FI119083B - RFID reader with antenna mismatch compensation - Google Patents

Description

119083 RFID reader with antenna mismatch compensation

Area

The invention relates to compensation for antenna mismatch in a radio frequency remote identification reader.

5 Background

Radio Frequency Identification (RFID) is a technology that uses radio frequency spectrum electromagnetic or electrostatic matching to identify objects to which RFID tags have been attached. In general, RFID systems offer the advantage of not requiring direct contact or sight-axis support. A typical RFID system includes an RFID reader and a plurality of RFID tags affixed to the objects of interest. The RFID reader includes an antenna and a transceiver. An RFID reader uses an antenna and a transceiver to transmit radio frequency signals to an RFID tag. In response to radio frequency signals received from the RFID reader, the identifier sends the data back to the reader by modulating the signal received at the RFID reader antenna. As an example, some tags use variable impedance applied to the antenna, which can be used to change the amount of energy reflected from the tag. These tags can send data to the reader by varying the impedance to selectively modulate the transmitted signals. RFID tags can be used as such to identify and track multiple items. In addition, since RFID tags are relatively inexpensive components, they can be used to track a large number of objects at relatively low cost.

··· ·:: * · Figure 1 shows an example of an RFID reader 100. The RFID reader 100 comprises an * *. * · *. The RFID reader 100 further comprises a receiving circuit 106 for enabling the reception of radio signals transmitted from the RFID tag 122. The RFID reader 1 preferably comprises a single antenna 110 for use in both transmission. * **; · 'that at reception to reduce the physical size of the reader. The transmitted sig- ") i * 30 signals are routed from the reader's transmission circuit 102 to the antenna 110 via the rotary member 104.

: ***: On the other hand, the same rotation member 104 transmits the sig- * · · / received by the antenna 110. signals to the receiver circuit 106. of the RFID reader 100. In practical embodiments, the *; "I cell 104 is not an ideal component, and therefore components of the transmitted signal may leak into the receiving circuit 106. In addition, mismatches in the 35 antenna ports may occur, resulting in reflection of a portion of the transmitted signal from the antenna port 2 119083 to the receiving circuit 106. the components of the signal may add up to the data signal received from the RFID tag 122 and impair the performance of the RFID reader 100. If the received data signal is degraded by high-level components of the transmitted signal, the RFID reader 5 may not be able to reliably detect the received data signal. Therefore, these components of the transmitted signal must be compensated for or attenuated to allow reliable data detection.

Further related to mismatches in the RFID reader antenna port, the reader antenna may occasionally be broken or disconnected from the antenna port. This results in a large 10 mismatch at the antenna port and almost complete reflection of the transmitted signal. The high level signal reflected in the reader's receiving circuit typically breaks the receiving circuit. It would be advantageous to find a solution to prevent the receiving circuit from breaking up in such cases.

WO2006037241 describes a solution for compensating interference caused by an RFID reader's transmitter to a receiver. The correction signal is generated by a digital signal processor and the correction signal is supplied to the receiver via a digital-to-analog converter (D / A converter) and a linear modulator. This compensates for the interfering signal in the receiver. The solution described is not cost-effective due to the over-20 expensive components contained in the reader. The solution described requires an additional signal processor, an extra D / A converter and an extra modulator to generate the correction signal and to perform the interference compensation. These additional components increase RFID reader costs: considerably.

• · • * * 25 Brief Description • · · • · ♦

It is an object of the invention to provide an improved solution to compensate for the effects of a transmitted signal leaking into the receiving circuit of a radio frequency reader.

• · \ v INVENTION According to one aspect is provided a component inconvenient 30 Vitus compensation method in a radio frequency identification (RFID) reader. The method comprises: transmitting a first signal to the antenna port of the RFID reader, also directing the first signal to a compensation circuit, generating a compensation signal based on information on the transmitted first signal components of the transmitted signal to the receiver side of the RFID reader, 35 generating a compensation signal; and combining a compensation signal with a second signal received from the antenna port to attenuate the signal components of the first signal from the received second signal. The method further comprises: transmitting the test signal to the antenna port at a lower transmit power level than the transmit power level used to transmit the data signal.

