ADAPTER DEVICE AND METHOD FOR MEASURING SIGNAL POWER IN A COAXIAL CONNECTION

Description

[0001] The invention relates to an adapter device and a method for measuring the signal power in a coaxial connection from an RFID reading device to a second device, in particular an antenna, according to the preamble of claim 1 and 9, respectively.

[0002] RFID readers are used to identify objects and goods and are used, among other things, to automate logistics movements. At an identification point, especially when the ownership of the goods changes or the means of transport changes, RFID transponders attached to the goods are read and, if necessary, information is written back to the transponder. This leads to fast and traceable logistics movements. The captured information is used to control the forwarding and sorting of goods and products. Important applications for automatic identification include logistics distribution centers, such as those of parcel shippers, or baggage drop-off at airports.

[0003] RFID transponders can, in principle, be active, meaning they have their own power supply and generate electromagnetic radiation independently. In practice, however, these transponders are less suitable for logistics because the power supply prevents the unit prices of such transponders from reaching the low level required for the mass market. Therefore, passive transponders without their own power supply are mostly used. In both cases, the transponder is stimulated to emit the stored information by electromagnetic radiation from the reader, with passive transponders drawing the necessary energy from the transmission energy of the reading system. In the established ultra-high frequency standard ISO 18000-6, passive transponders are read using the backscatter method.

[0004] RFID devices use internal or external antennas, with an external antenna typically being added later. This involves coaxial connections and coaxial cables whose properties are unknown. There are various reasons for this: The properties may not have been measured or specified in advance. Even with a pre-terminated coaxial cable, effects such as mechanical damage during installation or aging during operation can lead to deviations from the factory-specified specifications. However, if the transmission losses or cable attenuation values ​​are unknown, it is advisable to assume a lossless coaxial connection as a precaution, and therefore the transmission power must not be set to more than the maximum permitted value.However, this does not fully utilize the permitted transmission power, because the actual transmission power achieved is lower due to transmission losses, which in turn reduces the maximum reading range.

[0005] EP 2 712 021 A1 discloses an antenna for a read / write device for RFID systems. The antenna is equipped with a data memory with type information and / or property information and further comprises a measuring device for determining at least one value of the field strength or power of a radio-frequency signal fed into the antenna. The functionality is thus tied to specific antennas; it is not possible to use any antenna. In one embodiment, the contents of the data memory can be transmitted bit by bit by means of a clocked short-circuiting of the antenna line. During the periods in which a short circuit is generated, a suitably equipped read / write device can measure additional line parameters such as cable attenuation or reflection losses occurring at the antenna. This requires not only a specific antenna but also a specific read / write device that provides this measuring functionality.

[0006] EP 2 442 255 A1 describes an RFID reading device whose antenna has a data carrier in which the antenna parameters are stored to facilitate installation of the RFID reading device, wherein the data carrier can be an RFID transponder.

[0007] US 10 181 656 B2 deals with an antenna unit comprising an antenna and a coaxial connector. The coaxial connector has an internal memory that allows the connected antenna to be identified and is powered via the coaxial cable. Transmission losses of the antenna cable are not discussed, and no measurement of parameters is provided.

[0008] US 10 339 346 B2 discloses an antenna with an integrated RFID IC that allows one of several antenna elements to be selected using high-frequency switches. This allows, for example, the resonant frequency or directivity of the antenna to be adjusted. Again, neither transmission losses of the antenna cable nor a general possibility for measuring properties are addressed.

[0009] US 2,929,993 A discloses a measuring device for determining the peak power of a high-frequency signal in a coaxial line. The measuring device comprises a line section that is inserted into the coaxial line.

[0010] It is therefore an object of the invention to further improve the device of an RFID reading device.

[0011] This object is achieved by an RFID reading device and a method for measuring the signal power in a coaxial connection from an RFID reading device to a second device, in particular an antenna, according to claim 1 and 9, respectively. An RFID reading device, or RFID reader for short, despite the shortened name, is usually also capable of writing data to an RFID transponder. A first adapter device is inserted into a coaxial connection between the reading device and the second device, with which the second device is connected to the RFID reading device. The second device is preferably an antenna, and in the following, the antenna will always represent the second device.The coaxial connection is preferably a coaxial cable or an antenna cable, although a direct connection of the second device to the RFID reader is also conceivable. The coaxial connection transmits the signal whose signal power is to be measured, preferably a radio-frequency signal or RFID signal. The measurement of the signal power is preferably only an intermediate result; the actual goal is then a derived value, in particular the determination of the transmission loss or attenuation of the coaxial connection.

