DEVICE AND METHOD FOR DETERMINING THE POSITION OF A TRANSMITTER RELATIVE TO A DETECTION AREA

Description

[0001] The invention relates to a device for determining at least one piece of information about the position of at least one transmitter. Furthermore, the invention relates to a method for determining information about the position of a transmitter relative to a detection area.

[0002] In logistics and production, high-frequency transponders (RFID transponders or RFID tags for "radio-frequency identification") are increasingly used to identify objects. These transponders (referred to here and in the following as an alternative term for RFID transponders) are typically passive, meaning they must be activated by a high-frequency electromagnetic field in the form of an excitation signal. The transponder uses this signal to generate energy and, in response to the excitation, sends a modulated signal back to the RFID reader (also called an RFID reader or, in the following, simply a reader). The response signal contains information from the transponder that can be evaluated by the reader. This allows an object to be uniquely identified and assigned via a transponder.

[0003] RFID transponders are used, among other things, for controlling the flow of goods or workpieces. It is important to read the transponders at a specific position along the conveyor path. This allows, for example, conveyor belts to be regulated or stopped, doors to be opened automatically for authorized personnel, or the entry and exit of objects to be controlled.

[0004] Typically, several objects are located one behind the other, so their transponders are read almost simultaneously. Therefore, assigning a single transponder to a specific position is not always guaranteed, and transponders can be confused. However, for flow control of the objects, unambiguous identification at a predetermined position is required. Thus, two pieces of data must be determined: identification of the object and identification of the object's position, or at least the time when the object occupies or passes a selected position.

[0005] Today's systems, such as those used in gate passages or moving units, mostly consist of an RFID reader with one to four ports (so-called gates), to each of which an antenna can be connected. The high-frequency excitation signal is transmitted via the antenna(s), and the response signals from the RFID transponders are received.

[0006] RFID readers with only a single connector typically use an antenna consisting of a single emitter. While this allows for the detection of transponders, it does not provide unambiguous directional information.

[0007] In RFID readers with multiple gates, each gate is connected to an antenna consisting of a single emitter as its antenna element. The reader typically switches sequentially between the antennas by processing the signals received at each gate. The location of the transponders can be determined by the spatial distribution of the antennas. However, this directional information is very imprecise and often ambiguous. Furthermore, the distribution of antennas requires a significant amount of space and therefore increases installation effort.

[0008] In the UHF range (frequency range 860 MHz to 960 MHz for global use according to "EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz - 960 MHz"), one possible solution for flow control is to use short-range antennas. This allows the detection of only RFID transponders that are in close proximity to the antenna, particularly within a few centimeters (see, e.g., [1], [2]). During installation, care must therefore be taken to ensure that the transponders to be detected actually move very close to the antenna. This may require significant modifications to an established process to identify the transponders and control their flow.

[0009] Alternatively, RFID transponders and RFID readers for the HF range (frequency 13.56 MHz according to "EPC Radio-Frequency Identity Protocols EPC Class-1 HF RFID Air Interface Protocol for Communications at 13.56 MHz") can be used, which are typically employed in short-range applications such as electronic payment transactions. The range is limited to centimeters. Furthermore, special high-frequency RFID transponders are required. An object already equipped with a standard UHF RFID transponder would therefore need to carry an additional HF RFID transponder to be tracked along the value chain, for example, when passing through gates. This entails higher costs and greater logistical effort.

[0010] US patent 2011 / 169613 A1 discloses a portable RFID reader that features an active antenna array comprising a plurality of antenna elements for receiving RFID signals from RFID transmitters. A control circuit for controlling the directional characteristic of the antenna array is also disclosed.

[0011] Furthermore, WO 2009 / 147662 A1 discloses a direction finder for determining whether a target object is located within a predefined directional sector of interest, which is predefined as a specific threshold difference between an R reference value and an N zero value, wherein the direction finder comprises: a. at least two antennas arranged in a broadside configuration; b. a wireless communication unit for establishing communication with a target object via a wireless communication signal; c. a variable attenuator for attenuating the wireless communication signal; d. a hybrid link to enable wireless communication of the signal via the antennas in a generated in-phase or out-of-phase pattern; and e. a processing unit designed for the following: e.1.e.1. Switching the hybrid link at stage 1 to generate a phase-in-phase pattern, attenuating the signal until wireless communication is lost, and recording the attenuation value corresponding to the loss of wireless communication as an R reference value; e.2. Switching the hybrid link at stage 2 to generate a phase-out-of-phase pattern, attenuating the signal until wireless communication is lost, and recording the attenuation value corresponding to the loss of wireless communication as an N zero value; e.3. Determining the difference RN, where a difference above the predefined special threshold difference means that the target is within the direction sector of interest, and a difference below the predefined special threshold difference means that the target is outside the direction sector of interest.

[0012] WO 2011 / 110882 A1 discloses a positioning system that uses RF tags. The system comprises at least two phased-array antennas and a unit for determining the position of the RF tag using the at least two phased-array antennas.

[0013] DE 10 2008 012534 A1 further discloses a device equipped with a transceiver unit for determining the relative position with respect to a transponder or an RFID tag based on a relative movement of a transmitting coil of the device, which is intended for energy transfer to the transponder, relative to the transponder or the RFID tag. The invention further relates to a method for determining the relative position based on a relative movement of a transponder or RFID tag with respect to a transmitting coil of the transceiver unit, which is intended for energy transfer to the transponder, and with a coil arrangement.