5 According to another aspect of the present a radio frequency identification (RFID) reader, comprising a transmission circuit configured to generate radio frequency signals for transmission, a coupling unit configured to couple signals to be transmitted from the transmission circuit of the RFID reader antenna port and a compensation circuit, the compensation circuit, which is configured to 10 to create a compensation signal on the receiver side of the RFID reader, based on information on the signal components of the transmitted signal, and combining the compensation signal with a signal received from the antenna port, wherein the compensation circuit is further configured to create a compensation signal by modifying the signal transmitted from the transmission circuit and coupled by the switching unit. The RFID reader further comprises a processing unit configured to control the transmit circuit to transmit the test signal to the antenna port at a lower transmit power level than the data signal transmit power level.

According to a second side is provided a computer program product encoding a computer program of instructions for executing a computer process machine 20 to compensate for component mismatch in a radio frequency identification (RFID) reader. The process comprises: transmitting a first signal to the antenna port of the RFID reader and configuring a compensation circuit of the RFID reader to generate a compensation signal based on information on the transmitted first signal components of the transmitted first signal to the receiver side of the RFID reader and to create a compensation signal The process further comprises: controlling a transmission circuit to transmit a test signal to the antenna port at a lower transmission power level than the transmission power level used to transmit the data signal.

The invention provides a simplified structure for generating a compensation signal *; [* '30]. The signal to be transmitted can be used to create a compensation signal, and thus a separate signal generator is not necessary. to create a compensation signal.

* · · * ·· .: Pattern List •

The invention will now be described in more detail in connection with the preferred embodiments, with reference to the accompanying drawings, in which: Fig. 1 shows a block diagram of an RFID reader and an RFID identifier; Fig. 2 shows a structure of an RFID reader according to an embodiment of the invention; Fig. 3 is a detailed block diagram of an RFID reader comprising a compensation circuit according to an embodiment of the invention; Figure 5 is a block diagram of an RFID reader according to another embodiment of the invention, and Figure 5 is a flowchart illustrating a process for compensating for component mismatch in an RFID reader according to another embodiment of the invention.

10 Description of Embodiments

Referring to Figure 2, the overall structure of a radio frequency identification (RFID) reader 200, in which embodiments of the invention may be implemented, is contemplated. Furthermore, the general structure of the RFID tag 220 communicating with the RFID reader 200 is described.

The RFID reader 200 comprises a transmit / receive circuit 208 which enables the transmission and reception of radio signals. The transmitting / receiving circuit 208 may be functionally divided into a transmitting circuit and a receiving circuit. The transmission circuit performs the functions necessary to convert the transmitted signals into a format suitable for transmission. The transmitting circuit may perform upmix, amplification, and filtering procedures on the 20 signals to be transmitted. The receiving circuit • »: * ··, in turn, performs the functions necessary to convert the received signal *: to a format suitable for detecting data. The receiving circuit can •: *. perform a downmix, gain, and filter process on the received signal * * · ·:. ·, and then feed it to the analog-to-digital converter for further processing. The transmit / receive circuit 208 may use a single antenna for both transmitting and receiving radio signals.

The * * ··· * RFID reader 200 further comprises a processing unit 204 which controls the operations performed in the RFID reader. The processing unit 204 may control the transmission and reception of signals transmitted or received through the transmit / receive circuit 208: ***: 30. The processing unit 204 may also control the RFID reader • · · *. 204 other components. The processing unit may be an • · · ;;; It is equipped with a digital signal processor and suitable software stored on a computer readable medium or with separate logic circuits, such as ASIC (Application Specific Integrated Circuit).

. ·. * 35 The RFID reader 200 further comprises a memory unit 206 for storing parameters and information necessary for the operation of the RFID reader 200 * * ·.

5, 119083

The memory unit 206 may store the commands and parameters of the processing unit 204 for transmitting and / or receiving signals to be transmitted from the RFID reader / reader.

The RFID reader 200 may further comprise a user interface 202 for communicating between the user of the RFID reader 5200 and the RFID reader 200. The user interface 202 may comprise, for example, a display unit and an input device.

