Imported: 13 Feb '17 | Published: 18 Jan '11

Takuya Nagai, Kentaro Ushiyama

USPTO - Utility Patents

## Description

The present application is a Continuation-in-Part of International Application No. PCT/JP2005/007343 filed Apr. 15, 2005, which claims the benefits of Japanese Patent Applications No. 2004-145298 filed May 14, 2004 and No. 2004-190098 filed Jun. 28, 2004.

### BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a radio-frequency communication device operable to transmit and receive information to and from a desired communication object, and more particularly to techniques for eliminating an influence of a transmitter side of the device on a receiver side of the device.

2. Description of the Related Art

To solve the problem of the interfering leakage signal described above, it has been proposed to generate a cancel signal (compensating signal) for offsetting or canceling the unnecessary interfering leakage signal to be mixed in the reply wave, upon transmission of the transmitted wave, and to combine together the generated cancel signal and the unnecessary interfering leakage signal. JP-8-122429 A discloses an example of this conventional technique, wherein a device to identify mobile objects is provided with an interference compensating device. This interference compensating device includes a variable phase shifter and a variable attenuator for adjusting the phase and amplitude of the leakage signal which is a part of the transmitted wave, and a multiplexer for combining together a cancel signal generated by the phase and amplitude adjustment of the leakage signal, and the input to the receiver antenna, for thereby offsetting or canceling the unnecessary leakage signal. To generate the cancel signal, the variable phase shifter and the variable attenuator are manually adjusted so as to minimize the level of a composite signal obtained by combining together the cancel signal and the leakage signal which are generated while no reply wave is received from the transponders in response to the transmitted wave. To deal with a change of the unnecessary leakage signal changes due to aging deterioration of the variable phase shifter and attenuator, these variable phase shifter and attenuator are manually re-adjusted at a regular interval, for example, once per year.

There have been proposed techniques for enlarging the area of communication of the radio-frequency communication device. JP-5-128289 A discloses an example of such techniques, namely, a millimeter wave information reading system. This system uses an array antenna consisting of a plurality of antenna elements, and is arranged to control the phase of the transmitted signal transmitted from each of the antenna elements, and the phase of the received signal received by each antenna element, that is, to effect phased-array processing for transmission of the transmitted signal and reception of the received signal.

However, the conventional techniques described above have the following problems, in view of increasing introduction of the RFID system into various fields of industry. Namely, in the field of searching for desired articles of commodity within a warehouse, for example, radio communication between the interrogator and the transponders is adversely influenced by moving persons or metallic bodies, or existence of metallic bodies. Described in detail, the increasing introduction of the RFID system into the various fields of industry causes an increase of an influence of a change of the operating environment of the RFID system on the communication between the interrogator and the transponders, resulting in a considerable change of the condition in which the unnecessary leakage signal is generated from the transmitted signal or wave. According to the conventional technique wherein the cancel signal is optimized by manual adjustment of the variable shifter and attenuator, only a regular re-adjustment of the variable phase shifter and attenuator can be relied upon to deal with a change of the unnecessary leakage signal after the optimization of the cancel signal. Thus, it has been difficult to deal with a change of the operating environment of the RFID system in a real-time fashion, for sufficiently canceling the interfering leakage signal with the suitably adjusted cancel signal, to maintain a high degree of reception sensitivity of the interrogator or radio-frequency communication device.

The conventional techniques have another problem that the influence of the transmitted signal on the reception of the received signal changes each time the direction of transmission of the transmitted signal is changed. That is, a part of the transmitted signal transmitted from the radio-frequency communication device is mixed as a leakage signal into the received signal received by the radio-frequency communication device, so that the communication between the radio-frequency communication device and the communication object is adversely influenced by the leakage signal. Therefore, the leakage signal must be eliminated. However, the change of the direction of transmission of the transmitted signal causes a change of the influence of the leakage signal on the received signal, so that it is difficult to sufficiently eliminate the influence of the leakage signal. Namely, there has been a need of developing a radio-frequency communication device which can eliminate an influence of the transmitted signal on the reception of the received signal, according to a change of the direction of transmission of the transmitted signal.

### SUMMARY OF THE INVENTION

The present invention was made in view of the background art described above. Accordingly, it is an object of the present invention to provide a radio-frequency communication device which can effectively eliminate an influence of the transmitted signal on the reception of the received signal, according to a change of the direction of transmission of the transmitted wave and a change of the operating environment of the device.

In a first preferred form of the above-described first aspect of the invention, the radio-frequency communication device further comprises a cancel-signal generating portion operable to generate the cancel signal for eliminating the leakage signal which is generated by the receiver antenna device due to transmission of the transmitted signal from the transmitter antenna device. The receiver-circuit-constant setting portion sets, as the received-circuit constant, a constant for determining the phase and the amplitude of the cancel signal. This arrangement makes it possible to effectively eliminate the leakage signal that is a part of the transmitted signal transmitted from the transmitter antenna device, which part is mixed in the reply signal received by the receiver antenna device.

In one advantages arrangement of the above-descried first preferred form, the radio-frequency communication device further comprises a carrier generating portion operable to generate a carrier wave of the transmitted signal, and the cancel-signal generating portion generates the cancel signal on the basis of the carrier wave generated by the carrier generating portion. Accordingly, the frequency of the carrier wave of the transmitted signal can be made equal to that of the cancel signal, so that the leakage signal mixed in the reply signal received by the receiver antenna device can be more effectively eliminated.

In one advantageous arrangement of the above-described second preferred form, the radio-frequency communication device further comprises a carrier generating portion operable to generate a carrier wave of the transmitted signal, and the local-signal oscillator generates the local signal on the basis of the carrier wave generated by the carrier generating portion. Accordingly, the frequency of the carrier wave of the transmitted signal can be made equal to that of the local signal, so that the leakage signal mixed in the reply signal received by the receiver antenna device can be more effectively eliminated.

In a third preferred form of the first aspect of the invention, the receiver antenna device consists of a plurality of transmitter antenna elements. In the radio-frequency tag communication device provided with the receiver antenna device consisting of the plurality of transmitter/receiver antenna elements, the receiver-circuit constant can be easily set, and the area of communication can be enlarged.

In a fourth preferred form of the first aspect of the invention, the receiver antenna device consists of a plurality of receiver antenna elements. In the radio-frequency tag communication device provided with the receiver antenna device consisting of the plurality of receiver antenna elements, the receiver-circuit constant can be easily set, and the area of communication can be enlarged.

In a fifth preferred form of the first aspect of the invention, the transmitter antenna device and the transmitter antenna device include at least one common transmitter/receiver antenna element. Accordingly, the required size of the radio-frequency tag communication device can be minimized.

In a sixth preferred form of the first aspect of the invention, the transmitter antenna device consists of a plurality of transmitter antenna elements for transmitting respective transmitted signals, and radio-frequency communication device further comprises a phased-array control portion operable to control a phase of each of the transmitted signals to be transmitted from the plurality of transmitter antenna elements, for thereby controlling a direction of transmission of the transmitted signals. Accordingly, the direction of transmission of the transmitted signals can be suitably controlled.

In one advantageous arrangement of the above-described sixth preferred form, the receiver-circuit-constant setting portion sets the receiver-circuit constant each time the direction of transmission of the transmitted signals is changed by the phased-array control portion In the radio-frequency communication device provided with the transmitter antenna device in the form of a phased-array antenna device, the receiver-circuit constant can be set as needed, so that the area of communication can be enlarged.

In a seventh preferred form of the first aspect of this invention, the transmitter antenna device consists of a plurality of transmitter antenna elements, and the receiver antenna device consists of a plurality of receiver antenna elements. Further, the transfer-function calculating portion calculates, as the transfer function, a value obtained by dividing a transmitted-signal component included in received signals received by the receiver antenna elements, by the predetermined transmitted signals to be transmitted from the transmitter antenna elements. Accordingly, the leakage signal that is a part of the transmitted signals which part is included in the received signals received by the receiver antenna elements can be effectively estimated.

In an eighth preferred form of the first aspect of this invention, the transfer-function calculating portion calculates the transfer function at a predetermined time interval. Accordingly, the receiver-circuit constant can be updated on the basis of the transfer function calculated as needed.

In a ninth preferred form of the first aspect of the invention, the radio-frequency communication device further comprises a received-signal-quality detecting portion operable to detect a quality of a received signal received by the receiver antenna device, and the transfer-function calculating portion calculates the transfer function, depending upon the quality of the received signal detected by the received-signal-quality detecting portion. Accordingly, the transfer function can be updated as needed.

In one advantageous arrangement of the above-described ninth preferred form, the received-signal-quality detecting portion detects, as the quality of the received signal, a strength (intensity) of the received signal while the reply signal transmitted from the communication object is not received by the receiver antenna device, and the transfer-function calculating portion calculates the transfer function when the strength of the received signal detected by the received-signal-quality detecting portion is equal to or higher than the predetermined threshold. Accordingly, the transfer function can be updated when the strength of the leakage signal included in the received signals is estimated to be comparatively high.

In a tenth preferred form of the first aspect of this invention, the receiver-circuit-constant setting portion sets the receiver-circuit constant each time the transfer-function calculating portion calculates the transfer function. Accordingly, the received-circuit constant can be set on the basis of the transfer function calculated last by the transfer-function calculating portion.

In an eleventh preferred form of the first aspect of this invention, the communication object is the radio-frequency tag operable to transmit the reply signal including predetermined information, in response to the transmitted signal transmitted from the transmitter antenna device. In this case, the radio-frequency communication device is a radio-frequency tag communication device which is operable to communicate with the radio-frequency tag and in which the influence of the transmitted signal on the reception of the received signal can be effectively eliminated according to a change of the direction of transmission of the transmitted signal.

In a first preferred form of the second aspect of this invention, the cancel-signal control portion changes the phase and amplitude of the cancel signal to optimum values, such that the strength of the received signal detected by the signal-strength detecting portion is minimized. In this form of the invention, the phase and amplitude of the cancel signal generated by the cancel-signal generating portion are optimized such that the detected strength of the received signal is minimized. Accordingly, the unnecessary wave can be effectively eliminated in the real-time fashion even where the reception of the unnecessary wave by the signal receiving portion changes due to a change of the operating environment of the radio-frequency communication device.