[0012] The adapter device has a first coaxial connector and a second coaxial connector for insertion into the coaxial connection. When inserted, the adapter device is connected to the coaxial connection on both sides via the first coaxial connector and the second coaxial connector, so that the coaxial connection now passes through the adapter device. A measuring unit determines the forward and / or return signal power of the signal propagating through the adapter device.

[0013] The adapter can be subsequently inserted into the coaxial connection or removed from it. The first coaxial connector and the second coaxial connector are designed to be removable for this purpose. For example, a plug connection that can be secured by screwing or the like, such as a TNC or R-TNC connector, which is commonly used for antennas and coaxial cables, is suitable.

[0014] The first adapter device is inserted into the coaxial connection with its first coaxial connection and second coaxial connection, wherein the first adapter device is arranged at an end of the section of the coaxial connection to be measured that is remote from the RFID reading device. Various configurations are conceivable where the first coaxial connection and the second coaxial connection are connected. The first coaxial connection can be connected directly to the RFID reading device or to one end of a coaxial line of the coaxial connection. Accordingly, the second coaxial connection can be connected directly to the second device or to one end of a coaxial line of the coaxial line. If the coaxial line has multiple sections, the end of the coaxial line can also represent one end of a section.As yet another alternative, the RFID reader can originally be connected directly to the second device; in this case, the first adapter device replaces the direct connection. The first adapter device forms the end of the section of the coaxial connection to be measured that is farther from the RFID reader.

[0015] The invention has the advantage that the functionality of the adapter device is supplemented by an existing system of an RFID reading device and a second device connected to it, making the invention accessible to any RFID reading device and second device. A dedicated measuring functionality is required in an RFID reading device or an antenna connected to it. Parameters of the coaxial connection can be easily determined, in particular the attenuation or transmission losses. In the same way, statements about the quality of the second device are possible. During operation of the RFID reading device, the transmission power can be adjusted accordingly, taking transmission losses in the coaxial connection into account. This allows maximum permissible signal levels to be exploited and reliably maintained in order to optimize the reading range.In the case of cascaded coaxial connections, measurements can be taken at various points in the signal path to locate faulty components. The adapter device can be used sequentially in different coaxial connections to cost-effectively evaluate different systems of RFID readers and secondary devices. The adapter device is only needed during installation or maintenance, for example. If the adapter device remains in place, regular measurements can be used to detect deterioration early (predictive maintenance).

[0016] The measuring unit is preferably designed to determine a maximum signal power value. This allows statements regarding compliance with a permissible maximum power to be made independent of signal modulations during the signal power measurement, unlike, for example, averaging.

[0017] The adapter device preferably has a power supply unit with which the adapter device powers itself from the signal propagating on the coaxial connection. A battery or the like is therefore not required. The power supply unit can be based on phantom power or remote power and can have, for example, a bias-T for this purpose. An alternative is to charge an energy storage device, such as a capacitor, from the signal and use, for example, a rectifier or charge pump for this purpose, so that no phantom power needs to be provided.

[0018] The adapter device preferably has a memory in which the measuring unit stores a measured value for the signal power. Thus, at least the most recently measured signal power is available for readout. Multiple measured values ​​or variables derived from them can also be stored, particularly to obtain more accurate results from multiple measurements.

[0019] The memory is preferably readable using an RFID protocol and, in particular, has an RFID transponder circuit. As a result, the RFID reading device does not require a special communication or data interface for the adapter device, because an RFID reading device understands the RFID protocol anyway. An example of the RFID protocol is the standardized EPC Gen2 protocol or a protocol according to the closely related ISO 18000-6 standard mentioned above. The memory can be based on the same, inexpensively available technology as an RFID transponder, i.e., it can have a corresponding RFID transponder circuit.

