Antenna unit for detecting a radio frequency identification tag, an evaluation unit, a reading device and a method

Abstract

The invention relates to an antenna unit (10) for detecting a radio frequency identification tag (12) by means of a radio wave signal, wherein the antenna unit (10) can be connected to an evaluation unit (18) for transmitting the radio wave signal by means of a single connecting line (16), wherein the antenna unit (10) has an electrical input circuit (20) with a predefined ohmic identification resistor (RID), wherein the antenna unit (10) is selected from a predefined group of different antenna units with different antenna types, each antenna type being assigned an identification resistor (RID) with a different resistance value. The invention further relates to an evaluation unit (18), a readout device (50), and a method for operating an evaluation unit (18) with an antenna unit (10).

Description

The invention relates to an antenna unit according to the preamble of independent claim 1.The invention also relates to an evaluation unit for an antenna unit, to a reading device having at least one antenna unit and at least one evaluation unit, and to a method for operating an antenna unit having an evaluation unit.An antenna unit of the generic type can be used in the field of the Internet of Things applications in order to read out status information of an object. In particular, a radio tag is attached to the object, preferably an RFID transponder or ID tag, which can be read out and / or written to in contactless fashion by the antenna unit by means of a radio wave signal. The antenna unit is designed to generate a read-out signal and / or preferably to receive a response signal transmitted by the radio tag.Such an antenna unit can preferably be used in goods logistics, wherein the radio tags can be attached to goods or goods to be detected and pass through a type of detection gate in order to monitor a goods entrance and a goods exit. The detection gate is preferably formed by a plurality of antenna units which communicate with the radio tags by means of an emitted radio wave field. Furthermore, use of the antenna unit is also conceivable in the production of goods or in general conveying technology. For example, the antenna unit for selecting pharmaceutical products may be used to track a product over a manufacturing cycle.For different applications, antenna units with different antenna types can be used, wherein these antenna types differ, for example, in a radiation range with different transmission powers. For product monitoring of relatively small pharmaceutical products, a short range antenna type may be preferred. For goods logistics, in which different sizes of goods are to be detected, however, an antenna type with a longer range may be preferred.For operation of the antenna unit, an evaluation unit can be used, which in particular enables a data exchange between the antenna unit and a control unit. In this case, it can be provided that the evaluation unit is only provided or designed for antenna units having a specific antenna type. For example, a function of the evaluation unit is dependent on a transmission power and / or a transmission frequency of the antenna unit and / or a permissible port power of the control unit. Furthermore, the evaluation unit and / or the antenna unit can be designed differently in different countries in order to meet different legal approval requirements. In particular, the permissible transmission power of the antenna unit can vary depending on the country. For example, it may happen that an antenna type provided for the EU cannot or may not be used in the USA.In the prior art, it has proven to be disadvantageous that an operator can combine antenna units and evaluation units in an uncontrolled manner, which are not matched to one another. In particular, such a miscombination can lead to legal requirements being ignored and / or malfunctions in the detection of the radio tags being able to occur and / or electronic components being damaged.Furthermore, it has proven disadvantageous in the prior art that known evaluation units do not recognize whether an antenna unit is connected at all and / or whether the antenna unit performs its intended function. It may thus occur that a detection gate described above is not operated with the required number of antenna units, in particular due to missing or non-functional antenna units, wherein unreliable detection of a flow of goods may occur.It is the object of the invention to propose an antenna unit which, while avoiding the problems known from the prior art, enables reliable and legally permitted communication with radio tags.The object further consists in specifying an evaluation unit for an antenna unit, a reading device having at least one evaluation unit and at least one antenna unit, and a method for operating an antenna unit having an evaluation unit.The object is achieved with respect to the antenna unit having the features of independent claim 1, with respect to the evaluation unit having the features of claim 4, with respect to the reading device having the features of claim 8 and with respect to the method having the features of claim 9.Advantageous embodiments of the invention are specified in the dependent claims.According to the invention, an antenna unit for detecting a radio tag by means of a radio wave signal is claimed. In this case, the antenna unit can be connected by means of a single connecting line to an evaluation unit for transmitting the radio wave signal, wherein the antenna unit has an electrical input circuit having a predefined ohmic identification resistor, wherein the antenna unit is selected from a predefined