In one advantageous arrangement of the above-described first preferred form of the second aspect of this invention, the cancel-signal control portion comprises a first searching portion operable to change values of the phase and amplitude of the cancel signal within respective primary phase and amplitude search ranges at respective primary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective primary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for primary optimum values of the phase and amplitude, and a second searching portion operable to change values of the phase and amplitude of the cancel signal within respective secondary phase and amplitude search ranges at respective secondary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective secondary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for final optimum values of the phase and amplitude, the secondary phase and amplitude search ranges being respectively narrower than the primary phase and amplitude search ranges and respectively including the primary optimum values, and the secondary phase and amplitude searching pitches being respectively smaller than the primary phase and amplitude searching pitches. In this arrangement, the primary optimum values of the phase and amplitude of the cancel signal are initially found by a primary or rough search made within the comparatively wide search ranges by the first searching portion, and the final optimum values are then found by a secondary or fine search made within the comparatively narrow search ranges by the second searching portion. The combination of the primary and secondary searches (rough and fine searches) permits more efficient finding of the final optimum values of the phase and amplitude of the cancel signal, in a shorter length of time with a reduced operating load acting on the cancel-signal control portion.

In a second preferred form of the above-described second preferred form of the second aspect of the invention, wherein the cancel-signal control portion includes a first determining portion operable to determine whether a current set value of at least one of the phase and amplitude of the cancel signal should be changed, on the basis of the strength of the received signal detected by the signal-strength detecting portion. In this form of the invention, the determination as to whether the currently set value of the phase or amplitude should be changed can be made by the first determining portion after normal communication with the radio-frequency communication device with the transponder after the optimum values of the phase and amplitude have been once optimized, so that the currently set value of the phase or amplitude can be updated according to a change of the operating environment of the radio-frequency communication device.

In one advantageous arrangement of the above-described second preferred form of the second aspect of the invention, the first determining portion is arranged to determine that the currently set value of the phase or amplitude of the cancel signal should be changed, when the strength of the received signal detected by the signal-strength detecting portion is larger than a first threshold which is set after optimum values of the phase and amplitude of the cancel signal have been set, and on the basis of a strength of the received signal which corresponds to the optimum values. In this case wherein the first determining portion determines that the currently set value of the phase or amplitude should be changed, when the detected strength is larger than the first threshold, the currently set value can be suitably updated according to a change of the operating environment of the radio-frequency communication device.

Preferably, the cancel-signal control portion further includes a second determining portion operable prior to the determination by the first determining portion, to determine whether the currently set value of the at least one of the phase and amplitude of the cancel signal should be changed. In this arrangement, the determination as to whether the currently set value of the phase or amplitude should be changed can be made by the second determining portion after normal communication with the radio-frequency communication device with the transponder after the phase and amplitude have been once optimized, so that the currently set value of the phase or amplitude can be updated according to a change of the operating environment of the radio-frequency communication device.

The determination made by the second determining portion prior to the determination by the first determining portion is preferably a determination as to whether a re-adjustment of the cancel signal to optimize again the phase and amplitude is required, while the determination by the first determining portion is preferably a determination as to whether a fine adjustment of the cancel signal is required after the second determining portion has determined that the re-adjustment is no more required. In this case, either the re-adjustment or the fine adjustment of the cancel signal is selectively effected according to results of the determinations by the first and second determining portions, depending upon whether the amount of deviation of the currently set values of the phase and amplitude from the optimum values at which the unnecessary wave can be most adequately eliminated. Accordingly, the phase and amplitude of the cancel signal can be optimized with a high degree of efficiency in a shorter length of time, with a reduced operating load acting on the cancel-signal control portion.

Preferably, the second determining portion is arranged to determine that the currently set value of the at least one of the phase and amplitude of the cancel signal should be changed, when the strength of the received signal detected by the signal-strength detecting portion is larger than a second threshold value which is larger than the first threshold value and which is set after the optimum values of the phase and amplitude of the cancel signal have been set by the cancel-signal control portion, and on the basis of a strength of the received signal which corresponds to said optimum values. For example, the second determining portion determines that the currently set values of both of the phase and amplitude of the cancel signal should be changed, if the currently detected strength of the received signal is higher than the second threshold value larger than the first threshold value. Accordingly, the phase and amplitude of the cancel signal can be optimized as needed according to a change of the operating environment of the radio-frequency communication device.

In another advantageous arrangement of the second preferred form of the second aspect of this invention, the cancel-signal control portion further includes a control-signal generating portion operable to supply the cancel-signal generating portion with a control signal for changing at least one of the phase and amplitude of the cancel signal, when the first determining portion has determined that the currently set value of the at least one of the phase and amplitude of the cancel signal should be changed. In this case wherein the control signal is applied to the cancel-signal generating portion when the first determining portion has determined that the currently set value of the phase or amplitude of the cancel signal should be changed, the currently set value of the phase or amplitude can be finely adjusted according to a change of the operating environment of the radio-frequency communication device.

Preferably, the first determining portion determines whether the currently set value of the phase of the cancel signal generated by the cancel-signal generating portion should be changed, on the basis of the strength of the received signal detected by said signal-detecting portion, and the control-signal generating portion supplies the cancel-signal generating portion with the control signal to change the phase when the first determining portion has determined that the phase should be changed. In this case wherein the control signal is applied to the cancel-signal generating portion when the first determining portion has determined that the currently set value of the phase of the cancel signal should be changed, the currently set value of the phase can be finely adjusted according to a change of the operating environment of the radio-frequency communication device.

In a further advantageous arrangement of the above-described second preferred form of the second aspect of the invention, the cancel-signal control portion further includes a third determining portion operable to determine whether currently set values of the phase and amplitude of the cancel signal should be changed again, on the basis of the strength of the received signal detected by the signal-strength detecting portion after the currently set value of at least one of the phase and amplitude of the cancel signal is changed according to the determination by the first determining portion that the currently set value of the at least one of the phase and amplitude should be changed. In this arrangement, the determination as to whether the currently set value of the phase or amplitude should be changed again can be made by the third determining portion after normal communication with the radio-frequency communication device with the transponder after the fine adjustment of at least one of the phase and amplitude to the optimum value according to the determination of the first determining portion that the currently set value of the phase or amplitude should be changed. Accordingly, the currently set value of the phase or amplitude after the fine adjustment can be optimized according to a change of the operating environment of the radio-frequency communication device.

According to a third preferred form of the above-described second aspect of this invention, the cancel-signal control portion further includes a transmission/reception control portion operable to control the carrier transmitting portion to transmit toward the transponder the carrier wave modulated by the carrier modulating portion, immediately after an operation of the cancel-signal control portion for controlling the carrier generating portion, and to control the signal receiving portion to receive a reply signal transmitted from the transponder in response to the modulated carrier wave received from the carrier modulating portion through the carrier transmitting portion. In this form of the invention wherein the modulated carrier wave is transmitted from the carrier modulating portion through the carrier transmitting portion, and the reply signal transmitted from the transponder is received by the signal receiving portion, immediately after the operation of the cancel-signal control portion to control the phase and amplitude of the cancel signal. Accordingly, the communication with the transponder can be effected with a high degree of sensitivity of reception of the reply signal, and a high degree of elimination of the unnecessary wave by the cancel signal the phase and amplitude of which have been optimized by the cancel-signal control portion.

### DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of this invention will be described in detail by reference to the accompanying drawings.

### Embodiment 1

The canceling portion 22 includes: a plurality of cancel-signal-phase control portions (three control portions in the embodiment as shown in FIG. 2) 34a, 34b, 34c (hereinafter referred to simply as “cancel-signal-phase control portions 34”, unless otherwise specified) each operable to control the phase of the carrier wave; a plurality of cancel-signal-amplitude control portions (three control portions in the embodiment as shown in FIG. 2) 36a, 36b, 36c (hereinafter referred to simply as “cancel-signal-amplitude control portions 36”, unless otherwise specified) each operable to control the phase of the carrier wave; and a plurality of cancel-signal combining portions (three combining portions in the embodiment as shown in FIG. 2) 38a, 38b, 38c (hereinafter referred to simply as “cancel-signal combining portions 38”, unless otherwise specified) each operable to combine together the received signal and the cancel signal. The canceling portion 22 including the cancel-signal-phase control portions 34 and the cancel-signal-amplitude control portions 36 functions as a cancel-signal generating portion operable to generate the cancel signals for eliminating the leakage signals received by the plurality of transmitter/receiver antenna elements 20 due to transmission of the transmitted signals from the plurality of transmitter/receiver antenna elements 20. The cancel signals generated by the plurality of cancel-signal-amplitude control portions 36 are added through the cancel-signal combining portions 38 to the received signals received by the plurality of transmitter/receiver antenna elements 20, so that the leakage signals which are parts of the transmitted signals are offset or canceled by the cancel signals, and are thus eliminated.

The transmitted-data generating portion 49 is arranged to generate the transmitted data which is the transmission information signal used to generate the transmitted signal and which is applied to the transmitted-signal generating portion 18. The transmission control portion 50 is arranged to control the phases (and amplitudes, if necessary) of the transmitted signals to be transmitted from the transmitter/receiver antenna elements 20, for thereby controlling the direction of transmission of the transmitted signals. Namely, the transmission control portion 50 controls the directivity control portion 24 for controlling the phase of each transmitted signal, so that a transmitter antenna device consisting of the transmitter/receiver antenna elements 20 functions as a phased array antenna device. Alternatively, the transmission control portion 50 controls the directivity control portion 24 for controlling the phase and amplitude of each transmitted signal, so as to improve the quality of the transmitted signal, so that the transmitter antenna device consisting of the transmitter/receiver antenna elements 20 functions as an adapted array antenna device.

The received-signal combining portion 54 is arranged to combine together the received signals received through the transmitter/receiver antenna elements 20. The directivity of the receiver antenna device consisting of the transmitter/receiver antenna elements 20 is controlled by the directivity control portion 24 which controls the phases and amplitudes of the received signals under the control of the reception control portion 52 before the received signals are combined together by the received-signal combining portion 54.

The received-signal demodulating portion 56 is arranged to demodulate the received signals which have been combined together by the received-signal combining portion 54. Preferably, the received-signal demodulating portion 56 is arranged to first effect AM demodulation of the received signals and then effect FM decoding of the demodulated received signals, for thereby reading the modulated information transmitted from the radio-frequency tag 14.