[0020] The measuring unit is preferably designed to check the memory for a start signal stored there and, if a start signal is present, to perform a signal power measurement. Communication between the adapter device and the RFID reader is thus extremely simple via access to the memory, which requires no complex coordination or synchronization. The RFID reader signals its need for a signal level measurement via the start signal. The measuring unit determines this need based on the start signal, performs the measurement, and stores the measurement result in the memory for access by the RFID readers at any later time.

[0021] The transmission power of the RFID reading device is preferably known in the RFID reading device, and the RFID reading device is configured to determine a transmission loss of the coaxial connection from the known transmission power and a measured value of the first adapter device. In this embodiment, there is a certain amount of prior knowledge about the signal power, namely how much signal is originally generated by the RFID reading device. The RFID reading device is preferably adapted so that this original signal power is actually fed into the coaxial connection or a corresponding initial loss is known. For the transmission loss of the coaxial connection, more precisely the section of the coaxial connection from the RFID reading device to the first adapter device, only a comparison of the known original signal power with a corresponding measured value of the first adapter device is then required.If the transmission loss of the entire coaxial connection is to be measured, the first adapter device must be connected directly to the second device, as far away from the RFID reader as possible.

[0022] Preferably, a second adapter device is provided for measuring the signal power in the coaxial connection, wherein the second adapter device is arranged at an end of the section of the coaxial connection to be measured that is close to the RFID reading device, and the RFID reading device is designed to determine a transmission loss of the coaxial connection from measured values ​​of the first adapter device and the second adapter device. This allows the transmission loss to be determined for any RFID reading device whose transmission power is unknown and which is also not necessarily adapted to the coaxial connection. The second adapter device can be the first adapter device that is reused with a time delay, which is detached from its original position after a first measurement and inserted into the coaxial connection at its new position for a second measurement.Preferably, however, two adapter devices are inserted into the coaxial connection simultaneously. The transmission loss between the first and second adapter devices is determined by comparing their two measured values. To determine the transmission loss of the entire coaxial connection, the adapter devices must be connected directly to the second device or the RFID reader, with the entire coaxial connection between the two adapter devices.

[0023] For the inventive method for measuring the signal power in a coaxial connection from an RFID reading device to a second device, in particular an antenna, at least one first adapter device with its first coaxial connection and second coaxial connection is detachably inserted into the coaxial connection. The first adapter device is arranged at the remote end of the section of the coaxial connection to be measured, preferably directly next to the second device, i.e. its second coaxial connection is connected directly to the second device. The RFID reading device starts a measurement of the signal power, the first adapter device then determines the signal power of a signal from the RFID reading device propagating through the first adapter device, and the RFID reading device then reads out a measured value from the first adapter device.Evaluations and calculations can follow, either in the RFID reader, for example using an app or script, or in a higher-level controller (middleware), which can be responsible for several RFID readers.

[0024] Communication between the RFID reading device and the at least first adapter device preferably takes place via a memory of the adapter device, in particular by communication using an RFID protocol. Thus, both the RFID reading device and the first adapter device, in particular a measuring unit of the first adapter device, access the memory asynchronously. Communication between the RFID reading device preferably takes place via an RFID protocol. For this purpose, the memory can be equipped with an RFID circuit of an RFID transponder.

[0025] The RFID reading device preferably starts a measurement of the at least first adapter device by storing a start signal in the memory, wherein the adapter device checks the memory for a start signal stored there and, if a start signal is present, performs a measurement of the signal power. More complex direct communication between the RFID reading device and the adapter device or its measuring unit is thus not required. The RFID reading device communicates its measurement requirements via the start signal; the adapter device preferably checks cyclically for such a start signal and responds by performing a measurement. After the measurement, the corresponding measured value is available to the RFID reading device at any later time. The adapter device can also store a timestamp or the like for the measured value.

[0026] The RFID reader preferably generates a transmission signal of known transmission power, and during this time, the first adapter device performs a measurement of the signal power, wherein the RFID reader determines a transmission loss of the coaxial connection from the known transmission power and a measured value of the signal power determined by the first adapter device. The transmission signal can be a continuous signal or a modulated signal; the purpose of the transmission signal is to propagate a signal of known transmission power through the first adapter device in time for the measurement of the first adapter device and for its duration. The final determination of the transmission loss results from the known transmission power and the measured value of the signal line in the first adapter device that results from this known transmission power, in particular by forming the difference.

