WO2011060942A1 - Method for locating a passive rfid transponder - Google Patents

Abstract

The present invention relates to a method for locating a passive RFID transponder (1) in a monitoring field (2) which is spanned by at least three direction-finding antennas (3) and is assigned at least one complementary antenna (4). The direction-finding antennas (3) have an opening angle range (5) within which said antennas emit an electromagnetic field for activating the RFID transponder (1) in a manner that can be detected by the complementary antenna (4) or receive a locating signal (15) which is emitted by the RFID transponder (1) as a result of the RFID transponder (1) being activated by the complementary antenna (4). In this case, the position of the RFID transponder (1) in the monitoring field (2) is determined by means of direction-finding using the direction-finding antennas (3), wherein, in each of the direction-finding antennas (3), the opening angle range (5) is pivoted with a first detection angle (6) in a first, preferably horizontal plane over the monitoring field (2) and an angle range which is restricted by a critical angle and within which the direction-finding antenna (3) activates the RFID transponder (1) or receives a locating signal (15) from the RFID transponder (1) is determined. The intersection area (10) of the particular angle ranges of the direction-finding antennas (3) is then determined and the centre of gravity thereof is calculated as an estimated value of the position of the RFID transponder (1).

Description

 Method for locating a passive RFID transponder

The present invention relates to a method for locating a passive RFID transponder in a monitored field spanned by at least three DF antennas, to which at least one complementary antenna is assigned, the DF antennas having an opening angle range within which the DF antennas form an electromagnetic field for the activation of the antenna detectable by the complementary antenna Transmit RFID transponders, or received as a result of activation of the RFID transponder by the Komplementärantenne emitted by the RFID transponder localization signal, and wherein the position of the RFID transponder in the surveillance area is determined by bearing using the DF antennas.

RFID (Radio Frequency Identification) technology is a radio-based, contactless identification method that uses automatic radio frequency identification

Identify and locate items that are tagged with an RFID transponder, making it much easier to capture and store data. An RFID system generally consists of a transponder which is located on or in the article and identifies it by a digital identifier contained in the transponder, as well as a reader for reading out the transponder identifier. In this case, passive RFID transponders are used to identify objects usually without their own

Energy supply and get their energy from the electromagnetic field of the reader. For this purpose, the RFID transponder on a planar antenna, in which the radio field of the reader induces a voltage. Is the field strength of the electromagnetic field sufficiently high and the position of the planar antenna relative to the irradiated electromagnetic waves such that the induced voltage is sufficient to supply the RFID chip contained in the transponder, that is, the so-called activation threshold is reached, the RFID transponder sends out a signal with its identifier. Due to this behavior, a localization of the RFI D transponder is possible by bearing.

Bearing methods for determining the positional position of a passive RFID transponder in three-dimensional space are well known. They serve in particular the location of objects that are provided with passive RFI D transponders. According to the current state of the art, the position determination of an object usually takes place in such a way that using the fixed, omnidirectional antennas located on an RFID reader as well as from the read signals with the aid of methods for angular, transit time or signal strength measurement (RSSI) ), statistical methods and reference measurements, the position of an RFID transponder, also called RFID tag, is determined.

For example, a method for determining the position of a passive

Transponders in a radio system from the German Offenlegungschrift

DE 10 2006 049 862 A1. It describes an RFI D system for

Position determination of a passive transponder, in which at least one

Transceiver is provided which with a plurality of

is coupled to different localization antennas, wherein between the

Localization antennas, i. in the receiving area, one or a plurality of RFI D transponders to be located is arranged. The transceiver activates and identifies the RFI D transponders and causes only the RFID transponder to be located to begin transmitting a localization signal. To determine its position by the RFID system he creates

Localization signal or reflects a radiated from the transmitting / receiving device carrier signal with a modulation of the carrier signal with the

Localization signal, for example by load modulation. The fixed ones

Localization antennas whose position is known in space received

Time-shifted replica of the radio signal of the transponder and lead them to a Lokalisationsempfänger for evaluation. The evaluation is based on runtime differences, intensities and possibly directions of the replica of the Localization signal. On the basis of this information, the location of the transponder to be located or of the object to which the transponder to be located is attached can be determined. The primary variable in the evaluation is the transit time difference, which consists of the received signals of the

Localization antennas can be obtained. In contrast, the received signal intensity and direction are only included for a plausibility check.

For the determination of signal propagation time differences for the individual

Lokalisationsantennen the relative phase angles of the received signals of the localization antennas are determined. As a result, the method is particularly complex and expensive.

It is therefore an object of the present invention to provide an alternative method for locating passive RFID transponders that can be realized in a technically simple way and highest accuracy in the

Location of the RFID transponder offers. This object is solved by the features of claim 1, advantageous developments of the invention are formulated in the dependent claims and are explained below.