The received-signal-quality detecting portion 58 is arranged to detect the quality of the received signals received by the transmitter/receiver antenna elements 20. Preferably, the received-signal-quality detecting portion 58 is arranged to detect the strength of the received signals, as the quality of the received signals. That is, the received-signal-quality detecting portion 58 is preferably an RSSI (received-signal strength indicator) circuit.

$Sji = Rj Ti ( 1 ⁢ a ) Sji = R ′ ⁢ j Ti ( 1 ⁢ b ) Rj = SjiTi ( 2 ) Rj = ∑ i = 1 N ⁢ SjiTi ( 3 )$

Referring to FIG. 4, there is shown an arrangement of a circuit element To of each radio-frequency tag 14. As shown in FIG. 4, the circuit element To includes an antenna portion 64 operable to transmit and receive signals to and from the antenna device consisting of the plurality of transmitter/receiver antenna elements 20 of the radio-frequency tag communication device 12, and an IC circuit portion 65 operable to process the signals received by the antenna portion 64. The IC circuit portion 65 includes: a rectifying portion 66 operable to rectify the carrier wave received by the antenna portion 64; a power source portion 68 operable to store an energy of the carrier wave rectified by the rectifying portion 66; a clock extracting portion 70 operable to extract a clock signal from the carrier wave received by the antenna portion 64, and to apply the extracted clock signal to a control portion 76; a memory portion 72 functioning as an information storage portion operable to store a desired information signal; a modulating/demodulating portion 74 connected to the antenna portion 64 and operable to perform signal modulating and demodulating operations; and the above-indicated control portion 76 operable to control the operations of the circuit element To via the rectifying portion 68, clock extracting portion 70, modulating/demodulating portion 74, etc. The control portion 76 performs basic control operations such as a control operation to store the desired information in the memory portion 72 during communication with the radio-frequency tag communication device 12, and a control operation to control the modulating/demodulating portion 74 to modulate the carrier wave received through the antenna portion 64, according to the information stored in the memory portion 70, and to transmit the modulated carrier wave as the reflected wave through the antenna portion 64. Preferably, the antenna portion 64 is a half-wave dipole antenna consisting of a pair of linear elements.

Referring to the flow chart of FIG. 5, there is illustrated a transfer-function calculating control routine-executed by the control portion 32 of the radio-frequency tag communication device 12. This control routine is repeatedly executed with a predetermined cycle time.

The control routine of FIG. 5 is initiated with step SA1 to set a variable “i” to 1. The variable “i” designates one of the transmitter/receiver antenna elements 20 as a transmitter antenna element i. Then, the control flow goes to step SA2 in which a signal corresponding to a unit current Ti is transmitted from the designated transmitter antenna element i. The control flow then goes to step SA3 wherein each of the transmitter/receiver antenna elements 20 as a receiver antenna element receives the transmitted signal Rj. Step SA4 is then implemented to store in the RAM of the control portion 32 the received signals Rj received in step SA3. Then, the control flow goes to step SA5 to determine whether the variable “i” is smaller than the total number N of the transmitter/receiver antenna elements 20 as the transmitter antenna elements. If an affirmative decision is obtained in step SA5, the control flow goes to step SA6 to increment the variable “i” by one, and goes back to step SA2. If a negative determination is obtained in step SA5, the control flow goes to step SA7 to calculate the transfer function progression Sji.

Referring next to the flow chart of FIG. 6, there is illustrated a tag detecting communication control routine executed by the control portion 32 of the radio-frequency tag communication device 12. This control routine is repeatedly executed with a predetermined cycle time.

Further, the radio-frequency tag communication device 12 further comprises the cancel-signal generating portion in the form of the canceling portion 22 operable to generate the cancel signal for eliminating the leakage signal which is generated by the receiver antenna device in the form of the transmitter/receiver antenna elements 20 due to transmission of the transmitted signal from the transmitter antenna device in the form of the transmitter/receiver antenna elements 20. The receiver-circuit-constant setting portion 62 sets, as the received-circuit constant, a constant for determining the phase and the amplitude of the cancel signal. This arrangement makes it possible to effectively eliminate the leakage signal that is a part of the transmitted signal transmitted from the transmitter antenna device, which part is mixed in the reply signal received by the receiver antenna device.

Further, the radio-frequency tag communication device 12 further comprises the carrier generating portion 16 operable to generate the carrier wave of the transmitted signal, and the canceling portion 22 generates the cancel signal on the basis of the carrier wave generated by the carrier generating portion 16. Accordingly, the frequency of the carrier wave of the transmitted signal can be made equal to that of the cancel signal, so that the leakage signal mixed in the reply signal received by the receiver antenna device in the form of the transmitter/receiver antenna elements 20 can be more effectively eliminated.

Further, the transmitter antenna device consists of the plurality of transmitter/receiver antenna elements 20. In the radio-frequency tag communication device 12 provided with the transmitter antenna device consisting of the plurality of transmitter/receiver antenna elements 20, the receiver-circuit constant can be easily set, and the area of communication can be enlarged.

Further, the receiver antenna device consists of the plurality of transmitter/receiver antenna elements 20. In the radio-frequency tag communication device 12 provided with the receiver antenna device consisting of the plurality of transmitter/receiver antenna elements 20, the receiver-circuit constant can be easily set, and the area of communication can be enlarged.

Further, the transmitter antenna device and the transmitter antenna device include at least one common transmitter/receiver antenna element 20. Accordingly, the required size of the radio-frequency tag communication device 12 can be minimized.

Further, the radio-frequency tag communication device 12 further comprises the transmission control portion 50 (steps SB1, SB55 and SB7) operable to control the phase of each of the transmitted signals to be transmitted from the plurality of transmitter/receiver antenna elements 20, for thereby controlling the direction of transmission of the transmitted signals. Accordingly, the direction of transmission of the transmitted signals can be suitably controlled.

Further, the receiver-circuit-constant setting portion 62 sets the receiver-circuit constant each time the direction of transmission of the transmitted signals is changed by the transmission control portion 50. In the radio-frequency tag communication device 12 provided with the transmitter antenna device in the form of a phased-array antenna device, the receiver-circuit constant can be set as needed.

Further, the transfer-function calculating portion 60 calculates, as the transfer function, a value obtained by dividing the transmitted-signal component included in the received signals received by the transmitter/receiver antenna elements 20, by the predetermined transmitted signals to be transmitted from the transmitter/receiver antenna elements 20. Accordingly, the leakage signal that is a part of the transmitted signals which part is included in the received signals received by the transmitter/receiver antenna elements 20 can be effectively estimated.

Further, the transfer-function calculating portion 60 calculates the transfer function at a predetermined time interval. Accordingly, the receiver-circuit constant can be updated on the basis of the transfer function calculated as needed.

Further, the radio-frequency tag communication device 12 further comprises the received-signal-quality detecting portion 58 operable to detect the quality of the received signals received by the transmitter/receiver antenna elements 20, and the transfer-function calculating portion 60 calculates the transfer function, depending upon the quality of the received signals detected by the received-signal-quality detecting portion 58. Accordingly, the transfer function can be calculated as needed.

Further, the received-signal-quality detecting portion 58 detects, as the quality of the received signals, a strength of the received signals while the reply signal transmitted from the communication object is not received by the transmitter/receiver antenna elements 20, and the transfer-function calculating portion 60 calculates the transfer function when the strength of the received signal detected by the received-signal-quality detecting portion 58 is equal to or higher than the predetermined threshold. Accordingly, the transfer function can be updated when the strength of the leakage signal included in the received signals is estimated to be comparatively high.

Further, the receiver-circuit-constant setting portion 62 sets the receiver-circuit constant each time the transfer-function calculating portion 60 calculates the transfer function. Accordingly, the received-circuit constant can be set on the basis of the transfer function calculated last by the transfer-function calculating portion 60.

Further, the communication object is the radio-frequency tag 14 operable to transmit the reply signal including predetermined information, in response to the transmitted signal transmitted from the transmitter/receiver antenna elements 20. In the radio-frequency tag communication device 12 operable to communicate with the radio-frequency tag 14, the influence of the transmitted signal on the reception of the received signal can be effectively eliminated according to a change of the direction of transmission of the transmitted signal.

Referring to FIGS. 7-19, there will be described other embodiments of this invention. In the following embodiments, the same reference signs as used in the first embodiment will be used to identify the corresponding elements, which will not be described redundantly.

### Embodiment 2

The homodyne wave detecting circuit such as the wave detecting portion 82 described above provides an output signal Fj represented by the following equation (6), by multiplying the received signal R represented by the following equation (4), by the local signal L represented by the following equation (5). The output signal Fj does not include a component ω included in the equations (4) and (5). The component is an angular frequency of the carrier wave. In the equations (4)-(6), A and B are values relating to the amplitude, while θj and ψj are values relating to the phase. To maximize the level of the output signal Fj of the wave detecting portion 82, a value of cos(θj−ψj) must be a maximum value of 1, that is, the phase of the local signal Lj must be controlled so as to satisfy a relationship of θjj. When a weight given to the transmitter antenna device in the form of the transmitter/receiver antenna elements 20 is changed by controlling the directivity control portion 24, the level of the leakage signal that is a part of the transmitted signal which part is received by the receiver antenna device in the form of the transmitter/receiver antenna elements 20 is accordingly changed. An influence of this change of the level of the leakage signal can be reduced by controlling the phases and amplitudes with the local-signal-phase control portions 84 and the local-signal-amplitude control portions 86. Further, the level of the leakage signal received by the transmitter/receiver antenna elements 20 functioning as the receiver antenna device is changed by movements of reflecting bodies located around the radio-frequency tag communication device 80. However, an influence of this change of the level of the leakage signal can be eliminated by the receiver-circuit-constant setting portion 62.