group of different antenna types, wherein each antenna type is assigned an identification resistor having a different resistance value, wherein the identification resistor is connected to a ground connection and can be connected by means of the connecting line to a detection circuit of the evaluation unit in such a way that the identification resistor forms a loaded voltage divider with a DC voltage source and a voltage measuring element of the detection circuit in order to output the antenna type to the evaluation unit by means of a DC voltage signal.In other words, a DC voltage value at the voltage measuring element, which is dependent on the resistance value of the identification resistor and is characteristic of the antenna type of the antenna unit used, can be determined by the antenna unit. The measured DC voltage signal or a resistance value calculated therefrom is characteristic of a specific antenna type, wherein the predefining of the resistance value enables the determination of the antenna type of the antenna unit. In particular, the influencing of the DC voltage signal by the antenna unit according to the invention can transmit information about the antenna type used.The invention has thereby recognized that by using an ohmic identification resistor with a predetermined resistance value, the antenna unit can output a unique antenna type. This can prevent an operator from accidentally using an antenna unit with an incompatible evaluation unit and / or control unit. As a result, incorrect measurements and a violation against legal requirements can again be prevented. Furthermore, the antenna unit according to the invention ensures that the antenna type is automated and identifiable without user input. Furthermore advantageously, the antenna type of the antenna unit can be evaluated by means of a DC voltage as detection signal, wherein the detection signal is not influenced independently of the radio wave signal and a function of the antenna unit for detecting the radio tags is thus advantageously not influenced. Furthermore, it has proven to be particularly advantageous in this context that the ohmic identification resistor can be integrated particularly easily and cost-effectively into an input circuit of the antenna unit. In this case, the antenna type can advantageously be determined by means of the DC voltage signal using particularly simple electronic components. In addition, the antenna type of the antenna unit can advantageously be evaluated without additional connecting lines in the sense of a so-called "one-wire" principle, wherein, in addition to the transmission of radio wave signals of the antenna unit, information about the characteristic of the antenna type can also be evaluated.According to a preferred embodiment, the input circuit of the antenna unit comprises a first coil element between an input point for the connecting line and the identification resistor in such a way that the radio wave signals towards the identification resistor are blocked. This advantageously prevents the radio wave signal from being influenced by the identification resistor. Alternatively or preferably additionally, it is provided that the input circuit has a first capacitor element between the input point and an antenna circuit of the antenna unit in order to separate a DC voltage present at the input circuit from the antenna circuit. The antenna circuit preferably forms a circuit unit which emits the radio wave signals, wherein the first capacitor element prevents the radiation of the radio waves from being influenced by a DC voltage, and wherein the DC voltage is used to evaluate the antenna type of the antenna unit. In other words, the first capacitor element is preferably transparent to high-frequency radio wave signals and preferably blocks a DC voltage of the evaluation unit interacting with the antenna unit. Particularly preferably, the first coil element forms a so-called BIAS TEE with the first capacitor element.Preferably, the antenna unit is operated with a radio wave signal having a frequency between 865 MHz and 928 MHz.According to a further preferred embodiment, a resistance value of the ohmic identification resistor is predefined as a function of a characteristic identification value of the antenna type.The identification value is preferably a transmission power and / or a frequency and / or a code number of the antenna type. It can also preferably be a combination of the aforementioned identification values. Most preferably, the identification value is selected depending on the identification number or a predefined article number of the antenna type. This preferably ensures that an antenna unit with an allowed identification value that is allowed for an evaluation unit can be identified more easily.In this context, it may be preferred that an antenna type with a higher identification value is assigned an identification resistor with a higher resistance value, wherein a limit value for the DC voltage values measured at the evaluation unit is preferably predefined in order to detect impermissible antenna types with voltage values above the predefined limit value.It can furthermore be preferred that the invention relates to a group of antenna units described above, wherein the antenna units have antenna types with different identification resistances and can be identified in cooperation with an evaluation unit. In particular, each antenna type is assigned an identification resistor having a different resistance value.The invention also relates to an evaluation unit for detecting an antenna unit, in particular an antenna unit described above, from a predefined group of different antenna types, wherein the evaluation unit has