Patent Application
20120094599
The present invention relates to an antenna unit used in a mobile device, like an IC card of an RFID system, as well as relating to a portable wireless device equipped with the antenna unit.
An RFID (Radio Frequency Identification) system is generally used for electronic money, or the like. Communication between a mobile device that acts as an RFID card or an RFID-containing device and its counterpart equipment [a reader/writer (R/W)] that is a stationary machine disposed in a shop, or the like, is performed through wireless communication utilizing induction coupling. A wireless communication technique utilizing induction coupling allows establishment of communication only within a range where a high degree of coupling exists between an antenna of the mobile device and an antenna of its counterpart equipment, and a communication distance is as short as about one meter. When transmission power of the counterpart equipment is high, an amplitude of a signal input to a communication circuit section of the mobile device becomes considerably large while the mobile device and its counterpart equipment remain in considerably close to each other.
The clipping circuit 44 is implemented by use of: for instance, a diode, and shows a voltage-current characteristic, like that shown in
Incidentally, in the RFID system, a load modulation switch 45 provided in the antenna circuit section 42 of the mobile device 40 is turned on or off, thereby changing a resistance value of the antenna circuit section 42 and in turn changing a current value. A difference in electromagnetic induction thus develops in the antenna 41, which in turn effects communication from the mobile device 40 to the counterpart equipment 30. Therefore, when a resistance value of the clipping circuit 44 becomes smaller, a change in resistance value of the antenna circuit section 42 caused by activation or deactivation of the switch 45 also becomes smaller. Thus, the difference in electromagnetic induction becomes smaller, so that the counterpart equipment 30 can properly receive a radio wave transmitted from the mobile device 40. Specifically, there arises a Null phenomenon in which the mobile device 40 and the counterpart equipment 30 cannot establish communication while remaining in close to each other.
A hitherto proposed method for avoiding occurrence of the Null phenomenon involves a plurality of capacitors (condensers) and a voltage detection section that are provided in an IC control section of the mobile device. The voltage detection section detects a received voltage level of a signal received by an antenna after the signal has undergone rectification and smoothing. According to the thus-detected received voltage level, switching between the capacitors is carried out, to thus reduce an antenna gain (see; for instance, Patent Document 1).
However, there are generally a plurality of types of RFID counterpart equipment, and a resonance frequency varies from one counterpart equipment to another. As shown in
a) and 10(b) show a change in S21 characteristic induced by switching between the capacitors of the related art mobile device shown in
The object of the present invention is to provide an antenna unit capable of transmitting and receiving a wireless signal without involvement of occurrence of a Null phenomenon in a plurality of types of counterpart equipment that operate at different resonance frequencies and a portable wireless device having the antenna unit.
An antenna unit of the present invention that performs wireless communication utilizing induction coupling, the unit comprising: a loop antenna; a communication circuit section that is connected to the loop antenna in order to perform wireless communication utilizing induction coupling; a metallic plate provided outside or inside the loop antenna in a form of a loop by way of an openable and closable switch; and a detector that detects a receiving level of a wireless signal received by the loop antenna, wherein the communication circuit section controls opening and closing of the switch according to a receiving level of the wireless signal detected by the detector, thereby switching a state of the metallic plate between a closed looped state and an open non-looped state.
In the antenna unit, the metallic plate is provided on a same plane where the loop antenna is provided.
In the antenna unit, the metallic plate is a reader/writer antenna.
The antenna unit is built in a portable wireless device.
The portable wireless device of the present invention and a portable radio equipped with the antenna unit can perform wireless communication with a plurality of types of counterpart equipment that operate at different resonance frequencies even when the portable wireless device comes close to the counterpart equipment, like an RFID system, without involvement of occurrence of a Null phenomenon.
Embodiments of the present invention are hereunder described by reference to the drawings.
By reference to
The loop antenna 2 is used; for instance, as a main antenna of a mobile device of an RFID system. In the present embodiment, the loop antenna 2 is made up of a four-turn rectangular loop made of copper foil, or the like. Both ends 2a of the loop antenna 2 are pulled outside of the metallic plate 3 from a center of a lower side of the rectangular shown in
The metallic plate 3 is used as a control antenna for controlling a gain of the loop antenna 2. As shown in
The open ends 3a of the metallic plate 3 can be at any position on the metallic plate 3 formed into a loop shape.
The essential requirement for the metallic plate 3 is to be provided substantially in the same plane where the loop antenna 2 is provided. In addition to being provided in the same plane made by the loop antenna 2, the metallic plate 3 can also be provided while displaced by about one to two millimeters from the plane in the vertical direction. In the drawings, the open ends 3a of the metallic plate 3 are pulled outside the loop antenna 2 from the center of the lower side of the rectangular, and the switch 5 is interposed between the thus-pulled open ends 3a.