[0014] The object underlying the invention is to propose a device and a method that makes it possible to detect whether and preferably when an object passes a predetermined position, and which avoids - at least partially - the disadvantages of the prior art.

[0015] The invention solves the problem by providing a device for determining at least one piece of information about the position of at least one transmitter passing through the device, according to claim 1. The device comprises an antenna and a data processing device. The antenna is configured to receive signals emanating from the transmitter. The antenna has at least two distinct directional characteristics. These distinct directional characteristics each relate to a set of spatially distinct reception sensitivities of the antenna. The distinguished directional characteristics—alternatively also referred to as "special" or "selected"—each have at least one reception minimum that corresponds to a spatial detection area.Furthermore, the data processing device is designed in such a way as to evaluate at least the signals received by the antenna device with the excellent directional characteristic with regard to the position of the transmitter relative to detection areas.

[0016] The device according to the invention has an antenna with at least two distinct directional characteristics. These directional characteristics correspond to spatially different reception sensitivities. This means that the antenna with one of the directional characteristics receives signals from different areas of the room with varying strengths. The distinct directional characteristics are even designed so that a minimum signal reception exists in specific spatial detection areas. This means that signals from a transmitter located within one of the detection areas are received by the antenna only very weakly or not at all. Therefore, if the transmitter sends its signals with the same output power and moves through one of the detection areas, the field strength of the received signals will decrease significantly or even approach zero.Therefore, the data processing device is designed to evaluate the received signals to determine the position of the transmitter relative to the detection areas. In the simplest case, a minimum field strength of the received signal indicates that the transmitter is located within one of the detection areas. A higher field strength indicates that the transmitter is outside the respective detection area.

[0017] For position determination, one embodiment therefore provides for the use of historical data, i.e., stored measured values, so that the time at which the transmitter passed the detection areas is determined from the decrease and subsequent increase of the signal amplitude.

[0018] In one embodiment, the device has a control device designed to switch the excellent directional characteristics for receiving signals emanating from the transmitter.

[0019] In one embodiment, the control device also switches on the excellent directional characteristics.

[0020] The following design refers to the fact that, in addition to the excellent directional characteristic, there is also another directional characteristic.

[0021] The data processing device is designed to evaluate signals received from the antenna device at different times with regard to the transmitter's position relative to the detection zones. In this configuration, signals are received at different times, and the temporal progression of the signals, or the data derived from them, is evaluated in relation to the transmitter's position. This allows, for example, the intrapolation of the precise moment the transmitter crossed one of the detection zones. Since each detection zone is associated with a minimum signal strength, a case arises where the amplitude of the received signals decreases and then increases again. This means that the transmitter must have been located within the respective detection zone between the decrease and the increase.

[0022] In one embodiment, the transmitter moves only in one direction relative to the detection area. In this embodiment, the direction of movement is parallel to an axis on which the antenna elements of the antenna device are located. Furthermore, in another embodiment, the transmitter moves along an axis perpendicular to the detection area.

[0023] If the transmitter moves only along a known path relative to the detection area, this simplifies signal analysis. In particular, for the directional characteristics, a sequence of signal changes caused by the transmitter's movement can be deduced. This, in turn, allows the transmitter's position to be inferred from the signals. For example, the aforementioned type of excellent directional characteristic exhibits a sequence of amplitude decrease followed by amplitude increase. This is always assuming that the transmitter essentially always transmits the signals with the same field strength.

[0024] If, in a scenario, another transmitter follows the aforementioned transmitter, it is possible that the signals of the second transmitter will be received. However, because it is located spatially behind the first transmitter, its signals will be received with a different sensitivity, resulting in a different signal amplitude that differs from the values ​​expected for the first transmitter. For example, the signal amplitude may jump, whereas previously it had been decreasing. Therefore, it is possible to distinguish between multiple transmitters. Thus, the invention as a whole also relates to an arrangement of the device described herein and a transmitter track.

[0025] In a further embodiment, information about the sender is derived from the received signals. This embodiment relies on the fact that, for example, RFID transponders also transmit identification data with their response signals. This embodiment therefore allows the separation of signals from different senders by identifying each sender through its own unique signal.

[0026] One embodiment of the device includes a data storage unit. The data processing unit is configured to store data associated with signals received at different times in this data storage unit. Furthermore, the data processing unit is configured to determine, from the data stored in the data storage unit, the time at which the transmitter is located within and / or passes through a detection area. A previously mentioned pattern for the signal amplitude progression is: decrease in amplitude, reaching a minimum, increase in amplitude. This applies when only a single reception minimum is considered. Assuming a constant transmitter speed, the time of passage can also be extrapolated.

[0027] One of the excellent directional characteristics features multiple sensitivity minima, each corresponding to a different spatial detection area. The presence of multiple sensitivity minima allows for the monitoring of different detection areas. This enables a more precise determination of the transmitter's position, i.e., whether it is located, for example, between two detection areas. Furthermore, it allows for the verification of statements regarding the transmitter's position, particularly when evaluating signals received at different times.

[0028] In one embodiment, the device includes a signal processing device. This signal processing device is configured to process the signals received by the antenna device and to determine the amplitude value of each received signal's field strength. This embodiment simplifies the evaluation of the received signals, as each signal is assigned only one value. The data processing device is configured to process the amplitude values ​​of the received signals.