According to the invention, a method for locating a passive RFID transponder in one of at least three DF antennas spanned

Monitoring field proposed, which is associated with at least one Komplementärantenne, the DF antennas have an opening angle range within which the DF antennas an electromagnetic field from the

Komplementärantenne detectable activation of the RFID transponder or a result of an activation of the RFID transponder by the

Complementary antenna emitted by the RFID transponder

Receiving localization signal, and wherein the position of the RFID transponder in the monitoring field is determined by bearing using the DF antennas, further wherein in each of the DF antennas, the opening angle range with a first detection angle in a first, preferably a horizontal plane pivoted over the monitoring field and a by critical angle limited

Angle range is determined within which the pivoting DF antenna activates the RFID transponder or a localization signal of the RFID transponder then determines the intersection of the specific angular ranges of DF antennas and its center of gravity is calculated as an estimate of the position of the RFI D transponder.

The basic idea of the present invention is to carry out the localization of an RFID transponder by determining the direction or the angle within which the emission of an electromagnetic field of sufficient field strength of a DF antenna can activate the RFI D transponder or out of the in / A DF antenna receives a localization signal from the RFID transponder, which may be referred to as the "Direction of Arrival" (DoA) or "Angle of Arrival" (AoA). According to the invention, this direction or

Angle determination, also referred to as "aiming", with the aid of at least three directional position-dependent DF antennas, that is, from at least three different directions, taking into account the inaccuracy of the bearing by the detection angles of the DF antennas.

The at least three DF antennas have a directional characteristic for this purpose,

In particular, a lobe characteristic, so that the DF antennas a conical or viewed in a plane, a fan-shaped

Have opening angle range with a detection angle within which a radio signal can be sent or received. The detection angle is much smaller than the respective pivot angle range of a DF antenna. For example, the pivoting angle range between 90 ° and 360 °, wherein a pivoting angle of 90 °, for example, in a DF antenna with Inneneckenmontage, a pivoting angle of 180 ° in an open wall mounting or a pivoting angle of 360 ° in the case of mounting in open space offers. In contrast, depending on the characteristic of the lobe, the detection angle of the antennas typically used for this application can be between 10 ° and 45 ° and is due to the width of the lobe, which essentially defines the detection angle. A pivoting of the opening angle range can be done mechanically by pivoting the DF antenna or electronically by changing the directional characteristic of the antenna, as will be explained below. In a DF antenna can be a transmitting antenna that emits an electromagnetic field within the opening angle range, by means of which the RFID transponder can be activated, the RFID transponder emits a localization signal in its activated state, of the in this case as Reception antenna trained complementary antenna can be received. According to this embodiment of the invention, the bearing of the RFI D transponder is such that the opening angle range when transmitting the electromagnetic field on the monitoring field in a first plane pivots and first that pivot angle is determined from which the RFID transponder responds, ie the Komplementärantenne Localization signal is received. This occurs when the RFID transponder lies almost completely within the angular range of the DF antenna. Subsequently, further pivoting in the same direction and the pivoting angle is determined, from which the complementary antenna no longer receives the localization signal. This is the case when the RFID transponder has almost completely left the angular range of the DF antenna. The two determined by a DF antenna

Pivoting angles define two of the main beam direction of the DF antenna

corresponding straight lines in the plane or planes in space, the one

Limit the angle range within which the RFID transponder is located.

If the angle range in the first plane, within which the DF antenna or the other DF antennas each detect a localization signal as a consequence of the activation of the RFID transponder by the respective DF antenna, is also determined in the other, the surveillance area spanning antennas, the intersection of the particular Angular ranges A polygon whose boundaries are determined by the straight lines describing the principal ray directions present at the particular tilt angles.

Alternatively, a DF antenna may be a receive antenna that is within the aperture angle range of the RFID transponder

sent out localization signal. The complementary antenna in this embodiment is a transmitting antenna which emits an electromagnetic field for activating the RFID transponder. According to this embodiment of the invention, the bearing of the RFID transponder is such that the respective Opening angle range of the DF antennas in a first plane pivoted on the monitoring field and first the pivot angle is determined, from which the DF antenna receives the localization signal of the RFI D transponder. This takes place when the RFI D transponder lies substantially within the opening angle range of the DF antenna. Subsequently, that pivot angle is determined, from which the DF antenna no longer receives the localization signal. This is the case when the RFI D transponder the

Opening angle range of the DF antenna has essentially left.

The two tilt angles determined by a DF antenna correspond to two directions of the main receiving direction of the DF antenna, i. that

Receiving direction in which the DF antenna has the highest sensitivity. The swivel angles define straight lines in the plane or planes in space that define an angular range within which the RFI D transponder is located. If the angle range is also determined one after the other in the other DF antennas spanning the monitoring field, within each of them

Detecting the localization signal as a result of activation of the RFI D transponder by the complementary antenna is the intersection of the particular

Angular ranges a polygon whose boundaries are determined by the straight lines describing the said main receiving directions present at the determined tilt angles.

