Antenna for RFID Reader with Polarization Switching Device

Abstract

To improve an antenna capable of switching a polarization.SOLUTION: The present invention provides an antenna for an RFID reading device (12), that is an antenna comprising: an antenna element (22) having four power supply points (P1 to P4); and a power supply network selectively connecting an input signal (20) to the power supply points (P1 to P4) so that the antenna is driven in a circular polarization or a straight polarization. The power supply network comprises circuit devices (24 and 28) that can set a plurality of different switch states. In a various switch state, the power supply network supplies various phases and / or a power allocation of the input signal (20) in each switch state to the power supply point (P1 to P4). Also, in each of the circuit devices (24 and 28), the switch state that is corresponded to at least three kinds of four polarizations of a horizontal polarization, a vertical polarization, a right-handed circular polarization, and a left-hane circular polarization, can be set.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an antenna for an RFID reader and a method for switching the polarization of the antenna, which are respectively described in the preambles of claims 1 and 15.

Background Art

[0002] RFID readers are useful for identifying objects and goods, and are particularly used for the automation of logistics. At the identification location, especially when there is a change in the owner of the goods or the means of transportation, the RFID transponder fixed to the goods is read, and in some cases, information is written to the transponder conversely. The obtained information is used to control the transfer and sorting of commodities and products. Important applications for automatic identification include logistics distribution centers such as parcel carriers, or baggage check-in at airports.

[0003] An RFID reader excites an RFID transponder in the reading area by radiating electromagnetic waves through its antenna, causes the information stored therein to be radiated, and receives and evaluates the corresponding transponder signal. For this purpose, the UHF frequency band (ultra-high frequency) is often used. This is because there is a framework defined by the ISO18000-6 standard in this band, and in addition, transponders can be read at various distances from several millimeters to several meters. UHF-RFID transponders can be used in a very compact structural form and can therefore be attached to very small objects.

[0004] In many applications, the orientation of the RFID transponder relative to the RIFD reader is not fixed or at least not known. In that case, using a circularly polarized antenna to compensate for fluctuations in the orientation of the RFID transponder is advantageous for range and reading speed. However, since most RFID transponders use linearly polarized antennas, at best only half of the received energy is captured. Therefore, in applications where the orientation of the RFID transponder relative to the RIFD reader is fixed, a linearly polarized antenna with the appropriate orientation should be preferred. This is because then the RFID transponder can clearly capture significantly more energy, thereby increasing the identification range accordingly. Therefore, depending on the application scenario, the use of RFID readers with various polarizations can be considered.

[0005] Patent Document 1 discloses an RFID antenna device for transmitting and receiving electromagnetic waves of various polarizations. This antenna has two feeding points in its basic form. By itself, this already increases the cost of the circuit, especially the cost for driving the mixer used, and there are relatively large losses in the feeding network. Most importantly, only by using four feeding points can good antenna characteristics (especially regarding the axial ratio) finally be obtained, which brings robustness against interference, for example, by metallic objects near the antenna. Circuit modifications corresponding to the four feeding points are also introduced in Patent Document 1. However, this is based on the duplication of the feeding network for two-point feeding, thereby rather worsening the aforementioned drawbacks.

[0006] Patent Document 2 describes a method for changing the antenna polarization. For this purpose, a plurality of antennas are selectively used, which significantly increases the structural cost and the required assembly space.

[0007] Patent Document 3 discloses a patch antenna that can switch between vertical polarization and linear polarization. In this case, circular polarization cannot be used.

[0008] From Patent Document 4, an antenna switching device having an array of input wirings capable of selecting a signal path by switching the connection to the ground is known. According to this, signals of linear polarization or circular polarization appear at two output connection parts. In this way, circular polarization in both the left and right rotation directions cannot be generated.

[0009] The antenna device described in Patent Document 5 can switch between a plurality of different polarizations, but for this purpose, an antenna of horizontal polarization and an antenna of vertical polarization are used. In addition, its power supply network cannot be used for four power supply points.

[0010] Patent Document 6 discloses another antenna device for selectively generating linear polarization and circular polarization. The power supply network used can indeed drive four power supply points, but it cannot compensate for the mismatches that appear in the patch antenna.