As will be described later, the switch 5 effects a transition between an open state and a closed state under control of the communication circuit section 4 according to a receiving level of a signal received by the loop antenna 2 detected by the detector 12. When the switch 5 is turned on and brought into a closed state, the open ends 3a of the metallic plate 3 are physically connected by way of the switch 5. In the meantime, when the switch 5 is turned off and brought into an open state, the open ends 3a of the metallic plate 3 are physically disconnected. Therefore, when the switch 5 is closed, the open ends 3a of the metallic plate 3 are electrically connected by way of the switch 5. However, when the switch 5 is in an open state, the open ends 3a are not electrically connected.
When the switch 5 is closed, the switch 5 electrically connects the open ends 3a of the metallic plate 3, whereupon the metallic plate 3 enters a looped state where the metallic plate is closed in the form of the loop. In the meantime, when the switch 5 is in an open state, the switch 5 does not make an electrical connection of the open ends 3a of the metallic plate 3. The metallic plate 3 enters a discontinuous non-looped state because of the open ends 3a.
The mobile device 10 receives a communication radio wave from un-illustrated counterpart equipment by means of the loop antenna 2. The diode 9 rectifies a received signal of a resonance frequency selected by the LC resonance circuit of the antenna circuit section 8. By means of the detector 12, the mobile device 10 detects a voltage of the received signal passed through the clipping circuit 11. The comparator 13 converts the signal output from the detector 12 into a digital signal with reference to an REF signal. A control section (not shown) of the communication circuit section 4 performs processing for decoding received data, or the like. In the meantime, according to a transmission data signal from the control section of the communication circuit section 4, a current value is changed by means of a change in resistance value of the load modulation circuit 14. A difference in induction voltage is developed in the loop antenna 2, thereby performing communication from the mobile device 10 to the counterpart equipment.
In the meantime, the switch 5 is turned on and brought into a closed state, whereby the metallic plate 3 assumes a completely closed looped state around the inside of the loop antenna 2. In this state, the gain of the antenna unit 1 decreases over the entire frequency band as shown in
In the antenna unit 1 of the first embodiment, when the antenna unit 1 performs wireless communication utilizing induction coupling, the switch 5 is turned off under control of the communication circuit section 4 according to the receiving level of the loop antenna 2 detected by the detector 12. When the metallic plate 3 is in a non-looped state in which the metallic plate becomes discontinuous at the open ends 3a, around the inside of the loop antenna 2, the S21 characteristic of the antenna unit 1 can increase the gain over the entire frequency band. Therefore, the antenna unit 1 can be applied to the antenna section of the mobile device in response to a plurality of types of counterpart equipment that operate at different resonance frequencies.
In the antenna unit 1 of the first embodiment, when the antenna unit 1 performs wireless communication utilizing induction coupling; for instance, when the receiving level of the loop antenna 2 detected by the detector 12 is higher than a given level (an amplitude is high), the switch 5 is turned on under control of the communication circuit section 4. When the metallic plate 3 and the switch 5 are completely closed in the form of the loop around the inside of the loop antenna 2, the gain of the antenna unit 1 can be decreased over the entire frequency band. Therefore, even when the antenna unit 1 of the embodiment is applied to the antenna section of the mobile device 10 in response to the antenna section of the counterpart equipment and when the mobile device 10 is used in a short range from the counterpart equipment, communication can be performed without involvement of occurrence of the Null phenomenon.
By reference to
The metallic plate 6 is used as a control antenna for controlling the gain of the loop antenna 2. As shown in
The essential requirement for the metallic plate 6 is to be in substantially the same plane where the loop antenna 2 is present. In addition to being situated in the same plane as that made by the loop antenna 2, the metallic plate 6 can be provided while displaced by about one to two millimeters in the vertical direction from the plane. The switch 5 is interposed between the open ends 6a of the metallic plate 6, and the switch 5 is connected to an output side of the detector 12 shown in
As will be described later, under control of the communication circuit section 4, the switch 5 effects a transition between the open state and the closed state according to the receiving level of the signal received by the loop antenna 2 detected by the detector 12. When the switch 5 is turned on and brought into a closed state, the open ends 6a of the metallic plate 6 are physically connected by way of the switch. Meanwhile, when the switch 5 is turned off and brought into an open state, the open ends 6a of the metallic plate 6 are physically disconnected. Therefore, when the switch 5 is closed, the open ends 6a of the metallic plate 6 are electrically connected by way of the switch 5. However, when the switch 5 is in the open state, the open ends 6a are not electrically connected.
When the switch 5 is closed, the switch 5 electrically connects the open ends 6a of the metallic plate 6, whereupon the metallic plate 6 assumes a looped state in which the metallic plate is closed in the form of a loop. Meanwhile, when the switch 5 is in an open state, the switch 5 does not electrically connect the open ends 6a of the metallic plate 6, so that the metallic plate 6 assumes a non-looped state in which the metallic plate 6 becomes discontinuous at the open ends 6a.
