Antenna device

Abstract

To provide a configuration capable of switching a linearly polarized wave and a circularly polarized wave while suppressing antenna gain reduction in the linearly polarized wave.SOLUTION: The four antenna elements 61 to 64 respectively include the main body portions 61a to 64a arranged along the ground layer 52, the first conductive portion 61b to 64b connected to one end side in the longitudinal direction of the main body portions 61a to 64a and receiving power supply in which the phases of the power are controlled, and the second conductive portion 61a to 64a connected to the other end side in the longitudinal direction of the main body portions 61c to and having an open end. 64c, the longitudinal direction of the main body portion P1c to 64a is along four straight lines L1 to L4 extending radially at equal angles from a predetermined reference point 61a of the first substrate surface 51, and the first conductive portion 61b to 64b and the predetermined reference point P1c are disposed such that a first distance D1 between the first conductive portion to and the predetermined reference point is longer than a second distance between the second conductive portion to and the predetermined reference point. 61c 64c D2 P1c.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an antenna device. [Background technology]

[0002] Conventionally, wireless tag readers for reading RF tags and other wireless tags have tended to use circularly polarized waves, which enable reading regardless of the orientation of the wireless tag. However, because circular polarization is generated by equally dividing and supplying power with a phase difference to a horizontally polarized antenna and a vertically polarized antenna, the radiated power is half that of linearly polarized waves such as horizontal and vertical polarization, which results in a problem of reduced communication distance with the wireless tag.

[0003] On the other hand, linear polarization such as horizontal and vertical polarization has a higher radiated power than circular polarization, which means that the reading distance (communication distance) at which RF tags can be read can be extended. However, RF tags that are not aligned with the linear polarization are difficult to read, so in an environment where a large number of RF tags are placed in various orientations, the reading process takes longer than with circular polarization.

[0004] For this reason, a technology has been proposed that allows a single radio tag reader to switch to circular polarization when it is desired to read radio tags with ease of operation, and to switch to linear polarization (horizontal polarization and vertical polarization) when it is desired to extend the reading distance.

[0005] For example, the antenna disclosed in Patent Document 1 listed below includes first to N-th antenna elements and a control unit that controls signal input to each antenna element, and among the first to N-th antenna elements, the second to N-th antenna elements are arranged so that their open ends extend in directions that differ by approximately 360 / N degrees from the first antenna element. This antenna is configured so that, among signals input to the first to N-th antenna elements, signals input to the second to N-th antenna elements have phases that are shifted by approximately 360 / N degrees from the signal input to the first antenna element. The control unit controls the signal input to switch between a first state in which signals are input to the first to N-th antenna elements to radiate circularly polarized waves in a first direction, and a second state in which signals are input to some of the first to N-th antenna elements to radiate linearly polarized waves in a direction different from the first direction.

[0006] Furthermore, the antenna device disclosed in Patent Document 2 listed below is configured to include a first switch having one one-side terminal and four other-side terminals, a divider that divides power supplied through the first switch with a phase difference of 90° to the first distribution other-side terminal and the second distribution other-side terminal, a second switch that switches between a state in which the first other-side terminal of the first switch and the horizontally polarized antenna are conductive and a state in which the first distribution other-side terminal of the divider and the horizontally polarized antenna are conductive, a third switch that switches between a state in which the second other-side terminal of the first switch and the vertically polarized antenna are conductive and a state in which the second distribution other-side terminal of the divider and the vertically polarized antenna are conductive, and a control unit that controls the conductive states of each switch. In this antenna device, when the first other terminal of the first switch and the horizontally polarized antenna are conductive, horizontally polarized radio waves are output via the horizontally polarized antenna, and when the second other terminal of the first switch and the vertically polarized antenna are conductive, vertically polarized radio waves are output via the vertically polarized antenna. Furthermore, when power is supplied to the distributor via the first switch, there is a 90° phase difference between the horizontally polarized radio waves output via the horizontally polarized antenna and the vertically polarized radio waves output via the vertically polarized antenna, so that circularly polarized radio waves are output. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-141416 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-168891 Summary of the Invention [Problem to be solved by the invention]

[0008] Meanwhile, in the case of portable radio tag reading devices that are operated by the user while held in the hand, miniaturization is desirable from the standpoint of operability, and since the antenna device takes up a large amount of space in the entire reading device, there is a strong demand for miniaturization of the antenna device.

[0009] In the antenna of Patent Document 1, the antenna elements are arranged along the four sides of a rectangular substrate. In this arrangement, for example, if power is supplied to only one pair of opposing antenna elements out of phase with one another to radiate horizontally polarized waves, a current flows from the feed end of one antenna element to the feed end of the other antenna element during horizontally polarized radiation. This current generates a vertical component of radio waves, which interferes with the horizontally polarized waves. This results in a reduction in antenna gain, resulting in an undesirable horizontally polarized wave.

[0010] To eliminate the influence of the vertical current as described above, it is necessary to increase the antenna ground size. For example, the antenna in Patent Document 1 is configured as an inverted-F antenna, and if an antenna is configured with a size of approximately 80 mm for use in the 920 MHz frequency band of UHF RFID, the antenna ground size must be increased to at least 100 mm, which creates a problem of hindering miniaturization of the wireless tag reader.

[0011] On the other hand, the antenna device in Patent Document 2 is configured as a patch antenna or a cross dipole antenna, so assuming use at 920 MHz, the frequency band for UHF RFID, the antenna size would be approximately 160 mm. In order to reduce the size of the antenna device to approximately 80 mm, it would be necessary to use ceramics with a high dielectric constant, which would cause problems with cost, weight, durability, etc.

[0012] The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a configuration that can switch between linear polarization and circular polarization while suppressing a decrease in antenna gain in linear polarization. [Means for solving the problem]

[0013] In order to achieve the above object, one aspect of the present invention is to Four antenna elements (61 to 64) an antenna substrate (50) on which the four antenna elements can be arranged; An antenna device (40, 40a) comprising: The antenna substrate is provided with an antenna ground (52) extending in a plane on an outer or inner layer, and a dielectric layer (50a) is provided along one or both sides of the antenna ground, and the surface of the dielectric layer when viewed in a plane is defined as a first substrate surface (51), and the four antenna elements are respectively arranged on the first substrate surface; The phase of the power supplied to the four antenna elements is controllable for each of the antenna elements; The antenna element is made by folding a plate-shaped conductive material, and includes a main body portion (61a to 64a) arranged along the antenna ground, a first conductive portion (61b to 64b) connected to one longitudinal end of the main body portion and receiving power supply with controlled power phase, and a second conductive portion (61c to 64c) connected to the other longitudinal end of the main body portion and having an open end, The four antenna elements are characterized in that the longitudinal direction of the main body is aligned with four straight lines (L1 to L4) extending radially at equal angles from a predetermined reference point (P1c) on the substrate surface, and that a first distance (D1) between the first conductive part and the predetermined reference point is longer than a second distance (D2) between the second conductive part and the predetermined reference point.

[0014] Another aspect of the present invention is an antenna element (120) having a rectangular body (121); an antenna substrate (110) provided with an antenna ground (112) and on which the antenna element is disposed so that the main body is aligned with the antenna ground; An antenna device (100) comprising: The phase of the power fed to the antenna element via four feed elements (141 to 144) can be controlled for each of the feed elements; The four power supply elements are characterized in that their connection positions with the main body are point-symmetrical with respect to the center point (P2c) of the main body, and are arranged so as to be located on the perpendicular bisector of the four outer edges (121a to 121d) that form the outer periphery of the main body. The symbols in parentheses above indicate the correspondence with the specific means described in the embodiments to be described later. [Effects of the Invention]

[0015] In one form of the present invention, the four antenna elements each comprise a main body portion arranged along the antenna ground, a first conductive portion connected to one longitudinal end of the main body portion and receiving power supply with controlled power phase, and a second conductive portion connected to the other longitudinal end of the main body portion and having an open end, and are each arranged so that the longitudinal direction of the main body portion is aligned with four straight lines extending radially at equal angles from a predetermined reference point on the substrate surface, and so that a first distance, which is the distance between the first conductive portion and the predetermined reference point, is longer than a second distance, which is the distance between the second conductive portion and the predetermined reference point.