[0011] The antenna network described in Patent Document 7 can drive the antenna to be circularly polarized or elliptically polarized so that the antenna is polarized in left rotation and right rotation alternately. However, linear polarization is impossible with this.

[0012] Patent Document 8 describes an RFID multiplexer that distributes RFID signals to various antennas. This cannot generate various polarizations within one antenna.

[0013] Patent Document 9 presents a wiring structure for RFID signals composed of linear wiring parts on the ridges of a hexagonal raster. This document is not related to a polarization switching device.

[0014] Unpublished European Patent Application No. 22188151.9 discloses a manufacturing method of a modular antenna for an RFID device. This document mentions a polarization control logic circuit, but it is not described in detail.

Prior Art Documents

Patent Documents

[0015] [Patent Document 1] DE 20 2015 106 025 U1 [Patent Document 2] US 7 932 867 B2 [Patent Document 3] US 7 068 224 B2 [Patent Document 4] US 2011 / 0032079 A1 [Patent Document 5] EP 3 220 554 A1 [Patent Document 6] KR 10 0976087 B1 [Patent Document 7] EP 2 368 210 B1 [Patent Document 8] EP 1 987 468 B1 [Patent Document 9] DE 20 2015 105 455 U1 [Summary of the Invention] [Problems to be Solved by the Invention]

[0016] Therefore, the problem of the present invention is to further improve an antenna capable of switching polarization. [Means for Solving the Problems]

[0017] This problem is solved by the antenna for an RFID reader device and the method for switching the polarization of the antenna described in claims 1 and 15, respectively. This antenna includes antenna elements used for radiating or receiving signals. Four feeding points are provided in the antenna elements. A feeding network connects an input signal to the feeding points so that a circularly polarized or linearly polarized antenna appears selectively. At this time, according to the polarization state, all the feeding points are fed or only a part of them is selected and fed.

[0018] The basic idea that is the starting point of the present invention is to set a plurality of different switch states using circuit devices in a power supply network. Each switch state corresponds to one type of polarization. For RFID readers, a total of four types of polarization, namely, horizontal polarization, vertical polarization, right-handed circular polarization, and left-handed circular polarization, are of interest. The power supply network can set switch states for at least three of these four types of polarization. In each switch state, a certain phase derived from the input signal and the output signal are respectively supplied to each power supply point, and a selected polarization is generated as a whole from the signal. For some polarizations and power supply points, it may mean that no signal is applied. That is, the power supply network can output different output levels with different phase angles to different output parts, and the output and phase generate the corresponding polarization at the antenna element through the power supply point according to the switch state.

[0019] The present invention has the advantage that the antenna can be driven with the most suitable polarization each time according to the usage situation and the transponder to be read. The power supply network according to the present invention can couple an input signal to four power supply points with very little loss. On the other hand, the less the loss for signal distribution and transfer, the higher the antenna gain. Moreover, in the case of an RFID antenna, it has a double effect. This is because the same antenna is used for both transmission and reception operations. As a result, the reading speed and range are increased as a whole.

[0020] The power supply points are preferably arranged symmetrically, particularly in a square shape. In this way, the antenna characteristics and polarization characteristics are very good, and the structure becomes clear and simple.

[0021] The circuit device preferably includes a first switch element, a second switch element, and a number of connection wirings, particularly four connection wirings, therebetween. With a two-stage switch structure, sufficient flexibility for generating various polarizations is obtained while suppressing complexity.

[0022] It is preferable that a 90-degree hybrid coupler is provided, particularly on two of the connection wirings, on the connection wiring between the first switch element and the second switch element. According to this, the 90-degree hybrid coupler can be selectively included in power supply according to the switch state. Specifically, a phase of 90 degrees is used for circularly polarized waves. In the case of linearly polarized waves, the connection wiring having a 90-degree hybrid conductor can be bypassed according to the corresponding switch state. Thereby, the matching of the antenna becomes better.