an electrical detection circuit which can be connected to the antenna unit by means of a single connecting line in order to detect the antenna type of the antenna unit, wherein the detection circuit has a DC voltage source with a series resistor and a voltage measurement element, wherein the series resistor in the connected state forms an unloaded voltage divider with an identification resistor of the antenna unit, wherein the voltage measurement element is connected to a ground connection and in the connected state forms a loaded voltage divider with the identification resistor in order to measure a DC voltage signal dependent on the identification resistor, wherein the evaluation unit is configured to determine the antenna type of the antenna unit from the measured DC voltage signal. Alternatively or additionally, a resistance value for the identification resistor can be calculated from the measured DC voltage signal by means of the evaluation unit in order to determine the antenna type of the antenna unit.The evaluation unit advantageously has a particularly simple and cost-effective electronic detection circuit which is operated with a DC voltage and does not require any complicated or expensive electronic high-frequency components. In other words, a particularly cost-effective circuit arrangement can be realized by means of the evaluation unit, which circuit arrangement enables a detection of the predefined antenna type of the antenna unit in a surprisingly reliable manner.According to a preferred embodiment, the voltage measuring element is designed as an analog-to-digital converter, wherein the analog-to-digital converter has an internal detection resistor in order to form the loaded voltage divider with the identification resistor. An analog-to-digital converter has the advantage that the antenna type can be evaluated in digitized form and preferably further processed by a control computer. In particular, in order to calculate the resistance value of the identification resistor, the evaluation unit preferably interacts with a control computer or has a control computer, in particular a microcontroller.The use of the evaluation unit also has the advantage that it is possible to detect whether an antenna unit is connected at all and / or whether a defect is present in the antenna unit. In particular, a short circuit within the antenna unit and / or an open end of the detection circuit can be determined by means of the evaluation unit, wherein in the case of a short circuit a measured voltage value preferably outputs a zero value and for an open end a high measured voltage value can preferably be detected. Preferably, a measured voltage value at the upper voltage limit of the analog-to-digital converter is detectable for the open end. In this case, it can be established by measuring the open end whether or not an antenna unit is connected to the evaluation unit.The analog-to-digital converter preferably has a voltage resolution between 0 and 1V, wherein the resistance value of the predefined voltage resolution is determined.The identification resistor and / or a level of the DC voltage is / are preferably selected such that the maximum resolution of the analog-to-digital converter is utilized and a voltage is not greater than a voltage limit of the analog-to-digital converter.Advantageously, the predefined resistance values of different identification resistors for the predefined group of different antenna types are selected such that the voltage resolution of the analog-to-digital converter is as optimal as possible for a given DC supply voltage and can be used over a whole resolution range. Alternatively or additionally, the series resistor of the DC voltage source and / or the detection resistor can also be selected in such a way that the maximum resolution of the analog-to-digital converter is exploited.The evaluation unit particularly preferably has a memory unit with a list of reference voltage values for the various antenna types in order to determine the antenna type from a comparison of the measured voltage value with the reference voltage values.Alternatively or additionally, the list can contain reference resistance values for identification resistors of different antenna types in order to determine the connected antenna type from a comparison of the determined resistance value of the identification resistor and the reference resistance values.Alternatively or additionally, it can also be provided that the evaluation unit has a plurality of electronic comparators in order to compare the measured voltage value of the DC voltage signal with a predefined voltage window for the antenna type. In this case, the voltage window preferably has an upper and a lower voltage limit, wherein the measured voltage value lies between the voltage limits for detecting the antenna type. Preferably, with such a configuration, it is possible to implement the evaluation unit by means of analog electronic components.The memory unit preferably lists permissible reference resistance values for the evaluation unit in order to identify whether the antenna type connected to the evaluation unit can be used for detecting a radio tag and / or is permitted for the evaluation unit.Further preferably, the evaluation unit interacts with a control unit for the antenna unit in such a way that, in the event of detection of an impermissible antenna type, a signal exchange to the antenna unit can be interrupted and / or a warning signal and / or an error message can be output to an operator. Advantageously, it can thus be ensured and monitored that the operator reliably uses an antenna unit matching the evaluation unit. Preferably, it can also be provided that the