[0029] One embodiment provides that the signal processing device is an RFID reading device which generates a "Received Signal Strength Indication" value as the amplitude value of the field strength of the received signals.

[0030] In an alternative or supplementary configuration, data is also determined from the received signals that allows the identification of the sender.

[0031] In one embodiment, the device includes a signal source configured to generate an excitation signal. The antenna device is configured to radiate the excitation signal. In one embodiment, the signal source is part of the signal processing device, while in an alternative embodiment it is a separate component. In one embodiment, the signal source is specifically part of the signal processing device, which is configured as an RFID reader.

[0032] One embodiment provides for a detection area that is a single plane. In one embodiment, the detection area specifically extends only over one plane. This allows the system to detect whether the transmitter passes over a plane.

[0033] In one embodiment, the antenna device is designed as a multi-lobe antenna. A multi-lobe antenna, also known as a multibeam antenna, has different directional characteristics, each defined by a lobe or main lobe. These lobes are at least partially oriented differently in space, allowing different areas of the room to be measured with varying reception sensitivities.

[0034] One embodiment provides that the antenna device comprises several antenna elements. In one embodiment, the antenna elements are components of a patch antenna, and in an alternative embodiment, they are individual dipole antennas.

[0035] In one embodiment, the antenna device comprises two antenna elements. The control device is designed to switch the two antenna elements alternately in push-pull and co-push mode. In this embodiment, the two antenna elements are essentially identical and therefore have the same signal reception characteristics. The different power supplies to the antenna elements result in different directional characteristics.

[0036] In one embodiment, co-mode feeding of the antenna elements results in a sensitivity maximum in a plane perpendicular to a connecting axis between the two antenna elements. Differential-mode feeding produces a directional characteristic with a minimum or zero in the plane perpendicular to the connecting axis.

[0037] Therefore, one embodiment provides for the antenna elements to be arranged so that the relevant plane lies within the detection range. This also means that the directional characteristic resulting from push-pull feeding is simultaneously the preferred directional characteristic, and that the directional characteristic resulting from co-mode feeding is the reference directional characteristic.

[0038] According to the invention, the antenna device comprises a self-mode feed network. This self-mode feed network is configured to produce different directional characteristics of the antenna device. This applies to both the transmission and reception of signals. In one embodiment, the self-mode feed network is specifically designed to output the received signal for each directional characteristic, provided the antenna device with multiple directional characteristics receives signals simultaneously.

[0039] Furthermore, the invention solves the problem by a method for determining information about the position of a transmitter according to claim 9. The method includes at least the reception of signals emanating from the transmitter. This is accomplished using two distinct directional characteristics of an antenna device. These distinct directional characteristics have sensitivity minima for receiving signals in specific detection ranges.

[0040] The designs of the devices can also be implemented using the method, so the corresponding explanations apply accordingly. Conversely, the method can also be implemented using the device.

[0041] Depending on its embodiment, the present invention provides a method for assigning a transponder to a fixed spatial direction. In one embodiment, the method is based on the combination of a multi-lobe antenna with special switchable directional characteristics and an RFID reader that provides RSSI values ​​for identified transponders.

[0042] In detail, there are numerous possibilities for designing and further developing the device and method according to the invention. Reference is made, on the one hand, to the claims and, on the other hand, to the following description of exemplary embodiments in conjunction with the drawings. The drawings show: Fig. 1 a schematic representation of a device according to the invention and its application, Fig. 2 a schematic representation of two antenna elements of an antenna device and the associated directional characteristics, Fig. 3 a coordinate system for describing the antenna elements of the Fig. 2 , Fig. 4 a representation of the directional characteristics of the two antenna elements of the Fig. 2 In common-mode and differential-mode operation, Fig. 5 shows a schematic representation of determining the position of a transmitter relative to the antenna device with the antenna elements of the Fig. 2 , Fig. 6 a schematic representation of the time courses of the amplitudes of the received signals when the arrangement of the Fig. 5 , Fig. 7 the time courses of the Fig. 6 with superimposed noise, Fig. 8 a dependence of the standard deviation √ Var (θ) of the estimated angle of incidence θ on the signal-to-noise ratio ρ, Fig. 9 a schematic representation of an unclaimed device for illustrative purposes, Fig. 10 a functional representation of a ring coupler as an example of a feed network, Fig. 11 a schematic representation of the time responses of the amplitudes of the received signals when using three antenna elements with three modes, and Fig. 12 a representation of the dependence of the standard deviation of the determined angle of incidence θ on the noise for an antenna device with three antenna elements.

[0043] The Fig. 1 Figure 1 shows an application of the device 1 according to the invention, which, among other things, allows it to indicate whether and when a transmitter 2 passes through a detection area 6.

[0044] For this purpose, the device 1 has an antenna device 3 which has at least two excellent directional characteristics. The directional characteristics each refer to a spatial distribution of the sensitivity of the antenna device 3 for receiving signals, which in this case originate in particular from the transmitter 2.

[0045] In the illustrated embodiment, the antenna device 3 has several directional characteristics. In this exemplary embodiment, three antenna elements 10 serve this purpose, which are controlled by a control device 4 via the network 11. In one embodiment, the antenna device 3 is a patch antenna. Alternatively, the antenna elements 10 can be dipole antennas, monopole antennas, monopole-like antennas, chip antennas, or loop antennas. One of the directional characteristics is the aforementioned superior directional characteristic, to which the definition range 6 is assigned.

