Patent Publication Number: US-2017365926-A1

Title: Antenna device, control device, and radio communication device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is continuation application of, and claims the benefit of priority from the International Application PCT/JP2015/071550, filed Jul. 29, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an antenna device, a control device, and a radio communication device, 
     BACKGROUND 
     In radio communication devices such as mobile phones, power loss may occur due to a mismatch between an input impedance of an antenna and an output impedance of a radio. In order to suppress the power loss, there is a method of installing a matching circuit with variable impedance between an antenna and a radio, detecting an impedance mismatch through a probe, and matching the input impedance of the antenna with the output impedance of the radio automatically. In the above method, downsizing of an antenna device including the matching circuit and the probe is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of an antenna device and a radio communication device according to a first embodiment; and 
         FIG. 2  is a schematic diagram illustrating a configuration of an antenna device and a radio communication device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An antenna device according to an embodiment includes an antenna including a power feeding point; a matching circuit having variable impedance; a loop type probe being installed near the power feeding point, the loop type probe receiving a radio wave radiated from the antenna; a power detector detecting electric power of the radio wave received by the loop type probe; and a control circuit controlling an impedance of the matching circuit on the basis of power information output from the power detector. 
     Hereinafter, exemplary embodiments will be described with reference to the appended drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals. 
     Further, in an embodiment, connection between a circuit (an A circuit) and a circuit (a B circuit) means that a signal is transmitted from the A circuit having a specific function to the B circuit having another function. It does not necessarily mean that the A circuit is physically connected with the B circuit. 
     First Embodiment 
     An antenna device according to an embodiment includes an antenna including a power feeding point, a matching circuit having a variable impedance, a loop type probe being installed near the power feeding point and receiving a radio wave radiated from the antenna, a power detector detecting electric power of the radio wave received by the probe, and a control circuit controlling the impedance of the matching circuit on the basis of power information output from the power detector. 
     A radio communication device of the present embodiment further includes a radio configured to generate a signal and an amplifier configured to amplify the signal and output the amplified signal to the antenna device in addition to the antenna device, 
       FIG. 1  is a schematic diagram illustrating a configuration of an antenna device and a radio communication device according to the present embodiment. The radio communication device of the present embodiment includes an antenna device  100 , a power amplifier  200 , and a radio  300 . The radio  300  is, for example, a transceiver. The antenna device  100 , the power amplifier  200  connected to the antenna device  100 , and the radio  300  constitute the radio communication device. Examples of the radio communication device include a mobile phone and a wireless LAN device. 
     The antenna device  100  includes an antenna  10 , a matching circuit  12 , a probe  14 , a power detector  16 , and a control circuit  18 . A portion of the antenna device  100  from which the antenna  10  is excluded is referred to as a control device  90 . 
     The antenna  10  is a conductor. The antenna  10  transmits a signal to be transmitted from the radio  300  to the outside of the radio communication device. 
     The antenna  10  is, for example, an inverted L antenna having a power feeding point  10   a  and an end portion  10   b  on a side opposite to the power feeding point  10   a.  The end portion  10   b  is open end. It is desirable to use the inverted L antenna since it is possible to downsize the radio communication device including the antenna device  100 , and it is easy to design the antenna device  100 . However, the antenna  10  is not limited to the inverted L antenna. The antenna  10  may be any other kind of antennas such as an inverted F antenna, a comb antenna, a dipole antenna, a loop antenna, or the like. 
     The matching circuit  12  is installed between the antenna  10  and the power amplifier  200 . The matching circuit  12  is connected to the power feeding point  10   a  of the antenna  10 . The matching circuit  12  includes an access portion to which the antenna  10  is connectable. In the matching circuit  12  of the present embodiment, a connecting portion coincides with a position of the power feeding point  10   a  in  FIG. 1 . 
     The matching circuit  12  has a variable impedance. The radio communication device matches the input impedance of the antenna  10  with the output impedance of the radio  300  by adjusting the impedance of the matching circuit  12 . 