The RFID reader 200 communicates with the RFID tag 220 over a wireless radio connection. The RFID tag comprises a transmit / receive circuit 222 and a memory unit 224. The transmit / receive circuit is configured to receive a radio signal transmitted from an RFID reader 200, modulate the received radio signal with information stored in the memory unit 224, and transmit the modulated signal back to RFID reader 200. The RFID tag 220 can only respond to a specific type of activation signal received from an RFID reader. If the RFID tag 220 receives other types of signals, it may be configured not to respond to them. The RFID tag typically does not comprise an energy source, and so the energy required to operate the RFID tag 220 is taken from the received signal. The RFID reader 200 may also send additional energy bursts to provide the RFID tag 220 with sufficient energy.

Figure 3 shows a detailed block diagram of an RFID reader 200 according to an embodiment of the invention. The processing unit 204 is: the same as described above with reference to Figure 2. The processing unit 204 transmits signals through the transmitting circuit 302 to the antenna port 330. A digital-to-analog converter (D / A-: 25 converter) 322 may be provided between the processing unit 204 ·. · J and the transmitting circuit 302. The transmitting circuit 302 processes the information signal to be transmitted: radio frequency. The transmission circuit 302 may perform the same functions as above. transmission circuit described. The transmit circuit then supplies a radio frequency signal to antenna port 330 through rotary member 306.

. The rotary member 306 transmits the received signals from the transmit circuit 302 to the antenna connected to the antenna port 330 and the signals received from the antenna port 330 to the receiving circuit 310. The receiving circuit 310 may perform the same operations as the receiving circuit described above. The receiving circuit 310 then supplies the signals to the processing unit 204 through the analog-to-digital converter (A / D converter) 320 '*: **.

As mentioned above, the rotary member 306 may not be an ideal component, and components of the transmitted signals may leak into the receiving circuit 310 to degrade the data detection performance. The RFID reader 200 may first transmit a data signal to the RFID tag 220 and then energy bursts to provide energy to the RFID tag 220 so that the RFID tag 220 may generate a response signal to the data signal received from the reader 200. Thus, the RFID-5 reader 200 receives a response signal from the RFID tag 220 when transmitting energy bursts, and components of the transmitted signal (energy bursts) leak to the receiver side of the reader 200 when receiving a response signal from the tag 220. This may be a problem. Especially with RFID readers using the same antenna for simultaneous transmission. If signal 10 is transmitted while receiving another signal, the components of the transmitted signals will leak to the receiving circuit 310, impairing the detection performance of the received signal. In addition, there may be antenna mismatches between the antenna port and the antenna, resulting in a partial reflection of the transmitted signal from the antenna port. These signal components are also transmitted to the receiving circuit 15 310 via the rotation member 306.

To attenuate the components of the transmitted signal leaking to the receiving circuit 310, the RFID reader 200 according to one embodiment of the invention includes a compensation circuit 340. The signal produced from the transmission circuit 302 may be transmitted to the rotary member 306 via a switching unit 304. The switching unit 304 may be a directional switch configured to transmit a signal received from the transmitting circuit 302 to the compensation circuit 340 in addition to the rotary member 306.

The compensation circuit 340 comprises an amplitude control unit 312 and a phase control unit 314 which modulate the amplitude and phase of the input signal (signal received from the transmission circuit 302 ·: · the switching unit 304), j: *: 25 The amplitude control unit 312 and phase implemented by, for example, a vector modulator The operation of the compensation circuit 340 is controlled by a pro-. * 30 204 can supply parameter values to control units 312 and 314 via D / A converters 316 and 318. The purpose of the compensation circuit 340 is to provide a compensation signal which attenuates the transmitted signal leaking to the receiving circuit when these signals are combined. Also, combiner '*: ** 308 combines 35 signals received from antenna port 330 with rotation member 306 to supply a signal thus obtained to receive circuit 310190. Thus, combiner 308 may be disposed within the rotary member. 306 and receiving circuit 310.

