DE102020105844A1 - Method for examining the surroundings of a receiving antenna - Google Patents

Abstract

The invention is based on the use of double polarized test receiving antenna which can be reconfigured to different power levels. The configurability includes polarization purity and back lobe, i.e. the two main antenna parameters that influence the ability to suppress multipath propagation from the upper hemisphere and from the lower hemisphere, respectively. The invention provides a method of generically investigating the location for the installation of an antenna by using a reconfigurable probe or test receiving antenna capable of assuming various MPSI grades. The results obtained from this series of measurements then form a kind of “multipath map” of the location for each MPSI grade. Such a map then makes it possible to predict the performance achievable with any other antenna by simply comparing its MPSI values with the multipath map obtained with a corresponding MPSI of the probe or test receiving antenna.

Description

The invention relates to a method for examining the surroundings of a receiving antenna for satellite signals with regard to the existence of the multipath propagation of the satellite signals until they are received by the receiving antenna arranged at a predetermined altitude above a subsurface.

The use of global navigation satellite systems (GNSS) as a means of precise positioning, navigation and timing is increasing in a variety of use cases. In parallel with the widespread, low-cost use of GNSS, the need for precise reference stations and precise rovers is also becoming increasingly important.

In the case of precise position determination systems, such as those used in geodesy, as reference stations for international GNSS services (IGS), but also as rovers for real time kinematic applications (RTK), there are additional high demands on the performance of the antennas that are aimed at this to minimize any non-ideality. On the other hand, these non-idealities are very present in low-cost mobile applications, as a result of which the achievable position determination accuracy is considerably limited.

Examples of high-end antennas used in reference stations are the AR25 antenna from Leica and the GAL-EXP-ANT antenna from Space Engineering spa (now Airbus Italia Spa). An antenna design with excellent performance in this regard is in DE 10 2017 217 117 B3 described.

Although the antenna-related errors are minimized in the antennas mentioned above, both in terms of the variation in the group delay (GDV) and the variation in the phase centers (PCV), remaining errors in the GNSS processing chain are not completely eliminated, which means that the usability and / or the achievable accuracy of such stations can be impaired and / or limited. In addition to the errors caused by the satellite hardware, the atmospheric delays (ionosphere and troposphere) and non-idealities of the receiver, a large part of the remaining errors are caused by reflections of the GNSS signals in the immediate vicinity of the reference stations (the so-called "multipath propagation"). Multipath propagation enters the receiver through the antenna and causes errors in the estimation of the satellite range and ultimately in the positioning accuracy.

This problem is well known and several countermeasures have been taken over the past few decades to minimize it, but have not succeeded in completely eliminating it. Ad-hoc antennas are used, for example, in reference stations of ground-based augmentation systems (GBAS), which are able to greatly reduce the multipath propagation of negative elevations at the expense of a very large and expensive antenna. On the other hand, improvements from the receiver side are also available, with technologically advanced receivers today being able to provide "multipath propagation attenuation tools" to reduce the impact of such an effect on GNSS measurements.

However, the amount of multipath that will occur at a particular location (e.g. a location where a new reference station is to be built) is still difficult to predict and the effective performance can only be evaluated after it has been set up, with significant disadvantages in terms of flexibility and Costs. In addition, it is currently not possible to predict in advance how other antennas would behave in the same position, ie whether using a different antenna (e.g. a newer generation antenna) will improve multipath rejection and the remaining errors could minimize for that specific position.

In recent years, the authors have made the first attempts to define multipath suppression capability indicators (MPSI) (see S. Caizzone, M.-S. Circiu, W. Elmarissi, C. Enneking, M. Felux, K. Yinusa, “Multipath Rejection Capability Analysis of GNSS Antennas”, Proc. of ION GNSS + 2018, Miami (USA), Sept. 2018 ) released. These are parameters that are suitable for quantifying and predicting in advance how good a given antenna is in terms of suppressing / preventing incoming multipath. Different indicators have been defined, depending on what type of multipath is expected for the particular installation (e.g. from below the antenna as in geodetic applications where the antenna is installed on tripods; or from above the antenna in the event that For example, the antenna is near a tall building or surrounded by trees).

While generic, such indicators provide a better estimate of the antenna's “intrinsic” ability to prevent multipath than the traditionally used indicators used by antenna users without taking full account of the specific nature of the GNSS world (such as the axis ratio, the front-to-back or down-to-up ratio, etc.).

It has been recognized that antennas with similar indicators pick up a similar amount of multipath when placed in the same scenario.

However, there is still a lack of a method for appropriately performing multipath propagation characterization for a particular installation location of an antenna. Such a method would make it possible to perform some sort of mapping of the multipath that is present in the particular location and would be extremely valuable in various applications, for example in deciding the position of a new reference station.