[0016] As a result, when the four antenna elements are arranged circumferentially as the first antenna element, the second antenna element, the third antenna element, and the fourth antenna element, it is possible to switch between radiating horizontally polarized waves and radiating vertically polarized waves by making the phase of the power fed to the first and second antenna elements and the phase of the power fed to the third and fourth antenna elements 180 degrees different from that of the power fed to the first and fourth antenna elements and the phase of the power fed to the second and third antenna elements 180 degrees different from that of the power fed to the first and fourth antenna elements. Also, it is possible to radiate circularly polarized waves by setting the phase of the power fed to the first antenna element to 0 degrees, feeding power with a phase difference of 90 degrees to the second antenna element, feeding power with a phase difference of 180 degrees to the third antenna element, and feeding power with a phase difference of 270 degrees to the fourth antenna element. In particular, each antenna element is arranged such that the longitudinal direction of its main body is aligned with four straight lines extending radially at equal angles from a predetermined reference point on the substrate surface, with the first distance being longer than the second distance. Therefore, during horizontally polarized radiation, vertical components of radio waves generated by currents flowing through the antenna ground along the longitudinal direction of the main body of each antenna element interfere with and cancel each other out. During vertically polarized radiation, horizontal components of radio waves generated by currents flowing through the antenna ground along the longitudinal direction of the main body of each antenna element interfere with and cancel each other out. Because vertically or horizontally polarized radio waves generated by currents flowing through the antenna ground can be canceled out during linearly polarized radiation, an antenna device can be realized that can switch between linearly polarized and circularly polarized waves while suppressing antenna gain degradation in linear polarization. Furthermore, because the antenna ground does not need to be wider to obtain the required antenna gain, the antenna device can be made more compact.

[0017] In another aspect of the present invention, an antenna element having a rectangular main body and an antenna substrate are provided with an antenna ground and on which the antenna element is arranged so that the main body is aligned with the antenna ground, the phase of power supplied to the antenna element via four feed elements can be controlled for each feed element, and the four feed elements are arranged so that their connection positions with the main body are point-symmetrical with respect to the center point of the main body and are located on the perpendicular bisectors of the four outer edges that form the outer periphery of the main body.

[0018] As a result, when the four power supply elements are arranged clockwise as viewed from the main body side as the first power supply element, the second power supply element, the third power supply element, and the fourth power supply element, it is possible to switch between radiating horizontally polarized waves and radiating vertically polarized waves by not feeding power to the first and third power supply elements and making the phase of the power fed to the second power supply element and the phase of the power fed to the fourth power supply element 180 degrees apart, and not feeding power to the second and fourth power supply elements and making the phase of the power fed to the first power supply element and the phase of the power fed to the third power supply element 180 degrees apart. Furthermore, two types of obliquely polarized waves can be radiated by switching between making the phase of the power fed to the first and fourth feed elements 180 degrees different from that of the power fed to the second and third feed elements and making the phase of the power fed to the first and second feed elements 180 degrees different from that of the power fed to the third and fourth feed elements. Also, circularly polarized waves can be radiated by setting the phase of the power fed to the first feed element to 0 degrees, feeding power with a 90-degree phase difference to the second feed element, feeding power with a 180-degree phase difference to the third feed element, and feeding power with a 270-degree phase difference to the fourth feed element. In particular, the four feed elements are arranged so that their connection positions with the main body are point-symmetrical with respect to the center point of the main body and are located on the perpendicular bisectors of the four outer edges that form the outer periphery of the main body. Therefore, for example, when radiating obliquely polarized waves by setting the phase of the power fed to the second and third feed elements to 180 degrees and the phase of the power fed to the first and fourth feed elements to 0 degrees, strong currents flow along the rectangular outer periphery of the main body, on the side of the first feed element and the side of the fourth feed element, respectively, generating radio waves in the same direction. If each radio wave is divided into a first component traveling from the corner where the outer edge of the first feed element intersects with the outer edge of the fourth feed element toward the other corner diagonally positioned, and a second component perpendicular to the first component, the first components are combined and radiated as obliquely polarized waves, while the second components interfere with each other and cancel each other out. This makes it possible to realize an antenna device that can switch between linear polarization and circular polarization while suppressing antenna gain degradation in oblique polarization (linear polarization).Furthermore, since it is no longer necessary to widen the antenna ground to obtain the required antenna gain, the antenna device can be made smaller.

[0019] The antenna element may further include four first extension portions extending from the four corners of the main body portion so as to be orthogonal to the antenna ground.

[0020] As a result, the first extension functions as a path for a strong current that flows along the outer edge of the rectangular main body, lengthening the current path, which allows the main body of the antenna element to be made smaller while still ensuring the required length of the current path, thereby enabling the antenna device to be made more compact.

[0021] The antenna element may further include four second extension portions extending from the first extension portion so as to be parallel to the antenna ground, and these four second extension portions may be arranged so as to be point-symmetrical with respect to the center point of the main body portion.

