Device and method for determining the position of a transmitter relative to a detection region

Abstract

What is disclosed is a device for determining a piece of information on a position of a transmitter, having an antenna device and a data processing device. The antenna device receives signals emanating from the transmitter and has a distinguished directional characteristic which relates to a set of spatially different receive sensitivities of the antenna device. The distinguished directional characteristic has a sensitivity minimum associated to a spatial detection region. The data processing device evaluates the signals received from the antenna device with the distinguished directional characteristic, as regards the position of the transmitter relative to the detection region. In addition, a corresponding method is disclosed.

Claims

1. A device for determining at least one piece of information on a position of at least one transmitter, comprising an antenna device and a data processing device, wherein the antenna device is configured to receive signals emanating from the transmitter, wherein the antenna device comprises at least a distinguished directional characteristic, wherein the distinguished directional characteristic relates to a set of spatially different receive sensitivities of the antenna device, wherein the distinguished directional characteristic comprises a plurality of sensitivity minima, wherein each sensitivity minimum of the sensitivity minima is associated to a spatial detection region of a plurality of detection regions, wherein the data processing device is configured to evaluate at least signals received from the antenna device with the distinguished directional characteristic in order to determine the one piece of information on the position of the transmitter relative to the detection regions, wherein the data processing device is configured to evaluate the signals received from the antenna device at different times, as regards the position of the transmitter relative to the plurality of detection regions, wherein the device comprises a data storage, wherein the data processing device is configured to store data associated to the signals received at different times in the data storage, and wherein the data processing device is configured to establish from the data stored in the data storage that time when the transmitter passes one of the detection regions.

2. The device according to claim 1, wherein the antenna device comprises several different directional characteristics, wherein the directional characteristics each relate to a set of spatially different receive sensitivities of the antenna device, wherein the device comprises a control device, and wherein the control device is configured to switch several directional characteristics for receiving signals emanating from the transmitter.

3. The device according to claim 2, wherein the control device is configured to switch at least one comparative directional characteristic as one of the directional characteristics of the antenna device, wherein the comparative directional characteristic comprises at least one sensitivity maximum associated to the spatial detection region, and wherein the data processing device is configured to check, starting from the signals received from the antenna device with the comparative directional characteristic, the one piece of information on the position of the transmitter relative to the detection region.

4. The device according to claim 1, wherein the distinguished directional characteristic comprises several sensitivity minimums associated to different spatial detection regions.

5. The device according to claim 1, the device comprising a signal processing device, and wherein the signal processing device is configured to process the signals received from the antenna device and establish a respective amplitude value of a field strength of the signal received.

6. The device according to claim 5, wherein the signal processing device is an RFID reader which generates a respective “received signal strength indication” (RSSI) value as an amplitude value of the field strength of the signals received.

7. The device according to claim 1, the device comprising a signal source, wherein the signal source is configured to generate an excitation signal, and wherein the antenna device is configured to radiate the excitation signal.

8. The device according to claim 1, wherein the detection region is a plane.

9. The device according to claim 1, wherein the antenna device is implemented as a multi-beam antenna.

10. The device according to claim 1, wherein the antenna device comprises several antenna elements.

11. The device according to claim 10, wherein the antenna device comprises two antenna elements, wherein the device comprises a control device, and wherein the control device is configured to switch the two antenna elements alternatingly in an even mode and odd mode.

12. The device according to claim 2, wherein the antenna device comprises a feed network, and wherein the feed network is configured to cause different directional characteristics of the antenna device.

