Method and device for determining a relative alignment of two GPS antennas in relation to one another

Relative GPS antenna alignment uses a phase shifter electrically connected to a first GPS antenna. A combiner is electrically connected to the phase shifter, the second GPS antenna and to a GPS receiver. A GPS reception signal (Sig1) emitted by the first GPS antenna is phase-shifted by the phase shifter by a phase shift (φ) that can be set by way of a controller and is added by the combiner to a second GPS reception signal (Sig2) emitted by the second GPS antenna. The composite signal (Sum) thus produced is determined for at least three different phase shifts (φ). On the basis of these data, the profile of the composite signal (Sum) and the relative alignment of the two GPS antennas in relation to one another is determined.

This application is the U.S. national phase of International Application No. PCT/EP2013/002063, filed Jul. 11, 2013, which designated the U.S. and claims priority to German Application No. 10 2012 016 637.0, filed Aug. 22, 2012, the entire contents of each of which are hereby incorporated by reference.

The present invention relates to a method and to a device for determining a relative alignment of two GPS antennas in relation to one another. By means of the method and by means of the device it is possible to determine for example the azimuth angle and/or the elevation angle of the two GPS antennas in relation to one another and thus of an object to which the two GPS antennas are fixed.

U.S. Pat. No. 5,943,008 discloses a device for determining an alignment of an antenna array. The antenna array comprises at least three receiving antennas for receiving GPS satellite signals, which have a fixed and known positioning in relation to one another. The receiving antennas are electrically connected to an individual GPS receiver via an interface. A first antenna for emitting a first GPS signal is directly connected to the interface, a first delay circuit being arranged between a second antenna for emitting a second GPS signal and the interface, and a second delay circuit being arranged between a third antenna for emitting a third GPS signal and the interface. The first delay circuit delays the transfer of the GPS satellite signal received by the second receiving antenna to the interface and to the GPS receiver by a first fixed delay time of for example 200 ns, and the second delay circuit delays the transfer of the GPS satellite signal received by the third receiving antenna to the interface and to the GPS receiver by a second fixed delay time of for example 400 ns. Among other things, the first and second delay circuits provide that the first, second and third GPS signals can be received separately by the GPS receiver, without interfering with one another. The GPS receiver has a processing functionality, in such a way that the GPS receiver determines alignment factors using the relative positions of the receiving antennas, the known first and second delay times and the known positional relationship of the receiving antennas in relation to one another. The GPS receiver determines the small differences between the predetermined delay times associated with the different receiving antennas and the measured code information and phase information of the received signals. These small differences are subsequently used to determine the difference between the positions of the three receiving antennas. As a result, the transit time differences in the GPS satellite signals in relation to the individual receiving antennas are used to determine the relative alignment of the receiving antennas in relation to one another.

To increase the precision of the determination of the alignment of the antenna array, more than three receiving antennas may be provided, a delay circuit having to be arranged in each case between each individual antenna and the interface and the GPS receiver. The respective delay circuits have to have different delays from one another so as to make it possible for the respective GPS signals to be received separately by the GPS receiver, since the GPS signals must not interfere with one another.

The object of the present invention is to provide a simple, cost-effective and improved device and an improved method for determining a relative alignment of two GPS antennas in relation to one another, by means of which the determination of the alignment of the two GPS antennas in relation to one another can be established to an increased precision.

According to the invention, the object is achieved by the method having the features specified in claim1and by the device having the features specified in claim12. Advantageous configurations are specified in the dependent claims.