[0022] This not only further extends the current path, but also lowers the resonant frequency due to the capacitance component formed between the antenna ground and the second extension. While reducing the size of the main body increases the resonant frequency, the capacitance component formed as described above can lower the resonant frequency, allowing for the miniaturization of the antenna element, i.e., the antenna device, depending on the capacitance component formed. In particular, the four feed elements and the four second extensions are point-symmetrical with respect to the center point of the main body, making it possible to equalize the ratio (axial ratio) of the electric field strengths of the horizontal and vertical components radiated from the antenna device. This reduces the likelihood of differences in read distance due to the orientation of the radio tag when reading a radio tag using circularly polarized waves. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a side view showing a mobile terminal equipped with an antenna device according to a first embodiment. [Figure 2]FIG. 2 is a view of the portable terminal of FIG. 1 as seen from the reading unit side. [Figure 3] Figure 3(A) is a block diagram illustrating the electrical configuration of the mobile terminal of Figure 1, Figure 3(B) is a block diagram illustrating the wireless tag processing unit of Figure 3(A), and Figure 3(C) is a block diagram illustrating the information code reading unit of Figure 3(A). [Figure 4] FIG. 1 is a plan view schematically showing an antenna device according to a first embodiment. [Figure 5] FIG. 5 is a cross-sectional view schematically showing the X1-X1 cross section of FIG. 4. [Figure 6] 4 is an explanatory diagram illustrating the relationship between the phase of power supplied to each antenna element and the direction of radio waves radiated from each antenna element when radiating horizontally polarized waves in the first embodiment. FIG. [Figure 7] 4 is an explanatory diagram illustrating the relationship between the phase of power supplied to each antenna element and the direction of radio waves radiated from each antenna element when radiating vertically polarized waves in the first embodiment. FIG. [Figure 8] 4 is an explanatory diagram illustrating the relationship between the phase of power supplied to each antenna element and the direction of radio waves radiated from each antenna element when radiating a first obliquely polarized wave in the first embodiment. FIG. [Figure 9] 4 is an explanatory diagram illustrating the relationship between the phase of power supplied to each antenna element and the direction of radio waves radiated from each antenna element when radiating a second obliquely polarized wave in the first embodiment. FIG. [Figure 10] 4 is an explanatory diagram illustrating the phase of power supplied to each antenna element when a right-handed circularly polarized wave is radiated in the first embodiment. FIG. [Figure 11] 4 is an explanatory diagram illustrating the phase of power supplied to each antenna element when radiating a left-handed circularly polarized wave in the first embodiment. FIG. [Figure 12] 10A and 10B are explanatory diagrams illustrating the distribution of current flowing in the ground plane when a horizontally polarized wave is radiated by an antenna device having a conventional configuration. [Figure 13] 5A and 5B are explanatory diagrams illustrating the distribution of current flowing in the ground plane when the antenna device according to the first embodiment radiates horizontally polarized waves. [Figure 14] 10 is an explanatory diagram illustrating the angle of deviation between a straight line corresponding to a diagonal line of the ground plane and the longitudinal direction of the main body. FIG. [Figure 15] 15 is a graph showing the relationship between the deviation angle and the antenna gain in FIG. 14. [Figure 16] FIG. 10 is a plan view schematically showing an antenna device according to a modified example of the first embodiment. [Figure 17] FIG. 10 is a plan view schematically showing an antenna device according to a second embodiment. [Figure 18] FIG. 18 is a side view of the antenna device of FIG. [Figure 19] 10 is an explanatory diagram illustrating the relationship between the phase of the power fed to each feed element and the polarization direction of the radio wave radiated from the antenna element when radiating a horizontally polarized wave in the second embodiment. FIG. [Figure 20] 10 is an explanatory diagram illustrating the relationship between the phase of the power fed to each feed element and the polarization direction of the radio wave radiated from the antenna element when radiating a vertically polarized wave in the second embodiment. FIG. [Figure 21] 10 is an explanatory diagram illustrating the relationship between the phase of the power fed to each feed element and the polarization direction of the radio wave radiated from the antenna element when radiating a first obliquely polarized wave in the second embodiment. FIG. [Figure 22] 10 is an explanatory diagram illustrating the relationship between the phase of the power fed to each feed element and the polarization direction of the radio wave radiated from the antenna element when radiating a second obliquely polarized wave in the second embodiment. FIG. [Figure 23] 10 is an explanatory diagram illustrating the phase of power fed to each feed element when a right-handed circularly polarized wave is radiated in the second embodiment. FIG. [Figure 24] 10 is an explanatory diagram illustrating the phase of power fed to each feed element when radiating left-handed circularly polarized waves in the second embodiment. FIG. [Figure 25] 10 is an explanatory diagram illustrating the distribution of current flowing through an antenna element when an antenna device according to a second embodiment radiates obliquely polarized waves. FIG. [Figure 26] 10 is an explanatory diagram illustrating the distribution of current flowing through an antenna element when a horizontally polarized wave is radiated by the antenna device according to the second embodiment. FIG. [Figure 27] Figure 27(A) is an explanatory diagram illustrating the state in which a capacitive component is formed between the ground layer and the second extension portion, and Figure 27(B) is an explanatory diagram showing a conventional patch antenna as a comparison with Figure 27(A). [Figure 28] Figure 28(A) is an explanatory diagram showing a cross section of a main part of an antenna device according to a first modified example of the second embodiment, and Figure 28(B) is an explanatory diagram showing a cross section of a main part of an antenna device according to a second modified example of the second embodiment. [Figure 29] Figure 29(A) is an explanatory diagram showing the main parts of an antenna device related to a third modified example of the second embodiment, Figure 29(B) is an explanatory diagram showing the main parts of an antenna device related to a fourth modified example of the second embodiment, and Figure 29(C) is an explanatory diagram showing the main parts of an antenna device related to a fifth modified example of the second embodiment. [Figure 30] Figure 30(A) is an explanatory diagram showing the main parts of an antenna device according to a sixth modified example of the second embodiment, and Figure 30(B) is an explanatory diagram showing the main parts of an antenna device according to a seventh modified example of the second embodiment. [Figure 31] FIG. 10 is a plan view schematically showing an antenna device according to a third embodiment. [Figure 32] 32 is a side view showing a mobile terminal equipped with the antenna device of FIG. 31. [Figure 33] FIG. 33 is a view of the portable terminal of FIG. 32 as seen from the reading unit side. [Figure 34] Figure 34(A) is an explanatory diagram illustrating the state in which power is supplied to the first antenna by the distribution unit, and Figure 34(B) is an explanatory diagram illustrating the state in which radio waves for long-distance reading are emitted in the direction in which the reading surface is facing. [Figure 35] Figure 35(A) is an explanatory diagram illustrating the state in which power is supplied to the second antenna by the distribution unit, and Figure 35(B) is an explanatory diagram illustrating the state in which radio waves for short-range reading are emitted in the direction in which the left side is facing. [Figure 36] FIG. 10 is an explanatory diagram illustrating a reading operation when reading only one of the wireless tags attached to each of a large number of clothes hung on hangers. [Figure 37]FIG. 37(A) is a plan view showing an antenna device according to a first modified example of the third embodiment, and FIG. 37(B) is a plan view showing an antenna device according to a second modified example of the third embodiment. [Figure 38] 37(A) is an explanatory diagram illustrating a state in which a wireless tag near the bottom surface of a reading unit is read by a mobile terminal equipped with the antenna device of FIG. [Figure 39] FIG. 11 is a plan view showing an antenna device according to a third modified example of the third embodiment. [Figure 40] FIG. 10 is an explanatory diagram illustrating a circuit configuration of a conventional distribution unit. [Figure 41] 41 is an explanatory diagram illustrating the relationship between switch control and output polarized waves, etc., in the distribution unit of FIG. 40. FIG. [Figure 42] FIG. 10 is an explanatory diagram illustrating the circuit configuration of a distribution unit in a fourth embodiment. [Figure 43] 43 is an explanatory diagram illustrating the relationship between switch control and output polarized waves, etc., in the distributor of FIG. 42. FIG. [Figure 44] FIG. 13 is an explanatory diagram illustrating a circuit configuration of a distribution unit in a modified example of the fourth embodiment. [Figure 45] 45 is an explanatory diagram illustrating the relationship between switch control and output polarized waves, etc., in the distributor of FIG. 44. FIG. [Figure 46] FIG. 10 is a perspective view illustrating an antenna element employed in an antenna device according to a fifth embodiment. [Figure 47] Figure 47(A) is an explanatory diagram illustrating the magnitude of vibration caused by impact, etc. in an antenna element that does not have a notch or a bend, and Figure 47(B) is an explanatory diagram illustrating the magnitude of vibration caused by impact, etc. in the antenna element of Figure 46. [Figure 48] Figure 48(A) is an explanatory diagram explaining the stress distribution that occurs when an impact or the like is applied to the antenna element of Figure 46, Figure 48(B) is an explanatory diagram explaining the stress distribution that occurs when an impact or the like is applied in a configuration in which the cutout is provided near the main body, and Figure 48(C) is an explanatory diagram explaining the stress distribution that occurs when an impact or the like is applied in a configuration in which the cutout is provided near the first substrate surface. [Figure 49]Figure 49(A) is an explanatory diagram explaining the second conductive portion of the antenna element employed in an antenna device relating to a first variant of the fifth embodiment, Figure 49(B) is an explanatory diagram explaining the second conductive portion of the antenna element employed in an antenna device relating to a second variant of the fifth embodiment, and Figure 49(C) is an explanatory diagram explaining the second conductive portion of the antenna element employed in an antenna device relating to a third variant of the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] [First embodiment] A first embodiment of a mobile terminal equipped with an antenna device according to the present invention will be described below with reference to the drawings. The mobile terminal 1 shown in Figures 1 and 2 is configured as an information reading device that is carried by a user and reads specified information in various locations.In addition to functioning as a wireless tag reader / writer that reads and writes information stored in wireless tags such as RF tags using radio waves transmitted and received via an antenna unit, it also functions as an information code reader that optically reads information codes such as barcodes and two-dimensional codes, and is configured to be able to read in two ways.

[0025] 1 and 2, the mobile terminal 1 has an outer shell formed by a housing made of a synthetic resin material such as ABS resin, and is configured as a gun grip type by including a terminal main body 2, a gripping unit 3 attached to the terminal main body 2, and a reading unit 4. A trigger switch 14a is disposed on the outer surface of the gripping unit 3, near the rear surface of the terminal main body 2 and facing the reading unit 4, and is operated to start the reading process for a wireless tag or the like. Also, as shown in FIG. 2, a reading port 4b is provided above the reading surface 4a of the reading unit 4 to capture reflected light from an information code. The reading unit 4 houses at least some of the components that make up the reading function, such as an antenna device 40 described below.