13. A method for determining at least one piece of information on a position of a transmitter, the method comprising the steps of: receiving signals emanating from the transmitter with a distinguished directional characteristic of an antenna device, wherein the distinguished directional characteristic relates to a set of spatially different receive sensitivities of the antenna device, wherein the distinguished directional characteristic comprises a plurality of sensitivity minima for receiving signals, wherein each sensitivity minimum of the plurality of the sensitivity minima is associated with a detection region of a plurality of detection regions; evaluating, by using a data processing device, at least signals received from the antenna device with the distinguished directional characteristic in order to determine the one piece of information on the position of the transmitter relative to the plurality of the detection regions, wherein the data processing device is used for evaluating the signals received from the antenna device at different times, as regards the position of the transmitter relative to the plurality of detection regions; storing data associated to the signals received at different times in a data storage; and using the data processing device for establishing from the data stored in the data storage that time when the transmitter passes one of the detection regions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which:

(2) FIG. 1 shows a schematic illustration of an inventive device and the application thereof;

(3) FIG. 2 shows a schematic illustration of two antenna elements of an antenna device and respective directional characteristics;

(4) FIG. 3 shows a coordinate system for describing the antenna elements of FIG. 2;

(5) FIG. 4 shows an illustration of the directional characteristics resulting in the two antenna elements of FIG. 2 in an even mode and an odd mode;

(6) FIG. 5 shows a schematic illustration of determining the position of a transmitter relative to the antenna device with the antenna elements of FIG. 2;

(7) FIG. 6 shows a schematic illustration of the waveforms of the amplitudes of the receive signals in the arrangement of FIG. 5;

(8) FIG. 7 shows the waveforms of FIG. 6 with noise superimposed;

(9) FIG. 8 shows a dependence of the standard deviation √Var (θ) of the estimated angle of incidence θ on the signal-to-noise ratio ρ;

(10) FIG. 9 shows a schematic illustration of another implementation of the inventive device;

(11) FIG. 10 shows a functional illustration of a ring coupler as an example of a feed network;

(12) FIG. 11 shows a schematic illustration of the waveforms of the amplitudes of the receive signals when using three antenna elements with three modes; and

(13) FIG. 12 shows an illustration of the dependence of a standard deviation of the angle of incidence θ established on noise for an antenna device with three antenna elements.

DETAILED DESCRIPTION OF THE INVENTION

(14) FIG. 1 shows an application of the inventive device 1 which, among other things, allows indicating whether and when a transmitter 2 passes a detection region 6.

(15) Here, the device 1 comprises an antenna device 3 having at least a distinguished directional characteristic. The directional characteristic relates to a spatial distribution of the sensitivity of the antenna device 3 for receiving signals which in this case particularly emanate from the transmitter 2.

(16) In the implementation illustrated, the antenna device 3 comprises several directional characteristics. In the exemplary implementation, there are three antenna elements 10 controlled by a control device 4 via the network 11. In one implementation, the antenna device 3 is a patch antenna. Alternatively, the antenna elements 10 are dipole antennas, monopole antennas, monopole-type antennas, chip antennas or loop antennas. One of the directional characteristics is the distinguished directional characteristic, mentioned already, which the definition region 6 is associated to.

(17) In an alternative implementation—not illustrated—the antenna device 3 comprises only a single directional characteristic which consequently also is the distinguished directional characteristic. The implementation illustrated, having several switchable directional characteristics, will be discussed below.

(18) The feed network 11 is provided for switching the different directional characteristics for sending out an excitation signal or receiving the signals emanating from the transmitter 2. The feed network 11 in this example represents a realization of a Butler matrix (in an alternative implementation, an eigenmode network is used) and makes available at its output the signals as have been received with the individual directional characteristics. Switching the directional characteristics consequently means that the signal having been received with the switched directional characteristic is fed to evaluation or evaluated particularly. In another implementation—not illustrated—switching the directional characteristics means that only the respective switched directional characteristic is present by directly acting on the antenna device 3, i.e. the antenna device 3 can only receive signals with the switched directional characteristic.

(19) Processing the signals received and the data resulting from it is done by the data processing device 5. In the example shown, the data processing device 5 is connected to a signal processing device 7 which establishes a respective amplitude value of the field strength for the signals received.