[0023] The first switch element preferably includes at least one connection portion for an input signal on the input side and four connection portions to the antenna element on the output side. In this way, the first switch element can be prepared to switch the input signal to one of the four outputs, and preferably the four outputs are connected to the four connection wirings. In one embodiment, it has a 1:4 allocation. Particularly preferably, the first switch element includes another connection portion connected to the antenna termination on the input side. This is an embodiment of a 2:4 allocation. By including the antenna termination, the matching of the antenna is clearly improved.

[0024] The first switch element is preferably configured as a four-way switch, particularly as a DP4T (Double Pole Quadruple Throw), or as a combination of double-throw switches, particularly as one in which two SPDT (Single Pole Double Throw) are connected after one DPDT (Double Pole Double Throw). These are specific and simple switch components suitable for a 2:4 allocation. It is preferable that the input signal and the antenna termination are connected to the input side, and the four connection wirings leading to the second switch element are connected to the output side.

[0025] The first switching element has one connection part for the input signal on the input side and three connection parts to the antenna element on the output side, and it is preferable that the 90-degree hybrid coupler is fixedly connected to one antenna terminal. This corresponds to a 1:3 allocation, enabling selection of only three types of polarization, namely two types of linear polarization and one type of circular polarization, and is suitable for embodiments where the rotation direction of the circular polarization is determined by the power supply network. Here, since the antenna terminal is fixedly assigned to the switching state in which the 90-degree hybrid coupler is incorporated, two connection parts are not necessary on the input side. The rotation direction of the circular polarization is selected circuit-technically depending on whether the 90-degree hybrid coupler is connected to the first switching element or the antenna terminal on either side, and reversing it will reverse the rotation direction. A specific and exemplary switching component for this embodiment is SP3T (Single Pole Triple Throw).

[0026] It is preferable that the first switching element has an additional connection part for another antenna element on the output side. For that, an allocation of 1:n with n > 4 is required. For example, if another antenna capable of selecting four types of polarization is connected, n = 8. This can be achieved, for example, by a combination of a 2:2 type switch (DPDT) in the previous stage and two 4-way switches (SP4T).

[0027] It is preferable that the second switching element includes two double-throw switches, each of which can selectively connect one of two connection wirings to the antenna element. The two double-throw switches, particularly SPDT, are paired on the input side and connected to the four connection wirings from the first switching element. As a result, a pair of connection wirings is connected to one power supply point-direction output wiring of the double-throw switch with a 2:1 allocation each. In that case, it is preferable that each pair is composed of the direct connection wiring of the first switching element and the connection wiring passed through via the 90-degree hybrid coupler. It should be noted that in the above-described embodiment where the first switching element has a 1:3 allocation, there is also a fourth connection wiring, that is, the connection wiring of the antenna terminal on the 90-degree hybrid coupler.

[0028] The power supply network includes two 180-degree power distributors, one of the 180-degree power distributors is connected to two power supply points, and the other 180-degree power distributor is connected to the remaining two power supply points. It is preferable that each of the two connected power supply points supplies a partial signal of the input signal with a 180-degree phase difference. The 180-degree power distributor divides the incoming signal and supplies partial signals with a 180-degree phase difference to the respectively assigned power supply points. Preferably, two pairs of power supply points form a diagonal line within the arrangement of the power supply points. Preferably, each 180-degree power distributor is connected to one of the double-throw switches of the second switching element respectively.

[0029] The 180-degree power distributor is preferably configured as a hybrid ring coupler (rat-race hybrid). This is a well-known suitable circuit element for generating two partial signals with a 180-degree phase difference from one signal. As an alternative, the 180-degree power distributor is configured as a Wilkinson distributor or a T-shaped power distributor. In that case, the 180-degree phase difference is generated, in particular, by using a delay line for one of the partial signals in the connection between the Wilkinson distributor or the T-shaped power distributor and the power supply point.

[0030] The power supply network is preferably configured without intersections. This is possible by utilizing a clever geometric arrangement, in particular a circuit structure based on the hexagonal honeycomb described in Patent Document 9 cited at the beginning. On the other hand, a power supply network without intersections can be manufactured in a single layer, so there is no need to change the circuit board layer or the board layer. This results in a very inexpensive and easy-to-handle component.