evaluation unit transmits the detected antenna type to a user interface with user interface of the operator.According to a particularly preferred embodiment, the evaluation unit has a second coil element between the detection circuit and a connection point of the connecting line in such a way that a radio wave signal transmitted to the antenna unit is separated from the detection circuit. Particularly preferably, the evaluation unit additionally or alternatively forms a second capacitor element between the detection circuit and a control unit for the antenna unit in order to separate a DC voltage generated by the evaluation unit from the control unit. Preferably, such possible interference of the radio wave signal by the detection circuit can be prevented.According to a preferred embodiment, the evaluation unit can have a plurality of second coil elements for different antenna units, wherein a changeover element can be arranged between the plurality of second coil elements and the detection circuit in order to select the appropriate second coil element depending on the antenna type detected.Analogously to the aforementioned first coil element and the first capacitor element, the second coil element and the second capacitor element also preferably form a so-called BIAS TEE. The use of the second coil element and the second capacitor element has the advantage that an impedance of the connecting line between the evaluation unit and the antenna unit is not influenced. In particular, an impedance of the connecting line designed as a microstrip line and / or as a coaxial cable is not influenced in this case, wherein an impedance of the coaxial cable is preferably 50 Ohm.The invention also relates to a reading device for reading information from a radio tag, having at least one previously described antenna unit for generating a reading signal and / or for receiving a response signal from the radio tag, and having at least one previously described evaluation unit, wherein the at least one antenna unit is selected from a predetermined group of different antenna types and is connected or connectable to the at least one evaluation unit via a single connecting line in order to detect the antenna type of the at least one antenna unit, wherein the reading device has a control unit for generating a radio wave signal.Preferably, a signal exchange between the control unit and the at least one antenna unit can be monitored and / or controlled by means of the at least one evaluation unit; in particular, the signal exchange can be interrupted and / or a warning signal can be output if an impermissible antenna type is detected.Particularly preferably, the reading device is additionally connected or connectable to an interface unit for a user interaction in order to output to an operator the detected antenna type of the at least one antenna unit.Advantageously, an individual antenna unit is assigned to an individual evaluation unit in order to evaluate the antenna type of the individual antenna unit. For detecting a radio tag, a reading device can preferably have a plurality of antenna units, which are preferably each assigned to a plurality of evaluation units. In particular, a plurality of connecting lines can be used for each of the plurality of antenna units.However, it is also conceivable for a plurality of antenna units to be assigned to a single evaluation unit, wherein the antenna units preferably have the same antenna type. In this context, it may be preferred that the evaluation unit has a changeover element in order to connect one of the plurality of antenna units to the detection circuit.Furthermore, it can also be preferred that the evaluation unit has a plurality of detection circuits for detecting different antenna units.A control computer with a graphic user interface is preferably provided as the interface unit in order to output the antenna type to the operator and to indicate control options for the at least one antenna unit.Preferably, it is provided that the connecting line between the at least one antenna unit and the at least one evaluation unit is designed as a coaxial line with a characteristic impedance of 50 ohms, in order to transmit the radio wave signal as free of interference as possible. The use of such a connecting line has the advantage that a resistance value of the connecting line is very low, in particular with a value of 25 mOhm / m. A resistance value of the identification resistor is preferably between 100 Ohm and 1 MOh, particularly preferably 10 kOhm. In this case, the resistance value of the connecting line is preferably negligible with respect to the resistance value of the identification resistor even in connection lines having a length of several meters.Particularly preferably, the detection resistance R DE, in particular the internal resistance of the analog-to-digital converter, and the series resistance R v are in the following relationship to one another:With resistance values outside the definition according to equation GL1, corruptions of the measured values at the voltage measuring element, in particular due to connecting lines of different lengths, can be severely corrupted.Preferably, a detection voltage U DE at the voltage measuring element can be determined using the following equation GL2, wherein the voltage measuring element is preferably designed as an analog-to-digital converter:In the case of an optimization of the voltage divider, it is preferable to design the latter in such a way that the entire resolution of the analog-to-digital converter can be used in DE for determining the detection voltage U. With the series resistor R v and the identification resistor R ID a voltage divider with a supply DC voltage