[0026] As shown in FIG. 3(A), the mobile terminal 1 mainly includes a control unit 11 that is responsible for overall control, a memory unit 12 consisting of a semiconductor memory or the like, a display unit 13 whose display content is controlled by the control unit 11, an operation unit 14 that outputs an operation signal to the control unit 11 in response to an input operation such as a trigger switch 14a, an alarm unit 15 whose light emitting state of the light emitting unit, the alarm sound state of the speaker, the sounding state of the buzzer, etc. are controlled by the control unit 11, a communication unit 16 for wireless or wired communication with external devices, and a power supply unit 17 that supplies power from a battery 18 to various electrical components.

[0027] The mobile terminal 1 also has a wireless tag processing unit 20 for reading and writing information from the wireless tag Tg, and an information code reading unit 30 for optically reading the information code C, and the results of each reading are stored in the memory unit 12.

[0028] The RFID tag processing unit 20 communicates with the RFID tag Tg by electromagnetic waves in cooperation with the antenna device 40 and the control unit 11, and functions to read data stored in the RFID tag Tg or write data to the RFID tag Tg. The RFID tag processing unit 20 is configured as a circuit that transmits by a known radio wave method, and in addition to an oscillator, a modulator, etc., includes a signal generation unit 21 that converts a data signal generated by the control unit 11 into a high-frequency signal (AC signal) by a known method, and a distribution unit 22 that functions as a power distribution circuit that can distribute the signal generated by the signal generation unit 21 to the antenna device 40, as shown schematically in Fig. 3(B), which constitute a transmission circuit. A receiving circuit 23 that inputs and demodulates the radio waves received by the antenna device 40 is also provided.

[0029] The information code reading unit 30 functions to optically read the information code, and as shown in Figure 3(C), is configured with a light receiving sensor 33 consisting of a CCD area sensor, an imaging lens 32, an illumination unit 31 consisting of multiple LEDs, lenses, etc., and functions to work in cooperation with the control unit 11 to image and read the information code C (barcode or two-dimensional code) attached to the reading object R.

[0030] When reading using the information code reader 30, illumination light Lf is first emitted from the illumination unit 31 in response to a command from the control unit 11, and this illumination light Lf is irradiated onto the object R to be read through the reading port 4b. Reflected light Lr, which is the illumination light Lf reflected by the information code C, is taken into the device through the reading port 4b and received by the light-receiving sensor 33 through the imaging lens 32. The imaging lens 32, located between the reading port 4b and the light-receiving sensor 33, is configured to form an image of the information code C on the light-receiving sensor 33, and the light-receiving sensor 33 outputs a light-receiving signal corresponding to the image of the information code C. The light-receiving signal output from the light-receiving sensor 33 is stored in the memory unit 12 as image data and is used in a decoding process to acquire the information contained in the information code C. The information code reader 30 is equipped with an amplifier circuit that amplifies the signal from the light-receiving sensor 33, an AD conversion circuit that converts the amplified signal into a digital signal, and other circuits, but these circuits are not shown in the figure.

[0031] Next, the antenna device 40 will be described in detail with reference to the drawings. The antenna device 40 in this embodiment is an antenna device that is switchable between linear polarization (horizontal polarization, vertical polarization, and diagonal polarization) and circular polarization, and is intended for use in the 920 MHz frequency band of UHF RFID. As shown in Figures 4 and 5, the antenna device 40 is configured to include an antenna board 50 and four antenna elements 61, 62, 63, and 64 mounted on a first board surface 51 of the antenna board 50, which are configured as an integrated unit. As shown in Figure 2, the antenna device 40 is housed in the reading unit 4 with the first board surface 51 facing the inner side of the reading surface 4a, with the antenna elements 61 and 64 on the lower side and the antenna elements 62 and 63 on the upper side.

[0032] The antenna substrate 50 is a substrate having a dielectric layer 50a made of, for example, resin or ceramic, and has a first substrate surface 51 configured in a substantially square shape when the dielectric layer 50a is viewed from above in the direction of radio wave radiation. A predetermined pattern configured by a conductive layer is formed on the substantially square first substrate surface 51 and inside the substrate (inner layer).

[0033] A ground layer 52, which functions as an antenna ground, is provided on substantially the entire area of ​​the second substrate surface, which is the reverse side of the first substrate surface 51, so as to extend in a plane with a predetermined thickness and made of a conductive material. The ground layer 52 is a conductive layer whose potential is set to a predetermined ground level. In this embodiment, the center of the ground layer 52 in a planar view substantially coincides with the center of the first substrate surface 51 (a point equidistant from the four corners of the first substrate surface 51). Although not shown in FIG. 4 and other figures, other electronic components may be mounted on the first substrate surface 51 and the second substrate surface. The ground layer 52 is not limited to being provided in a planar view on the outer layer (second substrate surface) of the antenna substrate 50, but may be provided in a planar view on an inner layer of the antenna substrate 50, for example. The dielectric layer 50a may be provided along one or both surfaces of the ground layer 52. The antenna substrate 50 is not limited to having an approximately square outer shape in a planar view, but may have an approximately rectangular outer shape in a planar view, for example.

[0034] Each of the antenna elements 61 to 64 is made by bending a plate-like conductive material, and specifically, is formed into a predetermined shape by performing sheet metal processing on a conductive member (for example, a metal plate such as a copper plate). The antenna element 61 includes a main body 61a extending in a strip shape (longitudinal shape) along the ground layer 52, a first conductive part 61b connected to one longitudinal end of the main body 61a and receiving power via the distribution part 22, and a second conductive part 61c connected to the other longitudinal end of the main body 61a and having an open end.

[0035] Each of the antenna elements 62 to 64 has approximately the same shape as the antenna element 61, and the antenna element 62 has a main body portion 62a, a first conductive portion 62b that receives power, and a second conductive portion 62c that has an open end; the antenna element 63 has a main body portion 63a, a first conductive portion 63b that receives power, and a second conductive portion 63c that has an open end; and the antenna element 64 has a main body portion 64a, a first conductive portion 64b that receives power, and a second conductive portion 64c that has an open end.

[0036] As shown in Figure 4, each antenna element 61 to 64 is arranged so that the longitudinal direction of the main body portion 61a to 64a is aligned with four straight lines L1 to L4 that extend radially from a predetermined reference point P1c that coincides with the center of the first substrate surface 51 (the center of the ground layer 52) toward the four corners of the first substrate surface 51 at equal angles (90 degrees) in the circumferential direction.

[0037] The first conductive portions 61b-64b and the second conductive portions 61c-64c are arranged so as to be substantially perpendicular to the ground plane 52 (first substrate surface 51). In particular, the antenna elements 61-64 are arranged so that the distance between each of the first conductive portions 61b-64b and a predetermined reference point P1c is substantially the same first distance D1, and the distance between each of the second conductive portions 61c-64c and the predetermined reference point P1c is substantially the same second distance D2, with the first distance D1 being longer than the second distance D2. As a result, the antenna elements 61-64 are arranged at equal angles (equal intervals) in order counterclockwise around the predetermined reference point P1c. That is, the antenna elements 61-64 are arranged radially with the second conductive portions 61c-64c closer to the center. The predetermined reference point P1c does not necessarily have to be set to coincide with the center of the first substrate surface 51 (the center of the ground layer 52), but may be slightly deviated from the center.

[0038] Each of the first conductive parts 61b to 64b is configured so that power, the phase of which is controlled for each antenna element by the control unit 11, is supplied to the first conductive parts 61b to 64b via the distribution unit 22. That is, the antenna device 40 according to this embodiment is configured so that the phase of the power supplied to the four antenna elements 61 to 64 can be controlled for each antenna element.

[0039] Next, the control of the antenna device 40, distribution unit 22, etc., which is switched by the control unit 11 to horizontal polarization, vertical polarization, oblique polarization, or circular polarization when reading the RFID tag Tg, will be described with reference to the drawings.

[0040] First, a case where horizontally polarized waves are emitted to read RFID tag T will be described with reference to Fig. 6. In this case, distribution unit 22 controlled by control unit 11 sets the phase of power supplied to antenna element 63 and antenna element 64 to 180 degrees, and sets the phase of power supplied to antenna element 61 and antenna element 62 to 0 degrees, thereby making the phases different by 180 degrees.