More specifically, the device according to the invention for determining a relative alignment of a first GPS antenna in relation to a second GPS antenna comprises the first GPS antenna, the second GPS antenna at a distance from the first GPS antenna, a phase shifter electrically connected to the first GPS antenna, an adding apparatus connected to the phase shifter and to the second GPS antenna, a GPS receiver electrically connected to the combination apparatus, and a control apparatus electrically connected to the GPS receiver and to the phase shifter. Upon receiving the at least one GPS satellite signal, the first GPS antenna emits a first GPS received signal and the second GPS antenna emits a second GPS received signal. The phase shifter is configured to shift a phase of the first GPS received signal by a phase shift, the phase shift being variable and being settable by means of the control apparatus. The phase shift may have any desired value, including zero. The respective phase shifts may be mutually equidistant or may be at different angular distances from one another. The combination apparatus, which may comprise an adding apparatus and is also known as a power combiner, is configured to combine the second GPS received signal with the first GPS signal which has been phase-shifted by the phase shift, so as to produce a combination signal which is supplied to the GPS receiver. The combination signal may preferably be the added signal of the second GPS received signal and the first GPS received signal which has been phase-shifted by the phase shift. The GPS receiver generates a sampling signal and/or a signal-to-noise-ratio signal from the combination signal, and transmits the sampling signal and/or the signal-to-noise-ratio signal to the control apparatus, which stores the sampling signal and/or the signal-to-noise-ratio signal together with the set phase shift. The device is configured to carry out these method steps, also known as repetition steps, for each of at least three different phase shifts, it alternatively being possible for the GPS satellite signal merely to be received once. The individual above-described components are electrically connected via signal lines.

The phase shifter may be implemented in any manner known in the art. In particular, the phase shifter may comprise different lengths of signal lines or delay lines, inductors and capacitors. The phase shifter may also be implemented as an all-pass. The phase shifter may also be implemented as a digital phase shifter.

Since the frequency of the combination signal and thus the frequency of the sampling signal and/or the frequency of the signal-to-noise-ratio signal and the differently set phase shifts are known, the device establishes the progression of the sampling signal and/or of the signal-to-noise-ratio signal by means of the control apparatus, on the basis of the at least three sampling signals and/or signal-to-noise-ratio signal thus obtained, which have in each case been obtained at different phase shifts. Since the relative positioning of the first GPS antenna and the second GPS antenna is known, the progression thus established of the sampling signal and/or of the signal-to-noise-ratio signal is characteristic of the alignment of the first GPS antenna in relation to the second GPS antenna, in such a way that the device can establish the relative alignment of the GPS antennas in relation to one another by means of the control apparatus on the basis of the progression of the sampling signal and/or the signal-to-noise-ratio signal.

By means of the device according to the invention, alignment of the two GPS antennas in relation to one another is possible to a high precision. As a result of the method according to the invention being used, the device according to the invention merely requires two GPS antennas to establish the alignment of the two GPS antennas in relation to one another to a high precision. A further advantage is that the device according to the invention merely requires one GPS receiver. The precision of the alignment determination can be increased by carrying out the repetition steps more than three times for respectively different phase shifts, in such a way that the progression of the combination signal and thus the progression of the sampling signal and/or of the signal-to-noise-ratio signal can be established more precisely. For a peak deviation of the phase shifter of for example 360°, the combination signal may be determined for example for 360 different phase shifts having angularly equidistant spacings of 1°. In this case, the progression of the combination signal is very precise as a result of the high number of measurement points.

Further, the precision of the alignment determination can be increased in that more than one GPS satellite signal is received by means of the first and the second GPS antennas. On the one hand, for this purpose the GPS satellite signal emitted by a GPS satellite can be received by the first and second GPS antennas at different moments, and on the other hand, the GPS satellite signals of a plurality of GPS satellites can be received by the first and second GPS antennas at one or more moments.