V CC is formed. The detection voltage U DE is preferably tapped and digitized by the analog-to-digital converter. Particularly preferably, the identification resistor R ID forms a loaded voltage divider with the detection resistor R DE, in particular an internal resistance of the analog-to-digital converter. Most preferably, the analog-to-digital converter can use its maximum resolution at a maximum detection voltage. In particular, the resistance values and / or the DC voltage of the equation GL2 are selected in such a way that the analog-to-digital converter can use its maximum resolution. In other words, all quantization steps of the analog-to-digital converter are preferably within a maximum measurable voltage resolution of between 0 and 1V.It is further preferred in this context that the identification value can be evaluated from the equation GL2 and the measured detection voltage.The invention further relates to a method for operating an antenna unit having an evaluation unit, in particular an antenna unit having an evaluation unit as described above, having the following preferred steps. Wherein preferably a sequence of the method steps can be changed as desired.According to a preferred first step, the evaluation unit is connected to an antenna unit by means of a single connecting line. In a preferred second step, a DC voltage is generated by means of a voltage source of the evaluation unit and a DC voltage signal is measured at a voltage measuring element, wherein the voltage measuring element forms a loaded voltage divider with an ohmic identification resistor of the antenna unit. In a preferred third step, a voltage value of the DC voltage signal is evaluated in order to determine the antenna type of the connected antenna unit.Preferably, the resistance value of the identification resistor is calculated from the voltage value in order to determine the antenna type. In particular, the resistance value is calculated from an analytical equation for the loaded voltage divider. According to a preferred fourth step, the determined resistance value of the identification resistor is compared with a list of predefined reference resistance values for different identification resistors from a group of different antenna types, and the antenna type of the antenna unit connected to the evaluation unit is determined therefrom.Additionally or alternatively, the antenna type is determined directly from the measured voltage value, wherein the measured voltage value is compared with a list of predefined reference voltages in order to determine the antenna type.The evaluation unit is preferably connectable or connected to a control unit which generates the radio wave signal for the antenna unit. In particular, in addition to detecting the antenna type, the evaluation unit controls the connection of the control unit to the antenna unit.In this case, according to a preferred fourth step, the determined antenna type is compared with a list of antenna types permitted for the evaluation unit. According to a further preferred fifth step, the antenna unit is connected to the control unit by means of the evaluation unit if the detected antenna type of the antenna unit corresponds to an antenna type permitted for the evaluation unit. According to an alternative fifth step, a connection between the antenna unit and the control unit is switched off or interrupted by the evaluation unit and / or a warning signal is output if the antenna type is not permitted for the evaluation unit.The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawings.It shows schematically: FIG. 1 : Circuit arrangement of an evaluation unit and an antenna unit in the connected state.In the following description of the preferred embodiments, like reference numerals designate like or comparable components.FIG. 1 shows a reading device 50 having an antenna unit 10 and an evaluation unit 18, which are connected to one another by means of a single connecting line 16. Furthermore, the reading device 50 preferably has a control unit 28 in order to generate a radio wave signal which can be transmitted to the antenna unit 10 via the connecting line 16. Preferably, a 50 ohm shielded coaxial cable is used as the connecting line 16 to transmit the high frequency radio wave signals. In this case, the antenna unit 10 is designed with an antenna circuit 11 for detecting a radio tag 12, in particular in order to transmit a read-out signal to the radio tag 12 and / or to receive a response signal transmitted by the radio tag 12. The radio tag 12 is preferably a passive RFID tag which can be fastened to transport objects and wherein a product flow of transport objects can be detected by means of the reading device 50.Furthermore, FIG. 1 shows in detail an electrical input circuit 20 of the antenna unit 10, which according to the present invention has an ohmic identification resistor R ID with a predefined resistance value, which can be detected by means of a detection circuit 22 of the evaluation unit 18. The identification resistor R ID is characteristic of the antenna type used for the antenna unit 10, wherein the resistance value of the identification resistor R ID is selected from a predefined group of different antenna types with different identification resistors R ID. Advantageously, the predefined resistance value of the identification resistor R ID can be read out by means of the evaluation unit 18, the connected antenna type can be detected and it can be established whether it is an antenna unit 10 that is suitable or permitted for the evaluation unit 18.The detection circuit 22 of the evaluation unit 18 has, for detecting the identification resistor R ID a DC voltage source 24 with series