[0041] As a result, as shown in Figure 6, at a certain timing, radio waves are emitted from antenna element 61 along straight line L1 in a direction from the first conductive portion 61b to the second conductive portion 61c (see arrow F11 in Figure 6), from antenna element 62 along straight line L2 in a direction from the first conductive portion 62b to the second conductive portion 62c (see arrow F12 in Figure 6), from antenna element 63 along straight line L3 in a direction from the second conductive portion 63c to the first conductive portion 63b (see arrow F13 in Figure 6), and from antenna element 64 along straight line L4 in a direction from the second conductive portion 64c to the first conductive portion 64b (see arrow F14 in Figure 6). Therefore, a composite radio wave Fs consisting of the X-direction component F11x (left and right direction in FIG. 6) of the radio wave from antenna element 61, the X-direction component F12x of the radio wave from antenna element 62, the X-direction component F13x of the radio wave from antenna element 63, and the X-direction component F14x of the radio wave from antenna element 64 is radiated as a horizontally polarized wave. Note that the Y-direction component of the radio wave from antenna element 61 and the Y-direction component of the radio wave from antenna element 62 and the Y-direction component of the radio wave from antenna element 63 and the Y-direction component of the radio wave from antenna element 64 cancel each other out, as will be described later.

[0042] Next, a case where vertically polarized waves are emitted to read RFID tag T will be described with reference to Fig. 7. In this case, distribution unit 22 controlled by control unit 11 sets the phase of power supplied to antenna element 61 and antenna element 64 to 180 degrees, and sets the phase of power supplied to antenna element 62 and antenna element 63 to 0 degrees, thereby making the phases different by 180 degrees.

[0043] As a result, as shown in Figure 7, at a certain timing, radio waves are emitted from antenna element 61 along straight line L1 in a direction from the second conductive portion 61c to the first conductive portion 61b (see arrow F11 in Figure 7), from antenna element 62 along straight line L2 in a direction from the first conductive portion 62b to the second conductive portion 62c (see arrow F12 in Figure 7), from antenna element 63 along straight line L3 in a direction from the first conductive portion 63b to the second conductive portion 63c (see arrow F13 in Figure 7), and from antenna element 64 along straight line L4 in a direction from the second conductive portion 64c to the first conductive portion 64b (see arrow F14 in Figure 7). Therefore, a composite radio wave Fs consisting of a Y-direction component F11y (vertical direction in FIG. 7) of the radio wave from antenna element 61, a Y-direction component F12y of the radio wave from antenna element 62, a Y-direction component F13y of the radio wave from antenna element 63, and a Y-direction component F14y of the radio wave from antenna element 64 is radiated as a vertically polarized wave. Note that the X-direction component of the radio wave from antenna element 61 and the X-direction component of the radio wave from antenna element 62 and the X-direction component of the radio wave from antenna element 63 and the X-direction component of the radio wave from antenna element 64 cancel each other out, as will be described later.

[0044] Next, a case where obliquely polarized waves are emitted to read an RFID tag T will be described with reference to Fig. 8 and Fig. 9. In this case, the distribution unit 22 controlled by the control unit 11 does not supply power to the antenna elements 62 and 64, but sets the phase of the power supplied to the antenna element 61 to 180 degrees and the phase of the power supplied to the antenna element 63 to 0 degrees, thereby shifting the phases by 180 degrees.

[0045] 8, at a certain timing, a radio wave (see arrow F11 in FIG. 8) is emitted from antenna element 61 along straight line L1 from second conductive portion 61c to first conductive portion 61b, and a radio wave (see arrow F13 in FIG. 8) is emitted from antenna element 63 along straight line L3 from first conductive portion 63b to second conductive portion 63c. Therefore, a composite radio wave Fs obtained by combining these radio waves is emitted as a first obliquely polarized wave.

[0046] Furthermore, no power is supplied to antenna elements 61 and 63, the phase of the power supplied to antenna element 64 is set to 180 degrees, and the phase of the power supplied to antenna element 62 is set to 0 degrees, thereby causing a phase difference of 180 degrees.

[0047] 9, at a certain timing, a radio wave (see arrow F12 in FIG. 9) is emitted from the antenna element 62 along the straight line L2 from the first conductive portion 62b to the second conductive portion 62c, and a radio wave (see arrow F14 in FIG. 9) is emitted from the antenna element 64 along the straight line L4 from the second conductive portion 64c to the first conductive portion 64b. Therefore, a composite radio wave Fs combining these radio waves is emitted as a second obliquely polarized wave.

[0048] Next, a case where circularly polarized waves are emitted to read RFID tag T will be described with reference to Fig. 10 and Fig. 11. In this case, distribution unit 22 controlled by control unit 11 sets the phase of power supplied to antenna element 61 to 0 degree, supplies power with a phase difference of 90 degrees to antenna element 62, supplies power with a phase difference of 180 degrees to antenna element 63, and supplies power with a phase difference of 270 degrees to antenna element 64. As a result, circularly polarized waves (right-handed circularly polarized waves) as shown in Fig. 10 are emitted (see symbol Fs in Fig. 10).

[0049] Furthermore, the phase of the power supplied to antenna element 61 is set to 0 degrees, and power with a phase difference of 90 degrees is supplied to antenna element 64, power with a phase difference of 180 degrees is supplied to antenna element 63, and power with a phase difference of 270 degrees is supplied to antenna element 62. As a result, a circularly polarized wave (left-handed circularly polarized wave) as shown in Fig. 11 is radiated (see symbol Fs in Fig. 11).

[0050] Next, the effect of suppressing the decrease in antenna gain when the antenna device 40 according to this embodiment radiates horizontally polarized waves will be described with reference to Figures 12 and 13. For convenience, in Figures 12 and 13, only the antenna ground layer of the antenna substrate is shown in a roughly rectangular shape. In a conventional antenna device corresponding to the antenna of Patent Document 1, four antenna elements 1010, 1020, 1030, and 1040 are arranged along the four sides of a rectangular substrate surface, and horizontal polarization is radiated by not supplying power to antenna elements 1020 and 1040, setting the phase of the power supplied to antenna element 1010 to 180 degrees, and setting the phase of the power supplied to antenna element 1030 to 0 degrees.

[0051] During this horizontally polarized wave radiation, a current So flows in the ground plane 1100 from the feed end 1031 of the antenna element 1030 to the feed end 1011 of the antenna element 1010, as shown in Fig. 12. A vertical component of radio waves is radiated in response to the current So flowing in this way, and these radio waves interfere with the horizontally polarized wave. This results in a decrease in antenna gain, which causes a problem of not radiating an ideal horizontally polarized wave.

[0052] In contrast, in the antenna device 40 according to this embodiment, as shown in Fig. 6, power is supplied to each of the antenna elements 61-64, and as shown in Fig. 13, currents S11-S14 are generated in the ground plane 52 along the longitudinal direction of the main bodies 61a-64a of the antenna elements 61-64. Radio waves F11, F12, F13, and F14 generated by the currents S11-S14 radiate vertical components F11y, F12y, F13y, and F14y, respectively. However, because the radiation directions are opposite, the vertical components interfere with each other and cancel each other out. This suppresses a reduction in antenna gain during horizontally polarized radiation.

[0053] Similarly, when radiating vertically polarized waves, horizontal components of radio waves are radiated due to the radio waves generated in the ground layer 52, but because the radiation directions are opposite, the horizontal components interfere with each other and cancel each other out. This makes it possible to suppress the reduction in antenna gain when radiating vertically polarized waves.

[0054] Next, the influence of misalignment of the antenna elements 61 to 64 will be described with reference to FIGS. As shown in FIG. 14, when a deviation angle θ occurs between the straight lines L1 to L4 corresponding to the diagonal lines of the square ground plane 52 and the longitudinal direction of the main body portions 61a to 64a, as shown in FIG. 15, the antenna gain decreases as the deviation angle θ increases during horizontally polarized radiation or vertically polarized radiation. As can be seen from FIG. 15, when the deviation angle θ is greater than 5 degrees, the antenna gain decreases significantly. For this reason, even if each of the antenna elements 61 to 64 is positioned offset from the straight lines L1 to L4, it is desirable that the deviation angle θ be 5 degrees or less. Note that the relationship between the deviation angle θ and the antenna gain is approximately the same for horizontally polarized radiation and vertically polarized radiation, and therefore, in FIG. 15, the values ​​for horizontally polarized radiation and vertically polarized radiation are shown overlapping.

