signals can be received in both polarizations via this one probe. In the case of a coupling device, then a coupling device would have to be used for each polarization, that is to say that a pair of coupling devices would then be necessary in the case of the dual-polarized antenna array instead of a probe.