Another application could be in the field of antenna-robot calibration: in this case, GNSS antennas are calibrated with regard to phase center and group delay variation by means of a robot am, which is arranged on a roof on which the GNSS satellites are clearly visible to the antenna. By correctly processing the satellite signals and using fast movements of the robot, it is possible to obtain an estimate of the PCV and GDV of the antenna. However, this process is influenced by the extent of multipath propagation given at the location at which the robot arm is arranged and could therefore benefit from a characterization of the multipath propagation environment that can be achieved by the present invention. This enables an optimal placement of the robot in the available space and / or a correct consideration / rejection of measurements from directions in which the multipath degree of propagation is too high.

An object of the present invention is to create a method that simplifies the selection of an antenna for the reception of satellite signals that is to be set up at a specific location in advance, wherein the antenna should be suitable for certain requirements with regard to the suppression of To meet multipath propagation.

The invention therefore provides a method which can be used to characterize the multipath environment at a particular location before the final installation and establishment of a reference station, which is advantageous with regard to the early detection of problematic locations or obstacles.

1. a) eine konfigurierbare, doppelt polarisierte Test-Empfangsantenne bereitgestellt wird, die versehen ist mit
   • - einem ersten Antennenausgang für Messsignale bei Empfang von rechtszirkular polarisierten elektromagnetischen Wellen,
   • - einem zweiten Antennenausgang für Messsignale bei Empfang von linkszirkular polarisierten elektromagnetischen Wellen,
   • - einer Signaldämpfungseinheit zur Dämpfung der am zweiten Antennenausgang anstehenden Messsignale, wobei der Grad der Dämpfung zwischen einem Maximalwert und einem Minimalwert, der Null betragen kann, veränderbar ist, und
   • - einer Empfangsabschirmanordnung, die die Auswirkungen des Empfangs von rechtszirkular und linkszirkular polarisierten Wellen aus der bezogen auf die Standorthöhe der Test-Empfangsantenne unteren Hemisphäre auf die Messsignale einschränkt oder unterdrückt,
2. b) die Test-Empfangsantenne an einem Standort installiert wird,
3. c) über eine Zeitdauer mit vorbestimmter Länge Messsignale am ersten Antennenausgang erfasst werden,
4. d) die Messsignale am ersten Antennenausgang und am zweiten Antennenausgang der Test-Empfangsantenne überlagert erfasst werden, und zwar bei unterschiedlichen Graden der Dämpfung der Messsignale am zweiten Antennenausgang, wobei der Dämpfungsgrad ausgehend von einem Maximalwert in Richtung zu einem Minimalwert schrittweise verändert und damit die Fähigkeit der Test-Empfangsantenne, die Auswirkungen von empfangenen linkszirkular polarisierten Wellen auf die Messsignale zu unterdrücken, schrittweise verschlechtert wird und wobei für jeden veränderten Dämpfungsgrad die Messsignale an dem ersten Antennenausgang und an dem zweiten Antennenausgang für eine Zeitdauer vorbestimmter Länge überlagert erfasst werden, und
5. e) wobei anhand der Messungen gemäß den Schritt d) durch geeignete Verfahren wie z.B. das Code-Minus-Carrier-Verfahren ermittelt wird, welches Ausmaß an Mehrwegeausbreitung, insbesondere der Intensität und der Empfangsrichtung, von aus der, bezogen auf die Standorthöhe der Test-Empfangsantenne, oberen Hemisphäre zur Test-Empfangsantenne gelangenden rechtszirkular und linkszirkular polarisierten Wellen am Standort existiert.

The invention proposes a method for examining the surroundings of a receiving antenna for satellite signals with regard to the existence of the multipath propagation of the satellite signals until they are received by the receiving antenna, with the method

1. a) a configurable, double polarized test receiving antenna is provided which is provided with
   • - a first antenna output for measuring signals when receiving right-hand circularly polarized electromagnetic waves,
   • - a second antenna output for measurement signals when receiving left-circular polarized electromagnetic waves,
   • a signal attenuation unit for attenuating the measurement signals present at the second antenna output, the degree of attenuation being variable between a maximum value and a minimum value, which can be zero, and
   • - a reception shielding arrangement which restricts or suppresses the effects of the reception of right-hand and left-hand circularly polarized waves from the lower hemisphere in relation to the altitude of the test reception antenna on the measurement signals,
2. b) the test receiving antenna is installed at a location,
3. c) measurement signals are recorded at the first antenna output over a period of time with a predetermined length,
4. d) the measurement signals at the first antenna output and at the second antenna output of the test receiving antenna are recorded superimposed, namely with different degrees of attenuation of the measurement signals at the second antenna output, the degree of attenuation gradually changing starting from a maximum value towards a minimum value and thus the capability the test receiving antenna, to suppress the effects of received left-circular polarized waves on the measurement signals, is gradually deteriorated and for each changed degree of attenuation, the measurement signals at the first antenna output and at the second antenna output are detected superimposed for a period of predetermined length, and
5. e) where, based on the measurements according to step d), suitable methods such as the code-minus-carrier method are used to determine the extent of multipath propagation, in particular the intensity and the direction of reception, from the, based on the Location height of the test receiving antenna, upper hemisphere to the test receiving antenna, right-circular and left-circular polarized waves at the location.