Thus, the method for determining a relative alignment of a first GPS antenna in relation to a second GPS antenna at a distance therefrom is preferably configured in such a way that the method comprises the following steps:receiving at least one GPS satellite signal by means of the first GPS antenna, whilst emitting a number of first GPS received signals corresponding to the number of GPS satellite signals, and by means of the second GPS antenna, whilst emitting a number of second GPS received signals corresponding to the number of GPS satellite signals;shifting a phase of the first GPS received signal(s) by a phase shift, by means of a phase shifter;combining the second GPS received signal(s) with the corresponding first GPS received signal(s) which have been phase-shifted by the phase shift, to generate a number of combination signals corresponding to the number of GPS satellite signals, by means of a combination apparatus;generating a number of sampling signals and/or signal-to-noise-ratio signals corresponding to the number of GPS satellite signals from the combination signal(s), by means of a GPS receiver;storing the sampling signal(s) which are dependent on the phase shift and/or the signal-to-noise-ratio signal(s) which are dependent on the phase shift, by means of a control apparatus;establishing the progression(s) of the sampling signal(s) which are dependent on the phase shift and/or of the signal-to-noise-ratio signal(s) which are dependent on the phase shift, by means of the control apparatus; andestablishing the relative alignment of the first GPS antenna in relation to the second GPS antenna on the basis of the progression(s) of the sampling signal(s) and/or the signal-to-noise-ratio signal(s), by means of the control apparatus.

As was already explained above, the first method step is carried out either once for one phase shift or at least three times for at least three different phase shifts. The second to fifth method steps are carried out for at least three different phase shifts. Subsequently, the sixth and seventh method steps can be carried out.

Preferably, establishing the progression of the combination signal and/or of the signal-to-noise-ratio signal comprises establishing at least one first phase shift, for which the combination signal and/or the signal-to-noise-ratio signal has a maximum, and/or at least one second phase shift, for which the combination signal and/or the signal-to-noise-ratio signal has a minimum. Further, establishing the relative alignment of the first GPS antenna in relation to the second GPS antenna is based at least on the first phase shift thus established, for which the combination signal and/or the signal-to-noise-ratio signal has a maximum, and/or on at least the second phase shift, for which the combination signal and/or the signal-to-noise-ratio signal has a minimum.

Since the frequency of the added signal and thus the frequency of the combination signal and/or of the signal-to-noise-ratio signal is known, the progressions thereof can be characterised in a simple manner by specifying a first or second phase shift for which the combination signal and/or the signal-to-noise-ratio signal has a maximum or a minimum. The frequency of the added signal is known, since the frequency of the carrier wave of the GPS satellite signal is known (for GPS signals the frequency of the carrier wave is for example 1.5 GHz). The phase shift for which the added signal has a maximum or minimum is characteristic of the relative positioning of a satellite which emits the GPS satellite signal in relation to the first GPS antenna and the second GPS antenna, in such a way that, on the basis of at least the first phase shift and/or at least the second phase shift, the alignment of the first GPS antenna in relation to the second GPS antenna can be established in a simple manner, since the relative positioning of the first GPS antenna in relation to the second GPS antenna is known.

Preferably, establishing the progression of the combination signal which is dependent on the phase shift and/or of the signal-to-noise-ratio signal comprises calculating the progression of the combination signal and/or of the signal-to-noise-ratio signal as a function of the phase shift.

Thus for example, on the basis of merely three data pairs each consisting of a phase shift and an amplitude of the combination signal and/or of the signal-to-noise-ratio signal, the progression of the combination signal and/or of the signal-to-noise-ratio signal can be calculated. This calculation can for example be carried out using what is known as a fit. If the progression of the combination signal and/or of the signal-to-noise-ratio signal is calculated in this manner, the position of a phase shift for which the combination signal and/or the signal-to-noise-ratio signal has a maximum or minimum can be determined in a simple manner, for example. On the basis of the known frequency of the combination signal and/or of the signal-to-noise-ratio signal, and on the basis of the calculated phase shift(s) for which the combination signal and/or the signal-to-noise-ratio signal has a maximum or minimum or a plurality of maxima or minima, the alignment of the first GPS antenna in relation to the second GPS antenna can be determined in this manner to a high precision, without the need for many measurements of the combination signal and/or of the signal-to-noise-ratio signal at many different phase shifts.