[0055] As described above, in the antenna device 40 of this embodiment, the four antenna elements 61 to 64 each include a main body portion 61a to 64a arranged along the ground plane 52, a first conductive portion 61b to 64b connected to one longitudinal end of the main body portion 61a to 64a and receiving power supply with controlled power phase, and a second conductive portion 61c to 64c connected to the other longitudinal end of the main body portion 61a to 64a and having an open end, and are each arranged so that the longitudinal direction of the main body portion 61a to 64a is aligned with four straight lines L1 to L4 extending radially at equal angles from a predetermined reference point P1c on the first substrate surface 51, and so that a first distance D1, which is the distance between the first conductive portion 61b to 64b and the predetermined reference point P1c, is longer than a second distance D2, which is the distance between the second conductive portion 61c to 64c and the predetermined reference point P1c.

[0056] As a result, by controlling the phase of the power supplied to each antenna element 61 to 64 as described above, it is possible to switch between radiating horizontally polarized waves (see Figure 6), radiating vertically polarized waves (see Figure 7), radiating diagonally polarized waves (see Figures 8 and 9), and radiating circularly polarized waves (see Figures 10 and 11).

[0057] In particular, the antenna elements 61-64 are arranged such that the longitudinal direction of the main bodies 61a-64a is aligned with four straight lines L1-L4 that extend radially at equal angles from a predetermined reference point P1c on the first substrate surface 51, and the first distance D1 is longer than the second distance D2. Therefore, during horizontally polarized radiation, vertical components of radio waves generated along the longitudinal direction of the main bodies 61a-64a due to current flowing in the ground plane 52 interfere with and cancel each other out, while during vertically polarized radiation, horizontal components of radio waves generated along the longitudinal direction of the main bodies 61a-64a due to current flowing in the ground plane 52 interfere with and cancel each other out. In this way, vertically or horizontally directed radio waves generated along the current flowing in the ground plane 52 during linearly polarized radiation (horizontally polarized radiation or vertically polarized radiation) can be canceled out, thereby realizing an antenna device that can switch between linearly polarized and circularly polarized waves while suppressing antenna gain degradation in linearly polarized waves. Furthermore, since it is no longer necessary to make the ground layer 52 wider in order to obtain the required antenna gain, the antenna device 40 can be made smaller.

[0058] Note that the antenna elements 61-64 do not necessarily have to be arranged so that the longitudinal direction of the main body portions 61a-64a is aligned with the straight lines L1-L4, but may also be arranged so that the longitudinal direction of the main body portions 61a-64a is aligned with four straight lines (perpendicular bisectors) L1-L4 that extend radially from a predetermined reference point P1c toward the center of each side at equal angles (90 degrees), as illustrated in Fig. 16. In this case, the antenna elements 61-64 are arranged so that the distances between the first conductive portions 61b-64b and the predetermined reference point P1c are substantially the same first distances, and the distances between the second conductive portions 61c-64c and the predetermined reference point P1c are substantially the same second distances, the first distances being longer than the second distances.

[0059] [Second embodiment] Next, an antenna device according to a second embodiment of the present invention will be described with reference to the drawings. The antenna device 100 of this embodiment, like the antenna device 40 described above, is designed for use in the 920 MHz frequency band of UHF RFID and is capable of switching between linear polarization (horizontal polarization, vertical polarization, and diagonal polarization) and circular polarization. As shown in FIGS. 17 and 18 , the antenna device 100 includes an antenna substrate 110, an antenna element 120, and four feed elements 141, 142, 143, and 144, which are integrated into an integrated unit. The antenna device 100 is housed in the reader 4 with the first substrate surface 111 of the antenna substrate 110 facing the inner surface of the reading surface 4a, with the feed element 141 on the upper side and the feed element 143 on the lower side.

[0060] The antenna substrate 110 is a substrate made of, for example, resin or ceramic, and has an outer shape that is approximately square when viewed in a plane. A predetermined pattern made of a conductive layer is formed on the approximately square first substrate surface 111 and inside the substrate.

[0061] A ground layer 112 functioning as an antenna ground is provided in substantially the entire area of ​​the second substrate surface, which is the back side of the first substrate surface 111, as a conductive layer with a predetermined thickness, the potential of which is set to a predetermined ground level. Although not shown in FIG. 17 and other figures, other electronic components may be mounted on the first substrate surface 111 and the second substrate surface. The ground layer 112 is not limited to being provided on the second substrate surface of the antenna substrate 110, and may be provided, for example, as an inner layer of the antenna substrate 110. The antenna substrate 110 is not limited to having an outer shape that is substantially square when viewed in a plane, and may have an outer shape that is substantially rectangular when viewed in a plane, for example.

[0062] The antenna element 120 is formed from a conductive material and includes a substantially square, substantially flat main body 121, four first extensions 131a, 132a, 133a, and 134a, and four second extensions 131b, 132b, 133b, and 134b.

[0063] The first extension portion 131a is formed from a conductive plate material (for example, a metal plate such as a copper plate), and is formed to extend downward from one of the four corners of the main body portion 121 so as to be perpendicular to the ground plane 112. Similarly, the first extension portions 132a to 134a are formed to extend downward from the other four corners of the main body portion 121 so as to be perpendicular to the ground plane 112. Therefore, each of the first extension portions 132a to 134a is configured to be in a conductive state with the main body portion 121 and in a non-conductive state with the ground plane 112. In particular, each of the first extension portions 131a to 134a is arranged to be point-symmetric with respect to a center point P2c of the main body portion 121 (points equidistant from the four corners of the main body portion 121).

[0064] The second extension portion 131b is formed integrally with the first extension portion 131a by bending a conductive plate material or the like, and is formed by extending from an extension end (lower end) of the first extension portion 131a toward the center of the main body portion 121 so as to be parallel to the ground plane 112. Similarly, the second extension portion 132b is formed by extending from an extension end of the integrally formed first extension portion 132a toward the center of the main body portion 121 so as to be parallel to the ground plane 112, the second extension portion 133b is formed by extending from an extension end of the integrally formed first extension portion 133a toward the center of the main body portion 121 so as to be parallel to the ground plane 112, and the second extension portion 134b is formed by extending from an extension end of the integrally formed first extension portion 134a toward the center of the main body portion 121 so as to be parallel to the ground plane 112. In particular, as shown in FIG. 17, the second extending portions 131b to 134b are arranged along the diagonal lines of the main body portion 121 so as to be point-symmetric with respect to the center point P2c.

[0065] Each of the feed elements 141-144 is a conductive plate material for feeding power to the antenna element 120 via the antenna substrate 110. As shown in Fig. 17, each of the feed elements 141-144 is arranged such that the connection position with the main body 121 to which it is connected so as to be able to feed power is point-symmetrical with respect to the center point P2c of the main body 121 and is located on the perpendicular bisectors Lc1-Lc4 of the four outer edges 121a-121d that form the substantially square outer periphery of the main body 121.

[0066] Specifically, the feed elements 141 to 144 are arranged clockwise as feed element 141, feed element 142, feed element 143, and feed element 144 when viewed from the main body side. Therefore, feed element 141 is located on perpendicular bisector Lc1 of outer edge 121a of main body 121, feed element 142 is located on perpendicular bisector Lc2 of outer edge 121b of main body 121, feed element 143 is located on perpendicular bisector Lc3 of outer edge 121c of main body 121, and feed element 144 is located on perpendicular bisector Lc4 of outer edge 121d of main body 121. The perpendicular bisectors Lc1 to Lc4 are positioned such that they extend radially from center point P2c of main body 121 at equal angles (90 degrees) toward each outer edge. In this embodiment as well, the phase of the power fed to the antenna element 120 is configured to be controllable for each of the feed elements 141 to 144.