To investigate the environment in which any receiving antenna for satellite signals is to be installed, a double polarized test receiving antenna is used according to the invention, which is adjustable at least with regard to the attenuation of the measurement signals for left-circular polarized electromagnetic waves. To determine the extent of satellite signal multipath propagation in the upper hemisphere of the test receiving antenna, the attenuation of measurement signals that can be traced back to the reception of left-circular polarized waves is initially attenuated to the maximum. The antenna thus receives measurement signals for right-circular polarized electromagnetic waves at its first output. With the help of this procedure, the dominant residual error can then be determined, which is given by the multipath reception of right-hand circularly polarized waves. These received waves are, on the one hand, the satellite signals received directly from the satellite or from the satellites and the reception of signals that are at least twice, four times, six times or the like. have been reflected.

Following the method steps described so far, the degree of attenuation for the measurement signals at the second antenna output is then gradually reduced. For each set degree of attenuation, the maximum possible degree of attenuation is measured as before, for a period of predetermined length, so that ultimately the entire “skyplot” is covered if this is possible at the given location. On the basis of these measurements, that is to say on the basis of the measurement signals at both antenna outputs, different series of measurements are then produced for the different degrees of attenuation of the measurement signals at the second antenna output. The extent of multipath propagation is then determined from these, in particular with regard to the intensity and the direction of reception from which the satellite signals are transmitted, specifically for right-hand and left-hand circular polarized waves reaching the test receiving antenna from the upper hemisphere. This is done, for example, by means of code and phase measurements, as is the case with a code minus carrier method (CMC, sometimes also referred to as code minus phase). A method that can be used by way of example in this context is given in CIRCIU ET AL., Development of the dual-frequency dual-constellation airborne multipath models, DOI: 10.1002 / navi.344
(https://onlinelibray.wiley.com/doi/full/10.1002/navi.344).

During this previously described procedure according to the invention, electromagnetic waves reaching the test receiving antenna from the lower hemisphere are shielded as far as possible either by measures taken on the test receiving antenna or by measures in the immediate vicinity of the test receiving antenna (for example on its holder). In this respect, the test receiving antenna has a receiving shielding arrangement which restricts or even completely suppresses the effects of the reception of right-hand and left-hand circular polarized waves from the lower hemisphere in relation to the height of the test reception antenna on the measurement signals at the antenna outputs. Examples of receiving antennas of this type are so-called choke ring antennas, as already mentioned above.

• f) die Empfangsabschirmanordnung der Test-Empfangsantenne zur Erzielung unterschiedlicher Grade der Einschränkung der Auswirkung des Empfangs von rechtszirkular und linkszirkular polarisierten Wellen aus der unteren Hemisphäre auf die Messsignale veränderbar ist,
• g) der Grad der Einschränkung dieser Auswirkungen durch Veränderung der Empfangsabschirmanordnung, insbesondere in konstruktiver Art, ausgehend von einem Maximalwert bis zu einem Minimalwert, der auch Null betragen kann, schrittweise verändert wird und damit die Fähigkeit der Test-Empfangsantenne, die Auswirkungen von aus der unteren Hemisphäre zur Test-Empfangsantenne gelangenden polarisierten Wellen auf die Messsignale zu unterdrücken, schrittweise verschlechtert wird, wobei für jeden veränderten Grad der Einschränkung dieser Auswirkungen die Messsignale an dem ersten Antennenausgang für eine Zeitdauer vorbestimmter Länge erfasst werden,
• h) wobei anhand der Messungen gemäß Schritt i) ermittelt wird, welches Ausmaß an Mehrwegeausbreitung, insbesondere hinsichtlich der Intensität und der Empfangsrichtung von aus der unteren Hemisphäre zur Test-Empfangsantenne gelangenden elektromagnetische Wellen am Standort existiert,
• i) die Schritte g) und h) wiederholt werden, und zwar bei Überlagerung der Messsignale an dem ersten Antennenausgang und an dem zweiten Antennenausgang und bei unterschiedlichen Graden der Dämpfung der Messsignale an dem zweiten Antennenausgang, wobei für jeden mittels einer Änderung der Empfangsabschirmanordnung veränderten Grad der Einschränkung der Auswirkung des Empfangs von elektromagnetischen Wellen aus der unteren Hemisphäre der Dämpfungsgrad ausgehend von einem Maximalwert in Richtung zu einem Minimalwert hin verändert wird und für jeden veränderten Dämpfungsgrad die Messsignale an dem ersten Antennenausgang und an dem zweiten Antennenausgang für eine Zeitdauer vorbestimmter Länge überlagert erfasst werden,
• j) wobei anhand der Messungen gemäß den Schritten h) und i) durch ein geeignetes Verfahren, wie z.B. das Code-Minus-Carrier Verfahren, ermittelt wird, welches Ausmaß an Mehrwegeausbreitung, insbesondere hinsichtlich Intensität und Empfangsrichtung, von aus der unteren Hemisphäre zur Test-Empfangsantenne gelangenden rechtszirkular und linkszirkular polarisierten Wellen am Standort zusätzlich existiert.