Preferably, calculating the progression of the combination signal which is dependent on the phase shift and/or of the signal-to-noise-ratio signal comprises calculating at least a first phase shift, for which the combination signal and/or the signal-to-noise-ratio signal has a maximum, and/or at least a second phase shift, for which the combination signal and/or the signal-to-noise-ratio signal has a minimum. This calculation of the progression can for example be carried out using what is known as a fit, for which merely three data pairs are needed, each consisting of a phase shift and of an associated amplitude of the combination signal and/or of the signal-to-noise-ratio signal. In this way, the phase shifts for which the combination signal and/or the signal-to-noise-ratio signal have a maximum or minimum can be determined precisely, without determining the progression of the combination signal and/or of the signal-to-noise-ratio signal by means of many different phase shifts. A corresponding determination of the progression of the combination signal and/or of the signal-to-noise-ratio signal is therefore possible very rapidly.

Preferably, the predetermined distance of the second GPS antenna from the first GPS antenna is less than or equal to a half-wavelength of the carrier wave of the GPS satellite signal.

If the distance between the two GPS antennas is less than or equal to the half-wavelength of the carrier wave of the GPS satellite signal, the result of establishing the relative alignment of the two GPS antennas in relation to one another merely has two uniqueness ranges. If the line connecting the two GPS antennas and the line connecting a GPS antenna to the GPS satellite are aligned mutually parallel, and thus form an angle of 0°, the path length difference of the GPS satellite signal in relation to the two GPS antennas is exactly equal to the distance between the two GPS antennas. The first received signal emitted by the first GPS antenna thus has a phase shift of 180° in relation to the second received signal emitted by the second GPS antenna, in such a way that adding the two received signals results in a minimum. If the line connecting the two GPS antennas and the line connecting a GPS antenna to the GPS satellite are not aligned mutually parallel, and form an angle of more than 0°, the path length difference of the GPS satellite signal in relation to the two GPS antennas is less than the distance between the two GPS antennas, in such a way that the first received signal emitted by the first GPS antenna has a phase shift of less than 180° in relation to the second received signal emitted by the second GPS antenna. In this case, the GPS satellite may be positioned either closer to the first GPS antenna or closer to the second GPS antenna. For a distance of less than half the carrier wavelength between the two GPS antennas, this results in precisely two uniqueness ranges, since according to the determination result the GPS satellite may be in two hemispheres. If the line connecting the two GPS antennas and the line connecting a GPS antenna to the GPS satellite are not aligned mutually parallel, and form an angle of 90°, the path length difference of the GPS satellite signal in relation to the two GPS antennas is exactly zero, in such a way that the first received signal emitted by the first GPS antenna has no phase shift in relation to the second received signal emitted by the second GPS antenna.

If the distance between the two GPS antennas is more than half the carrier wavelength, there are more than two uniqueness ranges for a determination result of the alignment of the GPS antennas in relation to one another, since in this case the path length difference of the GPS satellite signal in relation to the two GPS antennas is exactly half the carrier wavelength for an angle greater than 0° between the line connecting the two GPS antennas and the line connecting a GPS antenna to the GPS satellite. If the distance between the two GPS antennas is n times half the carrier wavelength for some positive integer n, the path difference in the GPS satellite signal for the two GPS antennas, for an angle φ formed by the line connecting the two GPS antennas and the line connecting a GPS antenna to the GPS satellite, is exactly half the carrier wavelength, or λ/2, if the angle φ meets the following condition:
φ=arccos(1/n)

For n=2, φ=60°, and so the first uniqueness range is a cone of which the central axis is aligned perpendicular to the line connecting the two GPS antennas and of which the legs form an angle of 60° (=180°−2*60°). For n=3, φ=70.53°, and so the legs of the cone representing the first uniqueness range form an angle of 38.94° (=180°−2*70.53°).

By reducing the spacing of the two GPS antennas to at most half the carrier wavelength, the uniqueness ranges are thus reduced in such a way that the determination of the alignment of the GPS antennas in relation to one another is simplified.

In accordance with the method for determining a relative alignment of a first GPS antenna in relation to a second GPS antenna, it is also possible for more than one GPS satellite signal to be received by a plurality of GPS satellites, the additional data being used for increasing the precision of determination of the relative alignment of the GPS antennas in relation to one another. The additional data may further be used for a plausibility check, in which the plausibility of the determined alignment of the GPS antennas is analysed. If the evaluation of the GPS signals results in a plurality of possible alignments of the GPS antennas in relation to one another, the most plausible alignment can be determined.