(20) When the transmitter 2 is an RFID tag, the signal processing device 7 is correspondingly configured such that it will generate as an amplitude value a so-called “received signal strength indication” (RSSI) value. In another accompanying implementation, the signal processing device 7 is also configured to extract information from the signals received—like an identification characteristic or measuring data. The signal processing device 7 may exemplarily be an RFID reader.

(21) In an implementation—not illustrated—the data processing device 5 itself establishes a value for the amplitude of the signals received. In particular in connection with this implementation, but also independently of this, in one implementation, the data processing device 5 is a component of the antenna device 3 and consequently accommodated therein.

(22) For applications in transmitters 2 based on RFID tags, in the embodiment shown, there is an additional signal source 8 generating excitation signals. The excitation signals are—depending on the case of application with specific directional characteristics or in a basically omnidirectional manner—output via the antenna device 3. Thus, the excitation signals may be so-called request signals using which a transmitter 2 in the form of an RFID tag is requested to set up data communication and via which the transmitter 2 obtains, if applicable, the energy used for communication. For sending out the excitation signals, in one implementation, directional characteristics are combined such that superpositioning results for sending out the signals. Conversely, the feed network 11—as has already been mentioned—allows separation into the individual directional characteristics for the signals received.

(23) In an alternative implementation—not illustrated—the signal source 8 is a component of the signal processing device 7. This corresponds to the, in known technology, conventional implementation of RFID readers which generate the activation signals themselves.

(24) By the antenna device 3 serving for receiving and transmitting signals, the result is that the directional characteristics do not relate only to the spatial distribution of sensitivity, but also to the transmitting characteristics of the antenna device 3.

(25) Finally, the data processing device 5 is connected to a data storage 9 for storing data on the trajectory of the transmitter 2. Using the historic data relating to the respective positions established of the transmitter 2, the path of movement of the transmitter 2 is established and, for example when there are several transmitters, ambiguities are eliminated and the signals associated to the transmitter. Corresponding plausibility considerations are provided for this.

(26) The selected directional characteristic here comprises a detection region 6 perpendicular to which the transmitter 2 moves in the example shown. Thus, the transmitter 2 here moves in parallel to the antenna elements 10 and perpendicular to the detection region 6. The peculiarity of the detection region 6 is that the sensitivity of the antenna device 3 in this spatial region is at a minimum. In the device 1, a signal minimum is used for determining whether the transmitter 2 passes the associated detection region 6. This means that, in the detection region 6, when the transmitter 2 is located there, no or only a very weak signal is received by the antenna device 3.

(27) The antenna device 3 here comprises a total of three detection regions 6, 6′ where a respective receive minimum is located and which the transmitter 2 passes one after the other. The reliability of detecting passing of the central detection region 6 can be increased by this.

(28) The reliability of the measurement is particularly increased by the control device 4 setting different directional characteristics which each comprise different sensitivities and spatial associations so that measuring imprecision or ambiguities can be compensated.

(29) In one implementation, the antenna device 3 comprises at least one further directional characteristic which exhibits a sensitivity maximum in the detection region 6. This means that the antenna device 3, with this other directional characteristic, is very sensitive to receiving signals. Thus, in this implementation, the signals of the distinguished directional characteristic and the comparative characteristic are evaluated together in order to increase the measuring precision.

(30) FIG. 2 shows the two antenna elements 10 (referred to by A and B) of an exemplary antenna device implemented as a multi-beam antenna. The two antenna elements 10 each comprise a beam-shaped directional characteristic 12. The two directional characteristics 12 are each described by a complex-value directional characteristic with {right arrow over (f)}.sub.j=1 (or A) or j=2 (or B).

(31) Generally, a multi-beam antenna consists of a set of n antenna elements 10 (or radiators, like dipoles) which are connected to a feed network (see FIG. 1). An antenna or antenna element is connected to each of the n outputs of the feed network.

