JP5605027B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device using a loop antenna element.

  In recent years, in the ubiquitous society, various systems using active small wireless tags have been studied. A system that realizes safety and security such as healthcare, equipment security, hands-free entry / exit management, etc., and home networks, smart meters, and sensor networks that apply wireless tags to household electrical appliances. Etc. In addition, it is desirable that one wireless tag can support all these systems. In general, 400 MHz band and 900 MHz band are generally used as active wireless tags, and antennas corresponding to these frequency bands are required.

  Further, home networks, smart meters, and the like have a communication distance of several tens of meters or more and become an out-of-sight propagation environment, so that radio wave conditions are expected to change greatly depending on the antenna location and time. As a technique corresponding to a change in the radio wave condition, there is an antenna diversity technique in which a plurality of antennas having low correlation are switched and an antenna having a good reception condition is adaptively selected.

  Conventionally, in a system such as a wireless tag that requires a sufficiently small size with respect to a wavelength, polarization diversity has been generally used (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-88246

  However, in the above conventional configuration, since a plurality of antennas are arranged orthogonally on a plurality of surfaces of the casing, there is a problem that nulls are generated in the antenna directivity and the size is large.

  In view of the above conventional problems, an object of the present invention is to provide an antenna device capable of realizing polarization diversity with a sufficiently small size with respect to a wavelength.

  In order to solve the above-described problems, an antenna device according to the present invention includes a planar ground plate having a ground conductor, and a loop axis direction provided in a position separated from the ground plate in the horizontal direction is substantially the same direction. A first loop antenna, a second loop antenna, a signal feeding means for feeding a signal to a feeding point provided at one end of each of the first loop antenna and the second loop antenna, and a first loop antenna and a second loop antenna. The present invention relates to an antenna device including a common ground line that electrically connects the other end and a ground plate. The winding direction is a direction from the feeding point of the first loop antenna to the ground plate, and the feeding of the second loop antenna. The winding direction toward the direction from the point to the ground plate is opposite to each other, and the loop surfaces formed on the first loop antenna and the second loop antenna are Formed directly, and is formed symmetrically with respect to cross each other, and the loop axis.

  The antenna device of the present invention can realize polarization diversity with a sufficiently small size with respect to the wavelength.

The figure which shows the structure of the antenna apparatus in Embodiment 1 of this invention. The figure which shows the structural example of the phase shifters 104a and 104b whose phase change amount range in Embodiment 1 of this invention is 0 degree to 90 degree | times. The figure which shows the structural example of the phase shifters 104a and 104b whose phase change amount range in Embodiment 1 of this invention is 0 degree | times -90 degree | times. The figure which shows the structural example of the matching circuits 105 and 106 in Embodiment 1 of this invention. The figure which shows the structural example of the matching circuits 105 and 106 using the variable capacitance diode in Embodiment 1 of this invention. The figure which shows the structural example of the matching circuits 105 and 106 which inserted the parallel resonant circuit in the capacitor | condenser in Embodiment 1 of this invention. The figure which shows the structural example of the loop antennas 107 and 108 and the grounding wire 109 in Embodiment 1 of this invention. The figure which shows the structural example of the loop antennas 107 and 108, the grounding wire 109, and the ground capacity | capacitance 110 in Embodiment 1 of this invention. (A) The figure which shows operation | movement of the antenna apparatus when the phase difference which feeds the loop antennas 107 and 108 in Embodiment 1 of this invention is 0 degree | times (b) Loop antennas 107 and 108 in Embodiment 1 of this invention Showing the operation of the antenna device when the phase difference fed to the antenna is 180 degrees The figure which shows the equivalent circuit of the antenna apparatus in Embodiment 1 of this invention The figure which shows the calculation result of the mutual coupling amount between the electric power feeding ends in Embodiment 1 of this invention The figure which shows the equivalent circuit of the antenna apparatus in case the ground wire 109 in Embodiment 1 of this invention branches into two on the way, and one is connected to the ground capacity | capacitance 110 and the other is directly connected to the ground plate 101. In the first embodiment of the present invention, the ground line 109 is branched into two on the way, one of which is connected to the ground capacitor 110 and the other is directly connected to the ground plate 101. Figure showing calculation results The figure which showed the setting procedure of the electric power feeding phase difference of the antenna apparatus in Embodiment 1 of this invention The figure which showed the setting procedure of the electric power feeding phase difference of the antenna apparatus in Embodiment 1 of this invention The figure which showed the setting procedure of the electric power feeding phase difference of the antenna apparatus in Embodiment 1 of this invention