The device preferably further comprises an attenuation apparatus, which is electrically connected to the second GPS antenna, the adding apparatus and the control apparatus. The attenuation apparatus is adapted to attenuate the second GPS received signal. The phase shifter downstream from the first GPS antenna can attenuate the GPS received signal. The amplitudes of the first GPS received signal and the second GPS received signal can be adapted to one another by means of the attenuation apparatus.

In the following description, like reference numerals denote like components or like features, in such a way that a description made for one component in reference to one drawing also applies to the other drawings, avoiding repetition of the description.

FIG. 1is a schematic block diagram of the device according to the invention for determining a relative alignment of two GPS antennas10,20in relation to one another. The device comprises a first GPS antenna10and a second GPS antenna20which are at a predetermined distance from one another. The first GPS antenna10is configured to emit a first GPS received signal Sig1upon receiving a GPS satellite signal PDS emitted by a GPS satellite Sat (FIG. 2a, 3a, 4a). The GPS satellite signal PDS may in particular comprise a position data signal PDS. The first GPS antenna10is electrically connected to a band-pass filter12, in such a way that merely the first GPS received signal Sig1is passed on to an amplifier14connected to the band-pass filter12. Usually, the frequency of the carrier wave of the GPS satellite signal is 1.5 GHz, in such a way that the passband of the band-pass filter is in a tight range around 1.5 GHz. The amplifier14amplifies the first GPS received signal Sig1and transfers it to a phase shifter16electrically connected to the amplifier14. The phase shifter16is electrically connected to a control apparatus50, the phase shifter16obtaining control commands for setting a phase shift φ from the control apparatus15.

The second GPS antenna20is electrically connected to a band-pass filter22, which may be constructed identically to the band-pass filter12. The band-pass filter22is in turn electrically connected to an amplifier24, which is identical in construction to the amplifier14. An attenuation apparatus25is electrically connected to the amplifier24, and attenuates the second GPS received signal Sig2emitted by the second GPS antenna20. However, the attenuation apparatus25is not absolutely necessary for determining the alignment of the first GPS antenna10in relation to the second GPS antenna20using the device according to the invention.

The attenuation apparatus25is electrically connected to the control apparatus50and receives control signals for setting the variable attenuation therefrom. The attenuation apparatus25serves to adapt the amplitude of the second GPS signal Sig2to the amplitude of the first GPS signal Sig1, since the first GPS signal Sig1is also attenuated, in addition to the phase shift φ, by the phase shifter16.

The device for determining the relative alignment of the two GPS antennas10,20in relation to one another further comprises a combination apparatus30, also known as a power combiner30, which is implemented as an adding apparatus in the embodiment shown. Both the phase shifter16and the attenuation apparatus25are electrically connected to the adding apparatus30. The adding apparatus30adds or combines the first GPS received signal Sig1, which is phase-shifted by the phase shift φ, and the second GPS received signal Sig2, which is attenuated by the attenuation apparatus25. This addition takes into account the relative phase positions of the first GPS received signal Sig1and the second GPS signal Sig2.

A GPS receiver40is electrically connected to the adding apparatus30and configured to receive an added signal Sum, which is generated by the adding apparatus30by adding the phase-shifted first GPS received signal Sig1and the attenuated second GPS received signal Sig2. The GPS receiver40emits further data aside from the position, including a signal-to-noise-ratio signal SNR or a signal-to-noise-ratio of the GPS satellite signals PDS, as well as the azimuth and elevation of the respective received GPS satellite Sat. These data are all contained in a standard NMEA format. The GPS receiver40is electrically connected to the control apparatus50for emitting data to the control apparatus50. The control apparatus50in turn comprises a processor and/or a memory or is connected to a memory (not shown). Therefore, the control apparatus has a control functionality, a processing functionality and/or a memory functionality. Therefore, by means of the control apparatus50, data emitted by the GPS receiver50can be stored, the phase shift φ of the phase shifter16can be set, and the attenuation of the attenuation apparatus25can be set.