In the case of a transmitting antenna as a DF antenna can be used to determine the

Swing angles are checked as limit angle at each swivel angle of the angle range of the DF antenna, if a localization signal is sent from the RFID transponder, i. from the complementary antenna a localization signal

Will be received. If this is the case, this swivel angle value can be stored as the first swivel angle. Furthermore, in the case of a receiving antenna as a DF antenna, it can be checked at each swivel angle whether the pivoting DF antenna receives a localization signal from the RFID transponder. If this is the case, this swivel angle value can be stored as a second swivel angle. In both of the above-described embodiments, the determined pivoting angles are those angles which serve as the critical angle of the

Angular range can be used. On the basis of limit angle can the intersection of the angular ranges of all DF antennas determined and its center of gravity are calculated.

In a preferred embodiment of the method according to the invention can be provided that the opening angle range of a DF antenna in the first pivot plane is first pivoted in one direction and the first and second pivot angle are determined, from or to which the DF antenna a localization signal of the RFID transponder receives or the DF antenna activates this, and then pivoted back in the opposite direction and the determination of the second and the first pivot angle is repeated, wherein each of the two first pivot angles and the two second

Swing angles Mean values are formed and these are used as critical angle of the angular range for the Schnittbereichsbestimmung. This has the advantage that the error occurring as a result of the width of the RFID transponder in the pivoting plane is compensated. Because the RFI D transponder is only then recognized by a DF antenna or activated by this, if he is essentially completely in the

Aperture range rests, and no longer recognized or not activated, when he has stepped out substantially completely from the opening angle range. This results in a shift of the direction of the bearing in the direction of

Pivoting movement, which can be compensated by the re-determination of the swivel angle and subsequent averaging of the specific swivel angle values.

As already mentioned, at least one complementary antenna is provided according to the invention. This is in terms of their functionality complementary to the

DF antennas. This means that the at least one

Complementary antenna is designed as a transmitting antenna and a

emits electromagnetic field for activating the RFID transponder, when the DF antennas are designed as receiving antennas, which receive the emitted as a result of the activation of the RFID transponder localization signal, while its opening angle range is pivoted on the monitoring field. Furthermore, that the at least one complementary antenna is designed as a receiving antenna and receives a localization signal of the RFID transponder when the DF antennas are used as transmitting antennas pivotable opening angle range are formed, which activate the RFI D transponder to transmit the localization signal. Preferably, the

Directional characteristic of Komplementärantenne omnidirectional, so that the entire monitoring field is reliably covered.

In a further advantageous development of the method according to the invention, the signal strength of the localization signal received by the latter can be determined for the pivot angles of a pivoting DF antenna and the maximum received signal strength can be determined. This has the advantage that based on the signal strength of the localization signal additional information about the position of the RFID transponder can be obtained, as will be explained below.

The signal strength can be evaluated by the so-called RSSI value (Received Signal Strength Indication). Received Signal Strength Indication (RSSI) is an indicator of the reception strength of wireless communication applications.

For example, the determination of the signal strength of the localization signal can be used to that of the pivoting angle of one of the DF antennas

determine where the signal strength of the localization signal is maximum. This swivel angle can be used to determine the angular range to be determined, wherein a first angle value is added to this swivel angle to form the first critical angle of the angular range and a second angle value is subtracted to form the second critical angle of the angular range. The two angle values bear the width of the lobe of the lobe characteristic of

DF antenna, and thus the blur of the bearing calculation and are known at a certain set directivity. The sum of the two

Angle values describe that receiving range of the DF antenna in which it has a substantially identical reception sensitivity, so that it is not possible to determine exactly in this area the direction from which a signal was received. For example, the angle values can be between 5 ° and 10 °.

Preferably, the angle values for the calculation of the angular range are selected to be identical. Furthermore, it is advantageous to perform a plausibility check after the calculation of the angular range and / or center of gravity. If the measured

Pivoting angle of a DF antenna or the calculated center of gravity is not plausible, in one, several or even all DF antennas that pivot angle of the angular range determination can be used as the second highest signal strength of the localization signal was measured. This can be on n

DF results per DF antenna and testing of plausible results can be extended.

In a further advantageous embodiment of the method according to the invention can be provided that the detection angle of a DF antenna after the

Swiveling of the opening angle range decreases and the determination of the

Angular range within which the DF antenna activates the RFID transponder or receives a Lokaiisationssignal the RFI D transponder is repeated. As a result, the accuracy of the position determination of the RFID transponder can be improved.