In order to also be able to determine the extent of multipath propagation in the lower hemisphere of the test receiving antenna, it is provided according to an advantageous development of the invention that

• f) the reception shielding arrangement of the test reception antenna can be changed to achieve different degrees of restriction of the effect of the reception of right-hand circular and left-hand circular polarized waves from the lower hemisphere on the measurement signals,
• g) the degree of limitation of these effects by changing the receiving shielding arrangement, in particular in a constructive manner, starting from a maximum value to a minimum value, which can also be zero, is gradually changed and thus the ability of the test receiving antenna to reduce the effects of the lower hemisphere to the test receiving antenna to suppress polarized waves on the measurement signals, is gradually deteriorated, with the measurement signals being recorded at the first antenna output for a period of predetermined length for each changed degree of restriction of these effects,
• h) the measurements according to step i) being used to determine the extent to which multipath propagation exists at the location, in particular with regard to the intensity and reception direction of electromagnetic waves reaching the test receiving antenna from the lower hemisphere,
• i) steps g) and h) are repeated, namely with superimposition of the measurement signals at the first antenna output and at the second antenna output and with different degrees of attenuation of the measurement signals at the second antenna output, with for each by means of a change in the receiving shielding arrangement, the degree of restriction of the effect of the reception of electromagnetic waves from the lower hemisphere, the degree of attenuation is changed starting from a maximum value in the direction of a minimum value and the measurement signals at the first antenna output and at the second antenna output for each changed degree of attenuation are recorded superimposed for a period of predetermined length,
• j) using the measurements according to steps h) and i) using a suitable method, such as the code-minus carrier method, to determine the extent of multipath propagation, in particular with regard to intensity and reception direction, from the lower hemisphere to the test -Receiving antenna arriving right circular and left circular polarized waves at the location also exists.

According to the invention, the test receiving antenna now allows its receiving shielding arrangement to be configurable as well. In the example of a choke ring antenna, this can be done, for example, in that the individual ring elements can be assembled and disassembled. The receiving shielding arrangement could also have shielding disks of different sizes, which can be optionally mounted or dismantled. The choke rings are usually cylindrical in shape and are mounted upright on a base plate on which the antenna element is usually centered. The plate or disk could, for example, be expanded step-by-step by means of horizontal ring elements, an expansion ring then being arranged resting on the outer edge of a ring arranged further inside.

The procedure for determining the multipath propagation in the lower hemisphere of the test receiving antenna is now similar to that described above in connection with the detection of the multipath propagation in the upper hemisphere. The degree of shielding with respect to the reception of electromagnetic waves from the lower hemisphere is changed by gradually changing / configuring the reception shielding arrangement. For each such reception shielding arrangement configuration, the degree of attenuation of the measurement signals at the second antenna output is again changed step-by-step. The periods of time over which the test receiving antenna is measured in all these different configuration states is such that the entire “visible sky plot” at the location of the test receiving antenna is covered. This in turn provides the extent of multipath propagation in terms of intensity and direction of reception of electromagnetic waves reaching the test receiving antenna from the lower hemisphere, which is done on the basis of the measurements as described above.

It should be mentioned at this point that the measures according to the above-described development of the invention can also be implemented without examining the multipath propagation in the upper hemisphere of the test receiving antenna beforehand or afterwards. To this extent, the features of the further development of the invention described here form an independent inventive concept.

The procedures described above can now be carried out for different locations of the test receiving antenna within the environment to be examined, which makes it possible to determine the “optimal” location. This optimal location is, for example, the location with the lowest degree of effects from multipath propagation.

In a further expedient embodiment of the invention, it can be provided that the amount of multipath propagation determined in accordance with step e) is subtracted from the amount of multipath propagation determined in accordance with step j), so that the amount of multipath propagation that results in relation to from the lower hemisphere Right circular and left circular polarized waves reaching the test receiving antenna exist.

In a further expedient embodiment of the invention it can be provided that the attenuation of the measurement signals at the second antenna output in a signal processing unit connected to this antenna output and / or a receiver of the test receiving antenna by optional activation of electrical attenuators or the like. Power loss generating electrical components takes place.