In the following, the dependency of the progression of the added signal Sum both on the position of a GPS satellite Sat in relation to the first GPS antenna10and the second GPS antenna20and on the phase shift φ, which is set by the phase shifter16and by which the first GPS received signal Sig1is phase-shifted, is described with reference toFIGS. 2ato 4b.FIG. 2ashows a positioning of the GPS satellite Sat in which it is symmetrically arranged between the first GPS antenna10and the second GPS antenna20. Therefore, the GPS satellite Sat is located at a point on a plane which extends between the first GPS antenna10and the second GPS antenna20, in other words which intersects the connecting line between the first GPS antenna10and the second GPS antenna20in the centre thereof. Therefore, the distances of the GPS satellite Sat from the first GPS antenna10and from the second GPS antenna20are equal, in such a way that the distance to be covered by the GPS satellite signal PDS emitted by the GPS satellite Sat is of the same length for the first GPS antenna10as for the second GPS antenna20. Therefore, the first GPs received signal Sig1emitted by the first GPS antenna10and the second GPS received signal Sig2emitted by the second GPS antenna20have identical phases.

When the first GPS received signal Sig1and the second GPS received signal Sig2are added by the adding apparatus30, the first GPS received signal Sig1not having been phase-shifted by the phase shifter16, the two GPS received signals Sig1, Sig2are added with identical phases, in such a way that the added signal Sum thus generated has a maximum. By contrast, if the first GPS received signal Sig1emitted by the first GPS antenna10is phase-shifted by means of the phase shifter16, the first GPS received signal Sig1and the second GPS received signal Sig2cancel one another in part by interference, resulting in a minimum for the added signal Sum thus produced if the phase shift is an integer multiple of 180°.FIG. 2bshows the progression of the added signal Sum as a function of the phase shift φ by which the first GPS received signal Sig1has been phase-shifted, for the positioning shown inFIG. 2aof the GPS satellite Sat in relation to the first GPS antenna10and the second GPS antenna20.

FIG. 3ashows another positioning of the GPS satellite Sat with respect to the first and second GPS antennas10,20. The GPS satellite Sat is located at a point on a line approximately connecting the first GPS antenna10to the second GPS antenna20. Therefore, the path to be covered by the GPS satellite signal PDS between the GPS satellite Sat and the first GPS antenna10is longer than the path to be covered by the GPS satellite signal PDS between the GPS satellite Sat and the second GPS antenna20.

The distance between the first GPS antenna10and the second GPS antenna20is given as D inFIG. 3. Since the frequency of the carrier wave of the GPS satellite signal PDS is known and is usually 1.5 GHz, for a distance D of 0.1 m between the first GPS antenna10and the second GPS antenna20, the first GPS received signal Sig1emitted by the first GPS antenna10would be phase-shifted by 180° with respect to the second GPS received signal Sig2emitted by the second GPS antenna20, since in this case the distance D is exactly half the wavelength of the carrier wave, and so the transit time difference in the GPS satellite signal PDS from the GPS satellite Sat to the first GPS antenna10and to the second GPS antenna20leads to a phase shift φ of 180°. Thus, in general, for the first GPS received signal Sig1to be phase-shifted by 180° with respect to the second GPS received signal Sig2, the following condition has to be met for the positioning shown inFIG. 3a:
D=n*c/2f
where n is an odd integer (1, 3, 5, 7, . . . ). If the first GPS received signal Sig1is phase-shifted by 180° by means of the phase shifter16, the added signal Sum has a maximum, since in this case the phases of the first GPS received signal Sig1and the second GPS received signal Sig2are equal again.FIG. 3bshows the progression of the added signal Sum as a function of the set phase shift φ for the positioning shown inFIG. 3aof the satellite Sat with respect to the first and second GPS antennas10,20, the relation shown above for the distance between the two GPS antennas10,20being met in this case.

By contrast,FIG. 3cshows the progression of the added signal Sum as a function of the phase shift φ for a case where the distance D between the first GPS antenna10and the second GPS antenna20does not meet the relation shown above.