Preferably, the reduction of the detection angle of the respective

DF antenna and the re-determination of the angular range are repeated until this DF antenna no longer activates the RFID transponder or no longer receives the Lokaiisationssignal emitted by this. With the last determined angle range the determination of the cutting area and

Calculation of the center of gravity, a maximum accuracy of localization can be achieved.

The reduction of the detection angle can be achieved by reducing the transmission power of the DF antenna or by changing the directivity of the DF antenna to a narrower beam characteristic. Here, the sharp sensitivity of an RFID transponder is exploited. The threshold for the response is very sensitive in an RFID transponder. By controlling the transmission power of the DF antennas and pivoting the lobe, the angle can be detected as the direction at which the RFID transponder responds with minimal transmission line. In this case, a DF antenna initially with the maximum

Transmit power, reducing the transmission power for each subsequent swing until the RFID transponder stops responding. This means that the transmission power of the DF antenna is below the wake-up threshold necessary for the RFID transponder.

In the described embodiments of the method, the

Opening angle ranges pivoted over the entire pivoting range.

Subsequently, the detection angle can be reduced in all DF antennas and the angle ranges are redetermined.

Alternatively, however, it is also possible that a DF antenna is first pivoted so far until the DF antenna activates the RFID transponder or receives a localization signal of the RFID transponder, then the

Detection angle decreases and the pivoting movement is continued in the same direction, in which case the first and second pivot angle are determined. This can be repeated iteratively until no more activation is effected or no localization signal is received any more. Subsequently, this iterative method can be repeated in the other DF antennas, until finally the minimum detection angle for locating the RFID transponder is set in all DF antennas.

In one embodiment of the method, the opening angle ranges of the DF antennas can be pivoted one after the other in time. This is necessary in the case of transmitting DF antennas so that the complementary antenna can correctly determine when the RFID transponder enters or leaves the angular range of a particular DF antenna in order to determine the critical angles. In the case where the DF antennas are designed as receiving antennas, the pivoting of the DF antennas and the determination of the angular ranges can take place simultaneously, since the DF antennas will then not interfere with each other. This has the advantage that the

Localization of the RFID transponder can be performed faster.

So that the RFID transponder during the pivoting movement within the first

Tilting plane is detected, the detection range of DF antennas in the plane perpendicular to the first pivot plane should cover the entire space within which the RFID transponder can be located. So the recording or transmission range in a directional antenna mounted in a corner of the room relative to the plane perpendicular to the pivot plane, for example, 90 °, as is the case with a cardioid antenna. Preferred are as

However, DF antennas used directional antennas, which have a narrow conical opening area in all room dimensions, i. E. both in the first room level and with respect to a plane of space perpendicular thereto

Have opening angle range of up to 30 °.

For this reason, it may happen that, during a pivoting movement of one of the DF antennas within the first plane, no activation of the RFI D transponder by the electromagnetic field emitted by the DF antenna in the aperture angle range or no localization signal is received from the DF antenna. In this case, it may be provided according to the invention that the pivoting position of this DF antenna by an angle in one of the first

Tilting plane vertical plane is tilted and the pivoting movement of the DF antenna is repeated in this tilt angle to the first pivot plane. The tilt angle can be, for example, in the range between half and the full detection angle, so that the newly scanned space area itself

at least partially overlapped with the originally scanned space area. This ensures that the RFID transponder does not sink in the peripheral detection or transmission range. The movement of the main jet direction or

The main receiving direction of the DF antenna is in this case along the mantle of a cone whose tip is in the DF antenna. In this pivotal movement of the opening angle of the DF antenna on the monitoring field limited by critical angle range of the pivoting DF antenna can be determined within which the DF antenna activates the RFID transponder or receives the localization signal emitted by this. This one by the two

Limit angle limited angular range can in the inventive

Determining the intersection of the angular ranges of DF antennas in the first pivot plane can be used. This corresponds to a projection of the angle range tilted to the first pivot plane onto the first pivot plane. From the intersection of the angular ranges of the DF antennas can then be calculated its center of gravity and thus the position of the RFID transponder position in two directions can be determined. For determining the positional position of the RFID transponder in the third

In the spatial direction, the opening angle range of at least one of the DF antennas in the direction of the determined center of gravity can perform a further pivoting movement in a second plane that is perpendicular to the first pivot plane, wherein the angle range is determined during the further pivoting movement within which the DF antenna activates the RFID transponder or the receives from this emitted localization signal.

The determination of this angular range lying in the second plane can be carried out as in the angular range lying in the first plane. For example, the swivel angle can be used, wherein during the pivoting movement in the second plane, a first pivot angle is determined, from which the RFID transponder is activated by the electromagnetic field of the pivoting DF antenna or a localization signal of the RFID transponder is received by the DF antenna, and then a second swing angle is determined up to which the RFID transponder is activated or the localization signal is received.