According to an advantageous embodiment of the invention, it can be provided that the superimposed acquisition of the measurement signals at the first antenna output and at the second antenna output includes the combination, in particular the addition of the energies of these measurement signals in a so-called power combiner.

According to an advantageous further embodiment of the invention, it can be provided that a 3D map of the surroundings of the test receiving antenna, possibly for several locations, is determined based on the extent of multipath propagation determined in step f) and / or in step k).

In a further advantageous embodiment of the invention it can be provided that the Receiving shielding arrangement of the test receiving antenna optionally on this attachable shielding elements made of electrically conductive material and / or with coatings made of electrically conductive material such as discs, plates, rings, whereby to change the degree of the effects of the reception from the lower hemisphere to the test receiving antenna Arriving right-circular and / or left-circular polarized waves each have a different one of the shielding elements or several of the shielding elements are attached. According to this embodiment of the invention and according to the above-described features of the test receiving antenna used, the invention comprises, as a further independent concept, a configurable, doubly polarized receiving antenna which can be used for test purposes, for example.

Seen in this light, the invention thus relates to a method for the 3D characterization of the multipath propagation environment at a given location at which an antenna is to be installed.

The advantage of the invention is in particular to be able to examine in advance of the location determination for a satellite signal receiving antenna which situation exists with regard to the multipath propagation of satellite signals at the location in order to then be able to decide on the basis of the antenna diagrams of the receiving antennas which receiving antenna is suitable for the location . This is of particular interest for IGS reference stations. According to the invention, the preliminary examinations are carried out with a double polarized test receiving antenna. It should be pointed out that the receiving antenna ultimately installed at the location does not necessarily have to have two antenna outputs, as is the case with a double-polarized receiving antenna, for example. It is crucial that the so-called MPSI parameters of the candidates for receiving antennas are known, among which it is to be selected which of these receiving antennas is to be installed. Based on the information about the MPSI parameters of the antennas, it can now be determined in advance what influence the multipath propagation at the location of the test receiving antenna will have on the reception of electromagnetic waves on the selected receiving antenna. It is thus possible in advance to select that receiving antenna which, in view of the characterization of the environment according to the invention, has the MPSI parameters that satisfy the requirements placed on the receiving antenna.

The result of the method according to the invention is therefore a 3D map of the surroundings of the test receiving antenna over the intensity of the multipath signal propagation as a function of the solid angle (direction of the compass). These examinations are carried out in order to be able to decide in advance which receiving antenna is to be installed at the location of the test receiving antenna. The receiving antennas in question are qualified with regard to their MPSI parameters. These parameters indicate by how much the antenna attenuates signals depending on the direction of incidence. The investigation according to the invention therefore uses the MPSI parameters of an antenna to be installed to know the extent to which it can suppress the reception of multipath signal propagation, specifically as a function of the solid angle (direction of the compass). Thus, with the aid of the method according to the invention, the best possible receiving antenna can be selected under given boundary conditions before this antenna is installed. This is an advantage over the prior art, according to which it is only possible to detect after a receiving antenna has been installed to what extent the receiving antenna can suppress the signals as a function of the angle of incidence.

• 1 eine perspektivische Ansicht auf die konfigurierbare, doppelt polarisierte Test-Empfangsantenne und
• 2 eine Draufsicht auf die Test-Empfangsantenne in Richtung des Pfeils II der 1.

The invention is described below using an exemplary embodiment for a test receiving antenna which is shown in the drawing. In detail, show:

• 1 a perspective view of the configurable, double polarized test receiving antenna and
• 2 a plan view of the test receiving antenna in the direction of arrow II of FIG 1 .

As mentioned above, the method according to the invention is based on the use of a double polarized test receiving antenna, ie a GNSS antenna (which works correctly for the GNSS bands of interest) with two outputs for the RHCP and LHCP fields, which are used for reconfiguration are suitable for other power levels. The configurability includes the polarization purity and the back lobe, i.e. the two main antenna parameters that influence the ability to suppress multipath propagation from the upper hemisphere and from the lower hemisphere, respectively. Advantageously, such an antenna should have excellent stability in terms of phase center and group delay (in order to reduce the errors in the GNSS measurements caused by the GNSS antenna itself to a minimum) and in terms of outstanding polarization purity, such that cross-polar signals be heavily attenuated (ie LHCP signals are heavily attenuated by the RHCP output and vice versa).

As previously explained, the amount of multipath that an antenna can suppress is directly related to its MPSI. The MPSI are for each type of multipath propagation (from below, from above ...), and the corresponding multipath propagation type is selected in each individual case.

An exemplary embodiment of a test receiving antenna which can be used in the method according to the invention is described below.