In turn,FIG. 4ashows another further positioning of the GPS satellite Sat with respect to the first and second GPS antennas10,20, andFIG. 4bshows the progression of the added signal Sum as a function of the set phase shift φ for the positioning shown inFIG. 4aof the GPS satellite Sat.

The progression of the added signal Sum as a function of the phase shift φ is thus dependent on the different positioning of the GPS satellite Sat with respect to the first and second GPS antennas10,20, in such a way that the progression of the added signal Sum as a function of the phase shift φ for a known distance of the first GPS antenna10from the second GPS antenna20is characteristic of the position of the GPS satellite Sat. Therefore, from the progression of the added signal Sum together with the GPS satellite signal PDS transmitted by the GPS satellite Sat, a conclusion can be drawn as to the relative positioning of the first GPS antenna10in relation to the second GPS antenna20.

FIG. 5shows two added signals Sum, which are generated in the above-described manner. The two added signals shown differ in that the respective GPS received signals Sig1, Sig2result from GPS satellite signals PDS emitted from GPS satellites Sat having different positionings with respect to the first and second GPS antennas10,20. It can be seen fromFIG. 5that the added signals Sum generated in this manner are identical for two phase shifts φ. As a result, at least three phase shifts φ have to be carried out by means of the phase shifter16, and at the same time, the amplitudes of the associated added signals have to be determined so as to be able to establish the progression of the added signal Sum reliably and uniquely.

FIG. 6shows the dependence of two different signal-to-noise ratios SNR on a set phase shift φ. It can be seen fromFIG. 6that the maxima of the signal-to-noise ratios are more pronounced than the corresponding minima. This is due to the processing of the GPS received signals Sig1, Sig2in the GPS receiver40. It can be seen fromFIG. 6that the signal-to-noise ratio SNR has a characteristic progression which is dependent on the set phase shift φ, in such a way that the alignment of the first GPS antenna10in relation to the second GPS antenna20can also be determined as a function of the signal-to-noise ratio SNR.

FIG. 7is a flow chart of the method according to the invention, which is carried out by the device according to the invention. In a first repetition step S1, a GPS satellite signal PDS is received by means of the first GPS antenna10and by means of the second GPS antenna20. The first GPS antenna10emits the first GPS received signal Sig1, and the second GPS antenna20emits the second GPS received signal Sig2. The first repetition step S1is followed by a second repetition step S2, in which the phase of the first GPS received signal Sig1is shifted by a phase shift φ by means of the phase shifter16. The phase shift φ is controlled by the phase shifter16by means of the control apparatus50.

In a third repetition step S3, the second GPS received signal Sig2is added to the first GPS received signal Sig1which has been phase-shifted by the phase shift φ, to generate an added signal Sum. In a fourth repetition step S4, a sampling signal and/or the signal-to-noise-ratio signal SNR are generated from the added signal Sum. The sampling signal may for example comprise I data and Q data of the added signal Sum. In the following, merely the signal-to-noise-ratio signal SNR is discussed, but the following is also applicable to the sampling signal. Subsequently, in a firth repetition step S5, the signal-to-noise-ratio signal SNR is stored together with the information about the phase shift φ by means of the control apparatus50.

These repetition steps are carried out at least for three different phase shifts φ. It can be seen fromFIG. 7that after the fifth repetition step S5it is checked whether the set phase shift φ corresponds to a maximum phase shift φmax. If the set phase shift φ does not correspond to the maximum phase shift φmax, in other words is less than the maximum phase shift φmax, the set phase shift φ is increased by a phase increment Δφ, and there is a jump back either to the repetition step S1or to the repetition step S2. As already mentioned above, these repetition steps are carried out at least three times, in such a way that for a peak deviation of for example 360° the phase increment in the case may be at most 120°.