[0046] The feed network 11 is provided for switching the different directional characteristics for transmitting an excitation signal or for receiving the signals emanating from the transmitter 2. In this example, the feed network 11 represents an implementation of a Butler matrix (in one embodiment according to the invention, an eigenmode network is used) and provides at its output the signals as received with the individual directional characteristics. Switching the directional characteristics therefore means that the signal received with the switched directional characteristic is fed to the evaluation or specifically evaluated. In another embodiment – ​​not shown – switching the directional characteristics means that, by directly intervening in the antenna device 3, only the switched directional characteristic is present at any given time, i.e.,that the antenna device 3 can only receive signals with the switched directional characteristic.

[0047] The data processing device 5 processes the received signals and the resulting data. In the example shown, the data processing device 5 is connected to a signal processing device 7, which determines an amplitude value of the field strength for each of the received signals.

[0048] If transmitter 2 is an RFID tag, the signal processing device 7 is configured to generate a so-called "Received Signal Strength Indication" (RSSI) value as its amplitude. In a further related configuration, the signal processing device 7 is also designed to extract information from the received signals—for example, an identification number or measurement data. Thus, the signal processing device 7 can be considered, for example, an RFID reader.

[0049] In one embodiment (not shown), the data processing device 5 itself determines a value for the amplitude of the received signals. Particularly in conjunction with this embodiment, but also independently of it, in another embodiment the data processing device 5 is a component of the antenna device 3 and is therefore housed within it.

[0050] For use with transmitters 2 based on RFID tags, the illustrated embodiment also includes a signal source 8 that generates excitation signals. Depending on the application, these excitation signals are output via the antenna device 3, either with specific directional characteristics or essentially omnidirectionally. These excitation signals are, for example, so-called request signals, which instruct the transmitter 2 (in the form of an RFID tag) to establish data communication and which may also provide the transmitter 2 with the energy required for communication. In one embodiment, directional characteristics are combined for transmitting the excitation signals, resulting in superimposed signals. Conversely, as already mentioned, the feed network 11 allows the received signals to be separated into their individual directional characteristics.

[0051] In an alternative embodiment – ​​not shown – the signal source 8 is a component of the signal processing device 7. This corresponds to the prior art design of RFID readers, which themselves generate the activation signals. Since the antenna device 3 serves to receive and transmit signals, it follows that the directional characteristics relate not only to the spatial distribution of the sensitivity but also to the transmission characteristics of the antenna device 3.

[0052] Finally, the data processing device 5 is connected to a data storage device 9 to store data about the trajectory of transmitter 2. Using the historical data regarding the respective positions of transmitter 2, the movement path of transmitter 2 is determined, and ambiguities are resolved, for example, when multiple transmitters are present, and the signals are assigned to the respective transmitters. Appropriate plausibility checks are provided for this purpose.

[0053] The selected directional characteristic here has a detection range 6, perpendicular to which transmitter 2 moves in the example shown. Transmitter 2 moves parallel to the antenna elements 10 and perpendicular to the detection range 6. The special feature of the detection range 6 is that the sensitivity of the antenna device 3 is minimal in this spatial area. The device 1 thus uses a signal minimum to determine whether transmitter 2 passes through the assigned detection range 6. Therefore, if transmitter 2 is located within the detection range 6, no signal or only a very weak signal is received by the antenna device 3.

[0054] According to the invention, the antenna device 3 has a total of three detection areas 6, 6', each containing a reception minimum, which the transmitter 2 passes through successively. This increases the reliability of detecting the passage of the middle detection area 6.

[0055] The reliability of the measurement is increased in particular by the fact that the control device sets 4 different directional characteristics, each with different sensitivities and location assignments, so that measurement inaccuracies or ambiguities can also be compensated.

[0056] In one embodiment, the antenna device 3 has at least one additional directional characteristic that exhibits a sensitivity maximum in the detection range 6. This means that the antenna device 3 is particularly sensitive to receiving signals with this additional directional characteristic. Therefore, in this embodiment, the signals from the preferred directional characteristic and the reference characteristic are evaluated together to increase the measurement accuracy.

[0057] The Fig. 2 Figure 1 shows an exemplary antenna device, designed as a multi-lobe antenna, with two antenna elements 10 (labeled A and B). Each of the two antenna elements 10 has a lobe-shaped directional characteristic 12. The two directional characteristics 12 are each complemented by a complex-valued directional characteristic. f i is described by j = 1 (or A) or j = 2 (or B).

[0058] In general, a multi-lobe antenna consists of a set of n antenna elements 10 (or radiators, e.g. dipoles) connected to a feed network (see Fig. 1 ) are connected. An antenna or antenna element is connected to each of the n outputs of the feed network.

[0059] The m inputs of the feed network, which each serve to output the signals received by the antenna elements 10 or to feed in the RF signals to be transmitted via the antenna elements 10, each correspond in one configuration to a specific directional characteristic. C i , which is defined as: C → i = C → i ω → = C → i ϕ θ = C i co C i cross mit i = 1 , … m

[0060] Each of these components is a co-polarized component. C i co and a cross-polarized component C i cross given.