In 1 is a double polarized receiving antenna 10 shown resting on a concrete base 12th is positioned on the ground 14th stands upright. The receiving antenna 10 has an antenna element 16 on that on a disk 18th made of metal is arranged, the disc 18th far beyond the peripheral edge of the antenna element 16 survives. This annular projection area is located on the disc 18th removable upright rings 20th different diameters, which, as shown in the figures, are arranged essentially concentrically to one another. Both the disc 18th as well as the metallic ring elements 20th act as shielding elements 22nd who put together a reception shielding arrangement 24 form. This reception shielding arrangement 24 ensures that reflections of electromagnetic radiation from below the receiving antenna 10 , that is, from the lower hemisphere 26th to the receiving antenna 10 arrive, be shielded. By removing some or all of the ring members 20th the degree of shielding of such radiation can be influenced. It is also possible that the disc 18th consists of several horizontal ring elements of different diameters, which are positioned one on top of the other with adjacent edges and can accordingly be optionally removed.

In the situation according to the 1 and 2 receives the receiving antenna 10 essentially radiation from the related to the antenna 10 upper hemisphere 28 . These electromagnetic waves are those satellite signals that are either sent directly from the satellite to the receiving antenna 10 or that after multipath propagation from above onto the receiving antenna 10 hit.

The two outputs of the receiving antenna 10 for right-hand circularly polarized waves on the one hand and left-hand circularly polarized waves on the other hand are not shown in detail in the figures. It is also not shown that the receiving antenna 10 or its outputs can be connected to a receiver, with the receiving antenna between 10 and the receiver or in the receiver optionally connectable attenuation elements are arranged with which the degree of attenuation of the signal that can be optionally changed at the (second) antenna output for the left-circular polarized waves. A so-called “power combiner” is also arranged in front of or in the receiver, which can be optionally activated and with which the powers / energies of the measurement signals present at the two antenna outputs are combined or added.

An exemplary embodiment of the method according to the invention uses these previously described preferred features of the test receiving antenna by using them for a multi-stage calibration process. An example of such a process as an embodiment of the method according to the invention is described below:

CALIBRATION OF THE MULTI-PATH SPREAD COMING FROM POSITIVE ELEVATIONS (UPPER HEMISPHERE)

1. 1. The antenna is first provided with a "negative elevation multipath suppression structure" such as a choke ring or the one in the patent DE 10 2017 217 117 B3 described structures are provided to minimize the reception of any signals impinging on the antenna from below.
2. 2. The antenna is then installed at the point to be examined or characterized, and the position of the antenna in latitude, longitude and height is measured precisely (the height is particularly important in this process). Your RHCP output is connected to a GNSS receiver and GNSS measurements are collected over a period of time that is sufficiently long to cover the entire "sky plot" (the so-called "sky plot") as far as possible at the given location. When evaluating the remaining errors in the GNSS measurements, for example by carrying out code minus carrier processing and removing further errors (for example by methods for precise point positioning (PPP) or by using double-frequency ionospheric corrections and the predominant errors are due to the multipath propagation caused by the antenna with RHCP (due to its very high polarization purity, which is why LHCP components are suppressed, i.e. it is ensured that any polarized LHCP multipath propagation is attenuated by the antenna itself) Directions above the antenna horizon impinge (due to their very good suppression of the fields impinging from negative elevations).
3. 3. The output of the antenna's LHCP output is then used of a power coupler ("power combiner") added to the output signal of the RHCP output. This step is carried out with the addition of a variable attenuator at the LHCP output: as a result, the cumulative output signal represents a continuously degraded antenna pattern when the LHCP component is progressively increased. In this way the multipath suppression capability of the antenna (for the upper hemisphere) is artificially degraded (ie the MPSI are degraded). This in turn leads to a different (greater) degree of multipath propagation due to the progressive reduction in the antenna attenuation of LHCP components, which can be seen in the GNSS measurements.
4. 4. Using the measurements obtained in steps 2 and 3, it is possible to estimate the amount of multipath that the antenna will relay to the receiver for different MPSI grades. Such estimates are then a kind of “catalog” of the multipath environment in that specific installation for antennas with such MPSI grades.
5. 5. Steps 1 to 3 can then be repeated for different positions in the available installation area to identify the configuration in which (for the same MPSI level) minimum multipath is recorded.

CALIBRATION OF THE MULTI-PATH SPREAD COMING FROM NEGATIVE ELEVATIONS (LOWER HEMISPHERE)