  According to a first aspect of the present invention, there is provided a planar ground plate having a ground conductor, and a first loop antenna and a second loop antenna, which are provided at positions away from the ground plate in the horizontal direction and whose loop axis directions are substantially the same. The signal feeding means for feeding a signal to a feeding point provided at one end of each of the first loop antenna and the second loop antenna, and the other end of the first loop antenna and the second loop antenna and the ground plate are electrically connected And a common ground line connected to the antenna device, the winding direction going from the feeding point of the first loop antenna to the ground plate, and the direction going from the feeding point of the second loop antenna to the ground plate The winding directions are opposite to each other, and the loop surfaces formed on the first loop antenna and the second loop antenna are formed perpendicular to the ground plate, intersect each other, and Are those formed symmetrically with respect to the flop direction.

  This makes it possible to realize polarization diversity with a sufficiently small size with respect to the wavelength.

In the second invention, in particular, the signal feeding means of the first invention controls the phase of the signal fed to the first loop antenna and the second loop antenna. As a result, it is possible to realize an antenna device that can deal with a plurality of frequencies with a small size with respect to the wavelength and can reduce mutual coupling between antennas.

  The third invention is radiated by the polarized wave parallel to the loop surface radiated from the first loop antenna and the second loop antenna and the current flowing from the first loop antenna to the ground plate, particularly in the second invention. The first loop antenna and the second loop antenna are formed so that the polarized waves are orthogonal to each other. As a result, it is possible to realize an antenna device that can deal with a plurality of frequencies with a small size with respect to the wavelength and can reduce mutual coupling between the antennas.

  According to a fourth aspect of the present invention, in the third aspect of the invention, there is provided conductor detection means for detecting a conductor in the vicinity of the ground plate, and the signal power supply means is provided from the first power supply point according to the detection contents by the conductor detection means. The phase of the signal to be fed and the phase of the signal to be fed from the second feeding point are controlled.

  As a result, it is possible to obtain a good communication state by performing diversity communication that is adaptively set to a phase difference that always provides high transmission power and reception power.

  According to a fifth aspect of the invention, in particular, in the third aspect of the invention, there is provided posture detection means for detecting the inclination of the ground plate with respect to the reference plane, and the signal power supply means is configured to perform the first power supply according to the inclination detected by the posture detection means. The phase of the signal fed from the point and the phase of the signal fed from the second feeding point are controlled. As a result, good radiation characteristics can be realized regardless of the attitude of the antenna device.

  In the sixth aspect of the invention, in particular, the signal feeding means in the third aspect of the invention receives the phase difference between the phase of the signal fed from the first feeding point and the phase of the signal fed from the second feeding point with different values. The operation is performed, and the phase difference at the time when the received power is the highest is used. As a result, a good communication state can be obtained.

  Hereinafter, embodiments for implementing an antenna device of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
Details of Embodiment 1 of the antenna device of the present invention will be described below.

  FIG. 1 is a diagram showing a configuration of an antenna device of the present invention. X, Y, and Z denote the respective coordinate axes. In FIG. 1, a ground plate 101 is a ground plate having a ground conductor. The ground plate 101 has a longitudinal direction in the Z-axis direction. The length L in the Z-axis direction of the ground plate 101 is preferably longer than the length T in the X-axis direction.

  The transmission / reception circuit 102 is provided on the ground plate 101, and is a transmission / reception circuit that generates and outputs a transmission signal and processes an input reception signal. Note that the transmission / reception circuit 102 may be only a transmission circuit or only a reception circuit. In addition, the inclination information of the antenna device of the present invention is input to the transmission / reception circuit 102 from an attitude detector 111 described later. Further, the transmission / reception circuit 102 outputs a phase shift amount control signal for controlling phase shifters 104a and 104b described later.

  The distributor 103 is a distributor that is provided on the ground plate 101, has an input terminal connected to the transmission / reception circuit 102, divides the signal input from the transmission / reception circuit 102 into two, and outputs the signal. The distributor 103 is specifically composed of a Wilkinson distributor or the like.