(32) The m inputs of the feed network which serve for outputting the signals received from the antenna elements 10 or feeding the HF signals to be sent out via the antenna elements 10 in one implementation correspond to a certain directional characteristic {right arrow over (C)}.sub.i which is defined as follows:

(33) $\begin{array}{cc}{\stackrel{.fwdarw.}{C}}_i={\stackrel{.fwdarw.}{C}}_i\left(\stackrel{.fwdarw.}{\omega }\right)={\stackrel{.fwdarw.}{C}}_i\left(\varphi ,\theta \right)=\left(\begin{array}{c}{C}_i^{\left(\mathrm{co}\right)}\\ C_i^{\left(\mathrm{cross}\right)}\end{array}\right)\mathrm{with}i=1,\mathrm{.Math.}m& \left(1\right)\end{array}$

(34) Thus, a co-polarized component C.sub.i.sup.(co) and a cross-polarized component C.sub.i.sup.(cross) each are given here.

(35) FIG. 3 shows a coordinate system having three axes x, y and z and the reference point R at the origin of the coordinate system. The two antenna elements 10 (A and B) in the example illustrated are arranged along the x axis. A point of observation V is described by an azimuth angle ϕ in the x-y plane and a co-elevation angle θ relative to the z axis. The following area is to be considered here: dΩ=sin θ*dθ*dϕ.

(36) For associating a transmitter or, for example, particularly an RFID transponder to a certain direction, the directional characteristics {right arrow over (C)}.sub.i of the antenna device comprise specific features. The two-element antenna array of FIG. 2 is to be considered here.

(37) Relating to the point of reference R in accordance with FIG. 3 where the coordinate origin is placed for reasons of simplicity, both antenna elements 10 (i.e. A and B) each exhibit the (complex) radiation characteristic mentioned:

(38) $\begin{array}{cc}{\stackrel{.fwdarw.}{f}}_j=\left(\begin{array}{c}{f}_j^{\left(\mathrm{co}\right)}\\ f_j^{\left(\mathrm{cross}\right)}\end{array}\right)\mathrm{with}j=1,\mathrm{.Math.}n& \left(2\right)\end{array}$

(39) The so-called radiation matrix Ĥ (cf. [3]) can be established from this, the components of which are given by the following formula:

(40) $\begin{array}{cc}{\tilde{H}}_{\mathrm{pj}}=\frac{1}{4\pi }{\int }_{\Omega }{\stackrel{.fwdarw.}{f}}_p^H{\stackrel{.fwdarw.}{f}}_{j}d\Omega \mathrm{with}\left\{p,j\right\}=1,\mathrm{.Math.},n& \left(3\right)\end{array}$

(41) Since the radiation matrix Ĥ is a Hermite matrix, it can be diagonalized. What results is:
Ĥ={circumflex over (Q)}{circumflex over (∇)}{circumflex over (Q)}.sup.H with {circumflex over (∇)}=diag{λ.sub.1, . . . ,λ.sub.n}  (4)

(42) Equation (4) describes the eigenvalue decomposition of the radiation matrix Ĥ. Thus, each column in {circumflex over (Q)} represents one of the n eigenvectors {right arrow over (q)}.sub.j and each main diagonal element in {circumflex over (∇)} describes the respective eigenvalue λ.sub.j.

(43) The eigenvectors {right arrow over (q)}.sub.j describe the fundamental excitation vectors of the antenna device which in this case is an antenna array with the antenna elements. The eigenvectors {right arrow over (q)}.sub.j are orthogonal in pairs in case there are no eigenvalues λ.sub.j occurring several times. When eigenvalues λ.sub.j occur several times, an orthonormal basis has to be found for these, the basis vectors of which are mutually orthogonal.

(44) In addition, the eigenvectors {right arrow over (q)}.sub.j comprise a length of one. The eigenvectors are accompanied by certain directional characteristics:

(45) $\begin{array}{cc}{\stackrel{.fwdarw.}{C}}_j^{\left(m\right)}=\left(\begin{array}{c}{C}_j^{\left(m,\mathrm{co}\right))}\\ C_j^{\left(m,\mathrm{cross}\right)}\end{array}\right)& \left(5\right)\end{array}$

(46) which are mutually orthogonal.