     The matching circuit  12  is configured with, for example, two variable capacitors  12   a  and  12   b.  The two variable capacitors  12   a  and  12   b  are impedance variable element. There is no particular limitation to a use quantity of variable capacitors or a connection topology of a circuit. Besides the variable capacitor, a variable inductor or switch can also be used as an impedance variable element. A means for implementing a function of variable impedance is not limited to a semiconductor or a micro electro mechanical system (MEMS). Further, an inductor or a capacitor with a fixed characteristic value may be used for the sake of convenience of designing a variable impedance range. 
     The probe  14  is installed near the power feeding point  10   a  of the antenna  10 . The probe  14  receives a radio wave radiated from the antenna  10 . 
     The probe  14  is a loop type probe. The probe  14  includes a loop portion  14   a  formed at a leading end and a connection line  14   b.  The loop portion  14   a  has a loop-like shape. The loop-like shape may be a rectangular shape, a circular shape, or any other shape as long as it is a loop form. 
     “Near the power feeding point  10   a  of the antenna  10 ” indicates a position at which the probe  14  is able to detect a change in a radio wave caused by a change in an electric current of the power feeding point  10   a.  In other words, it indicates a position at which the probe  14  is able to detect a change in an electromagnetic field associated with a change in an electric current of power feeding point  10   a.    
     For example, at least a portion of the loop portion  14   a  is arranged in a sphere whose radius centering on the power feeding point  10   a  is ¼ of a wavelength corresponding to a maximum radio frequency used in the antenna device  100 . 
     In the control device  90 , the probe  14  is installed near the connecting portion. 
     The power detector  16  is connected to the probe  14 . The power detector  16  detects electric power of the radio wave received by the probe  14 . The power detector  16  has a function of outputting a DC voltage, a DC current, or binary data which corresponds to the intensity of the electric power of the radio wave received by the probe  14  as power information. 
     The control circuit  18  is installed between the power detector  16  and the matching circuit  12  to connect the power detector  16  with the matching circuit  12 . The control circuit  18  controls the impedance of the matching circuit  12  based on the power information output from the power detector  16 . The control circuit  18  controls the impedance of the matching circuit  12  so that the input impedance of the antenna  10  matches the output impedance of the radio  300 . 
     For example, the control circuit  18  is implemented by a combination of hardware such as a microcomputer and software stored in a semiconductor memory. Further, for example, the control circuit  18  may be constituted by hardware such as an analog circuit, a digital circuit, or the like. 
     The radio  300  is connected to a side of the matching circuit  12  opposite to the antenna  10 . The radio  300  is, for example, a transmitter. The radio  300  generates a signal to be transmitted to the antenna device  100 . 
     The power amplifier  200  is connected between the matching circuit  12  and the radio  300 . The power amplifier  200  amplifies a signal generated by the radio  300  and outputs the amplified signal to the antenna device  100 . The power amplifier  200  is, for example, a variable gain amplifier. 
     Next, functions and effects of the antenna device  100  and the radio communication device of the present embodiment will be described. 
     First, the impedance matching performed by the antenna device  100  and the radio communication device of the present embodiment will be described. 
     The probe  14  receives the radio wave radiated from a portion near the power feeding point  10   a  of the antenna  10 . An electromagnetic field (radio wave) near the power feeding point  10   a  is changed in accordance with a change in an electric current flowing to the power feeding point  10   a  of the antenna  10 . The power detector  16  detects the electric power of the radio wave received by the probe  14 . Then, the power detector  16  outputs a DC voltage, a DC current, or binary data which corresponds to the intensity of the detected electric power to the control circuit  18  as the power information. 
     The better the matching state between the input impedance of the antenna  10  and the output impedance of the radio  300  is, the greater the electric power supplied to the antenna  10  is. Further, when the electric power supplied from the power feeding point  10   a  of the antenna  10  increases, the electric current flowing to the power feeding point  10   a  of the antenna  10  increases. 