To obtain a more precise angular range determination, can also for the

Angle range in the second plane, the determination of the angular range during a pivoting movement in the opposite direction are repeated.

The DF antenna in the second level is first in a first

Pivoting pivoted and determines the first and second pivot angle and then in the opposite direction of pivoting

pivoted back and the first and second pivot angle determined again, in each case from the two first pivot angles and from the two second

Swing angles average values are formed. From the particular averaged first and the particular averaged second pivot angle can

then a mean angle relative to the first plane location is determined, i. an angle that is centered in the angle range. Since the position of the RFID transponder in two spatial directions by calculating the

Focusing the angular ranges in the first pivot plane is already determined, the position of the RFID transponder in the third spatial direction through the

Angular relationships can be determined in a right-angled triangle whose Corner points is formed by the known position of the DF antenna, the determined center of gravity and the position of the RFI D transponder.

Alternatively, the average angle of the angular range can be determined in such a way that, during the pivoting movement in the second plane relative to the pivoting angles of the DF antenna, the signal strength of the localization signal received therefrom is determined and the pivoting angle at which the signal strength is maximum is determined. This pivoting angle can be used as a mean angle of the angular range in order to carry out the previously explained calculation of the positional position of the RFID transponder in the third spatial direction.

In an advantageous development of the method, in order to improve the determination of the positional position of the RFI D transponder in the third spatial direction, all DF antennas, in particular one after the other, can be used in the direction of the determined

Center a further pivotal movement in a second plane, which is perpendicular to the first pivot plane, wherein in the other

Pivoting movement determines each of the DF antennas that angular range within which the respective DF antenna activates the RFI D transponder or receives the localization signal emitted by this. In each case, at each of the specific angle ranges, a mean angle relative to the first

Be determined pivoting plane according to the procedure described above, with an average then being formed from all mean angles. On the basis of this average mean angle, the position of the RFID transponder in the third spatial direction can be determined by the angular relationships in a right-angled triangle whose vertices are formed by the known position of one of the DF antennas, the determined center of gravity and the position of the RFI D transponder is. It is sufficient to use one of the DF antennas and their distance to the calculated center of gravity.

Furthermore, it is advantageous if the maximum signal strengths of the

DF antenna received localization signal are compared with each other and the angular range of those DF antenna receiving the localization signal with the highest signal strength, for the calculation of the center of gravity of the

Cutting area is reduced. This corresponds to a stronger mathematical Weighting of the center of gravity of the polygon. By the reduction of the

Angle range, the polygon is narrower and its center of gravity moves closer to that DF antenna, which has received the localization signal with the highest signal strength. The higher the signal strength, the lower the measurement inaccuracy of a DF antenna, so that a DF antenna with a particularly high signal strength of the localization signal provides more reliable bearing information than the other DF antennas. Preferably, the degree of reduction of the angular range may be made dependent on the received signal strength. So can the

The higher the signal strength of a DF antenna compared to the other DF antennas, the smaller the angular range.

Alternatively, according to the invention in the same way the angular range of a

DF antenna, which receives a localization signal with low signal strength compared to the other DF antennas, are increased. This corresponds to a weaker mathematical weighting of the center of gravity of the polygon in the direction of this DF antenna. Enlarging the angular range widens the polygon and brings its center of gravity closer to the other DF antennas where the localization signal has a higher signal strength.

By means of this aforementioned procedure, the accuracy of the localization of the RFI D transponder can be significantly improved.

According to the invention, the opening angle ranges of the DF antennas can be pivoted by electrical adjustment of the directional characteristic of the respective DF antenna. This will be explained in more detail below. Alternatively, a mechanical pivoting of the DF antenna can be done.

The calculation of the intersection of the angular ranges can by means of

mathematical methods of linear programming done. This is a well-known mathematical optimization method in which a

Inequality system is set up and this is solved. By applying this methodology, the intersection region can be determined mathematically from the straight lines defined by the critical angles and the known DF antenna positions, which delimit the intersection region in subsections. Furthermore, it can be provided that the monitoring field is divided into a network structure, and the probability is determined that the RFID transponder is located in a specific field of the network. This can be done under

Use of estimation results of bearing measurements and RSSI values.

Furthermore, more than three DF antennas can be used. For example, the monitoring field can be spanned by four, five or more DF antennas. Additionally or alternatively, subgroups of in each case three DF antennas can be used, which are selected as a function of the RSSI values measured by them (selective combination). The estimated value for the

Position of the RFI D transponder by a, in particular weighted averaging of the results of the subgroups are formed. An iterative and / or adaptive estimation can be done by combining subgroup results and repeated measurements.