(47) This means that the following applies:
({right arrow over (C)}.sub.p.sup.(m)).sup.H{right arrow over (C)}.sub.j.sup.(m)=0, if p≠j.  (6)

(48) The eigenvectors {circumflex over (Q)} represent a special orthonormal basis of the potential feed vectors. However, other orthonormal bases may also be established so that the feed network need not necessarily be an eigenmode network. At least one zero forms in one of the directional characteristics along a certain direction.

(49) For an array consisting of two equal antenna elements (see FIG. 2) with equal orientation, the following eigenvectors result:

(50) $\begin{array}{cc}\tilde{Q}=\frac{1}{\sqrt{2}}\left(\begin{array}{cc}1& 1\\ 1& -1\end{array}\right)& \left(7\right)\end{array}$

(51) The antenna elements 10 (like dipoles) are fed either in an even mode (1/√2 and 1/√2) or in an odd mode (1/√2 und −1/√2).

(52) As far as magnitude is concerned, the resulting directional characteristics are shown in FIG. 4 in a qualitative manner for the x-z plane. The directional characteristic 12 for an even mode is represented by continuous lines and that for the odd mode by broken lines. The directional characteristics illustrated particularly result from an eigenmode network.

(53) When feeding in an even mode, the result is a maximum perpendicular to the array which is formed from the two equal and equally oriented antenna elements. The maximum is located in the z direction or at a co-elevation angle of θ=0°.

(54) However, in an odd mode, a minimum or zero forms at this position. The zero or closest environment thereof is narrow compared to the environment of the maximum in an even mode, since the gradient relative to the co-elevation angle θ increases, as far as its magnitude is concerned, strongly in the environment of the zero.

(55) A radio signal impinging on the array of the antenna device from the direction of the zero, will consequently rarely be received, or not at all, in an odd mode, whereas, in an even mode, the receive signal is maximum. The direction of incidence may thus be deduced from the signal levels measured in the even and odd modes.

(56) FIG. 5 shows a scenario where an object with an RFID transponder as a transmitter 2 is transported at a constant speed (v) in parallel to the x axis. The antenna array formed from the two antenna elements 10 of the antenna device 3 is centered in the origin of the coordinate system and oriented such that the zero of the receive sensitivity in the odd mode occurs along the z axis θ=0°. This zero consequently is the detection region 6. In dependence on the position of the transponder 2 relative to the antenna device 3, the received signal of the individual modes will vary since the angle of incidence is a function of time.

(57) The position of the transponder in the x direction can be associated to a time t. The two positions of the transmitter 2 at the time t1 and, thus, before the detection region 6, and at the time t2, and, thus, after passing the detection region 6 are illustrated. The respective angle of incidence θ as the angle of the incident response signal (indicated by the arrows, starting from the transmitter 2) relative to the z axis thus varies over time t.

(58) FIG. 6 exemplarily illustrates the time signals of the arrangement of FIG. 5. What is shown is a waveform of the receive amplitude normalized to the maximum as a function of time t for the transmitter of FIG. 5 which moves in parallel to the x axis (z=z.sub.0) at a constant speed v. The two antenna elements are located on the x axis and are centered around the coordinate origin, i.e. are at equal distances to it.

(59) When the transponder as the transmitter is read out at different positions and, thus, at different times (this means that the transponder has been identified and its identification is known), an analysis of the time signal allows determining the time when the transponder is located in the direction θ=0° and, thus, at a certain position—i.e. the detection region—along the transport path.

(60) The receive signal in an odd mode (broken line) is minimal at this time of passing the detection region, whereas it is maximal in an even mode (continuous line). Thus, the transponder can be differentiated from a subsequent transponder which is also read out, at this time of passing the detection region, since the signal of the following transponder is received both in an even mode and in an odd mode. The transponder which consequently responds from the direction θ=0° and the signal of which can be received only in an even mode, will consequently be the selected transponder This result can be used to control and check the flow of the objects on, for example, a conveyor belt or when passing a gate.