     As a result, the electric power of the radio wave received by the probe  14  arranged near the power feeding point  10   a  increases as well. Therefore, if control is performed such that the electric power detected by the power detector  16  is increased, the matching state of the antenna  10  is improved. Therefore, when the electric power of the radio wave radiated from the power feeding point  10   a  of the antenna  10  is maximum, the impedance can be regarded as matching best. In other words, the impedance matching of the radio communication device is achieved. The implementation of the impedance matching suppresses the power loss of the radio communication device. 
     In the device of the present embodiment, the control circuit  18  implements automatic impedance matching by controlling the matching circuit  12  on the basis of the radio wave received by the probe  14 . The control circuit  18  controls the matching circuit  12  so that the electric power detected by the power detector  16  becomes maximum. 
     Specifically, for example, the control circuit  18  outputs a control signal for changing the impedance of the matching circuit  12  to the matching circuit  12 . An impedance value of the matching circuit  12  is changed, for example, by changing a reactance value of variable capacitance element  12   a  and  12   b  of the matching circuit  12  in response to the control signal. 
     For example, the impedance value of the matching circuit  12  may be randomly changed, and a control signal in which the electric power detected by the power detector  16  becomes maximum, may be stored. Further, for example, all combinations of all states given to the variable capacitance elements  12   a  and  12   b  maybe set, a control signal in which the electric power detected by the power detector  16  becomes maximum may be stored. Any control method such as the above-described simple method or a known method may be used as the control method in the control circuit  18  as long as it can maximize the electric power detected by the power detector  16 . 
     Next, effects of the antenna device  100  and the radio communication device of the present embodiment will be described. 
     The probe  14  is installed near the power feeding point  10   a  of the antenna  10 . In the state where the electric power is supplied to the antenna  10 , the amplitude of the electric current flowing through the antenna  10  becomes maximum in the power feeding point  10   a.  Therefore, when the probe  14  is installed near the power feeding point  10   a  of the antenna  10 , it is possible to detect a change in the electric current associated with a state change of the impedance matching with good sensitivity. 
     For example, as another method of performing the impedance matching of the radio communication device, there is a method of installing a probe at an end portion serving as an open end of an antenna, unlike the present embodiment. When the electric power supplied from the power feeding point of the antenna increases, the electric current of the antenna increases. For this reason, an amount of charges increases in the end portion serving as the open end on the opposite side of the power feeding point of the antenna. As a result, the electric power of the radio wave received by the probe also increases by capacitive coupling with the probe arranged near the end portion serving as the open end. 
     Therefore, in the above method, if control is performed such that the electric power detected by the power detector is increased, the matching state of the antenna is improved. In other words, the impedance matching is achieved. 
     However, in the case of the above-described method, since the probe is installed at the end portion of the antenna, a distance (a line length) of the probe—the power detector—the control circuit—the matching circuit—the antenna is likely to increase. Therefore, the size of the antenna device and the radio communication device is likely to increase. 
     In the case of the above method, the antenna need to include the open end, and a type of antenna to be used is limited. Therefore, the degree of freedom of design of the antenna device and the radio communication device may be impaired. 
     According to the antenna device and the radio communication device of the present embodiment, the probe  14  is installed near the power feeding point  10   a  of the antenna  10 , unlike the above-described method. With this structure, the distance (line length) of the probe  14 —the power detector  16 —the control circuit  18 —the matching circuit  12 —the antenna  10  is reduced. Therefore, the downsizing of the antenna device and the radio communication device is implemented. 
     In the antenna device and the radio communication device of the present embodiment, the impedance matching state is determined in accordance with the change in the electric current of the power feeding point  10   a.  Therefore, there is no limitation on a type of antenna  10 , and for example, the loop-like antenna having no open end can be applied to the device. 
     It is desirable that a separation distance (“d” in  FIG. 1 ) from the power feeding point  10   a  to the probe  14  be less than ¼ of the wavelength corresponding to the maximum radio frequency used in the antenna device  100 . The separation distance from the power feeding point  10   a  to the probe  14  is the shortest distance between the power feeding point  10   a  and the loop portion  14   a.  In other words, it is desirable that at least a portion of the loop portion  14   a  be arranged in a sphere whose radius centering on the power feeding point  10   a  is less than ¼ of a wavelength corresponding to a maximum radio frequency used in the antenna device  100 . 