Furthermore, an RFID system for carrying out the above

Proposed method, with at least three a monitoring field in which there is a passive RFI D transponder to be located spanning

DF antennas for emitting an electromagnetic field within an opening angle range for activating the RFID transponder or for receiving an emitted by the RFID transponder as a result of its activation

Localization signal in an opening angle range, and with at least one Komplementärantenne for activating the RFID transponder, while a

Localization signal from at least one of the DF antennas is receivable, and for receiving a localization signal, while the RFID transponder of

at least one of the DF antennas is activated, wherein the opening angle range of the DF antennas is pivotable and the DF antennas and at least one

Complementary antennas are networked to each other via a control and evaluation unit, wherein the control and evaluation unit is adapted to determine the respective limited angle angle range of a DF antenna within which this DF antenna activates the RFID transponder or receives the localization signal emitted by this, the Cutting area of the To determine the angular ranges of the DF antennas and its center of gravity as

Estimate the position of the RFID transponder.

The DF antennas and the at least one complementary antenna are over

Connecting lines connected to a control and evaluation, such as a computer, the pivoting movement of the DF antennas, as well as the emission of the electromagnetic field by the DF antennas or the

Complementary antenna controls, and receives and processes the antenna signals of the DF antennas and the at least one Komplementärantenne, in particular evaluates.

Preferably, at the location of each DF antenna, a complementary antenna may be provided

be arranged or arranged so that no additional

Complementary antenna is needed. Rather, a bearing and a

Komplementärantenne be summarized as an RFID base station with a transmitting / receiving unit. At least three of these RFID base stations can be provided, which span the surveillance field and which are identical

are executed. The RFID base stations are via the control and

Networked evaluation unit. The control and evaluation unit controls the pivoting movement of the detection angle of the RFID base stations and evaluates the antenna signals of the receiving antennas.

The DF antennas may be formed by one- or two-dimensional antenna arrays, which are controlled in multiple channels and together form a desired directional characteristic of the overall antenna arrangement. The individual antennas of the antenna array can for electronic influencing the directional characteristic, in particular for adjusting the main beam direction or main receiving direction, with signals of different phase angles and

Amplitudes are fed, as is known in radar systems without mechanically moving antennas or so-called phased array antennas.

Further features and advantages of the invention will be explained with reference to the following description of embodiments and the accompanying figures. Showing: Figure 1 RFID system for carrying out the method

Figure 2 RFID system with transmitting antennas as DF antennas

Figure 3 RFID system with receiving antennas as DF antennas

FIG. 1 shows an RFID system with three DF antennas 3 positioned at different, known locations, which span a monitoring field. The

Monitoring field is shown in plan view and extends in a horizontal plane. In the monitoring field, a passive RFID transponder 1 to be located is arranged, which can adhere to an object, for example. The DF antennas 3 are directional antennas with a lobe characteristic and have a main radiation direction 9 or main receiving direction 9 and a

Opening angle range 5 with a detection angle 6, within which they can emit or receive an electromagnetic field. Of the

Opening angle range 5 is always smaller than the mechanical or electronic pivoting range of the DF antennas. The maximum pivoting angle range 8 of the DF antennas 3 is 90 ° for the corner antennas DF antennas 3 and 180 ° for the DF mounted on the open wall. The opening angle ranges 5 of the DF antennas 3 can be pivoted within the maximum pivot angle ranges 8 by a Sehwenkwinkel 7.

The RFID system further comprises an omnidirectional complementary antenna 4, which is assigned to the monitoring field 2. Are the DF antennas 3 as

Transmitting antenna designed to activate the RFID transponder 1, is the

Complementary antenna 4 is a receiving antenna for receiving the localization signal 15 emitted by the RFID transponder 1 as a result of the activation. Conversely, if the complementary antenna 4 is implemented as a transmitting antenna for activating the RFID transponder 1, the search antennas are receiving antennas for receiving as a result of the activation of the RFID transponder 1 RFID transponder 1 emitted

Localization signal 15. The DF antennas 3 and the complementary antenna 4 are connected via connecting lines 13, in particular signal and control lines, to a control and evaluation unit 14. The control and evaluation unit 14 controls the pivoting of the opening angle range (5) of the DF antennas (3) and detects at which pivot angle 7 a DF antenna 3 the RFID transponder 1, ie the complementary antenna 4 receives a localization signal 15, or at which swivel angle 7 a direction finding antenna 15 receives a localization signal 15 of the RFI D transponder 1.

In FIG. 1, the boundary regions 12 of the angular regions are each through

Limit angle ßi _, ß _{2 are} defined, indicated by dashed lines. Within the angular ranges a DF antenna 3 activates the RFID transponder 1 or receives a localization signal 15 thereof. The detection angle 6 amount to about 20 °. In this illustration, the angular ranges essentially correspond to the opening angle ranges 5. The intersection area 10 of the angular ranges of

DF antennas 3 is defined by a polygon 11, which can be determined by mathematical methods of linear programming. The center of gravity of the polygon 1 is an estimate of the position of the RFI D transponder 1 im

Monitoring field 2, i. in two-dimensional space.