The phase shifters 104a and 104b are respectively connected to two output terminals of the transmission / reception circuit 102 and the distributor 103, and the phase of the input signal is determined based on the phase shift amount control signal output from the transmission / reception circuit 102. This is a phase shifter that converts the value into a value and outputs it. As a result, the feeding phase difference between two signals fed to loop antennas 107 and 108 to be described later is changed. As long as the phase difference between the two signals can be changed, only one of the two output terminals of the distributor 103 may be connected to the phase shifter. Further, when the phase shift amount is a fixed value and control of the phase shift amount is not necessary, the phase shift amount control signal may be unnecessary.

  FIG. 2 is a diagram illustrating a configuration example of the phase shifters 104a and 104b having a phase change amount range of 0 degrees to 90 degrees. It is configured by switching a phase shifter having a plurality of different phase shift amounts with a switch. Each of the phase shifters includes two series capacitors C and one parallel inductor L provided therebetween. When the amount of phase shift is 0 degree, input / output is directly connected.

  FIG. 3 is a diagram illustrating a configuration example of the phase shifters 104a and 104b having a phase change amount range of 0 degrees to −90 degrees. It is configured by switching a phase shifter having a plurality of different phase shift amounts with a switch. Each of the phase shifters includes two parallel capacitors C and one series inductor L provided therebetween. When the amount of phase shift is 0 degree, input / output is directly connected.

  Since each of the phase shifters 104a and 104b can be configured by an inductor or a capacitor that can use a chip component, the circuit can be reduced in size as compared with a case where a general phase shifter that switches a delay line is used.

  The matching circuit 105 is provided on the ground plate 101, is connected to a loop antenna 108 and a phase shifter 104a, which will be described later, and efficiently supplies power to the loop antenna 108 which will be described later. It is the matching circuit which performs the impedance matching between.

  The matching circuit 106 is provided on the ground plate 101, is connected to a loop antenna 107 and a phase shifter 104b, which will be described later, and efficiently supplies power to the loop antenna 107 which will be described later. It is the matching circuit which performs the impedance matching between.

  4A and 4B are diagrams illustrating configuration examples of the matching circuits 105 and 106. FIG. It consists of a series capacitor and a parallel capacitor. Since the loop antennas 107 and 108 to be described later have a small radiation resistance, a matching circuit with a very small loss is required. Since an inductor has a larger loss than a capacitor, when used in a matching circuit, the radiation efficiency is degraded and the gain is greatly reduced. Therefore, a configuration of a matching circuit using a capacitor is desirable.

  FIGS. 5A and 5B are diagrams illustrating configuration examples of the matching circuits 105 and 106 using variable capacitance diodes. Since the matching condition of the antenna changes depending on the frequency, the matching constant must be changed according to the frequency. The capacitance value can be controlled by using a variable capacitance diode for the capacitor of FIG. 4 and applying an arbitrary DC voltage via the inductor. With this configuration, matching can be achieved by changing the capacitance value in accordance with the operating frequency.

  FIGS. 6A, 6B, and 6C are diagrams illustrating configuration examples of the matching circuits 105 and 106 in which a parallel resonant circuit is inserted into a series capacitor. The impedance of the parallel resonance circuit varies depending on the frequency, and becomes an inductance when it is lower than the resonance frequency, and becomes a capacitance when it is higher than the resonance frequency.

By inserting a parallel resonant circuit whose impedance varies with the frequency into the series capacitor, the combined impedance of the capacitor and the resonant circuit varies with the frequency, and the two different frequencies have different capacitances. The constants of the inductor La and the capacitor Ca that constitute the parallel resonance circuit with the series capacitor C1 are adjusted so that the input impedance of the antenna is converted to an isoconductance line of 20 mS at two different frequencies of radio waves to be used. Furthermore, the internal impedance of the signal source is converted to 50Ω by a parallel capacitor according to the frequency of the radio wave used. The switching of the parallel capacitance is a method of selectively switching with a switch as shown in FIG. 6A, a method of adjusting the parallel capacitance C2 with a variable capacitance diode as shown in FIG. 6B, and a parallel as shown in FIG. 6C. Any of the methods of inserting a parallel resonant circuit into the capacitor may be used. As a result, matching can be achieved for two different frequencies.