resistor R V and a voltage measuring element 26 with integrated detection resistor R DE which are each connected to a ground terminal M. The identification resistor R ID is also preferably connected to a ground terminal M and forms an unloaded voltage divider with the series resistor R V and a loaded voltage divider with the detection resistor R DE. The voltage measuring element 26 is preferably designed as an analog-to-digital converter 27 with the detection resistance R DE as an internal resistance. By forming a voltage divider of the detection circuit 22 with the identification resistor R ID the resistance value of the identification resistor R ID can advantageously be read out via the individual connecting line 16. In particular, a DC voltage signal present at the voltage measuring element 26 can be read out and a DC voltage value can be measured. The resistance value can preferably be determined from an analytical calculation for the circuit arrangement shown of the evaluation unit 18 with antenna unit 10.The evaluation unit 18 preferably has a storage unit, not shown, having a list of reference voltage values and / or reference resistance values for identification resistors R ID of different antenna types, in order to determine the antenna type of an antenna unit 10 connected to the evaluation unit 18 from a comparison of the measured voltage value and / or the determined resistance value of the identification resistor R ID.Particularly preferably, the evaluation unit 18 interacts with the control unit 28 in such a way that, in the event of detection of an impermissible antenna type, a signal exchange to the antenna unit 10 can be interrupted and / or a warning signal can be output to an operator. It can thus be ensured that the reading device 50 can only be operated with an allowed antenna unit 10. Furthermore, the evaluation unit 18 has the advantage that a short circuit within the antenna unit 10 or an unconnected antenna unit 10 can be detected, wherein the control unit 28 can also then be controlled accordingly, in particular interrupted and / or a warning signal can be output. Thus, it can be provided that the reading device 50 has a plurality of antenna units 10, wherein it can be detected by means of the evaluation unit 18 whether all antenna units 10 are connected and functional, and have the antenna type matching the evaluation unit 18.Further preferably, the input circuit 20 comprises a first coil element L 1 between an input point 14 for the connecting line 16 and the identification resistor R ID in such a way that the radio wave signals towards the identification resistor R ID are blocked. Specifically, an inductance of the first coil element L 1 is formed such that the high-frequency radio wave signals from the first coil element L 1 are blocked so as not to change an impedance of the connection line 16 to the antenna circuit 11. Further preferably, the input circuit 20 has a first capacitor element C 1 between the input point 14 and the antenna circuit 11 of the antenna unit 10, in order to separate a DC voltage present at the input circuit 20 from the antenna circuit 11. In other words, the first coil element L 1 and the first capacitor element C 1 preferably form a so-called BIAS TEE in order to prevent the radio wave signal from being influenced by the DC voltage.It can further preferably be provided that the evaluation unit 18 has a second coil element L 2 between the detection circuit 22 and a connection point 32 of the connecting line 16 or an inductance is selected in such a way that a radio wave signal transmitted to the antenna unit 10 is separated from the detection circuit 22, in order here too to prevent an impedance of the connecting line 16 from being influenced. Furthermore, it is preferably provided that the evaluation unit 18 forms a second capacitor element C 2 between the detection circuit 22 and the control unit 28 or a capacitance is selected in such a way that a DC voltage generated by the evaluation unit 18 is separated from the control unit 28. Preferably, an influence on the radio wave signal by the DC voltage of the evaluation unit 18 can be prevented in this way.List of reference characters10 Antenna unit 11 Antenna circuit 12 Radio tag 14 Input point of the antenna unit 16 Connecting line 20 Input circuit 22 Detection circuit 24 Direct voltage source 26 Voltage measuring element 27 Analog-to-digital converter 28 Control unit 32 Connection point of the connecting line 50 Read-out device R DE Detection resistor R ID Identification resistor R V Series resistance of the voltage source C 1, C 2 First and second capacitor elements L 1, L 2 First and second coil elements M Ground connection

Claims

Antenna unit (10) for detecting a radio tag (12) by means of a radio wave signal, wherein the antenna unit (10) can be connected by means of a single connecting line (16) to an evaluation unit (18) for transmitting the radio wave signal, wherein the antenna unit (10) has an electrical input circuit (20) with a predefined ohmic identification resistor (R ID) wherein the antenna unit (10) is selected from a group of different antenna types, wherein each antenna type is assigned an identification resistor (R ID) with different resistance values, wherein the identification resistor (R ID) is connected to a ground connection (M) and can be connected in this way by means of the connecting line (16) to a detection circuit (22) of the evaluation unit (18), the identification resistor (R ID) forms a loaded voltage divider with a DC voltage source (24) and a voltage measuring element (26) of the detection circuit (22) in order to output the antenna type to the evaluation unit (18) by means of a DC voltage signal.Antenna