Figure 2 shows one of the DF antennas 3, which is designed as a transmitting antenna, to illustrate the method, which exploits the threshold of the RFI D transponder 1 according to the invention. In this case, the opening angle range 5, starting from a pivoting angle 7 of 0 °, is first pivoted in the direction of the arrow A in the horizontal plane over the monitoring field 2, wherein the

Transmitting antenna emits an electromagnetic field for activating the RFI D transponder 1. From a swivel angle αι the RFID transponder 1 is almost completely within the opening angle range 5, ie here the transmission range, so that it is activated and the Komplementärantenne 4 receives a localization signal. This first pivot angle α-ι can be used as the first limit angle ßi of the angular range to be determined. If the opening angle range 5 is further pivoted in the direction of the arrow A, the swivel angle 7 reaches a second swivel angle value a ₂ from which the RFID transponder essentially no longer rests in the opening angle range 5. The complement antenna in this case no longer receives a localization signal. This second pivoting angle can be used as the second critical angle for the calculation of the sectional area 0 with the other DF antennas 3. To improve the bearing, the method can be repeated, in the opposite direction, see arrow B, pivoted and first the second and then the first pivot angle are determined again. An average value is then formed from the respective two pivoting angles and these average values are used as the first and second critical angle.

FIG. 3 shows an alternative method in which the signal strength of the localization signal 15 is taken into account for the localization of the RFID transponder 1. The DF antennas 3 are designed as receiving antennas. In this case, the opening angle range 5 is pivoted starting from a pivoting angle 7 of 0 ° in the horizontal plane over the monitoring field 2, wherein for each tilt angle 7 of the direction finder 3 determines the signal strength of the localization signal 15 received from this and that pivot angle 7 of the direction finder 3 is determined in which the signal strength of the localization signal 15 is maximum. Starting from this swivel angle 7, a first angle value γι of 5 ° is subtracted to form the first critical angle ßi of the angular range and added to form the second critical angle ß _{2 of} the angular range, a second angle value γ ₂ of 5 °. The angle values γ-ι, γι depend on the width of the lobe of the directional characteristic of the direction finder antenna 3. These two limit angles β-1, βi can be used for the calculation of the intersection area 10 with the other direction finding antennas 3.