[0027] Preferably, a first measurement of the signal power is carried out with the first adapter device while the RFID reading device is generating a transmission signal. In addition, a second measurement of the signal power is carried out using a second adapter device that is detachably inserted into the coaxial connection, in particular a second adapter device according to the invention, wherein the RFID reading device determines a transmission loss of the coaxial connection from one measured value each of the two measurements. With this embodiment of the method, the transmission loss can be determined for any RFID reading device with an unknown transmission power and without adapting the RFID reading device to the coaxial connection. During the measurements, the RFID reading device is active with its unknown transmission power, for example through a continuous RFID query or a permanent inventory.In particular, the measurements are started simultaneously or sequentially by a respective start signal written into the memory of the adapter devices. After the measurements have been completed, the transmission loss is determined from the two measured values ​​of the two adapter devices, in particular by calculating the difference. For the arrangement of the two adapter devices, there are alternatives already discussed in connection with the design options of the device. The section of the coaxial connection to be measured lies between the two adapter devices. As also already discussed, the second adapter device can be the first adapter device arranged at a new position in the coaxial connection or a physical second adapter device that is inserted into the coaxial connection together with the first adapter device.The properties and use of the second adapter device are analogous to what was stated for the first adapter device.

[0028] Preferably, if the at least first adapter device does not remain in the coaxial connection during further operation, the RFID reading device corrects a transmission loss of the coaxial connection by a known transmission loss of the at least first adapter device. The first adapter device and, if present, the second adapter device each generate their own transmission loss. However, this is no longer relevant if an adapter device is only temporarily inserted and is removed from the coaxial connection again after the measurement has been taken. The transmission loss then decreases accordingly. The extent of the correction is a fixed parameter of the respective adapter device, which the RFID reading device knows or which is provided in particular in the memory of the adapter device.

[0029] The invention will be explained in more detail below with regard to further features and advantages, using exemplary embodiments and with reference to the accompanying drawings. The figures of the drawing show: Fig. 1 is a block diagram of an RFID reader with an adapter inserted into the coaxial connection to its antenna; Fig. 2 is a three-dimensional representation of the assembly of an RFID reader for use on a conveyor belt; Fig. 3 is a block diagram of an adapter; Fig. 4 is a block diagram of another embodiment of an adapter; Fig. 5 is a schematic representation of an arrangement of an adapter in a coaxial connection for measuring a transmission loss with known transmission power; Fig. 6 is a schematic representation of an arrangement of two adapters in a coaxial connection for measuring a transmission loss with unknown transmission power; Fig. 7 is a representation of an exemplary design of an adapter; and Fig. 8 is a representation of an alternative design of an adapter.

[0030] Figure 1shows a block diagram of an RFID reader 10 with an adapter 12, which is inserted into the coaxial connection 14 to an antenna 16 connected to the RFID reader 10. The adapter 12 is shown here only as a simple block and will be described later with reference to the Figures 3 to 6 explained in more detail. The antenna 16 represents a second component connected to the RFID reader 10 via a coaxial connection 14.

[0031] The RFID reader 10 has a transmitting / receiving unit 18 with a transmitter 20 and a receiver 22 for receiving RFID signals from the antenna 16 or transmitting RFID signals via the antenna 16. The transmitting / receiving unit 18 can be designed as a transceiver.

[0032] A control and evaluation unit 24 is connected to the transmitting / receiving unit 18. It has at least one digital computing component, such as a microprocessor or a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), an ASIC (Application-Specific Integrated Circuit), an AI processor, an NPU (Neural Processing Unit), a GPU (Graphics Processing Unit), or the like. Deviating from the illustration, the control and evaluation unit 24 can be provided at least partially externally, as a computer of any design, including notebooks, smartphones, tablets, as a controller, local network, edge device, cloud, or other computing unit. The control and evaluation unit 24 receives an electronic signal corresponding to the received RFID signals from the receiver 22 or causes the transmitter 20 to transmit an RFID signal.The control and evaluation unit 24 knows the RFID protocols to be used, for example, according to ISO 18000-6 or EPC Gen2, to encode information into an RFID signal or read it from an RFID signal. RFID communication as such is known. Therefore, the required components of the control and evaluation unit 24 and the steps required for RFID communication will not be explained in detail.