(61) The time when the transponder is located along the plane with a co-elevation angle θ=0°, can alternatively also be read from the even mode. The signal sent out by the transmitter is received at this position at a maximum amplitude.

(62) For a practical realization, however, the insecurities caused by superimposed noise should be kept in mind. FIG. 7 illustrates the waveform of the receive signals of FIG. 6 in an even mode (continuous line) and an odd mode (broken line) with superimposed noise starting from a signal-to-noise ratio of ρ=20 dB.

(63) Due to the wide radiation beam in an even mode, the noise has stronger an effect on the signal maximum in the detection region so that, when searching for the maximum, greater an insecurity occurs. Due to the relatively narrow minimum in an odd mode, the same can also be found with lower insecurity in the case of superimposed noise.

(64) In order to illustrate this, FIG. 8 exemplarily shows the standard deviation established of the angle of incidence θ established for varying signal-to-noise ratios for the setup according to FIG. 5. With an increasing signal-to-noise ratio ρ (illustrated on the x axis in dB), the insecurity when searching for minimums in an odd mode (broken line) decreases quickly, whereas the search for a maximum in an even mode (continuous line) shows considerably higher insecurities with high signal-to-noise ratios ρ. Thus, the standard deviation √Var (θ) of the estimated angle of incidence θ in degrees (°) is plotted on the y axis. Thus, for this example, the transponder moves at a constant speed of 3 m/s. The standard deviation was established over 10 000 test values per signal-to-noise ratio value ρ. Here, z.sub.0=5 m.

(65) The realization of the principle of even mode and odd mode feeding is based on a feed network providing the feed vectors used. The directional characteristics {right arrow over (C)}.sub.i associated to the input ports in accordance with equation (1) thus correspond to the directional characteristics of the eigenmodes {right arrow over (C)}.sub.j.sup.(m), wherein the feed network is an eigenmode network, wherein, in this implementation, m=n. This means that one signal output for outputting the respective signals received is available per antenna element 10.

(66) A possible implementation of the inventive device 1 having two antenna elements 10 is shown in FIG. 9. The antenna array of the two antenna elements 10 (referred to by A and B) is connected to an eigenmode network as a feed network 11. The inputs (referred to by C and D) of the feed network 11 are selectable via a radio-frequency signals switch. The input of the switch is connected to the RFID reader which in this case serves as the signal processing device 7. Thus, the RFID reader also includes the signal source 8 so that the RFID reader provides the excitation signal for the transponders and evaluates the response signals thereof. Switching the inputs of the feed network 11 is done using control logic 13 which in this case is part of the antenna device 3. The inputs C and D of the feed networks 11 are inputs for the RF signal as an excitation signal of the signal processing device 7. In addition, they are the outputs for the signals received by the antenna elements 10. Thus, a directional characteristic, i.e. either even mode or odd mode, is associated to each input so that the switch allows changing between the two directional characteristics.

(67) Reading out the transponder and, consequently, receiving the signals is regulated via a control device 4, acting on the control logic 13. In the implementation shown, the transponder signals are read out alternatingly in an even mode and odd mode. With the RSSI values made available by the RFID reader 7 as values for the amplitude of the signals received, the associated time signals of even mode and odd mode can be established for each transponder. Starting there, the time when the respective transponder crosses the z axis θ=0° is established in the data processing device 5. In one implementation, the data processing device 5 particularly establishes the angle of incidence of the signals received.

(68) The data processing device 5 here also is a component of the antenna device 3. In another implementation—no illustrated here—the control device 4 is also part of the antenna device 3 so that the device 1 in this implementation consists of two elements: antenna device 3 and RFID reader 7.