[0031] Preferably, the antenna includes a circuit board with antenna elements arranged on one side and a power supply network on the other side. This results in a very compact structural form. This is particularly advantageous when combined with the non-crossing power supply network described in the previous paragraph. In this way, a simple single circuit board is sufficient, and a complex multilayer structure is not necessary. Also, the antenna element is preferably configured as an antenna patch. This is because such a patch can also be flatly attached in a single layer. A very compact patch antenna with good antenna characteristics and the ability to select from up to four types of polarization can be obtained.

[0032] In a preferred development, the RFID reader includes the antenna according to the present invention, a transceiver connected to the antenna, and an RFID control and evaluation unit connected to the transceiver. In this case, the antenna can be driven as an internal or external antenna of the RFID reader. The antenna is used by the RFID reader to transmit RFID signals to and / or receive RFID signals from an RFID transponder. Here, any combination of a transmitter and a receiver is called a transceiver. The RFID control and evaluation unit includes at least one digital computing module such as a microprocessor, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit), and is configured to encode RFID information into RFID signals and / or read RFID information from RFID signals. The transceiver and the RFID control and evaluation unit can be a common computing module or at least partially share one computing module. Such an RFID reader is preferably fixedly attached near the reading area of a belt conveyor or a reading portal and is used to read at least one RFID transponder moving on the belt conveyor or passing through the reading portal. An appropriate polarization can be set according to the usage situation and can also be dynamically changed during its operation.

[0033] The method according to the present invention can be finished in a similar way, thereby showing similar advantages. Such advantageous features are exemplary described in the dependent claims following the independent claims of this application, but are not limited thereto.

[0034] Hereinafter, the present invention will be described in detail based on embodiments while also considering further features and advantages, with reference to the accompanying drawings by way of example. What is shown in each figure of the drawings is as follows.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0036] FIG. 1 shows a schematic diagram of an antenna 10 within an RFID reader 12. The antenna 10 is designed, for example, for the ISM band around approximately 900 MHz. A transceiver 14 of the RFID reader 12 is connected to the antenna 10, and further, a control and evaluation unit 16 for evaluating RFID signals received by the antenna 10 and sending information to a transponder as an RFID signal is connected thereto. The control and evaluation unit 16 is further connected to a wired or wireless interface 18 for performing data exchange, parameter setting, etc.

[0037] For example, the way the functions of an RFID reader in the UHF frequency range (extremely high frequency) compliant with ISO 18000-6 work is already known, and thus a detailed description will not be given. The present invention relates to the antenna 10 or its power supply network, which will be described in detail with continued reference to FIGS. 2 to 10. Instead of the illustrated internal antenna 10, an external antenna is also conceivable, in which case the transceiver 14 and the control and evaluation unit 16 are separated from the antenna 10 and housed in at least one separate casing connected through a cable.

[0038] FIG. 2 shows a schematic diagram of a power supply network for the antenna 10. The power supply network has a function of distributing an input signal 20 and coupling it to antenna elements 22 at four power supply points P1 to P4 at an appropriate power level and phase so that an antenna 10 with a desired polarization can be obtained as a whole. The antenna elements 22 are preferably antenna patches, and as a result, a patch antenna is obtained. In the illustrated power supply network, four types of polarizations, namely, horizontal polarization, vertical polarization, right-handed circular polarization, and left-handed circular polarization, are possible depending on the switch state. In the embodiment of the power supply network introduced later with reference to FIG. 10, there is only one type of circular polarization, and thus three types of polarizations are possible.