[0061] The Fig. 3 Figure 1 shows a coordinate system with the three axes x, y, and z, and the reference point R at the origin of the coordinate system. In the example shown, the two antenna elements 10 (A and B) are arranged along the x-axis. An observation point V is described by an azimuth angle Φ in the xy-plane and a co-elevation angle θ relative to the z-axis. The area under consideration is given to dΩ = sin θ * dθ * dΦ.

[0062] The directional characteristics indicate how a transmitter, or specifically an RFID transponder, is assigned to a particular direction. C The antenna device exhibits special properties. Here, the two-element antenna array of the Fig. 2 considered.

[0063] With reference to point R according to the Fig. 3 , in which the origin of the coordinate system is placed for the sake of simplicity, both antenna elements 10 (i.e. A and B) each possess the aforementioned (complex) radiation characteristic. f → j = f j co f j cross mit j = 1 , … n

[0064] From this, the so-called radiation matrix can be derived. H̃ (compare [3]) determine, whose components are given by the following formula: H ˜ pj = 1 4 π ∫ Ω f → p H f → j dΩ mit p j = 1 , … , n

[0065] Since the radiation matrix H̃ Since it is a Hermitian matrix, it can be diagonalized. Therefore, the following results: H ˜ = Q ˜ Λ ˜ Q ˜ H mit Λ ˜ = diag λ 1 , … , λ n

[0066] Equation (4) describes the eigenvalue decomposition of the radiation matrix H Each column represents a different element in the text. Q one of the n eigenvectors q j and each main diagonal element in Λ describes the corresponding eigenvalue λ j .

[0067] The eigenvectors q j These describe the fundamental excitation vectors of the antenna device, which in this case is an antenna array with the antenna elements. The eigenvectors q j The eigenvalues ​​are pairwise orthogonal, provided that no eigenvalues ​​λj occur multiple times. If eigenvalues ​​λj occur multiple times, an orthonormal basis must be found for them, whose basis vectors are orthogonal to each other.

[0068] Furthermore, the eigenvectors possess q j a length of one. Certain directional characteristics are associated with the eigenvectors. C → j m = C j m , co C j m , cross together, which are orthogonal to each other.

[0069] Therefore: ∮ C → p m H C → j m = 0 , falls p ≠ j .

[0070] The eigenvectors QThese represent a specific orthonormal basis of the possible feed vectors. However, contrary to the claimed inventions, other orthonormal bases can also be determined, so that the feed network does not necessarily have to be an eigenmode network. It is required that at least one zero is present in one of the directional characteristics along a specific direction.

[0071] For an array of two identical antenna elements (see Fig. 2 ) with the same orientation, the following eigenvectors result: Q ˜ = 1 2 1 1 1 − 1

[0072] The antenna elements 10 (for example dipoles) are therefore fed either in common mode ("even mode": 1 / √2 and 1 / √2) or in opposite mode ("odd mode": 1 / √2 and -1 / √2).

[0073] The resulting quantitative guideline characteristics are shown by the Fig. 4 Qualitatively for the xz-plane. The directional characteristic 12 for common-mode operation is shown with solid lines, and that for differential-mode operation with dashed lines. The depicted directional characteristics result primarily from a eigenmode network.

[0074] When fed in sync, a maximum occurs perpendicular to the array, formed by the two identical and identically oriented antenna elements. This maximum is therefore located in the z-direction, or at the co-elevation angle θ = 0°.

[0075] In contrast, in the opposite phase, a minimum or zero occurs at this point. The zero, or its immediate vicinity, is narrow compared to the vicinity of the maximum in the same phase, because the gradient with respect to the co-elevation angle θ increases sharply in magnitude in the vicinity of the zero.

[0076] A radio signal arriving at the antenna array from the direction of the zero point will therefore be barely or not at all received in differential mode, while in common mode the received signal will be at its maximum. The direction of incidence can thus be determined from the measured signal levels in common and differential mode.

[0077] In the Fig. 5 Figure 1 shows a scenario in which an object with an RFID transponder as transmitter 2 is transported parallel to the x-axis at a constant speed (v). The antenna array, formed from the two antenna elements 10 of the antenna device 3, is centered at the origin of the coordinate system and oriented such that the zero point of the receive sensitivity in push-pull mode occurs along the z-axis θ = 0°. This zero point is thus the detection range 6. Depending on the position of the transponder 2 relative to the antenna device 3, the received signal of the individual modes varies, since the angle of incidence is a function of time.

[0078] The position of the transponder in the x-direction can be assigned a time t. The diagram shows the two positions of transmitter 2 at time t1, i.e., before the detection area 6, and at time t2, i.e., after passing through the detection area 6. The respective angle of incidence θ, as the angle of the incident response signal (indicated by the arrows originating from transmitter 2) to the z-axis, thus varies with time t.

[0079] In the Fig. 6 are the time signals of the arrangement of Fig. 5 An example is shown. The curve of the received amplitude normalized to the maximum as a function of time t for the transmitter is shown. Fig. 5 , which moves parallel to the x-axis (z = z 0 ) at a constant velocity v. The two antenna elements are located on the x-axis and are centered around the origin, i.e., they are equidistant from it.

[0080] If the transponder is read as a transmitter at different locations and thus at different times (meaning that the transponder has been identified and its identifier is known), an analysis of the time signals allows the determination of the time at which the transponder is in the direction θ = 0° and thus at a specific location - namely the detection area - along the conveyor path.