(69) The separation into control logic 13, control device 4 and data processing device 5 here is to be understood to be relating to the functions thereof. Different implementations may be realized.

(70) One implementation of an eigenmode network as a feed network 11 is shown in FIG. 10 for the antenna array of FIG. 2 consisting of two antenna elements (antenna A and antenna B). In one implementation, this is a ring coupler (rat-race coupler) which, depending on the port fed (i.e. the respective input of the feed network in the direction of the RFID reader in accordance with FIG. 9, referred to here by C for odd mode input and D for even mode input), makes available an even mode signal or odd mode signal. Such a ring coupler is particularly used when realizing an eigenmode network.

(71) The principle of eigenmode feeding may be applied to arrays of any number of antenna elements:

(72) FIG. 11 exemplarily shows the signals of an antenna device comprising three antenna elements (cf. FIG. 1). The three antenna elements are located on the x-axis and are centered around the coordinate origin. Three modes can be seen. The time signals (time t on the x-axis, wherein t=0 is the point of passing the detection region, and with the receive amplitude normalized to the maximum of the y-axis) here are illustrated to be superimposed by noise. The signal-to-noise ratio is ρ=20 dB.

(73) In an even mode (continuous line), all three antenna elements are fed in phase. The corresponding directional characteristic thus exhibits a maximum along an angle θ=0°, which decreases on both sides.

(74) In an odd mode (broken line with longer sub-marks), the two outer elements are fed in opposite phases and at equal amplitude. The result is a minimum or zero which increases laterally to a maximum, which is smaller than the maximum of an even mode, and then decreases again, along the axis with an angle θ=0°.

(75) In the third mode (broken line with shorter sub-marks), respective neighboring elements are fed in opposite phases. The results are, symmetrically around the z-axis, two zeros in the radiation diagram with a small maximum around the region of an angle θ=0°. The two zeros increase laterally.

(76) The consideration here is limited to the upper half plane z≥0.

(77) Using the two additional zeros of the third mode, the point in time when a transponder passes the z-axis can be determined more precisely with superimposed noise when compared to the two-element array. For reasons of plausibility, the estimated time of the minimum in the odd mode signal has to occur between the times for the minimums in the signal of the third mode.

(78) In addition, in the three-element array, due to the grater aperture, the zeros in the odd mode are sharper than in the two-element array, wherein an equal distance between the antenna elements is entailed here.

(79) FIG. 12 shows the standard deviation √{square root over (Var{θ})} f the estimated angle of incidence θ as a function of the signal-to-noise ratio ρ having been established using the signals in the odd mode (continuous line) and using the signals in the odd mode and third mode (continuous thick line). The result for the odd mode of the two-element array is plotted for comparison (broken thin line, cf. FIG. 8).

(80) The transponder here moves in parallel to the x-axis (z=z.sub.0) with a constant speed v=3 m/s for the values established. The antenna elements are located on the x-axis and are centered around the coordinate origin. The standard deviation was established over 10,000 test values per ρ value. In addition, z.sub.0=5 m.

(81) The comparison of the variances between a two-element and a three-element array shows that the combination of odd mode and third mode exhibits smaller a standard deviation than the odd mode of the two-element array.

(82) With signal-to-noise ratios of less than 13 dB, the odd mode of the three-element array results in higher standard deviations than the odd mode of the two-element array. In the three-element array, with an increasing value for p, the standard deviation of the odd mode approximates the standard deviation which results from the combination of odd mode and third mode. This is due to the fact that the insecurity when estimating the angle of incidence and, thus, the scattering around the expected value decrease. The probability of the minimum in the time signal of the odd mode not to occur between the minimums of the third mode is decreasing.

(83) The invention is to be summarized below using one implementation: a transponder as a transmitter is detected based on the search for minimums in the time signal of at least one receive mode of a multi-beam antenna.