[0039] The power supply network includes a first switching element 24. In the illustrated example, it is a four-way switch (DP4T, Double Pole Quadruple Throw) having two input-side connection portions, and using this, the input signal 20 is distributed to four connection portions. An antenna terminal 26 is provided at the second input-side connection portion. A second switching element 28 is arranged downstream of the first switching element 24. This includes, for example, two single-pole double-throw switches (SPDT, Single Pole Double Throw). Four connection wirings from the four output-side connection portions of the first switching element 24 to the second switching element 28 are paired and connected to the input-side connection portions of the single-pole double-throw switches. A 90-degree hybrid coupler 30 is connected to one of each pair of connection wirings (branch-line hybrid, 90-degree 3dB divider). Two 180-degree power dividers 32 are connected to the output side of the second switching element 28, and in this embodiment, are connected as ring couplers (rat-race hybrids, 180-degree 3dB dividers), and each of them also has its own terminator 34. As a result, each of the two partial signals from the two single-pole double-throw switches of the second switching element 28 is redistributed, and the resulting partial signals are sent to the power supply points P1, P3 or P2, P4 with a 180-degree phase difference.

[0040] Figure 3 shows another view of the power supply network shown in Figure 2. The symmetry axis 36 is drawn in the region of the antenna element 22, and with respect to this, the power supply points P1 to P4 are also symmetrically arranged, preferably in a centered square shape. When the power supply points are arranged symmetrically, a 90-degree phase difference is required for circular polarization, and a 180-degree phase difference is required for linear polarization, and this power supply network provides that. Although an asymmetric arrangement different from that is possible, doing so requires correspondingly aligning the phases, or each desired polarization can only be obtained approximately.

[0041] Figure 4 shows a table of each polarization wave and the switch positions of the power supply network corresponding thereto. A plurality of different polarization waves are entered in the first column. The variants "Open1" and "Open2" are special cases not required for the original drive of antenna 10. Clearly switching the input signal 20 to a wiring end that is open or shorted to ground can be used for reference measurements or calibrations to examine the characteristics of the section between the RFID front end including transceiver 14 and the power supply network. This is done, for example, to measure the wiring attenuation when the antenna is removed using a relatively long cable.

[0042] The second column shows how the input side connections P1, P2 of the first switch element 24 are connected to the output side connections P3 - P6 of the same element for each polarization state in the first column. The third and fourth columns correspondingly show the switch states of the two single-pole double-throw switches 28a - b of the second switch element 28. Note that the symbol Px is used multiply for the connections of a plurality of different switch elements and is also used for the power supply points. However, it should be noted that what the symbol refers to is clearly defined uniquely from each context. The last four columns describe the signals arriving at the power supply points P1 - P4. The power supply points in the table are as already shown as out1 - out4 in FIG. 3. Also, Pin means the respective input power.

[0043] As a reading example, for the first circular polarization wave described in the first row of the table, the first switch element 24 creates a connection with each inner connection wiring with a 90-degree hybrid coupler via points P4 and P5, while the second switch element 28 conducts each of these inner connection wirings to the 180-degree power divider 32 via point P3 of the first single-pole double-throw switch 28a and point P2 of the second single-pole double-throw switch 28b. Therefore, the two partial signals output from the second switch element 28 are 90 degrees out of phase with each other, whereby the 180-degree power divider generates a partial signal of 0 degrees at the power supply point P1, a partial signal of 90 degrees at P2, a partial signal of 180 degrees at P3, and a partial signal of 270 degrees at P4.

[0044] Antenna 10 can generate a circularly polarized wave with a small axial ratio using its four feeding points. Thereby, antenna 10 becomes more robust against external interference, particularly against metallic objects or reflectors near antenna 10. To generate a linearly polarized wave, the partial signals may be respectively coupled to two feeding points with a 180-degree phase difference. The attenuation is slight in either case of polarization. In the case of linearly polarized waves, since the 90-degree hybrid coupler 30 is bypassed, the attenuation can even be further suppressed compared to the case of circularly polarized waves.

[0045] FIG. 5 shows a board or circuit board 38 on which the power supply network schematically shown in FIG. 3 is exemplary and specifically laid out. The antenna element 22 on the back side of the circuit board 38 is shown only in outline. The structure of the 90-degree hybrid coupler 30 and the structure of the two 180-degree power dividers 32 both utilize the wiring structure on the hexagonal raster described in Patent Document 9 cited at the beginning. They are connected by connection lines implemented as impedance-matched microstrip wiring 40. On the output side of the two 180-degree power dividers 32, connection wiring 42 leads from feeding points P1 to P4, and the symmetric arrangement of these points schematically drawn in the corresponding FIG. 3 can be better recognized.