The amplitude of the signal received through the switching unit 304 may be modified before phase adjustment or vice versa. Alternatively, the signal received through the switch-5 unit 304 may be divided into two signals. One of these two signals can be supplied to the amplitude control unit 312 and the other to the phase control unit 314. The responses of the amplitude control unit 312 and the phase control unit 314 can then be combined, for example, to sum them together.

The processing unit 204 provides the amplitude control unit 312 and the phase control unit with parameter values based on information on the signal components of the transmitted signals leaking to the receiving circuit 310. Based on this information, processing unit 204 may select an optimal set of parameter values to attenuate leaking components of the transmitted signal.

Information on the signal components of the transmitted signals leaking to the receiving circuit 310 may be obtained by transmitting a test signal to the antenna port 330 during the testing phase, whereby neither data transmission nor reception is performed. The processing unit 204 transmits a test signal to the antenna port 330 via a transmission circuit 302, a switching unit 304, and a rotation member 306. The switching unit 204 also directs the test signal to the compensation circuit 340. The components of the test signal "leak through the rotation member 306 and are reflected from the antenna port!" * 'Compensation circuit 340 to combiner 308.

• · • V *; During the test phase, processing unit 204 provides amplitude control unit 312 and phase control unit with different amplitude and phase shift •: *: 25 parameter combinations and monitors the receiving circuit 310 and the A / D converter • m ·. . ·. 320 signal level received. The idea is to produce a compensating, ···, sound signal that completely suppresses the leaking signal components, i.e., that the signal from the output of the 308 combiner 308 is minimized.

The amplitude and phase adjustment parameter combinations may be predefined and stored in an RFID reader memory unit 206. Test signal modifier ··· · * ... · * period in a compensation circuit with 340 different amplitude and phase shift parameter combinations leads to different test modifications a different residual signal when the modified test signal is combined with the * "* 'signal received from the rotary element. The combining is performed in combiner 308, which may be, for example, a summing unit. The residual signal obtained in combiner response is fed to processing unit 204 .

• · 8 119083

The processing unit 204 measures the level of the residual signal, supplies to the compensation circuit 340 a different combination of amplitude and phase shift parameter values, and measures the level of the residual signal (or composite signal) thus obtained. Alternatively, the processing unit 204 may measure another property of the residual signal, such as power. Thus, the processing unit 204 measures the levels of residual signals obtained by modifying the test signal with different combinations of amplitude and phase shift parameters, and selects a combination of parameters to obtain a Low residual signal level. The lowest level indicates that the lowest level compensating signal is optimal for attenuating signal components leaking through the rotation member and / or reflected from the antenna port 330. Ideally, the compensation signal has the same amplitude and opposite phase as the test signal leaking from the transmission side to the receiving side. The processing unit 204 then selects an amplitude and phase shift parameter combination that provides the most optimal compensation signal for use in transmitting and receiving information signals to the RFID reader 200.

If the RFID reader 200 comprises multiple antenna ports, the testing step may be performed on each of the antenna ports. Thus, a test signal may be transmitted to each antenna port, and a compensation signal may be generated for each antenna port according to the procedure described above. The parameters of the compensation signal associated with each antenna port 20 can be stored in the memory unit 206 and downloaded from the memory unit at the start of data transmission. Downloaded: ** · parameters then determine the compensation signal to be used for data transmission • · ♦ '. * ··. Although the antenna ports may have the same structure and components: the antenna port mismatches may vary. Therefore, it may be advantageous to provide each antenna port with a unique compensation signal.

»« * ·. . ·. During data transmission, the RFID reader 200 can further optimize the parameters (amplitude and / or phase parameter) of the com- pensation signal. Process - **** unit 204 may initiate a parameter optimization procedure according to a predetermined criterion. The parameter optimization procedure may be performed at pre-V: 30 characters at predetermined times during data transmission. Processing, ..: In the parameter optimization procedure, the unit 204 can input compensation parameters 340 different than those determined during the testing phase and monitor the effect of the new ** parameters on data reception. The values of the new parameters • e * ·; · * Effect monitoring may include sequential monitoring of successful read events If the number of successful read events is greater than those defined during the test phase, the processing unit 204 may keep the new parameters. Conversely, if the number of successful read events is smaller with the new parameters, the processing unit 204 may discard the new parameters and return to the old parameters. The advantage of optimizing the parameters of the compensation signal during data transmission is, for example, compensating for changes in component properties ation.