[0081] The received signal in anti-phase mode (dashed line) is minimal at this point in the passage of the detection area, while it is maximal in common-phase mode (solid line). The transponder can therefore be distinguished from a subsequent transponder, which is also being read, at this point in the passage of the detection area, since the signal of the subsequent transponder is received in both common-phase and anti-phase modes. The transponder that responds from the direction θ = 0° and whose signal can only be received in common-phase mode must therefore be the selected transponder. This result can be used to monitor and control the flow of objects, for example, on a conveyor belt or at a gate.

[0082] The point in time when the transponder is located along the plane with a co-elevation angle θ = 0° can alternatively be read from the common-mode signal. At this point, the signal transmitted by the transmitter is received with maximum amplitude.

[0083] However, for practical implementation, the uncertainties caused by superimposed noise must be taken into account. Fig. 7 illustrates the time course of the received signals of the Fig. 6 in common mode (solid line) and in differential mode (dipped line) with superimposed noise starting from a signal-to-noise ratio of ρ = 20 dB.

[0084] Due to the broad radiation pattern in common-mode operation, noise has a greater impact on the signal maximum in the detection range, resulting in a higher degree of uncertainty when searching for the maximum. The relatively narrow minimum in differential-mode operation allows it to be located with lower uncertainty, even with superimposed noise.

[0085] To illustrate this, the Fig. 8 The determined standard deviation of the determined angle of incidence θ for varying signal-to-noise ratios for the setup according to the Fig. 5 As the signal-to-noise ratio ρ (represented on the x-axis in dB) increases, the uncertainty in the differential-mode minimum search (dashed line) decreases rapidly, while the common-mode maximum search (solid line) shows significantly higher uncertainties even at high signal-to-noise ratios ρ. The standard deviation √Var(θ) of the estimated angle of incidence θ in degrees (°) is plotted on the y-axis. For this example, the transponder moves at a constant speed of 3 m / s. The standard deviation was determined over 10,000 test values ​​per signal-to-noise ratio value ρ. Here, z0 = 5 m.

[0086] The implementation of the common-mode and differential-mode power supply principle relies on a power supply network that provides the necessary power vectors. The directional characteristics C assigned to the input gates i According to equation (1), the directional characteristics thus correspond to the eigenmodes. C → j m The feed network is a eigenmode network, where m = n in the configuration. This means that each antenna element 10 also has a signal output available for outputting the received signals.

[0087] An unclaimed device 1, serving to illustrate the concept, with two antenna elements 10 shows the Fig. 9 The antenna array of the two antenna elements 10 (designated A and B) is connected to an intrinsic mode network as a feed network 11. The inputs (designated C and D) of the feed network 11 are selectable via a switch for high-frequency signals (RF switch). The input of the switch is connected to the RFID reader, which here serves as a signal processing device 7. The RFID reader also includes the signal source 8, so that the RFID reader provides the excitation signal for the transponders and evaluates their response signals. The switching of the inputs of the feed network 11 is carried out by a control logic 13, which here is part of the antenna device 3. Inputs C and D of the feed network 11 are the inputs for the RF signal as the excitation signal of the signal processing device 7. They are also the outputs for the signals received by the antenna elements 10. Each input also has a directional characteristic, i.e.It is assigned either differential or common-mode operation, so that the switch allows switching between the two directional characteristics.

[0088] The reading of the transponders, and therefore the reception of the signals, is controlled by a control device 4, which acts on the control logic 13. In the embodiment shown, the transponder signals are read alternately in common-mode and differential-mode modes. Using the RSSI values ​​available from the RFID reader 7, which represent the amplitude of the received signals, the corresponding time signals of the common-mode and differential-mode modes can be determined for each transponder. Based on this, the data processing device 5 determines the time at which the respective transponder crosses the z-axis θ = 0°. In one embodiment, the data processing device 5 also determines the angle of incidence of the received signals.

[0089] The data processing device 5 is also a component of the antenna device 3. In another embodiment – ​​not shown here – the control device 4 is also part of the antenna device 3, so that in this embodiment the device 1 consists of two elements: antenna device 3 and RFID reader 7.

[0090] The separation into control logic 13, control device 4, and data processing device 5 should be understood here in relation to their functions. Different configurations can be implemented for this purpose.

[0091] An implementation of an eigenmode network as a feed network 11, serving only for explanatory purposes but not claimed, shows the Fig. 10 for the antenna array consisting of two antenna elements (antenna A and antenna B) of the Fig. 2 In its design, it is a ring coupler which, depending on the fed gate (i.e., the respective input of the feed network in the direction of the RFID reader), Fig. 9 (Here denoted by C for differential-mode input and D for common-mode input) provides a common-mode signal or a differential-mode signal, respectively. Such a ring coupler is particularly useful when an eigenmode network is implemented.

[0092] The principle of self-mode feeding can be applied to arrays with any number of antenna elements: The Fig. 11 shows, by way of example, the signals of an antenna device according to the invention, which has three antenna elements (cf. Fig. 1 The three antenna elements are located on the x-axis and centered around the origin. Three modes are observed. The time signals (time t on the x-axis, where t = 0 is the time of passing through the detection range, and normalized to the maximum on the y-axis with the received amplitude) are shown here with superimposed noise. The signal-to-noise ratio is ρ = 20 dB.