[0067] Next, the control of the antenna device 100 and the distribution unit 22, etc., which are switched by the control unit 11 to horizontal polarization, vertical polarization, oblique polarization, or circular polarization when reading the RFID tag Tg, will be described with reference to the drawings.

[0068] First, a case where horizontally polarized waves are emitted to read RFID tag T will be described with reference to Fig. 19. In this case, distribution unit 22 controlled by control unit 11 does not feed power to feed elements 141 and 143, and causes the phase of power fed to feed element 142 and the phase of power fed to feed element 144 to differ by 180 degrees.

[0069] Each of the power supply elements 141 to 144 is connected to the approximately rectangular main body 121 at a position that is point-symmetrical with respect to the center point P2c of the main body 121, and therefore, as shown in FIG. 19, a horizontally polarized wave can be emitted as radio waves Fs in a direction along the line connecting the power supply element 142 and the power supply element 144.

[0070] Next, a case where vertically polarized waves are emitted to read RFID tag T will be described with reference to Fig. 20. In this case, distribution unit 22 controlled by control unit 11 causes the phase of power fed to feed element 141 to differ by 180 degrees from the phase of power fed to feed element 143 without feeding power to feed elements 142 and 144.

[0071] Since each of the power supply elements 141 to 144 is connected to the approximately rectangular main body 121 at a position that is point-symmetric with respect to the center point P2c of the main body 121, vertical polarization can be emitted as radio waves Fs in a direction along the line connecting the power supply elements 141 and 143, as shown in FIG. 20.

[0072] 21 and 22, a case where obliquely polarized waves are emitted to read an RFID tag T will be described. In this case, the distribution unit 22 controlled by the control unit 11 causes the phase of the power supplied to the power supply elements 141 and 144 to differ by 180 degrees from the phase of the power supplied to the power supply elements 142 and 143.

[0073] Since each of the power supply elements 141 to 144 is connected to the approximately rectangular main body 121 at a position that is point-symmetrical with respect to the center point P2c of the main body 121, as shown in FIG. 21, a first obliquely polarized wave can be emitted as radio waves Fs in directions along both the line connecting the power supply elements 141 and 142 and the line connecting the power supply elements 143 and 144.

[0074] Furthermore, the phase of the power fed to the feed elements 141 and 142 is made to differ by 180 degrees from the phase of the power fed to the feed elements 143 and 144.

[0075] Since each of the power supply elements 141 to 144 is connected to the approximately rectangular main body 121 at a position that is point-symmetrical with respect to the center point P2c of the main body 121, as shown in FIG. 22, a second obliquely polarized wave can be emitted as radio waves Fs in directions along both the line connecting the power supply elements 141 and 144 and the line connecting the power supply elements 142 and 143.

[0076] Next, a case where circularly polarized waves are emitted to read RFID tag T will be described with reference to Fig. 23 and Fig. 24. In this case, distribution unit 22 controlled by control unit 11 sets the phase of power fed to feed element 141 to 0 degree, feeds power with a phase difference of 90 degrees to feed element 144, feeds power with a phase difference of 180 degrees to feed element 143, and feeds power with a phase difference of 270 degrees to feed element 142. As a result, a circularly polarized wave (right-handed circularly polarized wave) as shown in Fig. 23 is emitted (see symbol Fs in Fig. 23).

[0077] Furthermore, the phase of the power fed to feed element 141 is set to 0 degrees, and power with a phase difference of 90 degrees is fed to feed element 142, power with a phase difference of 180 degrees is fed to feed element 143, and power with a phase difference of 270 degrees is fed to feed element 144. As a result, a circularly polarized wave (left-handed circularly polarized wave) as shown in Fig. 24 is radiated (see symbol Fs in Fig. 24).

[0078] Next, the effect of suppressing a decrease in antenna gain when the antenna device 100 according to this embodiment radiates obliquely polarized waves will be described with reference to FIG. In the antenna device 100 according to this embodiment, it is assumed that a first obliquely polarized wave is radiated by feeding power to each of the feed elements 141 to 144 as shown in Fig. 21. In this case, as shown in Fig. 25, strong currents (see arrows S21 and S22 in Fig. 25) flow along outer edges 121a and 121d of the rectangular outer periphery of the main body 121, and thus radio waves are generated in the same direction.

[0079] If each radio wave is divided into a first component that travels from a corner where outer edge 121a intersects with outer edge 121d toward another corner diagonally positioned, and a second component that is perpendicular to the first component, the first component F211 of the radio wave caused by current S21 and the first component F221 of the radio wave caused by current S22 are combined and radiated as a first obliquely polarized wave (see arrow Fs in FIG. 25). Meanwhile, the second component F212 of the radio wave caused by current S21 and the second component F222 of the radio wave caused by current S22 can interfere with each other and cancel each other out. This suppresses antenna gain reduction during radiation of the first obliquely polarized wave. The same is true for radiation of the second obliquely polarized wave, suppressing antenna gain reduction during radiation of the second obliquely polarized wave. Therefore, it is possible to realize antenna device 100 that can switch between linear polarization and circular polarization while suppressing antenna gain reduction during oblique polarization (linear polarization). Furthermore, since there is no need to make the ground layer 112 wider in order to obtain the required antenna gain, the antenna device 100 can be made smaller.

[0080] Next, the effects of the first extension portions 131a to 134a provided in the antenna element 120 of the antenna device 100 according to this embodiment will be described. The first extension portions 131a to 134a are formed by extending from the four corners of the main body portion 121 so as to be perpendicular to the ground layer 112, respectively.

[0081] As a result, the first extensions 131a to 134a function as paths for a strong current that flows through the outer edges 121a to 121d of the rectangular main body 121, and can lengthen the current path.

[0082] Here, in the antenna device 100 according to this embodiment, it is assumed that horizontally polarized waves are radiated by feeding power to each of the feed elements 141 to 144 as shown in Fig. 19. In this case, a current as shown in Fig. 26 is generated in the main body 121, and the strength of the generated current is weak near the lines connecting the feed point of the feed element 142 and the feed point of the feed element 144 (the perpendicular bisectors Lc2 and Lc4 of the outer edges 121b and 121d) and becomes stronger as it approaches the outer edges 121a and 121c of the main body 121.

[0083] Therefore, by arranging the first extension portions 131a to 134a extending toward the ground layer 112 at the four corners of the main body 121, which are nodes of a strong current, the length of the current path can be increased. This allows the main body 121 of the antenna element 120 to be made smaller while ensuring a current path of the required length, and therefore the antenna device 100 can be made more compact.

[0084] Next, the effects of the second extension portions 131b to 134b provided in the antenna element 120 of the antenna device 100 according to this embodiment will be described. Each of the second extension portions 131b to 134b is formed by extending from the extension end (lower end) of the corresponding first extension portion 131a to 134a so as to be parallel to the ground layer 112, and is arranged so as to be point-symmetrical with respect to the center point P2c of the main body portion 121.

[0085] This not only makes it possible to further lengthen the current path, but also forms a capacitance component between the ground plane 112 and each of the second extension portions 131b to 134b, as shown in Fig. 27(A), which lowers the resonant frequency. Although the resonant frequency increases when the size of the main body 121 is reduced, the resonant frequency can be lowered by the capacitance component formed as described above. Therefore, compared to an antenna device employing a conventional patch antenna 150 having equivalent antenna performance as shown in Fig. 27(B), the antenna element 120 can be made smaller in size in accordance with the capacitance component formed, i.e., the antenna device 100 can be made smaller.

[0086] In particular, the four feeding elements 141 to 144 and the four second extension portions 131b to 134b are point-symmetric with respect to the center point P2c of the main body portion 121, which makes it possible to equalize the ratio (axial ratio) of the electric field strength between the horizontal component and the vertical component radiated from the antenna device 100. Therefore, when reading the RFID tag Tg using circularly polarized waves, it is possible to make it difficult for differences in the reading distance to occur depending on the orientation of the RFID tag Tg.

[0087] The antenna element 120 may be configured such that the main body 121, the first extensions 131a to 134a, and the second extensions 131b to 134b are integrally formed from a conductive plate material or the like.