[0046] The feature of the illustrated power supply network lies in that it can be implemented within a single copper layer. The power supply network can be completed without wiring intersections, and thus without changing the board layer or the components required for wiring intersections. Anyway, special attention regarding attenuation and phase difference is required for impedance matching in proper intersections (vias). Therefore, by making the power supply network a single-layer layout as shown in Figure 5, the complexity is reduced, and very good antenna characteristics and polarization characteristics can be achieved while reducing costs. If the power supply network is provided on one side or surface (back side) of the circuit board 38 (especially in a single layer), and the antenna element 22 is provided on the other side or surface (front side) (especially in the form of an antenna patch), the structural form of the antenna 10 becomes very compact. With such a well-integratable structure, modular modifications for various housings as described in the unpublished European patent application No. 22188151.9 cited at the beginning can also be easily carried out.

[0047] Figure 6 shows a schematic diagram of another embodiment of the power supply network. Different from the embodiments described so far, here the first switch element is configured as a combination of one double-pole double-throw switch 24a (DPDT, Double Pole Double Throw) and two single-pole double-throw switches 24b (SPDT, Single Port Double Throw) arranged one after another. Thus, it can be replaced to simulate a four-way switch (DP4T, Double Port Quadruple Throw).

[0048] FIG. 7 shows a schematic diagram of another embodiment of the power supply network. Different from the embodiments described so far, here an additional connection portion 44 for using another antenna (not shown) with a plurality of different switchable polarization waves is provided in the first switch element. For this purpose, here as an example, two four-way switches (SP4T) are arranged after a double-pole double-throw switch (DPDT). Therefore, there are a total of eight connection portions on the output side of the first switch element. Among them, four connection portions are used to generate four types of polarization waves of the antenna 10 as before, and the other four connection portions can be used respectively as additional connection portions for another antenna.

[0049] FIG. 8 shows a schematic diagram of another embodiment of the power supply network. Different from the previous embodiments, here the 180-degree power divider 32 is no longer a hybrid ring coupler but is configured as a Wilkinson divider 32a. The 180-degree phase difference is achieved using a delay line with an appropriate delay. Instead, in order to be able to distribute power over a wider frequency range of the power supply network in the case of an appropriate phase difference, it may also be considered to use a Schiffman phase shifter. According to this, a 3 dB 180-degree power distribution is similarly possible based on the Wilkinson divider 32a. The advantage over the ring coupler is that if the dimensions are correctly determined, the transmission loss will be less. On the other hand, the isolation between the output ports will become weaker, but that is not very important for the structure of the antenna 10. This is because each signal is coupled to the same antenna element 22, and there, especially when designed as an antenna patch, there is a somewhat stronger coupling between any two adjacent feeding points anyway.

[0050] FIG. 9 also shows an alternative to FIG. 8, where now the Wilkinson divider 32a is replaced by a T-shaped power divider 32b. For the rest, please refer to the description of FIG. 8. The selection of suitable 180-degree power dividers 32, 32a, 32b is possible in any embodiment and is not limited to the special drawings of FIGS. 8 and 9.

[0051] FIG. 10 shows a schematic diagram of another embodiment. In this embodiment, the power supply network supports only one circular polarization rather than circular polarizations in both left and right rotation directions. Here, a three-way switch (SP3T, Single Pole Triple Throw) is used as the first switch element 24. There is only one connection that can be switched to the 90-degree hybrid coupler 30, and the other connection of the coupler is fixedly connected to the antenna matcher 48. The rotation direction of the circular polarization can be selected only by circuit design here. Therefore, the power supply network shown in FIG. 10 can be selected only among three types of polarizations, but instead has the advantage of reduced loss because the number of switches is smaller and the design of the switch components is simpler.