$Rj = Aj ⁢ ⁢ sin ⁡ ( ω ⁢ ⁢ t + θ ⁢ ⁢ j ) ( 4 ) Lj = Bj ⁢ ⁢ sin ⁡ ( ω ⁢ ⁢ t + ψ ⁢ ⁢ j ) ( 5 ) Fj = AjBj 2 ⁢ cos ⁡ ( θ ⁢ ⁢ j - ψ ⁢ ⁢ j ) ( 6 )$

The radio-frequency tag communication device 80 according to the second embodiment described above is provided with the wave detecting portion 82 operable to generate the local signals, and to combine the local signals and the received signals received by the plurality of transmitter/receiver antenna elements 20. In this second embodiment, the received-circuit-constant setting portion 62 is arranged to set, as the received-circuit constant, the constant used to control the local signals. Accordingly, the leakage signals that are parts of the transmitted signals which parts are included in the transmitter antenna device in the form of the transmitter/receiver antenna elements 20 can be effectively eliminated.

Further, the wave detecting portion 82 is arranged to generate the local signals on the basis of the carrier waves received from the carrier generating portion 16. Accordingly, the frequency of the local signals can be made equal to the frequency of the carrier wave of the transmitted signals, so that the leakage signals included in the received signals received by the transmitter/receiver antenna elements 20 functioning as the receiver antenna device can be effectively eliminated.

While the preferred embodiments of this invention have been described above by reference to the drawings, it is to be understood that the invention is not limited to these embodiments, but may be otherwise embodied.

In the above-described embodiments, the transmitted-data generating portion 49, transmission control portion 50, reception control portion 52, received-signal combining portion 54, received-signal demodulating portion 56, received-signal-quality detecting portion 58, transfer-function calculating portion 60 and received-circuit-constant setting portion 62 are functional portions of the control portion 32. However, those portions 49-62 may be separate control devices. Further, the portions 49-62 may be arranged to achieve their control functions by either digital signal processing or analog signal processing.

In the preceding embodiments, the transmission control portion 40 is arranged to control the phase and amplitude of each of the transmitted signals transmitted from the plurality of transmitter/receiver antenna elements 20, for thereby controlling the direction of transmission of the transmitted signals. However, the transmission control portion 40 may be arranged to control only the phase of each transmitted signal. Similarly, the reception control portion 42 may be arranged to control only the phase of each of the received signals, for thereby controlling the direction of reception of the received signals.

### Embodiment 3

Referring next to FIG. 8, there will be described an overall arrangement of a radio-frequency tag communication system S including a radio-frequency communication device in the form of an interrogator 100 constructed according to a third embodiment of this invention, and a transponder in the form of the radio-frequency tag 14 described above.

The interrogator 100 includes: an antenna 101 for radio communication between a circuit element To of the radio-frequency tag 14 and the antenna 101; a high-frequency circuit 102 operable to obtain access to (to read and write information on or from) an IC circuit portion 65 of the circuit element To; a signal-processing circuit 103 operable to process signals read out from the circuit element To; a control circuit 104 operable to control the operation of the interrogator 100.

The control circuit 104 is a so-called microcomputer incorporating a central processing unit (CPU), a ROM and a RAM, which are not shown in FIG. 8. The CPU operates to perform signal processing operations according to control programs stored in the ROM, while utilizing a temporary data storage function of the RAM.

The functional block diagram of FIG. 9 shows an arrangement of functional elements of the high-frequency circuit 102 of the interrogator 100.

As shown in FIG. 9, the high-frequency circuit 102 includes: a transmitter portion 132 (functioning as a carrier generating portion) operable to transmit a signal through the antenna 101 toward the circuit element To; a receiver portion 133 operable to receive through the antenna 102 a reflected wave transmitted from the circuit element To; a transmission/reception separator 134 (constituted by a circulator, for example) operable to transmit the signal form the transmitter portion 132 to the antenna 101, and to transmit the signal through the antenna 102, to the receiver portion 133; and a canceling circuit 200 (functioning as a cancel-signal generating portion) operable to generate a cancel signal (offset signal) for eliminating an unnecessary wave (leakage signal) that is a part of the transmitted signal transmitted from the transmitter portion 132, which part is included in the received signal received by the receiver portion 133.

The canceling circuit 200 includes a cancel-signal-amplitude control portion 201 and a cancel-signal-phase control portion 202 which are respectively operable to control an amplitude and a phase of the carrier wave received from the transmitter portion 132, for thereby generating the cancel signal. The canceling circuit 200 further includes a multiplexer 203 operable to combine together the cancel signal generated by the cancel-signal-amplitude control portion 201 and the cancel-signal-phase control portion 202, and the received signal received by the antenna 101.

The transmitter portion 132 includes: a carrier generating portion in the form of a quartz oscillator 135 operable to generate the carrier wave for obtaining access to the IC circuit portion 65 of the circuit element To (for reading and writing information from or on the IC circuit portion 65); a PLL (phase locked loop) 136; a VCO (voltage controlled oscillator) 137; a transmitter-side multiplying circuit 138 (carrier-wave modulating portion, which may be an amplification-factor-variable amplifier for amplitude modulation of the carrier wave) operable to modulate the carrier wave generated on the basis of a signal received from the control circuit 104 (e.g., to effect amplitude modulation of the carrier wave on the basis of a signal TX_ASK received from the control circuit 104); and a variable transmitter amplifier 139 operable to amplify the carrier wave modulated by the transmitter-side multiplying circuit 138, according to an amplification factor determined according to a signal TX_PWR received from the control circuit 104. The carrier wave is preferably around 950 MHz, or around 2.45 GHz. The modulated wave generated by the transmitter-side multiplying circuit 138 and amplified by the variable transmitter amplifier 139 is transmitted through the transmission/reception separator 134 and the antenna 101, to the IC circuit portion 65 of the circuit element To of the radio-frequency tag 14.

The receiver portion 133 includes: a first receiver-side multiplying circuit 140 operable to effect homodyne detection by multiplying a composite signal of the received signal received by the antenna 101 and the cancel signal, which composite signal has been obtained by the multiplexer 203, by the carrier wave generated by the transmitter portion 132; a first band pass filter 142 operable to extract a necessary frequency-band signal from an output of the first receiver-side multiplying circuit 140; a first receiver-side amplifier 143 operable to amplify an output of the first band pass filter 142 and apply the amplified output to a first limiter 142; a second receiver-side multiplying circuit 144 operable to effect homodyne detection by multiplying the above-indicated composite signal of the received signal and the cancel signal, by the carrier wave the phase of which has been retarded by 90° after the generation by the transmitter portion 132; a second receiver-side amplifier 147 operable to amplify an output of the second band pass filter 145 and apply the amplified output to a second limiter 146. A signal RXS-I generated by the first limiter 142 and a signal RXS-Q are processed by the above-described signal processing circuit 103.

The composite signal obtained by the multiplexer 203 by combining together the received signal received by the antenna 101 and the cancel signal is applied also to an RSSI circuit (received-signal strength indicator) 148, and a signal RSSI indicative of the strength or intensity of the composite signal detected by the RSSI circuit 148 is applied to the signal processing circuit 103. In the interrogator 100 constructed as described above, the reflected wave received from the circuit element To of the radio-frequency tag 14 is demodulated by I-Q demodulation.

The signal processing circuit 103 is arranged to perform a predetermined arithmetic operation regarding the received signal received from the receiver portion 133, and the other signals, and to apply a modulation control signal to the transmitter-side multiplying circuit 138, according to a result of the arithmetic operation.

The control circuit 104 is arranged to apply an amplitude control signal and a phase-control signal to the cancel-signal-amplitude control portion 201 and the cancel-signal-phase control portion 202 of the canceling circuit 200, respectively, according results of the arithmetic operations on the basis of the RSSI signal received from the RSSI circuit 148 (on the basis of the output signal of the multiplexer 203). For example, the control circuit 104 is connected to a communication line via an input/output interface (not shown), and is arranged to communicate with a route server, any other terminal, general-purpose computer and information server, which are connected to the communication line.

A dominant feature of the present third embodiment is that the transmitter portion 132 transmits the carrier wave through the antenna 101 before the radio communication of the interrogator 100 with the circuit element To of the radio-frequency tag 14, that is, while no reflected wave from the circuit element To is received by the interrogator 100. According to the signal received from the signal processing circuit 103 which has received the above-described RSSI signal, the control circuit 104 controls the amplitude control signal and the phase control signal to be applied to the cancel-signal-amplitude control portion 201 and the cancel-signal-phase control portion 202, for adjusting the phase and amplitude of the cancel signal to optimum values suitable for canceling or eliminating the unnecessary wave or leakage signal. This aspect of the third embodiment will be described in detail.

To cancel or eliminate the unnecessary wave which is a part of the transmitted signal transmitted by the transmitter portion 132 through the antenna 101, which part is received by the receiver portion 133 through the antenna 101, the cancel signal generated by the canceling circuit 200 should have the same phase P as the phase of the unnecessary wave, and the amplitude A opposite to the amplitude of the unnecessary wave.

FIG. 10 schematically shows a method of setting optimum amplitude A and phase P of the cancel signal according to the third embodiment of this invention, in a coordinate system wherein the amplitude A is taken along the horizontal axis while the phase P is taken along the vertical axis. The optimum values of the amplitude A and phase P of the cancel signal for canceling the unnecessary wave is represented by one point (optimum point) in this coordinate system. To search for this optimum point according to the principle of this invention, a large number of monitoring points are set in a matrix wherein the points are spaced apart from each other at a predetermined pitch ΔA1 along the axis of the amplitude A within a predetermined range from Astart to Aend, and at a predetermined pitch ΔP1 along the axis of the phase P within a predetermined range from Pstart to Pend, as indicated in FIG. 10. At each of the monitoring points, the strength of the signal which is received by the RSSI circuit 148 and which may include an unnecessary wave (leakage signal) is detected by the RSSI circuit 148, and one of the monitoring points at which the measured strength value is the smallest is determined as the optimum point.

In the present third embodiment, a primary search is initially implemented within a comparatively wide primary amplitude search range (Astart to Aend) and within a comparatively wide primary phase search range (Pstart to Pend). The primary search is implemented at a comparatively long primary searching pitch ΔA1 along the axis of the amplitude A, and at a comparatively long primary searching pitch ΔP1 along the axis of the phase P, as indicated in FIG. 10. This primary search is a rough search for a primary optimum point (at which an optimum amplitude Abest1 and an optimum phase Pbest1 are obtained). A rough adjustment of the canceling circuit 200 is made according to this primary or rough search.