The use of a compensation circuit 340 according to an embodiment of the invention is particularly advantageous in situations where the signal is transmitted and received simultaneously. However, the benefits 10 obtained by the compensation circuit 340 are not limited to this. If there is an external interference signal that is stronger than the transmitted signal leaking to the receiving side, the above procedure may be used to attenuate this external interference signal component. The above procedure for generating a compensation signal can thus be used to attenuate the strongest signal interfering with the reception of the desired data signal. If there are multiple interference signals, multiple pairs of amplitude and phase control units can be chained, each pair attenuating one interference signal.

The test signal may be transmitted to the antenna port at a lower power level than the power level used to transmit the data signal. Thus, the testing step can also be used to determine whether a properly functioning antenna is connected to the antenna port. When no antenna is connected to the antenna port or when: *** the antenna is broken, there is a bad mismatch in the antenna port and the test signal is reflected • · · '. * ·: Almost completely. On the other hand, if a right-hand antenna is connected to the antenna port, only a small part of the transmitted test signal is reflected back • · *; 25 sin antenna port.

. Figure 4 shows a structure for determining whether a properly functioning antenna is connected to a plurality of antenna ports 330, ***** 332 and 334 of an RFID reader according to an embodiment of the invention. The same reference numerals mean the same components as in Figure 3. Fig. 4 is a simplified block diagram of v: 30 showing only those components which are relevant to the description ··· · * ..,. * The switch mechanism 400 controlled by the processing unit 204 is arranged] by the rotation member 306 and the antenna ports 330-. The processing unit yV 204 controls the switching mechanism 400 to select the antenna port 330, 332 or 334, ***** where the signal is to be sent, so the processing unit 204 controls the switching mechanism: **: 35 to connect the transmission circuit 302 (via the rotation member 306) to the selected antenna port. .j 330, 332 or 334.

• ·

1190S S

10

The processing unit 204 may transmit a test signal to each antenna port 330, 332 and 334, and monitor the level of the reflected signal from the antenna ports 330, 332 and 334 through the rotary member 306 and the receiving circuit 310 to determine which antenna ports 330, 332 and 334 are properly connected. The processing unit 204 may control the switch mechanism 400 to connect the transmit circuit 302 to each of the antenna ports 330, 332, and 334 in turn, so that each antenna port is tested separately. The processing unit 204 may first control the switch mechanism 400 to connect the transmit circuit 302 to the first antenna port 330, transmit the test signal to the first antenna port 330 via the transmit circuit 302, receive the reflected signal component through the receiving circuit 310, and measure the received signal level. The test signal may be the same test signal as described above with reference to Figure 3. If the measured level of the received signal exceeds a predetermined threshold, the processing unit 204 determines that the first antenna port 330 is not connected with an oi-15 high-functioning antenna. On the other hand, if the measured level of the received signal is less than a threshold, the processing unit 204 determines that a properly functioning antenna is connected to the first antenna port 330. Other antenna ports 332 and 334 may be subjected to the same procedure. Now that the processing unit 204 has determined which of the antenna ports 330, 332, and 334 is connected to a properly functioning antenna, it can select the antenna port (or ports) for transmitting data. Thus, the processing unit 204 may transmit through the transmit: * ·· circuitry 302 to the data signal antenna port (s) to which a properly functioning antenna is connected, and prevent the data signal from being transmitted to the antenna ports: *; to which no properly functioning antenna is connected. If no antenna port is configured for any of the: 25 antenna ports, the * X processing unit 204 may prevent the data signal from being transmitted to all antenna ports.

If a high power data signal were sent to an antenna port without a properly functioning antenna connected, the signal would be almost completely reflected back from the antenna port to the receiving circuit and would likely violate the: ***; the input circuit. The above-described embodiment of the invention transmits to low-power antenna ports during the test phase to detect antenna ports that do not have a properly functioning antenna connected and to prevent high-power da- • * * ··· * signal from being transmitted to these antenna ports. The testing step may be performed periodically between data signal transmissions. This solution prevents the • • receiving circuit breakage if the antenna is accidentally removed from the antenna port • · 11 119083 or if it is broken. The RFID reader may further notify the reader user of a malfunction at the antenna port through the RFID reader interface. Alternatively, the RFID reader may report a malfunction to another entity, such as a central system that communicates with the RFID reader.