[0093] In common-mode mode (solid line), all three antenna elements are fed in phase. The corresponding directional characteristic therefore exhibits a maximum along the angle θ = 0°, which decreases on both sides.

[0094] In push-pull mode (dashed line with longer sub-lines), the two outer elements are fed out of phase and with the same amplitude. This creates a minimum or zero along the axis at an angle θ = 0°, which rises laterally to a maximum that is smaller than the maximum of the common-mode mode, and then falls again.

[0095] In the third mode (dashed line with shorter segments), adjacent elements are fed out of phase. This creates two zeros symmetrically around the z-axis in the radiation pattern, with a small maximum around the region with an angle θ = 0°. The two zeros rise again laterally.

[0096] The analysis is limited to the upper half-plane z ≥ 0.

[0097] The two additional zeros of the third mode allow for a more precise determination of the time at which a transponder crosses the z-axis, even with superimposed noise compared to the two-element array. For plausibility reasons, the estimated time of the minimum in the push-pull signal must occur between the times of the minima in the third-mode signal.

[0098] Furthermore, in the three-element array, the zero point in push-pull mode is sharper due to the larger aperture than in the two-element array, assuming an equal distance between the antenna elements.

[0099] The Fig. 12 shows the standard deviation Var θ of the estimated angle of incidence θ as a function of the signal-to-noise ratio ρ, which was determined using the signals in the push-pull mode (solid line) and using the signals in the push-pull mode and the third mode (dimpled thick line). For comparison, the result for the push-pull mode of the two-element array is plotted (dimpled thin line, cf. Fig. 8 ).

[0100] For the measured values, the transponder moved parallel to the x-axis (z = z₀) at a constant speed of v = 3 m / s. The antenna elements were located on the x-axis and centered around the origin. The standard deviation was determined over 10,000 test values ​​per ρ-value. Furthermore, z₀ = 5 m.

[0101] Comparing the variances between a two-element and a three-element array shows that the combination of push-pull mode and third mode has a lower standard deviation than the push-pull mode of the two-element array.

[0102] The push-pull mode of the three-element array leads to higher standard deviations than the push-pull mode of the two-element array at signal-to-noise ratios below 13 dB. For the three-element array, as the value of ρ increases, the standard deviation of the push-pull mode approaches the standard deviation resulting from the combination of the push-pull and third modes. This occurs because the uncertainty in estimating the angle of incidence, and thus the variation around the expected value, decreases. It becomes increasingly unlikely that the minimum in the time signal of the push-pull mode will not occur between the minima of the third mode.

[0103] The invention can be summarized again using one embodiment as an example: A transponder is detected as a transmitter based on the minimum search in the time signal of at least one receiving mode of a multi-lobe antenna.

[0104] Using an RFID reader that provides RSSI values ​​for the received signals offers the following advantages: With the aid of a processing unit, which can be housed within the multi-lobe antenna, a single RF path between the multi-lobe antenna and the RFID reader is sufficient for detecting a transponder in a specific direction. This allows the use of RFID readers with only one input or output port. These are more cost-effective than RFID readers with multiple ports.

[0105] Furthermore, there is the advantage that no additional infrastructure components are required for switching or calculation, since in this design the switching and the position determination are functionally covered by the multi-lobe antenna itself.

[0106] The number of antenna elements, and therefore the number of eigenmodes, can be chosen arbitrarily and is independent of the RFID reader. With an increasing number of elements, sharper zeros can be achieved and plausibility checks can be performed. This reduces the uncertainty caused by superimposed noise.

[0107] However, the same applies to other signal processing devices that provide a value for the signal strength of the received signals.

[0108] In contrast to short-range antennas, such as those used in the prior art for detecting RFID transponders, the following advantages arise: The antenna device in the form of a multi-lobe antenna can be positioned more flexibly, as it is not limited to a short range. Therefore, the multi-lobe antenna can be used in various scenarios.

[0109] Furthermore, a lower transmission power from the RFID reader is sufficient.

[0110] Technical applications include logistics and production, such as flow control for the import and export of goods, and baggage sorting. Flow control is also possible for conveying systems, such as conveyor belts and transport vehicles. Further applications include automated access control, such as personnel screening in hospitals, and speed measurement to determine throughput.

[0111] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, such that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the process steps can be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key process steps can be performed by such an apparatus.

[0112] Depending on specific implementation requirements, embodiments of the invention can be implemented in hardware, partially in hardware, or partially in software. The implementation can be carried out using a digital storage medium, such as a floppy disk, DVD, Blu-ray disc, CD, ROM, PROM, EPROM, EEPROM, FLASH memory, hard disk, or other magnetic or optical storage medium, on which electronically readable control signals are stored. These control signals can interact with, or interact with, a programmable computer system to execute the respective method. Therefore, the digital storage medium can be computer-readable.

[0113] Some embodiments according to the invention therefore include a data carrier which has electronically readable control signals which are able to interact with a programmable computer system in such a way that one of the methods described herein is carried out.

[0114] In general, embodiments of the present invention can be implemented as a computer program product with a program code, wherein the program code is effective in carrying out one of the methods when the computer program product runs on a computer.

[0115] The program code can also be stored on a machine-readable medium, for example.

[0116] Other embodiments include a computer program for carrying out one of the methods described herein, wherein the computer program is stored on a machine-readable medium. In other words, an embodiment of the method according to the invention is thus a computer program that includes program code for carrying out one of the methods described herein when the computer program is executed on a computer.