Then, a secondary search is implemented within a comparatively narrow secondary amplitude search range (Astart to Aend) and within a comparatively narrow secondary phase search range (Pstart to Pend). These secondary search ranges include the primary optimum point (Abest1, Pbest1) searched by the primary search, as an intermediate point in each of the ranges, as indicated in FIG. 11. The secondary search is implemented at a comparatively short secondary searching pitch ΔAmin along the axis of the amplitude A, and at a comparatively short secondary searching pitch ΔPmin along the axis of the phase P, as also indicated in FIG. 10. This secondary search is a fine search for a final optimum point (at which an optimum amplitude Abest2 and an optimum phase Pbest2 are obtained). A fine adjustment of the canceling circuit 200 is made according to this secondary or fine search.

In the secondary search shown in FIG. 11, the secondary amplitude search range is a distance equal to the primary searching pitch ΔA1, and includes the primary optimum amplitude point (Abest1) as a center point of the range. Namely, the secondary amplitude search range consists of a first sub-range which is equal to one half ΔA1/2 of the primary searching pitch ΔA1 and which is on one side of the center point (Abest1), and a second sub-range which is equal to the other half ΔA1/2 of the primary searching pitch ΔA1 and which is on the other side of the center point (Abest1). Similarly, the secondary phase search range consists of a first sub-range which is equal to one half ΔP1/2 of the primary searching pitch ΔP1 and which is on one side of the center point (Pbest1), and a second sub-range which is equal to the other half ΔP1/2 of the primary searching pitch ΔP1 and which is on the other side of the center point (Pbest1). However, the secondary amplitude and phase search ranges are not limited to those of FIG. 11, and may be modified as long as the secondary search ranges include the primary optimum point, and are narrower than the primary search ranges, so that the secondary search is made at shorter searching pitches than in the primary search, for fine setting of the final optimum point.

FIG. 12 is a flow chart illustrating a control routine performed by the control circuit 104 to generate the cancel signal described above.

The control routine of FIG. 12 is initiated with step S10 in which the interrogator 100 is initialized. The initialization of the interrogator 100 includes operations to reset various parameters of the interrogator 100.

Then, step S20 is implemented to set the final value of the strength of the received signal detected by the RSSI circuit 148 after the adjustment of the canceling circuit 200, as a threshold value subsequently used for controlling the cancel signal. The set final value is stored in a suitable memory (e.g., RAM of the control circuit 104).

The control flow then goes to step S30 to determine whether the strength of the received signal currently detected by the RSSI circuit 148 is equal to or lower than a sum of the threshold value set in step S20 and a predetermined extra value of α % (e.g., several % to about 20%) of the threshold value.

If an affirmative determination is obtained in step S30, this indicates that the unnecessary wave is adequately eliminated by the currently adjusted cancel signal, and the control flow goes to step S40.

In step S40, the interrogator 100 is operated for communication with the circuit element To of the transponder in the form of the radio-frequency tag 14, to read information from the IC circuit portion 65 or write desired information on the IC circuit portion 65.

Step S40 is followed by step S50 to determine whether it is necessary to communicate with the other transponder (radio-frequency tag 14). If a negative determination is obtained in step S50, the present control routine is terminated. If an affirmative determination is obtained in step S50, the control flow goes back to step S30.

Referring to the flow chart of FIG. 13, there will be described in detail the adjustment of the canceling circuit 200 in step S100 of the control routine of FIG. 12.

The control routine of FIG. 13 is initiated with step S110 to apply the control signals to the first receiver-side amplifier 143 and the second receiver-side amplifier 147, for example, for adjusting the gain of the received signals generated by these amplifiers 143, 147.

The control flow then goes to step S120 to make the rough search for optimum values of the amplitude A and phase P of the cancel signal to be generated by the canceling circuit 200. Described in detail, the amplitude A and phase P of the cancel signal are changed by changing the amplitude control signal and the phase control signal to be applied to the cancel-signal-amplitude control portion 201 and the cancel-signal-phase control portion 202 of the canceling circuit 200, by implementing the primary or rough search within the comparatively wide primary search amplitude and phase search ranges, at the comparatively long primary searching pitches, as indicated in FIG. 10, to determine the primary optimum point at which the strength of the received signal detected by the RSSI circuit 148 is the smallest.

Then, the control flow goes to step S140 to make the fine search optimum values of the amplitude A and phase P of the cancel signal to be generated by the canceling circuit 200. Described in detail, the amplitude A and phase P of the cancel signal are changed by changing the amplitude control signal and the phase control signal, by implementing the secondary or fine search within the comparatively narrow primary search amplitude and phase search ranges determined on the basis of the primary optimum point detected by the rough adjustment, as indicated in FIG. 10, to determine the final optimum point at which the strength of the received signal detected by the RSSI circuit 148 is the smallest.

Step S160 is then implemented to control the amplitude control signal and the phase control signal to be applied to the cancel-signal-amplitude control portion 201 and the cancel-signal-phase control portion 202 of the canceling circuit 200, according to the determined final optimum point indicative of the optimum amplitude value Abest2 and the optimum phase value Pbest2.

The control flow then goes to step S170 to apply the control signals to the first receiver-side amplifier 143 and the second receiver-side amplifier 147, for example, for adjusting the gain of the received signals generated by these amplifiers 143, 147, as in step S110. The control routine of FIG. 12 is terminated after step S170 is implemented.

Referring to the flow chart of FIG. 14, there will be described in detail the operation in step S120 of FIG. 13 to make the rough search for the optimum amplitude and phase of the cancel signal to be generated by the canceling circuit 200.

The control routine of FIG. 14 is initiated with step S121 to set a minimum value RSSImin1 of the strength of the received signal at a predetermined initial value (sufficiently large value). The minimum value RSSImin1 is used in step S125 which will be described.

Then, the control flow goes to step S122 to set a start value Astart and an end value Aend of the primary amplitude search range to Amin and Amax, respectively, and the primary amplitude searching pitch ΔA to ΔA1, and to set a start value Pstart and an end value Pend of the primary phase search range to Pmin and Pmax, respectively, and the primary phase searching pitch ΔP to ΔP1. The values Amin, Amax, ΔA1, Pmin, Pmax and ΔP1 may be suitably determined constant values, or variables determined each time step S122 is implemented.

Step S123 is then implemented to apply the amplitude control signal to the cancel-signal-amplitude control portion 201, so that the amplitude A of the cancel signal to be generated by the canceling circuit 200 is adjusted to the start value Astart, and to apply the phase control signal to the cancel-signal-phase control portion 202, so that the phase P of the cancel signal is adjusted to the start value Pstart.

The control flow then goes to step S124 in which the current strength value RSSIcur1 of the received signal is detected by the RSSI circuit 148, and then to step S125 to determine whether the detected strength value RSSIcur1 is lower than the minimum value RSSImin1.

If an affirmative determination is obtained in step S125, this indicates that the cancel signal has the optimum amplitude and phase, and the control flow goes to step S126 in which the current amplitude value A is set as the primary optimum value Abest1, while the current phase value P is set as the primary optimum value Pbest1, and the current value RSSIcur1 of the received signal is set as the minimum value RSSImin1. Step S126 is followed by step S127.

If a negative determination is obtained in step S126, this indicates that the current amplitude and phase values of the cancel signal are not the optimum values, and the control flow goes directly to step S127, while skipping step S126.

Step S127 is provided to determine whether the current phase value P is equal to the end value Pend of the primary phase search range. If a negative determination is obtained in step S127, the control flow goes to step S128 to increment the phase P by a predetermined value equal to the primary phase searching pitch ΔP, and goes back to step S124. If an affirmative determination is obtained in step S127, the control flow goes to step S129 to determine whether the current amplitude value A is equal to the end value Aend of the primary amplitude search range. If a negative determination is obtained in step S129, the control flow goes to step S130 to increment the amplitude A by a predetermined value equal to the primary amplitude searching pitch ΔA, and to step S131 to reset the phase P to the start value Pstart of the primary phase search range, and then goes back to step S124.

Referring to the flow chart of FIG. 15, there will be described in detail the operation in step S140 of FIG. 13 to make the fine search for the optimum amplitude and phase of the cancel signal to be applied

The control routine of FIG. 15 is initiated with step S141 to set a minimum value RSSImin2 of the strength of the received signal at a predetermined initial value (sufficiently large value). The minimum value RSSImin2 is used in step S145 which will be described.

Then, the control flow goes to step S142 to set a start value Astart and an end value Aend of the secondary amplitude search range, by using the optimum amplitude value Abest1 and the primary amplitude searching pitch ΔA1, and to a set start value Pstart and an end value Pend of the secondary phase search range, by using the optimum phase value Pbest1 and the primary phase searching pitch ΔP1. That is, the start value Astart and the end value Aend of the primary amplitude search range are set to Abest1−ΔA1/2, and Abest1+ΔA1/2, respectively, and the start value Pstart and the end value Pend of the primary phase search range are set to Pbest1−ΔP1/2, and Pbest1+AP1/2, respectively. Further, the secondary amplitude searching pitch ΔA is set to ΔAmin (minimum value available in the system), and the secondary phase searching pitch ΔP is set to ΔPmin (minimum value available in the system).

Step S143 similar to step S123 of FIG. 14 is then implemented to apply the amplitude control signal to the cancel-signal-amplitude control portion 201, so that the amplitude A of the cancel signal is adjusted to the start value Astart, and to apply the phase control signal to the cancel-signal-phase control portion 202, so that the phase P of the cancel signal is adjusted to the start value Pstart.

The control flow then goes to step S144 in which the current strength value RSSIcur2 of the received signal is detected by the RSSI circuit 148, and then to step S145 to determine whether the detected strength value RSSIcur2 is lower than the minimum value RSSImin2.

If an affirmative determination is obtained in step S145, this indicates that the cancel signal has the optimum amplitude and phase, and the control flow goes to step S146 in which the current amplitude value A is set as the secondary optimum value Abest2, while the current phase value P is set as the secondary optimum value Pbest2, and the current value RSSIcur2 of the received signal is set as the minimum value RSSImin2. Step S146 is followed by step S147.

If a negative determination is obtained in step S146, this indicates that the current amplitude and phase values of the cancel signal are not the optimum values, and the control flow goes directly to step S147, while skipping step S146.