     The power feeding point  10   a  of the antenna  10  is a position of an antinode of an electric current when the antenna  10  is in the resonant state. In a state in which the electric power is being supplied to the antenna  10 , the amplitude of the electric current becomes maximum at the power feeding point  10   a.    
     On the other hand, a position which is ¼ of a wavelength of a maximum, radio frequency to be used from the power feeding point  10   a  of the antenna to the end portion  10   b  side of the antenna is a first position of node of current when the antenna  10  is in the resonant state at the maximum radio frequency to be used. The node of current has a minimum current value when the antenna  10  is in the resonant state. The amplitude of the electric current is zero at this position, and this position is not suitable as a position for detecting the electric current flowing to the antenna  10 . 
     A position which is less than ¼ of the wavelength corresponding to the maximum radio frequency to be used from the power feeding point  10   a  of the antenna  10  along the antenna  10  is a position which is less than ¼ of a wavelength from the power feeding point  10   a  for all use radio frequencies of the antenna device  100 . In other words, this position is a position at which node of current does not exist for all the use radio frequencies of the antenna device  100 . 
     When the probe  14  is arranged at a position which is less than ¼ of the wavelength corresponding to the maximum radio frequency to be used from the power feeding point  10   a  of the antenna, the probe  14  is arranged at the position which is ¼ of the wavelength for all the use radio frequencies of the antenna device  100 . In other words, when the probe  14  is arranged at a position at which the amplitude of the electric current is obtained regardless of the radio frequency to be used, detection sensitivity for the impedance matching state is improved. Therefore, it is desirable to install the probe  14  at a position closer to the power feeding point  10   a  than the position which is ¼ of the wavelength of the maximum radio frequency. 
     It is more desirable that the separation distance (“d” in  FIG. 1 ) from the power feeding point  10   a  to the probe  14  is equal to or less than ⅛ of the wavelength corresponding to the maximum radio frequency used in the antenna device  100 . 
     The position which is ⅛ of the wavelength corresponding to the maximum radio frequency to be used from the power feeding point  10   a  of the antenna is the midpoint between the power feeding point  10   a  and the position which is ¼ of the wavelength corresponding to the maximum radio frequency. A region between the power feeding point  10   a  and the midpoint shows a large current change in association with a large current change of the power feeding point  10   a . Therefore, when the probe  14  is arranged at the position which is equal to or less than ⅛ of the wavelength corresponding to the maximum radio frequency to be used from the power feeding point  10   a  of the antenna, it is easy to improve the impedance matching state of the antenna device  100 . 
     Further, as the distance between the antenna  10  and the probe  14  increases, the amount of the radio wave received by the probe  14  decreases. If a spatial separation distance (“d” in  FIG. 1 ) from the power feeding point  10   a  of the antenna  10  to the probe  14  is less than ¼ of the wavelength of the radio frequency to be used, the decrease in the amount of the radio wave falls within a sufficient allowable range for matching the impedance. Therefore, when the probe  14  is arranged at a position which is less than ¼ of the wavelength corresponding to the maximum radio frequency to be used, it is possible to detect the magnitude of the electric power supplied to the antenna  10  with satisfactory sensitivity for all the use radio frequencies and the impedance matching of the antenna  10  can be realized. 
     In order to detect the magnitude of the electric power supplied to the antenna  10  with satisfactory sensitivity, it is desirable that the spatial separation distance (“d” in  FIG. 1 ) from the power feeding point  10   a  of the antenna  10  to the probe  14  be a position which is equal to or less than ⅛ of the wavelength of the maximum radio frequency used in the antenna device  100 . 
     Further, the maximum radio frequency used in the antenna device  100  or the radio communication device can be specified from, for example, a specification or a data sheet of the antenna device  100  or the radio communication device. Further, the separation distance from the power feeding point  10   a  to the probe  14  can be specified by, for example, direct measurement according to a ruler or measurement according to a photograph scale on a photographic image which is enlarged and captured. 