  The loop antenna 107 is provided such that a loop surface to be formed is substantially perpendicular to the surface of the ground plate 101, and two feeding ends include a matching circuit 106, a grounding wire 109 described later, and a ground capacitance 110 described later. This is a loop antenna made of a loop-shaped conductor that is electrically connected to the ground plate 101 via the via.

  The loop antenna 108 is provided so that a loop surface to be formed is substantially perpendicular to the surface of the ground plate 101, and two feeding ends include a matching circuit 105, a ground line 109 described later, and a ground capacitor 110 described later. This is a loop antenna made of a loop-shaped conductor that is electrically connected to the ground plate 101 via the via.

  The loop antennas 107 and 108 have the same axial direction of the loop.

  The loop antennas 107 and 108 have a total length of one wavelength or less of radio waves transmitted and received. Therefore, the maximum dimension of the antenna is less than half a wavelength. The number of turns of the loops of the loop antennas 107 and 108 is one, but any number is acceptable. The loop shape of the loop antennas 107 and 108 may not be a rectangle as shown in FIG. The loop antennas 107 and 108 are provided so as to protrude from the ground plate 101.

  The loop antennas 107 and 108 are connected to the ground plate 101 from the power feeding side (the power feeding end side connected to the matching circuits 105 and 106) via the ground side (a ground line 109 described later and a ground capacitor 110 described later). The winding direction of the loop toward the feeding end side must be opposite to each other. Although the loop sizes of the loop antennas 107 and 108 are preferably the same, they may be different.

  The ground line 109 is a ground line having an inductance component by electrically connecting the respective feeding ends of the loop antennas 107 and 108 and the ground plate 101 via a ground capacitor 110 described later. In FIG. 1, the terminals connected to the ground plate 101 side of each of the loop antennas 107 and 108 are connected to each other to form one terminal, and the ground plate is connected via a common ground line 109 and a ground capacitor 110 described later. 101 is connected.

  The ground capacitor 110 is a capacitor element that connects the ground line 109 and the ground plate 101.

In FIG. 1, the loop antennas 107 and 108 are arranged so that their loop surfaces intersect with each other, and a ground line 109 is connected to the upper loop. Assuming that the Z-axis direction is the vertical direction, the loop antennas 107 and 108 each have a bilaterally symmetric structure, and the loop antenna has a loop surface bent in a step shape. The loop antennas 107 and 108 intersect with each other in the vicinity of the middle point of each feeding end. That is, the symmetrical loop surfaces bent in a step shape intersect. FIGS. 7A, 7B, and 7C are diagrams illustrating configuration examples of the loop antennas 107 and 108 and the ground line 109. FIG. As shown in FIG. 7A, the loop surfaces do not have to intersect. When the loop surfaces intersect as shown in FIG. 7B, the ground line 109 may be connected by a lower loop. Further, when the loop surfaces intersect as shown in FIG. 7C, for example, a loop shape in which some lines of the loop are directed obliquely may be employed.

  FIGS. 8A and 8B are diagrams showing a configuration example of the loop antennas 107 and 108, the ground line 109, and the ground capacitor 110. FIG. FIG. 8A shows an example in which the ground wire 109 is partially bent, and FIG. 8B shows an example in which the ground wire 109 branches into two in the middle and is connected to the ground plate 101. The impedance including the inductance component of the ground wire 109 and the ground capacitance 110 is partially bent or branched or branched to connect one end to the ground capacitance 110 and the other directly connected to the ground plate 101. Adjust by doing so. The ground line 109 may have any shape. However, when the ground wire 109 is bent, it is formed by the ground wire 109 as shown in FIGS. 8A and 8B in order to prevent mutual inductance between the loop antennas 107 and 108 and the ground wire 109. It is desirable that the axial direction of the loop to be made is orthogonal to the loop axial direction of the loop antennas 107 and 108.

  The attitude detector 111 is an attitude detector that is provided on the ground plate 101 and detects the inclination of the antenna device of the present invention and outputs inclination information to the transmission / reception circuit 102. Specifically, the posture detector 111 is composed of a sensor that can detect an inclination with respect to the ground, such as an acceleration sensor or a fall switch.