Step S147 is provided to determine whether the current phase value P is equal to the end value Pend of the primary phase search range. If a negative determination is obtained in step S147, the control flow goes to step S148 to increment the phase P by a predetermined value equal to the primary phase searching pitch ΔP, and goes back to step S144. If an affirmative determination is obtained in step S147, the control flow goes to step S149 to determine whether the current amplitude value A is equal to the end value Aend of the primary amplitude search range. If a negative determination is obtained in step S149, the control flow goes to step S150 to increment the amplitude A by a predetermined value equal to the primary amplitude searching pitch ΔA, and to step S151 to reset the phase P to the start value Pstart of the primary phase search range, and then goes back to step S154.

Referring to the flow chart of FIG. 16, there will be described in detail the fine adjustment of the canceling circuit 200 in step S200 of FIG. 12. This fine adjustment of the canceling circuit 200 is more or less similar to the fine search for the optimum amplitude and phase of the cancel signal illustrated in the flow chart of FIG. 15. Namely, the strength of the received signal is monitored by incrementing only the phase P at a comparatively short searching pitch within a comparatively narrow search range.

The control routine of FIG. 16 is initiated with step S210 in which the strength RSSIcur3 of the received signal (sum of the cancel signal and the unnecessary wave) currently received by the RSSI circuit 148 is measured by the RSSI circuit 148.

The control flow then goes to step S220 to set a minimum value RSSImin3 of the strength of the received signal at a predetermined initial value (sufficiently large value). The minimum value RSSImin3 is used in step S260 which will be described.

Then, the control flow goes to step S230 to set a start value Pstart and an end value Pend of a fine adjustment search range, by using the current amplitude value Pcur and the primary phase searching pitch ΔP1. That is, the start value Pstart and the end value Pend of the fine adjustment phase search range are set to Pcur−ΔP1/2, and Pcur+ΔP1/2, respectively. Further, a fine adjustment phase searching pitch ΔP is set to ΔPmin (minimum value available in the system).

Step S240 is then implemented to apply the phase control signal to the cancel-signal-phase control portion 202, so that the phase P of the cancel signal is adjusted to the start value Pstart.

The control flow then goes to step S250 in which the current strength value RSSIcur3 of the received signal is detected by the RSSI circuit 148, and then to step S260 to determine whether the detected strength value RSSIcur3 is lower than the minimum value RSSImin3.

If an affirmative determination is obtained in step S260, the control flow goes to step S270 in which the current phase value P is set as the fine adjustment optimum value Pbest3, and the current value RSSIcur3 of the received signal is set as the minimum value RSSImin3. Step S270 is followed by step S280.

If a negative determination is obtained in step S260, the control flow goes directly to step S280, while skipping step S270.

Step S280 is provided to determine whether the current phase value P is equal to the end value Pend of the fine adjustment phase search range. If an affirmative decision is obtained in step S280, the present control routine is terminated. If a negative determination is obtained in step S280, the control flow goes to step S290 to increment the phase P by a predetermined value equal to the fine adjustment phase searching pitch ΔP, and goes back to step S250.

Referring to FIG. 17, there is shown a change of the strength RSSI of the received signal detected by the RSSI circuit 148, as a result of the adjustments of the canceling circuit 200 described above. In this figure, the time is taken along the horizontal axis while the signal strength RSSI is taken along the vertical axis.

As shown in FIG. 17, the signal strength RSSI is considerably reduced from an initial value, as indicated at (a) in FIG. 17, as a result of the first adjustment of the canceling circuit 200 in step S100 of FIG. 12. If the signal strength RSSI exceeds the threshold value by the predetermined α % or more due to a change in the operating environment of the interrogator 100, for instance, as indicated at (b) in FIG. 17, the fine adjustment of the canceling circuit 200 in step S200 of FIG. 12 is implemented, so that signal strength RSSI is reduced below the threshold value, as indicated at (c) in FIG. 17. If the signal strength RSSI again exceeds the threshold value by a large amount, as indicated at (d) in FIG. 17, the fine adjustment of the canceling circuit 200 is again implemented. If the signal strength RSSI is not reduced below the threshold value plus the predetermined α %, as indicated at (e), the adjustment of the canceling circuit 200 in step S12 of FIG. 12 is again implemented, so that the signal strength RSSI is reduced below the threshold value, as indicated at (f) in FIG. 17.

It will be understood from the foregoing description of the third embodiment that the quartz oscillator 135, PLL 136 and VCO 137 cooperate to function as a carrier generating portion operable to generate the carrier wave, and the transmitter-side multiplying circuit 138 functions as a carrier modulating portion operable to modulate the carrier wave, while the antenna 101 and the transmission/reception separating portion 134 cooperate to function as a carrier transmitting portion operable to transmit the modulated carrier wave, and cooperate with the receiver portion 133 to function as a signal receiving portion operable to receive a signal. It will also be understood that the transmitter portion 132 functions as a carrier output portion including the carrier generating portion and the carrier modulating portion, and the RSSI circuit 148 functions as a signal-strength detecting portion operable to detect the strength of the received signal received by the signal-receiving portion, while the canceling circuit 200 functions as a cancel-signal generating portion operable to generate the cancel signal. It will further be understood that the control circuit 104 functions as a cancel-signal control portion operable to control the carrier generating portion, the carrier transmitting portion and the cancel-signal generating portion, such that the phase and amplitude of the cancel signal generated by the cancel-signal generating portion are changed and optimized, on the basis of the strength of the received signal which is detected by the signal-strength detecting portion when the received signal is received by the signal receiving portion while the carrier wave generated by the carrier generating portion is transmitted from the carrier transmitting portion, without transmission of the carrier wave modulated by the carrier modulating portion from the carrier transmitting portion.

It will also be understood that a portion of the control circuit 104 assigned to implement the rough search for the optimum values of the amplitude and phase of the cancel signal according to the control routine of FIG. 14 constitutes a first searching portion operable to change values of the phase and amplitude of the cancel signal within respective primary phase and amplitude search ranges at respective primary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective primary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for primary optimum values of the phase and amplitude, while a portion of the control circuit 104 assigned to implement the fine search for the optimum values of the amplitude and phase of the cancel signal according to the control routine of FIG. 15 constitutes a second searching portion operable to change values of the phase and amplitude of the cancel signal within respective secondary phase and amplitude search ranges at respective secondary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective secondary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for final optimum values of the phase and amplitude, the secondary phase and amplitude search ranges being respectively narrower than the primary phase and amplitude search ranges and respectively including the primary optimum values, and the secondary phase and amplitude searching pitches being respectively smaller than the primary phase and amplitude searching pitches.

It will further be understood that a portion of the control circuit 104 assigned to implement step S30 of the control routine of FIG. 12 constitutes a first determining portion operable to determine whether a current set value of at least one of the phase and amplitude of the cancel signal should be changed, on the basis of the strength of the received signal detected by the signal-strength detecting portion, and that the sum of the predetermined threshold value and the predetermined α % used in step S30 corresponds to a first threshold of the strength of the received signal, which first threshold is set after the final optimum values of the phase and amplitude of the cancel signal have been set.

It will also be understood that a portion of the control circuit 104 assigned to implement the fine adjustment of the canceling circuit 200 according to the control routine of FIG. 16 constitutes a control-signal generating portion operable to supply the cancel-signal generating portion with a control signal for changing at least one of the phase and amplitude of said cancel signal, when said first determining portion has determined that the currently set value of said at least one of the phase and amplitude of said cancel signal should be changed.

It will further be understood that a portion of the control circuit 104 assigned to implement step S60 of the control routine of FIG. 12 constitutes a third determining portion operable to determine whether currently set values of the phase and amplitude of the cancel signal should be changed again, on the basis of the strength of the received signal detected by the signal-strength detecting portion after the currently set value of at least one of the phase and amplitude of the cancel signal is changed according to the determination by the first determining portion that the currently set value of the at least one of the phase and amplitude should be changed. It will also be understood that a portion of the control circuit 104 assigned to implement step S40 of the control routine of FIG. 12 constitutes a transmission/reception control portion operable to control the carrier transmitting portion to transmit toward the transponder the carrier wave modulated by the carrier modulating portion, immediately after an operation of the cancel-signal control portion for controlling the carrier generating portion, and to control the signal receiving portion to receive a reply signal transmitted from the transponder in response to the modulated carrier wave received from the carrier modulating portion.

It will further be understood that a portion of the control circuit 104 assigned to implement step S30 of the control routine of FIG. 12 constitutes a first determining portion operable to determine whether a currently set value of at least one of the phase and amplitude of the cancel signal should be changed, on the basis of the strength of the received signal detected by the signal-strength detecting portion. It will also be understood that the sum of the threshold value and the predetermined α %, which is used in step S30, corresponds to a first threshold which is set after optimum values of the phase and amplitude of the cancel signal have been set by the cancel-signal control portion, and on the basis of a strength of the received signal which corresponds to the optimum values.

It will also be understood that a portion of the control circuit 104 assigned to implement the control routine of FIG. 16 for the fine adjustment of the canceling circuit 200 constitutes a control-signal generating portion operable to supply the cancel-signal generating portion with a control signal for changing at least one of the phase and amplitude of the cancel signal when the first determining portion has determined that the currently set value of the at least one of the phase and amplitude of the cancel signal should be changed.

It will further be understood that a portion of the control circuit 104 assigned to implement step S60 of the control routine of FIG. 12 constitutes a third determining portion operable to determine whether currently set values of the phase and amplitude of the cancel signal should be changed again, on the basis of the strength of the received signal detected by the signal-strength detecting portion after the currently set value of at least one of the phase and amplitude of the cancel signal is changed according to the determination by the first determining portion that the currently set value of the at least one of the phase and amplitude should be changed. It will also be understood that a portion of the control circuit 104 assigned to implement step S40 of the control routine of FIG. 12 constitutes a transmission/reception control portion operable to control the carrier transmitting portion to transmit toward the transponder the carrier wavet modulated by the carrier modulating portion, immediately after an operation of the cancel-signal control portion for controlling the carrier generating portion, and to control the signal receiving portion to receive a reply signal transmitted from the transponder in response to the modulated carrier wave received from the carrier modulating portion through the carrier transmitting portion.