[0117] Another embodiment of the methods according to the invention is thus a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for carrying out one of the methods described herein is recorded. The data carrier or the digital storage medium or the computer-readable medium is typically tangible and / or non-volatile.

[0118] Another embodiment of the method according to the invention is thus a data stream or a sequence of signals that represents the computer program for carrying out one of the methods described herein. The data stream or sequence of signals can be configured, for example, to be transferred via a data communication connection, such as the Internet.

[0119] Another embodiment comprises a processing device, for example a computer or a programmable logic device, which is configured or adapted to perform one of the methods described herein.

[0120] Another embodiment comprises a computer on which the computer program for performing one of the procedures described herein is installed.

[0121] Another embodiment of the invention comprises a device or system designed to transmit a computer program for carrying out at least one of the methods described herein to a receiver. The transmission can be, for example, electronic or optical. The receiver can be, for example, a computer, a mobile device, a storage device, or a similar device. The device or system can, for example, include a file server for transmitting the computer program to the receiver.

[0122] In some embodiments, a programmable logic device (for example, a field-programmable gate array, an FPGA) can be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array can interact with a microprocessor to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware device. This can be general-purpose hardware such as a computer processor (CPU) or method-specific hardware such as an ASIC or, for example, a microprocessor, e.g., in the form of an ARM architecture.

[0123] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments. References:

[0124] [1] UHF RFID Low Range Antenna (LoRa), datasheet, Kathrein. [2] UHF RFID Ultra Low Range Antenna, datasheet, Kathrein. [3] C. Volmer et al., "An Eigen-Analysis of Compact Antenna Arrays and Its Application to Port Decoupling", IEEE transactions on antennas and propagation, vol. 56, no. 2, pages 360-370, 2008.

Claims

1. A device (1) for determining at least one piece of information on a position of at least one transmitter (2) passing the device (1), comprising an antenna device (3) and a data processing device (5), wherein the antenna device (3) is configured to receive signals emanating from the transmitter (2), wherein the antenna device (3) comprises at least two distinguished directional characteristics, wherein the distinguished directional characteristics each relate to a set of spatially different receive sensitivities of the antenna device (3), wherein a first one of the distinguished directional characteristics comprises a first receive minimum, wherein a second one of the distinguished directional characteristics comprises a second receive minimum and a third receive minimum, wherein the first receive minimum, the second receive minimum and the third receive minimum are each associated to a different spatial detection region (6, 6'), wherein the data processing device (5) is configured to evaluate signals received at different times from the antenna device (3) as regards the position of the transmitter (2) relative to the detection region (6), wherein the device (1) comprises a data storage (9), wherein the data processing device (5) is configured to store data associated to the signals received at different times in the data storage (9), and wherein the data processing device (5) is configured to establish, from the data stored in the data storage (9), points in time when the transmitter (2) passes the detection regions (6, 6'), wherein signal minima in the respective detection regions (6, 6') are used for establishing said points in time, characterized in that the antenna device (3) comprises an eigenmode feed network (11), and the eigenmode feed network (11) is configured to cause different directional characteristics of the antenna device (3).

2. The device (1) according to claim 1, wherein the device comprises a control device (4), and wherein the control device (4) is configured to switch the distinguished directional characteristics for receiving signals emanating from the transmitter (2).

3. The device (1) according to claim 1 or 2, wherein the device comprises a signal processing device (7), and wherein the signal processing device (7) is configured to process the signals received from the antenna device (3) and to establish a respective amplitude value of a field strength of the signal received.

4. The device (1) according to claim 3, wherein the signal processing device (7) is an RFID reader which generates a respective inverted "received signal strength indication" (RSSI) value as an amplitude value of the field strength of the signals received.

5. The device (1) according to any of claims 1 to 4, wherein the device (1) comprises a signal source (8), wherein the signal source (8) is configured to generate an excitation signal, and wherein the antenna device (3) is configured to radiate the excitation signal.

6. The device (1) according to any of claims 1 to 5, wherein each of the detection regions (6, 6') is a plane.

7. The device (1) according to any of claims 1 to 6, wherein the antenna device (3) is implemented as a multi-beam antenna.

8. The device (1) according to any of claims 1 to 7, wherein the antenna device (3) comprises several antenna elements (10).

9. A method for establishing a piece of information on a position of a transmitter (2) wherein signals are received, emanating from the transmitter (2) with two distinguished directional characteristics of an antenna device (3), while passing the antenna device (3), wherein a first one of the distinguished directional characteristics comprises a first receive minimum, wherein a second one of the distinguished directional characteristics comprises a second receive minimum and a third receive minimum, wherein the first receive minimum, the second receive minimum and the third receive minimum are each associated to a different spatial detection region (6, 6'), wherein signals received at different times from the antenna device (3) as regards the position of the transmitter (2) relative to the detection regions (6, 6') are evaluated by a data processing device (5), wherein data associated to signals received at different times are stored in a data storage (9) by the data processing device (5), and wherein points in time when the transmitter (2) passes the detection regions (6, 6') are established from the data stored in the data storage (9) by the data processing device (5), wherein signal minima in the respective detection regions (6, 6') are used for establishing said points in time, characterized in that the antenna device (3) comprises an eigenmode feed network (11) used to cause different directional characteristics of the antenna device (3).