[0033] Figure 2 1 shows a three-dimensional representation of a typical application of the RFID reader 10 in a stationary installation on a conveyor belt 26. Objects 28 are conveyed through a reading area 32 in a direction indicated by an arrow 30. The RFID transponders 34 are arranged on the objects 28 and are read by the RFID reader 10 when they are located in the reading area 32.

[0034] Above the reading area 32, a shield 36 is preferably provided, which is only shown schematically and which protects both the RFID reader 10 from external interference signals and the environment from the electromagnetic radiation of the RFID reader 10. The RFID reader 10 at the resulting reading tunnel comprises, in contrast to the representation of the Figure 1 two antennas 16a-b. Additional RFID readers or additional antennas are conceivable, including internal antennas of the RFID reader 10 itself, to detect RFID signals at additional positions and from additional directions. Other sensors may also be provided to obtain additional information about the objects 28, for example, their entry into and exit from the reading area 32 or the volume or weight of the objects 28.

[0035] Figure 3shows a block diagram of an embodiment of the adapter 12. The adapter 12 has two coaxial connectors 38, 40, preferably of a type commonly used for RFI D applications such as R-TNC (Threaded Neill Concelman Reverse Polarity). Thus, the adapter 12 can be connected to a coaxial connector 38, 40, according to the very schematic representation of the Figure 1 , are inserted into the coaxial connection 14. There are various possibilities for this: The first coaxial connection 38 can be connected directly to the RFID reader 10 or to a coaxial line connected thereto, and the second coaxial connection 38 can be connected directly to the antenna 16 or a coaxial line connected thereto. The coaxial connection 14 can comprise only a single coaxial line, several coaxial lines as partial sections, with the coaxial connections 38, 40 being able to be connected at the transitions of the coaxial lines, or, in a direct connection between the RFID reader 10 and the antenna 16, no coaxial line at all.

[0036] The adapter 12 comprises a measuring unit 42 for determining the signal power of a signal propagating through the adapter 12 in the forward direction, the reverse direction, or both directions. For this purpose, a signal output 44 is provided via at least one of the diodes D1, D2. The measuring unit 42 is preferably configured to determine the maximum power of the transmitted signal, i.e., not an average value, for example, in order to exclude deviations in the measured signal power due to the modulation of the transmitted signal.

[0037] The adapter 12 preferably has at least one programmable memory 46, which can be addressed via a standardized protocol via a further coupling 48. Particularly preferably, communication takes place via an RFID protocol. For this purpose, the memory 46 can be equipped with corresponding circuits of an RFID transponder. Alternatively, another form of communication is conceivable, for example, through modulated voltage as in the 1Wire protocol. However, the RFID reader 10 must then understand this protocol, while an RFID protocol is implemented anyway. A start signal for a measurement is preferably stored in the memory 46 by the RFID reader 10, and after the measurement has been completed, the measured value for the signal power is stored by the measuring unit 42. Furthermore, a value for the adapter 12's own transmission attenuation can be stored there.

[0038] Preferably, the adapter 12 also has, in order to avoid the need for an alternatively conceivable energy source or battery, a circuit 50 for supplying energy from the signal transmitted on the coaxial connection 14. In the embodiment according to Figure 3 This is a supply via phantom or remote power, for example via a bias-T.

[0039] Figure 4 shows a block diagram of another embodiment of the adapter 12. In contrast to Figure 3 No phantom power is required here. The power supply circuit 50 includes a rectifier or charge pump to ensure the supply via energy harvesting. For this purpose, the circuit 50 includes an energy storage device (not shown separately), such as a capacitor, which is charged by the energy harvesting.

[0040] Figure 5shows a schematic representation of an arrangement of the adapter 12 in a coaxial connection 14 for measuring a transmission loss or antenna matching with a known transmission power and a matched RFID reader 10. A measurement with an adapter 12, which is preferably connected to the end of the coaxial connection facing the antenna 16, is then sufficient. With a different arrangement, only the transmission loss of the section up to the adapter 12 is determined, which can be useful, for example, in the case of a multi-part coaxial connection.