In the adjustment of the canceling circuit 200, the primary or rough search for the primary optimum value Pbest1 of the phase P and the primary optimum value Abest1 of the amplitude A is initially implemented within the primary phase and amplitude search ranges, and the secondary or fine search for the final optimum value Pbest2 of the phase P and the final optimum value Abest2 of the amplitude A is then implemented within the secondary phase and amplitude ranges. The combination of the primary and secondary searches (rough and fine searches) permits more efficient finding of the final optimum values Pbest 2 and Abest2 of the phase P and amplitude A of the cancel signal, in a shorter length of time with a reduced operating load acting on the cancel-signal control portion.

If the detected strength of the received signal is higher than the sum of the threshold value and the predetermined α % of the threshold value even after the optimization of the phase and amplitude of the cancel signal by the rough and fine searches, it is determined in step S30 of FIG. 12 that at least one of the phase and amplitude of the cancel signal should be changed from the currently set value. In this instance, the currently set value of the phase of the cancel signal is changed again by the fine adjustment of the canceling circuit 200 according to the control routine of FIG. 16. Accordingly, the currently set value of the phase can be further optimized by the fine adjustment of the canceling circuit 200 according to a change of the operating environment of the interrogator 100. Even after the fine adjustment, the determination is made in step S60 as to whether the phase P and amplitude A of the cancel signal should be changed again. That is, if the negative determination is obtained in step S60 due to insufficiency of the fine adjustment, the control flow goes back to step S100 to make the primary and secondary searches again to re-adjust the phase and amplitude of the cancel signal according to a change of the operating environment of the interrogator 100.

In the third embodiment described by reference to the flow chart of FIG. 12, the fine adjustment of the canceling circuit 200 is implemented in step S200 if the strength of the received signal detected after the initial adjustment of the canceling circuit 200 in step S100 is higher than the sum of the threshold value and the predetermined α %. Further, the re-adjustment in step S100 is implemented if the strength of the received signal detected after the fine adjustment is higher than the sum. However, the fine adjustment and re-adjustment of the canceling circuit 200 are not limited to those illustrated in the flow chart of FIG. 12, and may be made otherwise in the following fourth embodiment of FIGS. 18 and 19.

### Embodiment 4

Referring to the flow chart of FIG. 18 corresponding to that of FIG. 12, there will be described a control routine executed by the control circuit 104 in the present fourth embodiment to adjust or control the canceling circuit 200.

The control routine of FIG. 18 is initiated with steps S10 and S100 to initialize the interrogator 100 and implement the initial adjustment of the canceling circuit 200. Step S100 is followed by steps S300, S310 and S320 which are characteristic of this fourth embodiment.

Step S300 is provided to detect or measure the strength of the received signal currently received by the RSSI circuit 148, and to set a +x % of the detected strength as a first threshold value, and set a +y % of the detected strength as a second threshold value. The x % and y % are about several % to about 20%, and the x % is lower than the y %, namely, value x<value y.

Step S300 is followed by step S310 to determine whether the strength of the received signal currently received by the RSSI circuit 148 is equal to or lower than the second threshold value set in step S300.

If a negative determination is obtained in step S310, this indicates that the detected strength of the currently received signal is higher than the comparatively large second threshold value (y % of the strength detected in step S300), and the control flow goes back to step S100 to make the re-adjustment of the canceling circuit 200. If an affirmative determination is obtained in step S310, the control flow goes to step S320.

Step S320 is provided to determine whether the strength of the received signal currently received by the RSSI circuit 148 is equal to or lower than the first threshold value (x % of the strength detected in step S300).

If a negative determination is obtained in step S320, this indicates that the currently set values of the amplitude and phase of the cancel signal slightly deviate from the optimum values for adequately eliminating the unnecessary wave (leakage signal), and the control flow goes to step S200 to make the fine adjustment of the canceling circuit 200 as described above with respect to step S200 of FIG. 12. Step S200 is followed by step S40.

If an affirmative determination is obtained in step S320, this indicates that the currently set values of the amplitude and phase of the cancel signal are optimum for adequately eliminating the unnecessary wave, and the control flow goes to step S40.

Steps S40 and S50 have been described above by reference to the flow chart of FIG. 12. Namely, the communication with the circuit element To of the transponder (radio-frequency tag) 14 is implemented to obtain an access to the transponder in question, and the determination is made as to whether it is necessary to implement the communication with any other transponder. If a negative determination is obtained in step S40, the present control routine of FIG. 18 is terminated. If an affirmative determination is obtained in step S40, the control flow goes back to sep S310 and the following steps.

Referring to FIG. 19 corresponding to FIG. 17 showing the third embodiment, there is shown a change of the strength RSSI of the received signal detected by the RSSI circuit 148, as a result of the adjustments of the canceling circuit 200 according to the control routine of FIG. 18.

As shown in FIG. 19, the signal strength RSSI is considerably reduced from an initial value, as indicated at (a) in FIG. 19, as a result of the first adjustment of the canceling circuit 200 in step S100 of FIG. 18. If the signal strength RSSI exceeds the first threshold value due to a change in the operating environment of the interrogator 100, for instance, as indicated at (b′) in FIG. 19, the fine adjustment of the canceling circuit 200 in step S200 of FIG. 18 is implemented, so that signal strength RSSI is reduced below the first threshold value, as indicated at (c) in FIG. 19. If the signal strength RSSI again exceeds the first threshold value and then the second threshold value, as indicated at (d′) in FIG. 19, the re-adjustment of the canceling circuit 200 is implemented in step S100, so that the detected strength of the received signal is reduced below the first threshold value, and the first and second threshold values are set in step S300 on the basis of the last detected strength of the received signal, as indicated at (e′) in FIG. 19.

It will be understood from the foregoing description of the fourth embodiment that a portion of the control circuit 104 assigned to implement step S320 of the control routine of FIG. 18 constitutes a first determining portion operable to determine whether a currently set value of at least one of the phase and amplitude of the cancel signal generated by the cancel-signal generating portion should be changed, on the basis of the strength of the received signal detected by the signal-strength detecting portion, and that a portion of the control circuit 104 assigned to implement step S310 of the control routine of FIG. 18 constitutes a second determining portion operable prior to the determination by the first determining portion, to determine whether the currently set value of at least one of the phase and amplitude of the cancel signal should be changed.

The present fourth embodiment has substantially the same advantages as the third embodiment.

In the fourth embodiment descried above, the determination by the second determining portion is made in step S310 as to whether the re-adjustment of the canceling circuit 200 is required, prior to the determination made by the first determining portion in step S320 as to whether the fine adjustment of the canceling circuit 200 is required. termination by the first determining portion is preferably a determination According to this assignment of the first and second determining portions, either the re-adjustment or the fine adjustment of the canceling circuit 200 is selectively effected according to results of the determinations by the first and second determining portions, depending upon whether the amount of deviation of the currently set values of the phase and amplitude from the optimum values at which the unnecessary wave can be most adequately eliminated. Accordingly, the phase and amplitude of the cancel signal can be optimized with a high degree of efficiency in a shorter length of time, with a reduced operating load acting on the cancel-signal control portion.

It is to be understood that the present invention may be embodied with various other changes which may occur to those skilled in the art, without departing from the spirit and scope of this invention.