1. 1. The antenna is now provided with another (or several other, one after the other) structure (base plate or ground plane), which is expressly NOT fully capable of suppressing multipath propagation coming from negative elevations. Such a structure could, for example, be a “reconfigurable” choke ring structure in which the rings can be increasingly removed, as a result of which the suppression of multipath propagation from negative elevations is increasingly less effective. In another embodiment, different metal plates can be used that provide different degrees of back lobe suppression (and thus suppression of negative elevation multipath).
2. 2. Similar to step 2 in section A, the antenna configured in this way is then installed at the location to be characterized or examined and (only via the RHCP output) connected to the GNSS receiver in order to carry out GNNS measurements for each of the antenna configurations via the collect the entire sky.
3. 3. Step 2 is repeated with other baseplates (other configurations) of the "reconfigurable" choke ring structure in order to have a multipath map for different MPSI for negative elevations.
4. 4. Steps 2 and 3 can then be repeated using different combinations of RHCP output and LHCP output again for each antenna and baseplate configuration to obtain different levels of the two in the lower hemisphere.
5. 5. In this series of measurements, the antenna is exposed to such multipath propagations that come from both negative elevations (due to the ad-hoc base plate) and positive elevations. In order to obtain an estimate of the multipath propagation coming only from negative elevations, the measurements carried out in the previous part of the calibration (part A, relating to positive elevations) can be used and subtracted from the measurements of part B to provide a statement about those only from negative elevations Elevations to receive future multipath propagation.

PREDICTION OF REPRODUCTION FAILURE FOR OTHER CANDIDATE ANTENNAS

The multipath "maps" obtained in the previous steps for different MPSI grades can then be used to predict the performance that one (or more) additional antennas (hereinafter referred to as "candidate antennas") would have once they are installed in the same place. For this purpose, the candidate antenna (mounted on the holder that is actually used during installation) only needs to be measured in an anechoic chamber in order to be able to evaluate its MPSI for both positive and negative elevations.

It is then possible to predict the multipath performance of the candidate antenna using the multipath estimates obtained in steps 1 to 3 of part A and / or B, which correspond to the MPSI level which is closest to the one of the candidate antennas .

This point is particularly advantageous as it enables the antenna performance to be predicted, without the need to install them in the (remote) location.

The method described has general validity and enables valuable information to be obtained about the arrival of satellite signals from all directions. Using it, it is also possible to identify areas of the sky that are particularly affected by multipath propagation and to analyze them in more detail or even to exclude them from the PNT processing.

By using non-omnidirectional antennas, but rather directional antennas (which continue to have the same characteristics as described above, but in a limited angular range), on the other hand, it is possible to obtain the aforementioned "multipath maps" for very specific areas, for example for the angular ranges that are most interesting in terms of multipath propagation at that specific location.

In this case, the antenna could be interpreted as a "reconfigurable multipath probe" capable of estimating the amount of multipath that exists at a given position and comes from a given angular direction. Optionally, the conductive antenna could then be angularly moved to perform the analysis for multiple angular sectors. This would lead to an even more precise multipath map of the environment at the expense of a more complex process.

The latter process could be used, for example, to generate a multipath map of the location of the robots used to calibrate the GNSS antennas, where the robot actually has the ability to rotate the antenna in a precise manner and the There is a great need to examine the environment more closely to ensure the accuracy of the robot calibrations.

REFERENCE LIST

10

Receiving antenna

12th

Concrete base

14th

ground

16

Antenna element

18th

disc

20th

Ring elements

22nd

Shielding elements

24

Reception shielding arrangement

LIST OF ABBREVIATIONS

GNSS

global navigation satellite system

IGS

International GNNS Services

RTK

Real time kinematic

GDV

Group delay variation

PCV

Phase center variation

GBAS

ground based augmentation system

MPSI

multipath suppression capability indicators

RHCP

right hand circular polarized

LHCP

left hand circular polarized

PPP

precise point positioning

BIBLIOGRAPHY

• DE 10 2017 217 117 B3
• S. Caizzone, M.-S. Circiu, W. Elmarissi, C. Enneking, M. Felux, K. Yinusa, “Multipath Rejection Capability Analysis of GNSS Antennas”, Proc. of ION GNSS + 2018, Miami (USA), Sept. 2018
• CIRCIU ET AL., Development of the dual-frequency dual-constellation airborne multipath models, DOI: 10.1002 / navi.344 (https://onlinelibrary.wiley.com/doi/full/10.1002/navi.344)

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102017217117 B3 [0004, 0039]

Non-patent literature cited

• S. Caizzone, M.-S. Circiu, W. Elmarissi, C. Enneking, M. Felux, K. Yinusa, “Multipath Rejection Capability Analysis of GNSS Antennas”, Proc. of ION GNSS + 2018, Miami (USA), Sept. 2018 [0008, 0046]
• CIRCIU ET AL., Development of the dual-frequency dual-constellation airborne multipath models, DOI: 10.1002 / navi.344 [0046]

Claims (9)