5 The present solution further enables the antenna to be replaced by a fly lift. For example, if the antenna connected to the antenna port of the RFID reader is replaced with another antenna, the exchange may be performed while the RFID reader is on or even transmitting. Together with the compensation circuit 340 described above, this automated inspection of antenna port connections further enables one type of antenna to be exchanged with another type of antenna without impairing the detection performance of the received signals. If the antenna is replaced by another type of antenna, there may be mismatch between the antenna port and the new type of antenna, resulting in stronger reflection components of the signal transmitted to the antenna port. Compensation circuit 340 is now used to attenuate these components which are reflected back to the receiving circuit, thereby eliminating the effects of impairing data reception. Thus, the RFID reader according to an embodiment of the invention automatically adapts to a new type of antenna, and no separate testing and antenna tuning arrangements are required.

FIG. 5 is a flowchart illustrating a process for compensating component mismatch in an RFID reader according to an embodiment of the invention. An RFID reader can use one antenna for simultaneous transmission: '·· and for reception. Thus, the transmitted and received signals are transmitted: through a circulating means. The process begins in block 500.

: In block 502 of one or more RFID reader antenna ports:. *. 25, a test signal is transmitted during the test phase. Because the RFID reader components are not ideal and because one or more antenna ports may be mismatched, components of the transmitted signal leak into the RFID reader's receiving circuit. These leaking components of the transmitted test signal are received in block 504 .

• * \ v 30 Block 506 determines whether a properly functioning antenna is connected to each of one or more. ****: antenna ports. This can be determined by measuring the level of the signal components received from one or more antenna ports. The antenna * · *; · * port connected to a properly functioning antenna can then be selected to be used for data transmission.

In block 508, a compensation signal is generated based on the signal components received from the selected antenna port. The compensation signal can be generated by directing a test signal sent to a selected antenna port to a compensation circuit which modifies the test signal to form a compensation signal to attenuate components of the test signal leaking to the receiver side. The compensation signal may be generated by modifying the amplitude and phase of the test signal in the compensation circuit, combining the modified test signal with the components of the test signal leaking to the receiver side, and measuring the level of the combined residual signal. This can be accomplished by various amplitude and phase shift modifications, and the amplitude and phase shift parameters of the compensation signal that best attenuates the components of the test signal leaking to the receiver side can be selected.

During the data transmission and reception step, a first data signal and energy bursts can be transmitted to the selected antenna port and also to the compensation circuit at step 510. When transmitting energy bursts, a second data signal can be received from the RFID tag to which the first data signal was transmitted. Signal components leaking to the receiver side may be attenuated by a compensation signal formed by modifying the signal controlled by the compensation circuit with selected amplitude and phase shift parameters in block 512. The compensation signal and the received second data signal may then be combined to receive outgoing signals from block 204. The received second data signal may then be detected in block 516.

• f; * ·· In block 518, the parameters of the compensation signal (s): \ j are optimized. Optimization can be performed by changing parameters and observing •: *; affecting the quality of data reception. New parameters can be test ··· ·:. ·. 25 parameters in the background. If the use of the new para-V meters results in a better reception quality, the new parameters will be retained. Otherwise, the new parameters will be discarded and the parameters specified in the test phase • e ***** will be reset. The optimization can be performed for each RFID reader antenna port during.

• · v 30 In block 520, it is determined whether a second testing step is performed to modify the parameters used to generate the compensation signal and to re-check the antenna ports. If it is determined that the testing step * ;;; is performed, the process returns to block 502 for a second test step. Otherwise, the process returns to block 510 to transmit a second data signal for * ·, · 35.