## Claims

1. A radio-frequency communication device arranged to transmit a transmitted signal from a transmitter antenna device toward a communication object, and to receive through a receiver antenna device a reply signal transmitted from the communication object, for radio communication with the communication object, said radio-frequency communication device comprising:
a transfer-function calculating portion configured to calculate a transfer function indicative of a relationship between a signal input to said transmitter antenna device and a signal generated by said receiver antenna device due to said signal input to said transmitter antenna device;
a receiver-circuit-constant setting portion configured to set a receiver-circuit constant for improving a quality of said reply signal received by said receiver antenna device, on the basis of said transfer function calculated by said transfer-function calculating portion, and said signal input to said transmitter antenna device; and
a cancel-signal generating portion configured to generate a cancel signal, which is added to a leakage signal that is generated by said receiver antenna device due to transmission of said transmitted signal from said transmitter antenna device, for canceling the leakage signal,
wherein said receiver-circuit-constant setting portion is configured to set, as said received-circuit constant, a constant for determining a phase and an amplitude of said cancel signal.
a transfer-function calculating portion configured to calculate a transfer function indicative of a relationship between a signal input to said transmitter antenna device and a signal generated by said receiver antenna device due to said signal input to said transmitter antenna device;
a receiver-circuit-constant setting portion configured to set a receiver-circuit constant for improving a quality of said reply signal received by said receiver antenna device, on the basis of said transfer function calculated by said transfer-function calculating portion, and said signal input to said transmitter antenna device; and
a cancel-signal generating portion configured to generate a cancel signal, which is added to a leakage signal that is generated by said receiver antenna device due to transmission of said transmitted signal from said transmitter antenna device, for canceling the leakage signal,
wherein said receiver-circuit-constant setting portion is configured to set, as said received-circuit constant, a constant for determining a phase and an amplitude of said cancel signal.
2. The radio-frequency communication device according to claim 1, further comprising a carrier generating portion configured to generate a carrier wave of said transmitted signal, and wherein said cancel-signal generating portion generates said cancel signal on the basis of said carrier wave generated by said carrier generating portion.
3. The radio-frequency communication device according to claim 1, further comprising:
a local-signal oscillator configured to generate a local signal;
a local-signal adjusting portion configured to adjust a phase and an amplitude of said local signal generated by said local-signal oscillator, on the basis of a predetermined constant; and
a frequency converting portion configured to convert a frequency of said reply signal received by said receiver antenna device, by combining together said local signal the phase and amplitude of which have been adjusted by said local-signal adjusting portion, and said reply signal,
and wherein said receiver-circuit-constant setting portion sets, as said receiver-circuit constant, said constant on the basis of which the phase and amplitude of said local signal are adjusted by said local-signal adjusting portion.
a local-signal oscillator configured to generate a local signal;
a local-signal adjusting portion configured to adjust a phase and an amplitude of said local signal generated by said local-signal oscillator, on the basis of a predetermined constant; and
a frequency converting portion configured to convert a frequency of said reply signal received by said receiver antenna device, by combining together said local signal the phase and amplitude of which have been adjusted by said local-signal adjusting portion, and said reply signal,
and wherein said receiver-circuit-constant setting portion sets, as said receiver-circuit constant, said constant on the basis of which the phase and amplitude of said local signal are adjusted by said local-signal adjusting portion.
4. The radio-frequency communication device according to claim 3, further comprising a carrier generating portion configured to generate a carrier wave of said transmitted signal, and wherein said local-signal oscillator generates said local signal on the basis of the carrier wave generated by said carrier generating portion.
5. The radio-frequency communication device according to claim 1, wherein said transmitter antenna device consists of a plurality of transmitter antenna elements.
6. The radio-frequency communication device according to claim 1, wherein said receiver antenna device consists of a plurality of receiver antenna elements.
7. The radio-frequency communication device according to claim 1, wherein said transmitter antenna device and said receiver antenna device include at least one common transmitter/receiver antenna element.
8. The radio-frequency communication device according to claim 1, wherein said transmitter antenna device consists of a plurality of transmitter antenna elements for transmitting respective transmitted signals, said radio-frequency communication device further comprising a phased-array control portion configured to control a phase of each of the transmitted signals to be transmitted from said plurality of transmitter antenna elements, for thereby controlling a direction of transmission of the transmitted signals.
9. The radio-frequency communication device according to claim 8, wherein said receiver-circuit-constant setting portion sets said receiver-circuit constant each time the direction of transmission of the transmitted signals is changed by said phased-array control portion.
10. The radio-frequency communication device according to claim 1, wherein said transmitter antenna device consists of a plurality of transmitter antenna elements, and said receiver antenna device consists of a plurality of receiver antenna elements, said transfer-function calculating portion calculating, as said transfer function, a value obtained by dividing a transmitted-signal component included in received signals received by said receiver antenna elements, by predetermined transmitted signals to be transmitted from said transmitter antenna elements.
11. The radio-frequency communication device according to claim 1, wherein said transfer-function calculating portion calculates said transfer function at a predetermined time interval.
12. The radio-frequency communication device according to claim 1, further comprising a received-signal-quality detecting portion configured to detect a quality of a received signal received by said receiver antenna device, and said transfer-function calculating portion calculates said transfer function, depending upon the quality of the received signal detected by said received-signal-quality detecting portion.
13. The radio-frequency communication device according to claim 12, wherein said received-signal-quality detecting portion detects, as the quality of the received signal, a strength of said received signal while said reply signal transmitted from said communication object is not received by said receiver antenna device, and said transfer-function calculating portion calculates said transfer function when the strength of the received signal detected by said received-signal-quality detecting portion is equal to or higher than a predetermined threshold.
14. The radio-frequency communication device according to claim 1, wherein said receiver-circuit-constant setting portion sets said receiver-circuit constant each time said transfer-function calculating portion calculates said transfer function.
15. The radio-frequency communication device according to claim 1, wherein said communication object is a radio-frequency tag configured to transmit said reply signal including predetermined information, in response to said transmitted signal transmitted from said transmitter antenna device.
16. A radio-frequency communication device comprising:
a carrier output portion including a carrier generating portion configured to generate a carrier wave for obtaining an access to a transponder, and a carrier modulating portion configured to modulate the carrier wave generated by said carrier generating portion, said carrier output portion outputting the carrier wave from said carrier generating portion or a modulated carrier wave from said carrier modulating portion;
a carrier transmitting portion configured to transmit the carrier wave from said carrier generating portion toward said transponder;
a signal receiving portion configured to receive a signal transmitted from said transponder in response to the carrier wave received from said carrier output portion;
a cancel-signal generating portion configured to generate a cancel signal for eliminating an unnecessary wave that is a part of the carrier wave transmitted from said carrier transmitting portion, which part is received by said signal receiving portion;
a signal-strength detecting portion configured to detect a strength of a received signal which is received by said signal receiving portion and from which said unnecessary wave is at least partially eliminated by said cancel signal generated by said cancel-signal generating portion; and
a cancel-signal control portion configured to control said carrier generating portion, said carrier transmitting portion and said cancel-signal generating portion, such that the carrier wave generated by said carrier generating portion is transmitted from said carrier transmitting portion, and a phase and an amplitude of said cancel signal generated by said cancel-signal generating portion are changed and optimized on the basis of the strength of said received signal, which is detected by said signal-strength detecting portion, before the modulated carrier wave modulated by said carrier modulating portion is transmitted from said carrier transmitting portion and received by said signal receiving portion.
a carrier output portion including a carrier generating portion configured to generate a carrier wave for obtaining an access to a transponder, and a carrier modulating portion configured to modulate the carrier wave generated by said carrier generating portion, said carrier output portion outputting the carrier wave from said carrier generating portion or a modulated carrier wave from said carrier modulating portion;
a carrier transmitting portion configured to transmit the carrier wave from said carrier generating portion toward said transponder;
a signal receiving portion configured to receive a signal transmitted from said transponder in response to the carrier wave received from said carrier output portion;
a cancel-signal generating portion configured to generate a cancel signal for eliminating an unnecessary wave that is a part of the carrier wave transmitted from said carrier transmitting portion, which part is received by said signal receiving portion;
a signal-strength detecting portion configured to detect a strength of a received signal which is received by said signal receiving portion and from which said unnecessary wave is at least partially eliminated by said cancel signal generated by said cancel-signal generating portion; and
a cancel-signal control portion configured to control said carrier generating portion, said carrier transmitting portion and said cancel-signal generating portion, such that the carrier wave generated by said carrier generating portion is transmitted from said carrier transmitting portion, and a phase and an amplitude of said cancel signal generated by said cancel-signal generating portion are changed and optimized on the basis of the strength of said received signal, which is detected by said signal-strength detecting portion, before the modulated carrier wave modulated by said carrier modulating portion is transmitted from said carrier transmitting portion and received by said signal receiving portion.
17. The radio-frequency communication device according to claim 16, wherein said cancel-signal control portion changes the phase and amplitude of said cancel signal to optimum values, such that the strength of said received signal detected by said signal-strength detecting portion is minimized.
18. The radio-frequency communication device according to claim 17, wherein said cancel-signal control portion comprises:
a first searching portion configured to change values of the phase and amplitude of said cancel signal within respective primary phase and amplitude search ranges at respective primary phase and amplitude searching pitches, for said signal-strength detecting portion to detect values of the strength of the received signal at respective primary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for primary optimum values of the phase and amplitude; and
a second searching portion configured to change values of the phase and amplitude of said cancel signal within respective secondary phase and amplitude search ranges at respective secondary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective secondary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for final optimum values of the phase and amplitude, said secondary phase and amplitude search ranges being respectively narrower than said primary phase and amplitude search ranges and respectively including said primary optimum values, and said secondary phase and amplitude searching pitches being respectively smaller than said primary phase and amplitude searching pitches.
a first searching portion configured to change values of the phase and amplitude of said cancel signal within respective primary phase and amplitude search ranges at respective primary phase and amplitude searching pitches, for said signal-strength detecting portion to detect values of the strength of the received signal at respective primary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for primary optimum values of the phase and amplitude; and
a second searching portion configured to change values of the phase and amplitude of said cancel signal within respective secondary phase and amplitude search ranges at respective secondary phase and amplitude searching pitches, for the signal-strength detecting portion to detect values of the strength of the received signal at respective secondary monitoring points defined by respective sets of the changed values of the phase and amplitude of the cancel signal, to search for final optimum values of the phase and amplitude, said secondary phase and amplitude search ranges being respectively narrower than said primary phase and amplitude search ranges and respectively including said primary optimum values, and said secondary phase and amplitude searching pitches being respectively smaller than said primary phase and amplitude searching pitches.
19. The radio-frequency communication device according to claim 16, wherein said cancel-signal control portion includes a first determining portion configured to determine whether a current set value of at least one of the phase and amplitude of said cancel signal should be changed, on the basis of the strength of the received signal detected by said signal-strength detecting portion.
20. The radio-frequency communication device according to claim 19, wherein said first determining portion determines that the currently set value of at least one of the phase and amplitude of said cancel signal should be changed, when the strength of said received signal detected by said signal-strength detecting portion is larger than a first threshold which is set after optimum values of the phase and amplitude of said cancel signal have been set by said cancel-signal control portion, and on the basis of a strength of said received signal which corresponds to said optimum values.
21. The radio-frequency communication device according to claim 20, wherein said cancel-signal control portion further includes a second determining portion configured prior to the determination by said first determining portion, to determine whether the currently set value of said at least one of the phase and amplitude of the cancel signal should be changed.
22. The radio-frequency communication device according to claim 21, wherein said second determining portion determines that the currently set value of said at least one of the phase and amplitude of said cancel signal should be changed, when the strength of said received signal detected by said signal-strength detecting portion is larger than a second threshold value which is larger than said first threshold value and which is set after the optimum values of the phase and amplitude of the cancel signal have been set by said cancel-signal control portion, and on the basis of a strength of said received signal which corresponds to said optimum values.
23. The radio-frequency communication device according to claim 19, wherein said cancel-signal control portion further includes a control-signal generating portion configured to supply said cancel-signal generating portion with a control signal for changing at least one of the phase and amplitude of said cancel signal, when said first determining portion has determined that the currently set value of said at least one of the phase and amplitude of said cancel signal should be changed.
24. The radio-frequency communication device according to claim 23, wherein said first determining portion determines whether the currently set value of the phase of said cancel signal generated by said cancel-signal generating portion should be changed, on the basis of the strength of said received signal detected by said signal-detecting portion, and said control-signal generating portion supplies said cancel-signal generating portion with said control signal to change the phase when said first determining portion has determined that the phase should be changed.
25. The radio-frequency communication device according to claim 19, wherein said cancel-signal control portion further includes a third determining portion configured to determine whether currently set values of the phase and amplitude of said cancel signal should be changed again, on the basis of the strength of the received signal detected by said signal-strength detecting portion after the currently set value of at least one of the phase and amplitude of the cancel signal is changed according to the determination by said first determining portion that the currently set value of the at least one of the phase and amplitude should be changed.
26. The radio-frequency communication device according to claim 16, wherein said cancel-signal control portion further includes a transmission/reception control portion configured to control said carrier transmitting portion to transmit toward the transponder the carrier wave modulated by said carrier modulating portion, immediately after an operation of said cancel-signal control portion for controlling said carrier generating portion, and to control said signal receiving portion to receive a reply signal transmitted from the transponder in response to the modulated carrier wave received from said carrier modulating portion through said carrier transmitting portion.