[0041] An example sequence begins with the RFID reader 10 storing a start signal, in particular with a start time, in the memory 46 of the adapter 12. For this purpose, the transmission signal of the RFID reader 10 is switched on, which then accesses the memory 46. In the adapter 12, the measuring unit 42 queries the memory 46 at regular intervals and therefore independently and asynchronously detects the change in state in the memory 46. It starts a measurement of the transmission power immediately, with a generally agreed-upon delay, or at a time stored with the start signal. Accordingly, the RFID reader 10 is set to its transmission power, known, for example, through factory calibration, at the latest since the start signal was sent, with the agreed delay, or at the time stored with the start signal, and has its transmission signal switched on at this transmission power at least for the duration of the measurement. The signal level is therefore measured at the known transmission power.The measuring unit 42 stores the signal power it determines, or the measured maximum signal level, in the memory 46. The RFID reader 10 accesses the memory 46 to read the measured value. A signal can be agreed upon with which the measuring unit 42 signals the end of the measurement; this signal can simply consist of the measured value itself, as opposed to, for example, an empty memory location.

[0042] The how to Figure 1The possibly external control and evaluation unit 24 of the RFID reader 10, as described above, determines the attenuation of the coaxial connection 14, or the transmission loss, from the difference between the known transmission power and the measured value of the adapter 12. Optionally, a final query is made as to whether the adapter 12 should remain in the coaxial connection 14 for further operation. If the adapter 12 is now removed, the transmission loss can be corrected by the adapter 12's own transmission loss, as this portion of the transmission loss is eliminated after removal. The corresponding value can be parameterized in the RFID reader 10 or read from the memory 46. By removing the adapter 12, it can be reused elsewhere. On the other hand, keeping the adapter in place is certainly beneficial for diagnostic purposes (predictive maintenance) for periodically repeated measurements and checking for changes.

[0043] Figure 6 shows a schematic representation of an arrangement of two adapters 12a-b in a coaxial connection 14 for measuring a transmission loss with unknown transmission power and any RFID reader 10 that is not or only randomly matched. The two adapters 12a-b are preferably used at the two ends of the coaxial connection 14, i.e., at the antenna 16 and at the RFID reader 10. Otherwise, the transmission loss is not determined in the entire coaxial connection 14, but only in the section between the adapters 12a-b. As an alternative to a joint physical presence of two adapters 12a-b, it is conceivable to move the same adapter 12 to the two specified positions one after the other for a respective measurement.

[0044] An example process is largely similar to the one used for Figure 5has been described, so only the differences will be discussed in more detail. The start signal is now stored in both memories 46 of the adapters 12a-b. The measurements triggered thereby are carried out either simultaneously or sequentially. The respective measuring unit 42 of the adapters 12a-b queries its memory 46 at regular intervals and, if necessary, starts its measurement at the corresponding time. The RFID reader 10 is set to a mode for continuous query (permanent inventory) or ensures in some other way that a signal is present. It is conceivable to precede the measurement with a phase in which the transmission signal is switched on, in which a charge pump according to Figure 4The energy storage device is being charged. The charge pump can then be switched off in a timely manner to avoid affecting the measurement. After both measurements have been performed, the RFID reader reads the corresponding measured values ​​from both adapters 12a-b. The attenuation or transmission loss of the coaxial connection 14 is determined from the difference between the two measured values. Finally, an optional query can be made as to whether the adapters 12a-b remain in the coaxial connection 14 or whether one of the adapters 12a-b remains in place, in order to correct for the transmission loss of a removed adapter 12a-b if necessary.

[0045] The Figures 7 and 8show two exemplary designs of the adapter 12 with largely universally usable coaxial connectors 38, 40. The adapter 12 requires essentially the same installation space as a short section of the coaxial connection 14 and is very simple and intuitive to handle. The subsequent processes are preferably carried out automatically; only a corresponding control program in the RFID reader 10 or an external control and evaluation unit 24 of a higher-level processing unit is required. The invention is described using the example of an RFID reader 10, but is equally applicable to other transceivers or radio systems or coaxial connections 14 between components thereof.