  The conductor detector 112 is a conductor detector that is provided on the ground plate 101 and detects whether the antenna device of the present invention is close to a conductor such as a human body or metal, and outputs conductor detection information to the transmission / reception circuit 102. is there. Specifically, the conductor detector 112 is a method using a proximity sensor such as an infrared sensor or a capacitance sensor, a method of detecting a change in mutual inductance with a nearby conductor using a minute loop antenna, and feeding of the loop antennas 107 and 108. By using the fact that the amount of mutual coupling generated between the ends changes due to the influence of adjacent conductors, a method of detecting adjacent conductors by the amount of change in mutual coupling is used.

  The operation of the antenna device configured as described above will be described.

  The transmission signal output from the transmission / reception circuit 102 is divided into two powers by the distributor 103. One of the two divided signals is converted into a predetermined phase by the phase shifter 104 a, impedance-converted by the matching circuit 105, and output to the loop antenna 108. The other of the two divided signals is converted into a predetermined phase by the phase shifter 104 b, impedance-converted by the matching circuit 106, and output to the loop antenna 107. Based on the phase shift amount control signal output from the transmission / reception circuit 102, phase difference feeding is performed to the loop antennas 107 and 108.

  Next, radio wave radiation of the antenna device configured as described above will be described.

  In the antenna device of the present invention, the loop antennas 107 and 108 operate as a magnetic current antenna using a magnetic current source as a radiation source, and the ground plate 101 operates as a current antenna using a current source as a radiation source. In addition, as for the radiated polarization, if the ground is parallel to the XY plane in FIG. 1, the polarization in the Z-axis direction is vertical polarization, and the polarization orthogonal to the vertical polarization is horizontal polarization, loop antenna 107, In 108, a current flows in a loop on the XY plane, and radiates horizontally polarized waves. Since the ground plate 101 has a loop antenna element in the Z-axis direction and the longitudinal direction is the Z-axis direction, a current flows in the Z-axis direction and radiates vertically polarized waves. The magnetic current antenna component radiates horizontally polarized waves, and the current antenna component radiates vertically polarized waves.

FIG. 9A is a diagram illustrating the operation of the antenna device when the phase difference fed to the loop antennas 107 and 108 is 0 degrees. The feeding phase of the loop antenna 107 is α1, the feeding phase of the loop antenna 108 is α2, and the feeding phase difference is α1−α2. When the phase difference is 0 degree, the currents flowing through the loop antennas 107 and 108 are in opposite directions, so the magnetic currents formed from the loop antennas 107 and 108 cancel each other. In addition, since the directions of currents flowing from the loop antennas 107 and 108 into the ground line 109 are the same, current flows through the ground plate 101.

  FIG. 9B is a diagram illustrating the operation of the antenna device when the phase difference fed to the loop antennas 107 and 108 is 180 degrees. When the phase difference is 180 degrees, the currents flowing in the loop antennas 107 and 108 are in the same direction, so that a magnetic current is formed in the loop antennas 107 and 108. In addition, since the directions of currents flowing from the loop antennas 107 and 108 to the ground line 109 are opposite to each other, the currents cancel each other.

  From FIG. 9, by changing the feeding phase difference, it is possible to operate the antenna in either the current antenna mode or the magnetic current antenna operation mode, and whether it is vertical polarization, horizontal polarization, or polarization having an arbitrary inclination. It is possible to control whether to radiate with the polarized wave.

  Further, when the loop surfaces intersect as shown in FIG. 1, FIG. 7B, and FIG. 7C, when the phase difference is 180 degrees, it is more effective than the configuration of FIG. The current antenna component can be suppressed. In FIG. 1, FIG. 7 (b), and FIG. 7 (c), the loop antennas 107 and 108 have a symmetrical structure, and the current flowing through the linear portion in the Z-axis direction connecting the upper and lower loops This is because they have the same amplitude and opposite phase. Therefore, when the antenna device of the present invention is used for the purpose of polarization control, it is desirable that the loop antennas 107 and 108 have a symmetrical structure and the loop surfaces intersect each other.

  Next, mutual coupling reduction in a plurality of frequency bands of the antenna device will be described.