LIST OF REFERENCE NUMBERS

 1 RFID transponder

 2 monitoring field

 3 DF antenna

 4 complementary antenna

 5 opening angle range

 6 detection angle

 7 swivel angle

 8 swivel range

 9 main beam direction, main receiving direction

 10 cutting area

11 polygon 12 border area

13 connecting lines

14 control and evaluation unit

15 Localization signal α1, α2 Pivot angle ß1, ß2 Limit angle γ1, γ2 Angle values

Claims

claims 1 . Method for locating a passive RFID transponder (1) in a monitoring field (2) spanned by at least three DF antennas (3), to which at least one complementary antenna (4) is assigned, the DF antennas (3) having an opening angle range (5) within the DF antennas (3) an electromagnetic field from the  Complementary antenna (4) detectable activation of the RFID transponder (1) or receive a result of an activation of the RFID transponder (1) by the complementary antenna (4) from the RFID transponder (1) emitted localization signal (15) received, and wherein the position of the RFID transponder (1) in the monitoring field (2) is determined by bearing using the DF antennas (3), characterized in that in each of the DF antennas (3) the opening angle range (5) with a first detection angle (6) in a first, preferably a horizontal plane is swiveled over the monitoring field (2) and an angle range limited by limiting angle is determined, within which the DF antenna (3) activates the RFID transponder (1) or a localization signal (15) of the RFID transponder (1 ), wherein subsequently determines the intersection region (10) of the specific angular ranges of DF antennas (3) and whose center of gravity as an estimate for the position d it is calculated RFID transponders (1). 2. The method according to claim 1, characterized in that the  Angular range of a DF antenna (3) by pivoting angle (α-ι, a-ι) as Limit angle (ßi, ß is limited, wherein during the pivoting movement, a first pivot angle (α-ι) is determined from which the RFID transponder (1) by the electromagnetic field of the DF antenna (3) activated or a localization signal (15) of the RFID Transponders (1) from the DF antenna (3) is received, and then a second pivot angle (a ₂ ) is determined, to which the RFI D transponder (1) is activated or  Localization signal (15) is received. 3. The method according to claim 2, characterized in that the DF antennas (3) pivoted in a first pivoting direction (A) while the first and second pivot angle (α-ι, α ₂ ) are determined and then pivoted back in the opposite direction of pivoting (B) and the first and second pivot angle (αι, ₂ ) are determined again, in each case from the two first pivoting angles (α-ι) and from the two second pivoting angles (a ₂ ) averages formed and these are used as limit angle (β-ι, ßi) for the Schnittbereichsbestimmung. 4. The method according to any one of the preceding claims, characterized in that the signal strength of the received localization signal (15) is determined to the pivoting angles (7) of the DF antenna (3). 5. The method according to claim 4, characterized in that the one  Pivoting angle (7) of one of the DF antennas (3) is determined in which the signal strength of the localization signal (15) is a maximum, wherein at this pivot angle (7) for forming the first critical angle (ßi) of the Angle range a first angle value (γ-ι) deducted and to form the second critical angle (ß ₂ ) of the angular range, a second angle value (γ ₂ ) is added. 6. The method according to claim 5, characterized in that the Angle values (γι _, γ ₂ ) between 5 ° and 10 °. 7. The method according to claim 5 or 6, characterized in that a  Plausibility check of the angle range or the calculated Center of gravity is carried out and at least one DF antenna (3) that pivoting angle (7) is based on the angular range determination, in which the second highest signal strength of the localization signal (15) was measured. 8. The method according to any one of the preceding claims, characterized in that the detection angle (6) of the DF antennas (3) decreases according to their respective pivoting and the determination of the respective angular range (5) is subsequently repeated. 9. The method according to claim 8, characterized in that the  Reduction of the detection angle (6) of the respective DF antenna (3) and the redetermination of the angular range is repeated until this DF antenna (3) no longer activates the RFID transponder (1) or the localization signal (15) emitted by it no longer receives. 10. The method according to any one of claims 8 or 9, characterized in that the detection angle (6) is reduced in that the  Reduced transmission power of the DF antenna (3) or the directivity of the DF antenna (3) is changed to a narrower lobe characteristic. 11. The method according to any one of the preceding claims, characterized in that the opening angle range (5) of a DF antenna (3) is first pivoted so far until the DF antenna (3) activates the RFID transponder (1) or a localization signal (15) of the RFID Transmitters (1) receives, then the detection angle (6) is reduced and the pivoting movement is continued in the same direction, in which case the first and second pivot angle (α-ι _, 012) are determined. 12. The method according to any one of the preceding claims, characterized in that the opening angle range (5) is pivoted at least one of the DF antennas (3) in the direction of the determined center of gravity in a second plane which is perpendicular to the first pivot plane, wherein in the further pivoting movement either an angle range is determined within which the DF antenna (3) activates the RFID transponder (1) or receives the localization signal (15) emitted by it, and the average angle of this angular range is determined, or the pivoting angle (7) is determined the signal strength of the DF antenna (3) received localization signal (15) is maximum, and wherein from the mean angle or the swivel angle (7), the center of gravity and the position of the DF antenna (3) the position of the RFID transponder (1) is calculated in a third spatial direction. 13. The method according to any one of claims 4 to 12, characterized in that the maximum signal strengths of the DF antennas (3)  received localization signal (5) are compared with each other and the angular range of those DF antenna (3) receiving the localization signal (15) with the highest signal strength, for the calculation of the  Center of gravity of the cutting area (10) is reduced. 14. The method according to any one of the preceding claims, characterized in that the opening angle ranges (5) by electrical adjustment of the directional characteristic of the respective DF antenna (3) or mechanical  Adjustment of the DF antenna (3) are pivoted. 15. The method according to any one of the preceding claims, characterized in that the cutting area (10) of the angular ranges is determined by means of mathematical methods of linear programming. 16. RFI D system for performing the method according to one of claims 1 to 15, with at least three a monitoring field (2), in which there is a passive RFID transponder to be located (1), spanning DF antennas (3), for transmission an electromagnetic field within an opening angle range (5) for activating the RFID transponder or for receiving a localization signal (15) emitted by the RFID transponder (1) as a consequence of its activation in an opening angle range, and with at least one complementary antenna (4) for activation the RFID transponder (1), while a localization signal (15) of at least one of the DF antennas (3) is receivable, and for receiving a localization signal (15), while the RFID transponder (1) of at least one of the DF antennas (15) is activated, thereby in that the opening angle range (5) of the DF antennas (3) is pivotable and the DF antennas (3) and the at least one Complementary antenna (4) are networked together via a control and evaluation unit (14), wherein the control and evaluation unit (14) is adapted to determine a respective limited by critical angle (ßi, 2) angular range of a DF antenna (3) within the DF antenna (3) activates the RFID transponder (1) or receives the localization signal (15) emitted by the latter, to determine the intersection (10) of the angular ranges of the DF antennas (3) and whose center of gravity is used as an estimate of the position of the RFID Transponders (1) to calculate.