Claims

1. An antenna (10) for an RFID reader (12), comprising an antenna element (22) having four feed points (P1-P4) and a feed network configured to selectively couple an input signal (20) to said feed points (P1-P4) such that the antenna (10) is driven with circular or linear polarization, the power supply network comprises a circuit arrangement (24, 28) capable of setting a number of different switch states, which in each switch state supplies different phases and / or power portions of the input signal (20) to the power supply points (P1 to P4); in the circuit arrangement (24, 28), switch states corresponding to at least three of the four types of polarization, namely horizontal polarization, vertical polarization, right-handed circular polarization and left-handed circular polarization, are configurable; and the power supply network is configured without crossings. An antenna (10) comprising:

2. The antenna (10) according to claim 1, wherein the feed points (P1-P4) are arranged symmetrically, in particular in a square shape.

3. 2. The antenna (10) according to claim 1, wherein the circuit arrangement (24, 28) comprises a first switch element (24) and a second switch element (28) and a number of connecting wires therebetween, in particular four connecting wires.

4. 4. The antenna (10) according to claim 3, wherein a 90-degree hybrid coupler (30) is provided in the connection wiring between the first switch element (24) and the second switch element (28), in particular in two of the connection wirings.

5. 4. The antenna (10) according to claim 3, wherein the first switch element (24) has at least one connection for the input signal (20) on the input side and four connections to the antenna element (22) on the output side, in particular the first switch element (24) has another connection on the input side connected to an antenna termination (26).

6. 6. The antenna (10) according to claim 5, wherein the first switch element (24) is configured as a four-way switch, in particular a DP4T, or as a combination of double-throw switches (24a-b), in particular one DPDT followed by two SPDTs.

7. 4. The antenna (10) according to claim 3, wherein the first switch element (24), in particular configured as an SP3T, has one connection for the input signal on the input side and three connections to the antenna element (22) on the output side, and the 90° hybrid coupler (30) is fixedly connected to one antenna termination (48).

8. 4. The antenna (10) of claim 3, wherein the first switch element (24) is provided with an additional connection (44) at the output side for a further antenna element.

9. 4. The antenna (10) according to claim 3, wherein the second switch element (28) comprises two double-throw switches, each of which is capable of selectively connecting in particular one of the two connecting wires to the antenna element (22).

10. 3. The antenna (10) according to claim 2, wherein the power supply network comprises two 180 degree power splitters (32), one of which is connected to two power supply points (P1, P3) and the other 180 degree power splitter is connected to the remaining two power supply points (P2, P4), such that each of the two connected power supply points (P1, P3; P2, P4) supplies partial signals of the input signal (20) with a phase difference of 180 degrees, in particular each 180 degree power splitter (32) being connected to one double-throw switch of the second switch element (28).

11. the 180 degree power splitter (32) is configured as a hybrid ring coupler (rat race hybrid); or The 180-degree power divider (32) is configured as a Wilkinson divider or a T-type power divider, and includes delay wiring (46) for generating a phase difference of 180 degrees between the connection between the Wilkinson divider or the T-type power divider and the power supply points (P1 to P4), The antenna (10) according to claim 10.

12. 2. The antenna (10) according to claim 1, comprising a circuit board (38) on one side of which the antenna element (22) is arranged and on the other side of which the feeding network is arranged, in particular the antenna element (22) being configured as an antenna patch.

13. An RFID reading device (12) comprising an antenna (10) according to any one of claims 1 to 12, the RFID reading device (12) comprising a transceiver (14) connected to the antenna (10) and an RFID control and evaluation unit (16) connected to the transceiver (14).

14. 1. A method for switching polarization of an antenna (10) for an RFID reader (12), the antenna (10) comprising an antenna element (22) having four power feed points (P1-P4), the method comprising using a power feed network of the antenna (10) to selectively couple an input signal (20) to the power feed points (P1-P4) in a number of different ways so that the antenna (10) is driven with either circular or linear polarization, the method comprising: A circuit device (24, 28) of the power supply network, which can set switch states corresponding to at least three of four types of polarization, i.e., horizontal polarization, vertical polarization, right-handed circular polarization, and left-handed circular polarization, is switched to a switch state corresponding to a selected polarization, thereby supplying a phase and / or power allocation of the input signal (20) corresponding to the selected polarization to the power supply points (P1 to P4), and the power supply network is configured without crossings. The method comprising:

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