  FIGS. 10A and 10B are diagrams showing an equivalent circuit of the antenna device of the present invention. The self-inductances of the loop antennas 107 and 108 are L1 and L2, the mutual inductance generated between the loop antennas 107 and 108 is M, the capacitance generated between the loop antennas 107 and 108 is C12, the self-inductance of the ground line 109 is L3, and the ground capacitance 110 Let Cg be the capacitance. The antenna device of the present invention is replaced with an equivalent circuit as shown in FIG. 10A and converted as shown in FIG.

  A parallel resonant circuit is generated between the feeding ends by the inductance component generated in each part of the capacitor C12 and the antenna. In addition, a series resonance circuit is generated between the feeding end and the ground due to the inductance component generated in each part of the capacitor Cg and the antenna. These two resonance circuits operate as a band rejection filter and have an effect of suppressing mutual coupling between the power supply ends. By adjusting the respective resonance frequencies so as to coincide with the frequencies of the two radio waves to be used, it is possible to prevent deterioration of the antenna gain due to mutual coupling. Specifically, the resonance frequency is adjusted by adjusting the inductance L3 according to the length and shape of the ground wire 109, adjusting the capacitance value Cg of the ground capacitor 110, the distance between the loops of the loop antennas 107 and 108, the loop area, the line This is done by adjusting the self-inductances L1 and L2, the mutual inductance M, and the capacitance C12 depending on the thickness. FIG. 11 is a diagram illustrating a calculation result of the mutual coupling amount between the power feeding ends. It can be seen that the mutual coupling is greatly reduced at the two frequencies.

12 (a) and 12 (b), when the ground line 109 branches into two along the way as shown in FIG. 8, one is connected to the ground capacitor 110 and the other is directly connected to the ground plate 101. It is a figure which shows the equivalent circuit of the antenna apparatus of this invention. The antenna device is replaced with an equivalent circuit as shown in FIG. 12A and converted as shown in FIG. Of the self-inductance of the ground wire 109, the one directly connected to the ground plate 101 is newly set as L 3 ′. When metal or the like approaches the antenna device of the present invention, a capacitance Cgnd is generated between the loop antennas 107 and 108 and the metal. This capacitor Cgnd forms a parallel resonance circuit with the ground line inductance L3. When the distance from the metal is large, the capacitance Cgnd is close to 0, so the parallel resonance frequency due to the capacitance Cgnd and the inductance L3 of the ground line is very high. However, as the distance from the metal is reduced, the capacitance Cgnd increases, and the parallel resonance frequency is related to the frequency of the radio wave used, which greatly affects the two resonance vibration frequencies adjusted to reduce the mutual coupling described above. The ground line 109 is branched, an inductance L3 ′ is newly provided, and the length of the ground line 109 after branching is adjusted so that L3 ′ becomes a small value with respect to L3. The inductor constituting the parallel resonant circuit with the capacitor Cgnd is a combined inductance in which L3 and L3 ′ are connected in parallel. The combined inductance of L3 and L3 ′ is L3 ′ having a substantially low value. Thereby, it is possible to sufficiently increase the frequency band of the radio wave using the parallel resonance frequency due to the inductance component of the capacitor Cgnd and the ground line 109, and to reduce the fluctuation of the mutual coupling characteristics due to the influence of the metal. FIG. 13 shows the amount of mutual coupling between the power supply ends when the ground line 109 branches into two in the middle as shown in FIG. 8, one is connected to the ground capacitor 110 and the other is directly connected to the ground plate 101. It is a figure which shows a calculation result. It can be seen that the mutual coupling is greatly reduced at the two frequencies.

  Next, a method for controlling the phase difference of the antenna device will be described.

  FIG. 14 is a diagram showing a procedure for setting the feeding phase difference of the antenna device of the present invention.

  In step 1, the setting of the feeding phase difference is started. In step 2, the conductor detection information detected by the conductor detector 112 is output to the transmission / reception circuit 102. When the transmission / reception circuit 102 recognizes the conductor detection information output from the conductor detector 112 (step 3), if the conductor detection information indicates that a human body or metal is in proximity, the transmission phase difference is set to 180 degrees. When the conductor detection information indicates that no human body or metal is in proximity, the feeding phase difference is set to 0 degrees to operate as a current antenna (step 4). .

  Thereby, good radiation characteristics can be realized regardless of the distance between the human body or metal and the antenna.