Claims

1. An RFID reading device (10) comprising a second device (16), in particular an antenna, and a coaxial connection (14) to the second device (16) and at least one first adapter device (12) for measuring the signal power in the coaxial connection (14), the first adapter device (12) comprising a first coaxial connector (38) and a second coaxial connector (40) for inserting the first adapter device (12) into the coaxial connection (14) and a measuring unit (42) configured for determining the signal power of a signal propagating from the first coaxial connector (38) to the second coaxial connector (40) and / or vice versa, wherein the first coaxial connector (38) and the second coaxial connector (40) are detachable so that the first adapter device (12) can be selectively inserted into or removed from the coaxial connection (14), and wherein the first adapter device (12) is inserted into the coaxial connection (14) with its first coaxial connector (38) and second coaxial connector (40) at an end of the section of the coaxial connection (14) to be measured which is remote with respect to the RFID reading device (10).

2. The RFID reading device (10) according to claim 1, wherein the measuring unit (42) is configured to determine a maximum value of the signal power.

3. The RFID reader device (10) according to claim 1 or 2, wherein the first adapter device (12) comprises a power supply unit (50) with which the first adapter device (12) powers itself from the signal propagating on the coaxial connection (14).

4. The RFID reader device (10) according to any of the preceding claims, wherein the first adapter device (12) comprises a memory (46) in which the measuring unit (42) stores a measured value for the signal power.

5. The RFID reading device (10) according to claim 4, wherein the memory (46) can be read by means of an RFID protocol, in particular comprises an RFID transponder circuit.

6. The RFID reading device (10) according to claim 5, wherein the measuring unit (42) is configured to check the memory (46) for a start signal stored therein and to perform a measurement of the signal power if a start signal is present.

7. The RFID reader device (10) according to any of the preceding claims, wherein the transmission power of the RFID reading device (10) in the RFID reading device (10) is known and the RFID reading device (10) is configured to determine a transmission loss of the coaxial connection (14) from the known transmission power and a measured value of the first adapter device (12).

8. The RFID reading device (10) according to any of claims 1 to 6, comprising a second adapter device (12b) for measuring the signal power in the coaxial connection (14), the second adapter device (12b) being arranged at an end of the section of the coaxial connection (14) to be measured which is close with respect to the RFID reading device (10), and the RFID reading device (10) being configured to determine a transmission loss of the coaxial connection (14) from measured values of the first adapter device (12a) and the second adapter device (12b).

9. A method for measuring the signal power in a coaxial connection (14) from an RFID reading device (10) to a second device (16), in particular an antenna, by means of at least one first adapter device (12, 12a), which is detachably inserted into the coaxial connection (14) with a first coaxial connector (38) and a second coaxial connector (40), wherein the RFID reading device (10) starts a measurement of the signal power, the first adapter device (12, 12a) then determines the signal power of a signal of the RFID reading device (10) propagating through the first adapter device (12, 12a) and the RFID reading device (10) then reads out a measured value of the first adapter device (12, 12a).

10. The method according to claim 9, wherein the communication between the RFID reading device (10) and the at least first adapter device (12, 12a) takes place via a memory (46) of the adapter device (12, 12a), in particular by communication by means of an RFID protocol.

11. The method according to claim 9 or 10, wherein the RFID reading device (10) starts a measurement of the at least first adapter device (12, 12a) by storing a start signal in the memory (46) and wherein the adapter device (12, 12a) checks the memory (46) for a start signal stored therein and performs a measurement of the signal power if a start signal is present.

12. The method according to any of claims 9 to 11, wherein the RFID reading device (10) generates a transmission signal of known transmission power and meanwhile the first adapter device (12) performs a measurement of the signal power, and wherein the RFID reading device (10) determines a transmission loss of the coaxial connection (14) from the known transmission power and a measured value of the signal power determined by the first adapter device (12).

13. The method according to one of claims 9 to 11, wherein a first measurement of the signal power is carried out with the first adapter device (12a), while the RFID reading device (10) generates a transmission signal, and additionally a second measurement of the signal power is carried out with a second adapter device (12b), which is detachably inserted into the coaxial connection (14), and wherein the RFID reading device (10) determines a transmission loss of the coaxial connection (14) from a measured value of each of the two measurements.

14. The method according to any one of claims 9 to 13, wherein, if the at least first adapter device (12, 12a-b) does not remain in the coaxial connection (14) during further operation, the RFID reading device (10) corrects a transmission loss of the coaxial connection (14) by a known transmission loss of the at least first adapter device (12, 12a-b).