As in the case of the first embodiment, when the antenna unit 1A of the second embodiment performs wireless communication utilizing induction coupling, the switch 5 is turned off under control of the communication circuit section 4 according to the receiving level of the loop antenna 2 detected by the detector 12. When the metallic plate 6 is in a non-looped state in which the metallic plate 6 is discontinuous at the open ends 6a around the outside of the loop antenna 2, the S21 characteristic of the antenna unit 1A enables an increase in gain over the entire frequency band. Therefore, the antenna unit 1 can be applied to the antenna section of the mobile device even in response to a plurality of types of counterpart equipment that operate at different resonance frequencies.
As in the case of the first embodiment, when the antenna unit 1A of the second embodiment performs wireless communication utilizing induction coupling; for instance, when the receiving level of the loop antenna 2 detected by the detector 12 is higher than a given value (an amplitude is large), the switch 5 is turned on under control of the communication circuit section 4. When the metallic plate 6 is completely closed in the form of a loop around the outside of the loop antenna 2 by means of the switch 5, the gain of the antenna unit 1A can be reduced over the entire frequency band. Therefore, even when the antenna unit 1A of the embodiment is applied to the antenna section of the mobile device 10 in response to the antenna section of the counterpart equipment and when the mobile device 10 is used in a short range from the counterpart equipment, communication can be performed without involvement of occurrence of the Null phenomenon.
As in the case of the antenna unit 1A of the first embodiment. when the metallic plate 6 is provided in the form of a loop outside the loop antenna 2, an effect of reducing the S21 characteristic of a mobile device 20 becomes greater when compared with a case where the metallic plate 3 is provided in the form of a loop within the loop antenna 2.
Incidentally, in the antenna unit 1 (1A) of each of the embodiments, the metallic plate 3 (the metallic plate 6) and the switch 5 make up a loop-shaped conductor. Therefore, the metallic plate 3 (the metallic plate 6) and the switch 5 can be caused to act as an antenna element. Put another way, in addition to having the loop antenna 2, the antenna unit 1 (1A) of each of the embodiments has a loop-shaped antenna built from the metallic plate 3 (the metallic plate 6) and the switch 5. Therefore, the antenna unit of the present invention can be applied to a mobile device equipped with a reader/writer function of the RFID system. In this case, the metallic plate 3 (the metallic plate 6) of the antenna unit of the present invention acts as an antenna for transmitting and receiving a wireless signal with respect to the counterpart equipment by means of induction coupling with the antenna of the counterpart equipment.
By reference to
As in the antenna unit 1 shown in
The mobile device 20 shown in
According to the antenna unit 1B of the present embodiment, the metallic plate 3 can also be used as a reader/writer antenna and an element for controlling a receiving level of the loop antenna 2. Hence, the mobile device 20 can also be miniaturized and made less expensive.
As in the first embodiment, when the antenna unit 1B of the present embodiment performs wireless communication utilizing induction coupling, the communication circuit section 4 controls the switch 5 so as to become deactivated according to the receiving level of the loop antenna 2 detected by the detector 12, whereupon the metallic plate 3 comes into a non-looped state in which the metallic plate 3 becomes discontinuous at the open ends 3a around the inside of the loop antenna 2. Therefore, the S21 characteristic of the antenna unit 1B enables the gain of the antenna unit to increase over the entire frequency band. Consequently, the antenna unit 1B can be applied to the antenna section of the mobile device 10 even in response to a plurality of types of counterpart equipment that operate at different resonance frequencies.
As in the first embodiment, in a case where the antenna unit 1B of the present embodiment performs wireless communication utilizing induction coupling, for instance, when the receiving level of the loop antenna 2 detected by the detector 12 is higher than a given value (an amplitude is large), the communication circuit section 4 controls the switch 5 so as to become activated, whereby the metallic plate 3 comes into the looped state where the metallic plate 3 becomes fully closed in the form of a loop by the switch 5 around the inside of the loop antenna 2. Thus, the gain of the antenna unit 1 can be reduced over the entire frequency band. Therefore, even when the antenna unit 1B of the present embodiment is applied to the antenna section of the mobile device 10 in response to the antenna section of the counterpart equipment and when the mobile device 10 is used in a short range from its counterpart equipment, communication can be performed without involvement of occurrence of a Null phenomenon.
Although the present invention has been described in detail by reference to the specific embodiments, it is manifest to those skilled in the art that the present invention be susceptible to various alterations or modifications without departing from the spirit and scope of the invention.
The present patent application is based on Japanese Patent Application (JP-2009-155294) filed on Jun. 30, 2009, the entire subject matter of which is incorporated herein by reference.
The antenna unit of the present invention and the portable wireless device equipped with the same yield an advantage of the ability to establish wireless communication without involvement of occurrence of a Null phenomenon even when the mobile device has come close to its counterpart equipment, in response to a plurality of types of counterpart equipment that operate at different resonance frequencies. Hence, the antenna unit and the portable wireless device are useful as a cell phone, or the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-155294 | Jun 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/001529 | 3/4/2010 | WO | 00 | 12/22/2011 |