  The transmission / reception circuit 102 switches the polarization radiated from the antenna device based on the tilt information of the antenna device obtained from the attitude detector 111. FIG. 15 is a diagram showing a procedure for setting the feeding phase difference of the antenna device of the present invention. In step 1, the setting of the feeding phase difference is started. In step 2, the attitude detector 111 detects the inclination of the antenna device. When the transmission / reception circuit 102 recognizes the inclination information output from the attitude detector 111 (step 3), the transmission / reception circuit 102 sets the feeding phase difference so as to have the same polarization as the polarization of the incoming radio wave based on the inclination information. (Step 4). Thereby, favorable radiation characteristics can be realized regardless of the attitude of the antenna device.

  In addition, regardless of conductor detection information or inclination information, it is possible to perform communication by switching between multiple patterns of the feeding phase difference at all times, and performing diversity communication that is adaptively set to a phase difference that always provides high transmission power and reception power. A communication state can be obtained. FIG. 16 is a diagram showing a procedure for setting the feeding phase difference of the antenna device of the present invention. In step 1, the setting of the feeding phase difference is started. In step 2, the transmission / reception circuit 102 sets the feeding phase difference to A and measures the received power of the radio wave. In step 3, the transmission / reception circuit 102 sets the feeding phase difference to B and measures the received power of the radio wave. In step 4, the transmission / reception circuit 102 sets the feeding phase difference to C and measures the received power of the radio wave. In step 5, the transmission / reception circuit 102 sets the power supply phase difference having the highest radio wave reception power among the power supply phase differences A, B, and C.

  The feeding phase differences A, B, and C are different values. These values may be determined in advance or may be determined randomly at the start of setting.

  According to the above, the antenna device of the present invention is sufficient for the wavelength by adopting a configuration in which two loop antennas whose winding directions are opposite to each other have a symmetrical structure and adaptively switch the feeding phase difference. Polarization diversity can be realized with small dimensions.

  The antenna device of the present invention can be applied as an antenna device of a system using a wireless tag such as healthcare, device security, hands-free entry / exit management system, home network, smart meter, sensor network.

DESCRIPTION OF SYMBOLS 101 Ground plate 102 Transmission / reception circuit 103 Divider 104a, 104b Phase shifter 105, 106 Matching circuit 107, 108 Loop antenna 109 Ground line 110 Ground capacity 111 Attitude detector 112 Conductor detector

Claims (6)

A planar ground plate having a ground conductor;
A first loop antenna and a second loop antenna, which are provided at positions away from the ground plate in the horizontal direction and whose loop axis directions are substantially the same;
Signal feeding means for feeding a signal to a feeding point provided at one end of each of the first loop antenna and the second loop antenna;
A common ground line that electrically connects the other end of the first loop antenna and the second loop antenna and the ground plate;
The winding direction toward the direction from the feeding point of the first loop antenna to the ground plate is opposite to the winding direction toward the direction from the feeding point of the second loop antenna to the ground plate,
Loop surfaces formed on the first loop antenna and the second loop antenna are formed perpendicular to the ground plate, intersect with each other and formed symmetrically with respect to the loop axis direction, and the ground line is An antenna device electrically connected to the ground plate via a capacitive element . The antenna apparatus according to claim 1, wherein the signal feeding unit controls a phase of a signal fed to the first loop antenna and the second loop antenna. The polarized waves radiated from the first loop antenna and the second loop antenna parallel to the loop surface are orthogonal to the polarized waves radiated by the current flowing from the first loop antenna to the ground plate. The antenna device according to claim 2, wherein a first loop antenna and a second loop antenna are formed. Provided conductor detection means for detecting a conductor in the vicinity of the ground plate,
The said signal electric power feeding means controls the phase of the signal electrically fed from the said 1st electric power feeding point, and the phase of the signal electrically fed from the said 2nd electric power feeding point according to the detection content by the said conductor detection means. Antenna device. Provide posture detection means to detect the inclination of the grounding plate with respect to the reference plane,
4. The signal feeding unit controls a phase of a signal fed from the first feeding point and a phase of a signal fed from the second feeding point according to the inclination detected by the posture detection unit. 5. The antenna device described. The signal feeding means performs a receiving operation with a phase difference between the phase of the signal fed from the first feeding point and the phase of the signal fed from the second feeding point being different values, and the received power is the highest The antenna device according to claim 3, wherein a phase difference when large is used.