Once at least three data pairs, each consisting of a signal-to-noise-ratio signal SNR and a phase shift φ associated with the signal-to-noise-ratio signal SNR, have been stored in this manner, in a method step S6the progression of the signal-to-noise-ratio signal SNR, which is dependent on the phase shift φ, is determined by means of the control apparatus50. This determination of the progression of the signal-to-noise-ratio signal SNR may for example take place in that, for a sufficiently precise measurement or sampling of the progression of the signal-to-noise-ratio signal SNR, the phase shift φ at which the signal-to-noise-ratio signal SNR has a maximum or minimum is determined in a look-up table. For example, the phase increment Δφ may merely be 1°, in such a way that for a peak deviation of 360° 360 signal-to-noise-ratio signals SNR are generated, in such a way that in the look-up table thus generated merely the phase shift φ at which the signal-to-noise-ratio signal SNR is a minimum or maximum has to be determined, it being possible to position the minimum or maximum of the signal-to-noise-ratio signal SNR very exactly for such a high-resolution measurement or sampling of the signal-to-noise-ratio signal SNR.

Alternatively or in addition, the method step S6for determining the progression of the signal-to-noise-ratio signal SNR may comprise a method step for calculating the progression of the signal-to-noise-ratio signal SNR as a function of the phase shift φ. If for example the progression of the signal-to-noise-ratio signal SNR is merely determined as a function of three different phase shifts φ, it is possible to draw a conclusion as to the progression of the signal-to-noise-ratio signal SNR, or to calculate it, by means of what is known as a fit, on the basis that the frequency of the signal-to-noise-ratio signal SNR is known. Therefore, it is possible to precisely determine minima and maxima of the signal-to-noise-ratio signal SNR even if merely a few phase shifts φ are carried out.

In a further method step S7, the relative alignment of the first GPS antenna10in relation to the second GPS antenna20is determined on the basis of the progression of the signal-to-noise-ratio signal SNR by means of the control apparatus50.

FIG. 8shows an example application of the device according to the invention for determining a relative alignment of a first GPS antenna10in relation to a second GPS antenna20.FIG. 8shows a holding and carrying device200, for example in the form of a mast200, on which three antennas or single antennas100a,100b,100care held positioned offset in the circumferential direction, which consist for example of three single-gap or multi-gap antenna arrays, which usually comprise a substantially vertically aligned reflector and radiator apparatuses arranged in front thereof. These may be single-polarised or dual-polarised radiator apparatuses for transmitting in one frequency band or for two-frequency or multi-frequency bands, if for example this is a dual-band or multi-band antenna arrangement. In the embodiment shown, the individual antenna apparatuses100a,100b,100care each enclosed by a radome as a protector.

By suitable mechanical or controllable measures, the antennas100a,100b,100c, which are in principle positioned mutually offset for example at a 120° angle, may also be offset at an angle deviating at least slightly therefrom, for example so as to illuminate the different three sectors.

In the embodiment shown, two GPS antennas10,20having a lateral offset are provided in each case on the upper end face102or above the end face region102. The antenna arrangement further comprises the further components according to the invention which were shown or described in the description with reference toFIG. 1. By means of the above-described method, it is possible to align the first GPS antenna10in relation to the second GPS antenna20and thus to align the individual antennas100a,100b,100c.

Thus, the alignment of an antenna arrangement or of individual antennas100a,100b,100cwhich are each equipped with a device according to the invention can be exactly determined.

LIST OF REFERENCE SIGNS

10first GPS antenna11signal line12band-pass filter14amplifier16phase shifter20second GPS antenna21signal line22band-pass filter24amplifier25attenuation apparatus30combination apparatus, adding apparatus, power combiner31signal line40GPS receiver41,42,43signal line50control apparatus100,100a,100b,100cobject, antenna, individual antenna102end face region200holding and carrying device/mastφ phase shiftφ1first phase shift, for which the added signal has a maximumφ2second phase shift, for which the added signal has a minimumφmax maximum phase shiftΔφ phase shift incrementD distance between first GPS antenna and second GPS antennan number of times repetition steps are carried outPDS GPS satellite signalS1-S6method stepsSat GPS satelliteSig1first GPS received signalSig2second GPS received signalSum added signal