Method for examining the surroundings of a receiving antenna for satellite signals with regard to the existence of the multipath propagation of the satellite signals up to their reception by the receiving antenna, wherein in the method a) a configurable, double polarized test receiving antenna is provided which is provided with - a first antenna output for measurement signals when receiving right-circular polarized electromagnetic waves, - a second antenna output for measurement signals when receiving left-hand circular polarized electromagnetic waves, a signal attenuation unit for attenuating the measurement signals present at the second antenna output, the degree of attenuation being variable between a maximum value and a minimum value, which can be zero, and - a reception shielding arrangement which restricts or suppresses the effects of the reception of right-hand circular and left-hand circular polarized waves from the lower hemisphere in relation to the altitude of the test reception antenna on the measurement signals, b) the test receiving antenna is installed at a location, c) measurement signals on the first over a period of time with a predetermined length d) the measurement signals at the first antenna output and at the second antenna output of the test receiving antenna are recorded superimposed, namely with different degrees of attenuation of the measurement signals at the second antenna output, the degree of attenuation gradually changing starting from a maximum value towards a minimum value and thus the capability the test receiving antenna, to suppress the effects of received left-circular polarized waves on the measurement signals, is gradually deteriorated and for each changed degree of attenuation, the measurement signals at the first antenna output and at the second antenna output are detected superimposed for a period of predetermined length, and e) with the measurements according to step d) using a suitable method such as the code minus carrier method to determine the extent of multipath propagation, in particular the intensity and the direction of reception, from the, based on the altitude of the test -Receiving antenna, upper hemisphere to the test receiving antenna, right circular and left circular polarized waves exist at the location. Procedure according to Claim 1 , characterized in that steps b) to e) are carried out for different locations of the test receiving antenna within the environment to be examined and that the location with the lowest degree can be determined based on a comparison of the dimensions of the multipath propagation determined for each location. Procedure according to Claim 1 or 2 , characterized in that f) the receiving shielding arrangement of the test receiving antenna can be changed to achieve different degrees of restriction of the effect of the reception of right-circular and left-circular polarized waves from the lower hemisphere on the measurement signals, g) the degree of restriction of these effects by changing the Receiving shielding arrangement, in particular in a constructive manner, starting from a maximum value to a minimum value, which can also be zero, is gradually changed and thus the ability of the test receiving antenna, the effects of polarized waves coming from the lower hemisphere to the test receiving antenna on the To suppress measurement signals is gradually deteriorated, with the measurement signals at the first antenna output being recorded for a period of predetermined length for each changed degree of restriction of these effects, h) with the aid of the measurements according to step g) by a a suitable method such as code minus carrier method is determined what extent of multipath propagation, in particular with regard to the intensity and reception direction of electromagnetic waves reaching the test receiving antenna from the lower hemisphere, exists at the location, i) steps g) and h ) are repeated, namely with superimposition of the measurement signals at the first antenna output and at the second antenna output and with different degrees of attenuation of the measurement signals at the second antenna output, whereby for each degree of restriction of the effect of the reception of electromagnetic signals changed by a change in the receiving shielding arrangement Waves from the lower hemisphere the degree of attenuation is changed starting from a maximum value in the direction of a minimum value and for each changed degree of attenuation overlaid the measurement signals at the first antenna output and at the second antenna output for a period of predetermined length gert are detected, j) using the measurements according to steps h) and i) using a suitable method such as code-minus-carrier method to determine the extent of multipath propagation, in particular with regard to intensity and direction of reception, from the lower hemisphere Right circular and left circular polarized waves reaching the test receiving antenna also exist at the location. Procedure according to Claim 3 , characterized in that steps h) to j) are carried out for different locations of the test receiving antenna within the environment to be examined and that the location with the lowest degree can be determined based on a comparison of the dimensions of the multipath propagation determined for each location. Procedure according to Claim 1 and 3 or after Claim 2 and 4th , characterized in that the amount of multipath determined according to step e) is subtracted from the amount of multipath determined according to step j), so that the amount of multipath results with respect to the right-hand circular reaching the test receiving antenna from the lower hemisphere and left circularly polarized waves exist. Method according to one of the Claims 1 until 5 , characterized in that the attenuation of the measurement signals at the second antenna output in a signal processing unit connected to this antenna output and / or a receiver of the test receiving antenna by optional activation of electrical attenuators or the like. Power loss generating electrical components takes place. Method according to one of the Claims 1 until 6th , characterized in that the superimposed acquisition of the measurement signals at the first antenna output and at the second antenna output comprises the combination, in particular the addition of the energies of these measurement signals in a so-called power combiner. Method according to one of the Claims 1 until 7th , characterized in that a 3D map of the surroundings of the test receiving antenna, possibly for several locations, is determined on the basis of the extent of multipath propagation determined in step e) and / or in step h) and / or in step j) . Method according to one of the Claims 1 until 8th , characterized in that the receiving shielding arrangement of the test receiving antenna optionally has shielding elements made of electrically conductive material and / or with coatings of electrically conductive material such as disks, plates, rings, which can be attached to it, whereby to change the degree of effects of the reception from the Right-hand circular and / or left-hand circularly polarized waves reaching the test receiving antenna in the lower hemisphere each have a different one of the shielding elements or a plurality of shielding elements.

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