unit according to Claim 1, characterized in that the input circuit (20) has a first coil element (L 1) between an input point (14) for the connecting line (16) and the identification resistor (R ID) in such a way that the radio wave signals are blocked and / or in that the input circuit (20) has a first capacitor element (C 1) between the input point (14) and an antenna circuit (11) of the antenna unit (10) in order to disconnect a DC voltage present at the input circuit (20) from the antenna circuit (11).Antenna unit according to Claim 1 or 2, characterized in that the resistance value of the ohmic identification resistor (R ID) is predefined as a function of a characteristic identification value, in particular a transmission power and / or a frequency and / or a code number, of the antenna type.Evaluation unit for detecting an antenna unit (10), in particular according to one of Claims 1 to 3, from a predefined group of different antenna types, wherein the evaluation unit (10) has an electrical detection circuit (22) which can be connected to the antenna unit (10) by means of a single connecting line (16) in order to detect the antenna type of the antenna unit (10), wherein the detection circuit (22) has a DC voltage source (24) with series resistor (R V) and a voltage measurement element (26), wherein the series resistor (R V) in the connected state forms an unloaded voltage divider with an ohmic identification resistor (R ID) of the antenna unit (10), wherein the voltage measuring element (26) is connected to a ground connection (M) and, in the connected state with the identification resistor (R ID) of the antenna unit (10), forms a loaded voltage divider in order to measure a DC voltage signal dependent on the identification resistor (R ID) wherein the evaluation unit (10) is configured to determine the antenna type of the antenna unit (10) from the measured DC voltage signal and / or a resistance value for the identification resistor (R ID) calculated from the DC voltage signal.Evaluation unit according to Claim 4, characterized in that the voltage measurement element (26) is designed as an analog-to-digital converter (27), the analog-to-digital converter (27) having an internal detection resistor (R DE) in order to form the loaded voltage divider, the evaluation unit having a memory unit with a list of reference voltage values for the various antenna types, in order to determine the antenna type from a comparison of the measured voltage value of the DC voltage signal with the reference voltage values.Evaluation unit according to Claim 4 or 5, characterized in that the evaluation unit (18) interacts with a control unit (28) for the antenna unit (10) in such a way that, in the event of detection of an impermissible antenna type, signal exchange with the antenna unit (10) can be interrupted and / or a warning signal and / or an error message can be output to an operator.Evaluation unit according to one of Claims 4 to 6, characterized in that the evaluation unit (18) has a second coil element (L 2) between the detection circuit (22) and a connection point (32) of the connecting line (16) in such a way that a radio wave signal transmitted to the antenna unit (10) is separated from the detection circuit (22), and / or in that the evaluation unit (18) forms a second capacitor element (C 2) between the detection circuit (22) and a control unit (28) for the antenna unit (10), in order to separate a DC voltage generated by the evaluation unit (18) from the control unit (28).Reading device for reading information from a radio tag (12), having at least one antenna unit (10) according to one of Claims 1 to 3 for generating a reading signal and / or for receiving a response signal emitted by the radio tag, and having at least one evaluation unit (18) according to one of Claims 4 to 7, wherein the at least one antenna unit (10) is selected from a predetermined group of different antenna types and is connectable or connected to the at least one evaluation unit (18) via a single connecting line (16) in order to detect the antenna type of the at least one antenna unit (10), wherein the reading device (50) has a control unit (28) for generating a radio wave signal.Method for operating an antenna unit (10), in particular according to one of Claims 1 to 3, and an evaluation unit (18), in particular according to one of Claims 4 to 7, having the steps: - connecting the evaluation unit (18) to the antenna unit (10) by means of a single connecting line (16), - generating a DC voltage by means of a voltage source (24) of the evaluation unit (18) and measuring a DC voltage signal at a voltage measurement element (26) of the evaluation unit (18), wherein the voltage measurement element (26) forms a loaded voltage divider with an ohmic identification resistor (R ID) of the antenna unit (10), - evaluating a voltage value of the DC voltage signal in order to determine the antenna type of the connected antenna unit (10).Method according to Claim 9, wherein the evaluation unit is connectable or connected to a control unit (28) which generates a radio wave signal for the antenna unit (10), having the following steps: - comparing the antenna type with a list of antenna types permitted for the evaluation unit (18), - connecting the antenna unit (10) to a control unit (28) by means of the evaluation unit (18) if the detected antenna type of the antenna unit (10) corresponds to an antenna type permitted for the evaluation unit (18), - switching off a connection between the antenna unit (10) and the control unit (28) and / or outputting a warning signal if the antenna type is not permitted for the evaluation unit (18).

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