(84) When using an RFID reader which provides RSSI values for the signals received, the following advantages will result:

(85) When using a computing device which may be accommodated in the multi-beam antenna, a single HF path between the multi-beam antenna and the RFID reader is sufficient for detecting a transponder in a certain direction. This also allows using RFID readers comprising only one port as output and/or input. These are cheaper than RFID readers having several ports.

(86) Additionally, there is the advantage that no additional infrastructural components are used for switching or computing since, in this implementation, switching and determining the position are covered functionally by the multi-beam antenna itself.

(87) The number of antenna elements and, consequently, the number of eigenmodes may be selected as desired and is not dependent on the RFID reader. With an increasing number of elements, sharper zeros can be caused and plausibility checks performed. The insecurity caused by superimposed noise may thus be reduced.

(88) This, however, applies in analogy for other signal processing devices which provide a value for the signal strength of the signals received.

(89) In contrast to low-range antennas as are, for example, used in known technology for detecting RFID transponders, the following advantages result:

(90) The antenna device in the form of a multi-beam antenna can be positioned more flexibly since it is not limited to a low range. Thus, the multi-beam antenna can be used in different scenarios.

(91) Additionally, smaller a transmitting power of the RFID reader is sufficient.

(92) Technical fields of application are, for example, in the fields of logistics or production with flow control of importing or exporting goods or, for example, in the field of sorting luggage. In particular, flow control is also possible in transport means, like conveyer belts, transport vehicles. Further applications relate to automated access control, like person identity check in hospitals, or determining a speed as a throughput speed.

(93) Although some aspects have been described in the context of a device, it is clear that these aspects also represent a description of the corresponding method, such that a block or element of a device also corresponds to a respective method step or a feature of a method step. Analogously, aspects described in the context of or as a method step also represent a description of a corresponding block or item or feature of a corresponding device. Some or all of the method steps may be executed by (or using) a hardware apparatus, like, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some or several of the most important method steps may be executed by such an apparatus.

(94) Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software or at least partly in hardware or at least partly in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray disc, a CD, an ROM, a PROM, an EPROM, an EEPROM or a FLASH memory, a hard drive or another magnetic or optical memory having electronically readable control signals stored thereon, which cooperate or are capable of cooperating with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer-readable.

(95) Some embodiments according to the invention include a data carrier comprising electronically readable control signals, which are capable of cooperating with a programmable computer system such that one of the methods described herein is performed.

(96) Generally, embodiments of the present invention can be implemented as a computer program product with program code, the program code being operative for performing one of the methods when the computer program product runs on a computer.

(97) The program code may, for example, be stored on a machine-readable carrier.

(98) Other embodiments comprise the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine-readable carrier. In other words, an embodiment of the inventive method is, therefore, a computer program comprising program code for performing one of the methods described herein, when the computer program runs on a computer.

(99) A further embodiment of the inventive methods is, therefore, a data carrier (or a digital storage medium or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier or the digital storage medium or the computer-readable medium is typically tangible and/or non-volatile.

(100) A further embodiment of the inventive method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may, for example, be configured to be transferred via a data communication connection, for example via the Internet.

(101) A further embodiment comprises processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

(102) A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

(103) A further embodiment according to the invention comprises a device or a system configured to transfer a computer program for performing one of the methods described herein to a receiver. The transmission can be performed electronically or optically. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The device or system may, for example, comprise a file server for transferring the computer program to the receiver.

(104) In some embodiments, a programmable logic device (for example a field-programmable gate array, FPGA) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field-programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, in some embodiments, the methods are performed by any hardware apparatus. This can be a universally applicable hardware, such as a computer processor (CPU), or hardware specific for the method, such as ASIC, or a microprocessor, like in the form of an ARM architecture.

(105) While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which will be apparent to others skilled in the art and which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.

REFERENCES

(106) [1] UHF RFID Low Range-Antenne (LoRa), data sheet, Kathrein company. [2] UHF RFID Ultra Low Range-Antenne, data sheet, Kathrein company. [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, pp. 360-370, 2008.