• · • · • * · • ·· • · 119083 13

Embodiments of the invention may be implemented in an RFID reader comprising a transmission circuit, a reception circuit, a compensation circuit, and a processing unit operatively coupled to the transmission, reception and compensation circuits. The processing unit may be configured to perform at least some of the steps described in connection with the flow chart of Figure 5 and Figure 4. Embodiments may be implemented as computer software comprising commands for compensating component mismatching to perform a computer process for use in an RFID reader.

The computer software may be stored on a computer software distribution medium readable by a computer or a processor. The computer software distribution means may include, but are not limited to, electrical, magnetic, optical, infrared or semiconductor systems, devices, or transmission media. The computer software distribution media may include at least one of the following: a computer readable medium, a software storage medium, a storage medium, computer readable memory, operating memory, erasable programmable read only memory, computer readable software distribution package, computer readable signal, , computer readable printed matter and computer readable compressed software package.

Although the invention has been described above with reference to the example of the accompanying drawings, it will be understood that the invention is not limited thereto but can be modified in many ways within the scope of the appended claims.

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Claims (19)

A method of compensating a component's mismatch in a radio frequency non-contact reader, which method comprises: a first signal is transmitted (502, 510) to the RFID reader's antenna port; The first signal is also controlled to a compensation circuit; a compensation signal is created (512) on the basis of data relating to the signal components leaking to the receiver side of the RFID reader of the transmitted first signal, the compensation signal being generated by processing the first signal in the compensation circuit; The compensation signal is combined (514) with a second signal received from the antenna port to attenuate the signal components of the first signal from the received second signal; characterized in that a test signal is transmitted (502) to the antenna port at a smaller transmit power level than the transmit power level used for transmitting the data signal. Method according to claim 1, characterized in that the first signal is transmitted upon receipt of the second signal. Method according to claim 1, characterized in that the first signal is sent to the antenna port via a circulator and the first signal 20 is controlled to the compensation circuit before the circulator. ϊ Method according to Claim 1, characterized in that the information is provided by the leakage components of the RFID reader's receiver jt $ ': of the transmitted first signal: • · *; by transmitting (502) during the test stage a test signal to RFID • t # ». . ·. The reader's antenna port; * * t by controlling (504) the test signal also to the compensation circuit; **** by receiving the receiver side of the RFID reader leaking components of the transmitted test signal; v: by creating (508) in the compensation circuit one or more modifications of the test signal to different parameters; by combining (508) the received test signal's received signal, components with each or one of the modifications of the test signal, thus producing a or multiple combined signals; \ S by selecting (508) parameters which are combined into a modifier, which produces the lowest level of the combined signal, and using ( 512, 514) selected parameters when receiving data to attenuate the signal components of the first signal from the received second signal. Method according to Claim 1 or 4, characterized in that the processing in the compensation circuit comprises: controlling at least one of the amplitude and phase of the test signal, which amount of control is determined by an amplitude control parameter and a phase control parameter. Method according to claim 1, characterized in that the RFID reader comprises one or more antenna ports, the method comprising: the test signal is transmitted (502) during the test stage to one or more of the RFID reader's antenna ports; components of the transmitted test signal to the receiver side of the RFID reader are received (504); (506), based on the received components of the test signal, it is determined whether a properly functioning antenna is coupled to one or more antenna ports; the data signal is transmitted (510) to the antenna port which is defined to be coupled to the properly functioning antenna, and transmission of the data signal is prevented to an antenna port or ports, which have been defined as unconnected to the properly functioning antenna. Method according to claim 6, characterized in that the definition comprises: * · \ * ·· from a certain antenna port, the level of the received components j (: of the transmitted test signal is measured; with a predetermined threshold value, and ··· · it is determined that the data signal can be transmitted to the antenna port, if the • · 9 measured level is less than the threshold value, and that the data signal cannot be transmitted to the antenna port, if it is measured. level is greater than the threshold. Method according to any of the preceding claims, characterized in that the compensation signal parameters are optimized during the ··· ·…: transmission of data. ) ·. A radio frequency contactless reader (200), comprising: mlV with a transmission circuit (302) configured to generate radio frequency transmitting signals, a switching circuit (304) configured to switch the signals: * ·. · to be transmitted from the transmission circuit to the RFID reader antenna port (330) • · 21 1 19083 and the compensation circuit (340), a compensation circuit (340) configured to generate a compensation signal on the basis of data relating to The receiver side of the RFID reader is leaking signal components of the transmitted signal and combining the compensation signal with the signal received from the antenna port, the compensation circuit is additionally configured to create a compensation signal by processing a transmit circuit (302) transmitted and switched off. 304) signal coupled to the compensation circuit (340); characterized in that the RFID reader further comprises a processing unit (204) configured to control the transmission circuit (302) to transmit the test signal to the antenna port at a lower transmit power level than the transmit power level of the data signal. RFID reader according to claim 9, characterized in that the RFID reader simultaneously transmits and receives radio signals. RFID reader according to claim 9, characterized in that the RFID reader further comprises a circulator (306) configured to transmit a signal from the transmission circuit (302) to the antenna port (330) and a signal from the antenna port to the compensation circuit (340). , and that the switching unit (340) is located between the transmission circuit (302) and the circulator 20 (306). RFID reader according to claim 9, characterized in that the · ·: processing unit is configured to control the transmission circuit to transmit the test signal to the antenna port of the RFID reader via the switching unit, to receive · via the receiving circuit the receiver side of the RFID reader leakage components of the transmitted test signal, to control the compensation circuit to create modifications of one or more test signals with different parameters, and to com- •··. bind the received test signal's received components with the modification of each of one or more test signals and select the parameters which are combined. . with the modifications, which generate the lowest level of the combined signal. : ···: 13. RFID reader according to claim 9, characterized in that • f. the processing unit controls the compensation circuit to control at least one of »··«. ···. the amplitude and phase of the test signal, which amount of control is determined by an amplitude control parameter and phase control parameter given by the processing unit given in the *. ·. ϊ • ·· • «22 1 1 9 0 8 3 RFID reader according to claim 9, characterized in that the compensation circuit comprises a vector modulator and a combiner (308). An RFID reader as claimed in claim 9, characterized in that the RFID reader comprises one or more antenna ports (330, 332, 334) and a processing unit (204) configured to control the transmission circuit (302) to transmit a test signal to one or more of the RFID reader's antenna ports, receiving via the receiver circuit (310) the components of the transmitted test signal leaking to the RFID reader's receiver side, and determining on the basis of the received signal of the test signal whether or not one or more antenna ports are connected 10 a properly functioning antenna. RFID reader according to claim 15, characterized in that the RFID reader further comprises a coupling mechanism (400) controlled by the processing unit, and the processing unit is further configured to control the coupling mechanism to connect the transmission circuit to the antenna port, which is defined to be connected to it. properly operate the antenna, and disconnect the transmission circuit from the antenna port (s), which has been defined as unconnected to the properly functioning antenna. RFID reader according to claim 15, characterized in that the processing unit is configured to perform determination by measuring the level of one or more received components of a transmitted test signal received from a particular antenna port by comparing the measured level with a predetermined level. : ** determined threshold value and by determining that the transmit circuit can be connected to the antenna port if the measured level is lower than the threshold value, and that the transmit circuit cannot be connected to the antenna port if the measured: level is higher than the threshold value. ··· ·: 18. RFID reader according to any of claims 9-17, characterized by ·· *. characterized in that the processing unit is also configured to optimize the compensation signal parameters during the transmission of data. ,, 19. Computer software product which encodes the computer software • e · ** V 30 commands to perform a computer process to compensate for a component's mismatch in a radio frequency-free reader: which process comprises: "t1, a first signal is sent to a RFID Reader Antenna Port; ♦ ♦ The RFID Reader Compensation Circuit is configured to create a compensation signal based on data referring to the RFID Reader Receiver Side Leaking Signal Components of the transmitted first signal and A compensation signal by also processing the first signal controlled by the compensation circuit; characterized in that the transmission circuit is controlled to transmit a test signal to the antenna port at a smaller transmit power level than the transmit power level used for transmitting the data signal. • · 1 • · «* · •« • «· * · · ··· · · · · · ·« · · M1 · «· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ··· • · · · 1 · ·· • · · · · 1 • · »• ·