     Further, in the antenna element and the radio communication device of the present embodiment, the loop type probe  14  is used. The loop type probe  14  is suitable for the purpose of detecting a change in the magnetic field. The power feeding point  10   a  become an antinode of an electric current or has maximum amplitude of an electric current when the antenna  10  is in the resonant state. Therefore, the change in the magnetic field near the power feeding point  10   a  is larger than the change in the electric field. In the device of the present embodiment, it is possible to detect the current change of the power feeding point  10   a  with high sensitivity using the loop type probe  14 . 
     It is desirable that the element length of the probe  14  be less than ½ of the wavelength corresponding to the maximum radio frequency used in the antenna device  100 . In other words, it is desirable that the resonance frequency of the probe  14  be higher than the maximum radio frequency used in the antenna device  100 . The element length of the probe  14  is a physical length along the loop of the loop portion  14   a.    
     As the probe  14  resonates, reception of the radio wave radiated from the antenna  10  by the probe  14  is likely to be unstable. Further, the resonant state of the antenna  10  is likely to be unstable due to the resonance of the probe  14 . With the above configuration, the resonance of the probe  14  is prevented, and the antenna device and the radio communication device that operate stably are realized. 
     In order to reliably prevent the resonance of the probe  14 , it is more desirable that the element length of the probe  14  is equal to or less than ¼ of the wavelength corresponding to the maximum radio frequency used in the antenna device  100 . 
     On the other hand, when the element length of probe  14  is too short, the receiving sensitivity of the radio wave detected by probe  14  may be insufficient. In order to secure the receiving sensitivity of the probe  14 , it is desirable that the element length of probe  14  be equal to or more than 1/25 of the wavelength corresponding to the maximum, radio frequency used in the antenna device  100 . 
     The element length of the probe  14  can be specified by, for example, direct measurement according to a ruler or measurement according to a photograph scale on a photographic image which is enlarged and captured. 
     It is also possible to apply a two-dimensional spiral shape or a three-dimensional helical shape as the shape of the loop type probe  14 . When the spiral shape or the helical shape is applied, it is possible to increase the element length by suppressing an increase in the size of the probe  14 . Therefore, it is possible to improve the receiving sensitivity of the radio wave radiated from the antenna  10  while suppressing the increase in the size of the device. 
     According to the present embodiment, it is possible to provide an antenna device, a control device and a radio communication device, which are capable of performing automatic impedance matching and realizing downsizing, 
     Second Embodiment 
     The antenna device and the radio communication device of the present embodiment are similar to those of the first embodiment except that the antenna includes a plurality of end portions. Therefore, description overlapping with that of the first embodiment is omitted. 
       FIG. 2  is a schematic diagram illustrating a configuration of an antenna device and a radio communication device of the present embodiment. 
     An antenna  50  includes, for example, a power feeding point  50   a  and a plurality of end portions  50   b,    50   c,  and  50   d  on a side opposite to the power feeding point  50   a.  The antenna  50  is a monopole antenna. The antenna  50  includes a plurality of resonance frequencies. Further, the antenna device and the radio communication device of the present embodiment have a function of operating at multiple frequencies and a wide band. 
     The probe  14  is installed near the power feeding point  50   a  of the antenna  50 . For example, at least a portion of the loop portion  14   a  is arranged in a sphere whose radius centering on the power feeding point  50   a  is ¼ of a wavelength corresponding to a maximum radio frequency used in the antenna device  100 . The probe  14  receives the radio wave radiated from the antenna  50 . 
     When the impedance of the radio communication device is matched, an electric current of the power feeding point  50   a  increases even when the antenna  50  uses any one of a plurality of corresponding resonance frequencies. Therefore, when the probe  14  is installed near the power feeding point  50   a  of the antenna  50 , it is possible to detect the impedance matching state regardless of the used resonance frequency. Therefore, it is possible to provide the antenna device, the control device, and the radio communication device, which are capable of automatically matching the impedance and realizing downsizing even when the antenna  5   0  has a plurality of resonance frequencies and operates at multiple frequencies and a wide band as in the device of the present embodiment. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the antenna device, the control device, and the radio communication device described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the devices and methods described herein maybe made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.