[0088] Assuming that the second extensions 131b to 134b are point-symmetric with respect to the center point P2c of the main body 121, the second extensions 131b to 134b may be formed of a copper foil pattern or the like provided on the front surface of the antenna substrate 110, as can be seen from a first modified example illustrated in Fig. 28(A). The second extensions 131b to 134b may be formed of a copper foil pattern or the like provided on the rear surface of the antenna substrate 110 having the ground layer 112 as an inner layer, as can be seen from a second modified example illustrated in Fig. 28(B). Note that Fig. 28 schematically illustrates a cross section taken along a line connecting the feed element 142 and the feed element 144, and the first and second modified examples employ the main body substrate 120a.

[0089] Furthermore, the second extension portions 131b to 134b may be arranged point-symmetrically with respect to the center point P2c of the main body portion 121. For example, as in a third modified example illustrated in Fig. 29(A), the second extension portions 131b to 134b may be formed by extending from the extending end of the first extension portions 131a to 134a in a direction away from the center of the main body portion 121 so as to be parallel to the ground plane 112. Furthermore, as in a fourth modified example illustrated in Fig. 29(B), the second extension portions 131b to 134b may be formed by extending from the extending end of the first extension portions 131a to 134a in a direction along the outer edges 121a to 121d so as to be parallel to the ground plane 112. Furthermore, for example, each of the second extension portions 131b to 134b may be formed to curve from the extension end of each of the first extension portions 131a to 134a toward the center so as to be parallel to the ground layer 112, as in a fifth modified example illustrated in Figure 29(C).

[0090] 30(A), the main body 121 may be formed so that notches 122a-122d are provided in the outer edges 121a-121d, respectively. This allows the length of the outer edges 121a-121d of the main body 121 to be increased according to the shape of the notches 122a-122d, and also allows the current path length to be increased, thereby allowing the size of the main body 121 to be reduced.

[0091] 30(B), the main body 121 may have an opening 123 formed in the center. In this way, the opening 123 is formed in the center of the main body 121 where a weak current is generated, thereby reducing the weight of the antenna element 120 while suppressing a decrease in antenna gain. The antenna element 120 may be configured with the main body 121 and the first extensions 131a to 134a excluding the second extensions 131b to 134b, or may be configured with only the main body 121 excluding the first extensions 131a to 134a and the second extensions 131b to 134b.

[0092] [Third embodiment] Next, an antenna device according to a third embodiment of the present invention will be described with reference to the drawings. The third embodiment differs from the first embodiment mainly in that a second antenna is newly provided on the antenna substrate 50 in addition to the first antenna consisting of antenna elements 61, 62, 63, and 64. Therefore, components that are substantially the same as those in the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0093] Clothing stores, warehouses, and other locations often use portable wireless tag readers to read product information from wireless tags attached to products for inventory and product inventory checks. In these environments, it is expected that products located over a wide area or a large number of products stored in one location, such as cardboard boxes or shelves, will need to be quickly scanned. In such cases, setting the wireless output (radiated power) of the wireless tag reader to a high level can reduce the number of missed products and improve work efficiency. Meanwhile, in tasks such as receiving and shipping goods, it is expected that workers (users) will only scan products in their hands. If the wireless output is left high, they may end up scanning surrounding wireless tags that do not need to be scanned. In such cases, setting the wireless output of the wireless tag reader to a low level allows for scanning only the products in hand.

[0094] In environments such as inventory management and inventory control, it is important for workers to be able to read data in a comfortable posture. For example, there is a case where a worker needs to individually read some of the RFID tags attached to a large number of garments hung on hangers from a single pipe. In such a case, the RFID reader must be pushed between the garments while setting the radio output to a low level and aligning the direction of the RFID tag reader's radio waves with the direction of the RFID tag (the direction in which the RFID tag faces: the longitudinal direction of the pipe) to perform the reading operation. Unlike simply pointing the RFID tag reader at the product, this type of work often requires workers to perform the work in a relaxed posture, which can be straining for the worker and reduces work efficiency.

[0095] For this reason, the antenna device 40a in this embodiment is configured so that the direction in which the reading surface 4a faces is the first reading direction, and a direction different from the first reading direction (a direction perpendicular to the first reading direction) is the second reading direction, enabling batch reading at long distances based on the first reading direction and individual reading at close distances based on the second reading direction.

[0096] 31, the antenna device 40a is configured such that, in addition to a first antenna (inverted-F antenna) consisting of antenna elements 61, 62, 63, and 64, an antenna element 65 is provided as a second antenna on the first substrate surface 51 using a copper foil pattern or the like. The antenna element 65 configured as the second antenna for short-distance reading is formed so as to have a lower antenna gain than the first antenna (antenna elements 61, 62, 63, and 64).

[0097] The antenna element 65 is disposed relative to the first substrate surface 51 so that its longitudinal direction is along the outer edge 51a of the outer periphery of the first substrate surface 51, which is closest to the line connecting the first conductive portion 61b of the antenna element 61 and the first conductive portion 62b of the antenna element 62. The outer edge 51a is the outer edge on the left side of the outer periphery of the first substrate surface 51 when viewed from the operator holding the grip portion 3.

[0098] When radio waves are radiated by the first antenna (antenna elements 61, 62, 63, and 64), the current generated in the ground layer 52 decreases with increasing distance from each of the antenna elements 61, 62, 63, and 64. Therefore, as shown in FIG. 31 , by arranging the antenna element 65 between the first conductive portion 61b of the antenna element 61 and the first conductive portion 62b of the antenna element 62, it is possible to reduce the effect of the antenna element 65 reducing the radiation intensity of the radio waves radiated from the first antenna. On the other hand, in a configuration in which a patch antenna used as the first antenna is arranged on the first board surface 51 together with a copper foil pattern or the like used as the second antenna, it is necessary to provide installation spaces for the first antenna and the second antenna on the first board surface 51. Therefore, when a second antenna is provided separately, by constructing the first antenna using each antenna element 61 to 64 extending radially as in this embodiment, the antenna substrate 50 can be made smaller than when the first antenna is constructed using a patch antenna, thereby making it possible to miniaturize the antenna device 40a.

[0099] 32 and 33, the antenna device 40a is accommodated in the reading unit 4 such that the first substrate surface 51 faces the inner surface of the reading surface 4a and the outer edge 51a of the first substrate surface 51 is close to and along the inner surface of the left side surface 4c of the reading unit 4. Therefore, in this embodiment, the second reading direction can be the direction in which the left side surface 4c faces (the right direction in FIG. 33).

[0100] As described above, the antenna device 40a housed in the reading unit 4 can selectively switch the antenna that emits radio waves by controlling the distribution unit 22, which functions as an antenna switching unit, by the control unit 11. Therefore, when switching to a state in which radio waves for long-distance reading are emitted in the direction in which the reading surface 4a is facing (first reading direction), power is supplied to the first antenna (antenna elements 61, 62, 63, 64) by the distribution unit 22. Also, when switching to a state in which radio waves for short-distance reading are emitted near the left side surface 4c (second reading direction), power is supplied to the second antenna (antenna element 65) by the distribution unit 22.

[0101] In this embodiment, the control unit 11 receives a predetermined switching instruction from an external device in response to a request from an operator via the communication unit 16, and the antenna that emits radio waves is selectively switched in response to the switching instruction. The switching instruction may be a wireless instruction using Bluetooth (registered trademark) or a wired instruction using a USB cable or the like from the external device. The antenna that emits radio waves may also be selectively switched in response to a predetermined operation on the operation unit 14, reading of an information code for the switching instruction by the information code reading unit 30, or the like.

[0102] In the portable terminal 1 equipped with the antenna device 40a configured in this way, when a switching instruction to select the first antenna in response to a request for long-distance reading from an operator is received via the communication unit 16, power is supplied to the first antenna (antenna elements 61, 62, 63, 64) by the distribution unit 22, as illustrated in Fig. 34(A). Therefore, radio waves for long-distance reading are emitted in the direction in which the reading surface 4a is facing, as illustrated in reading area E1 in Fig. 34(B).

[0103] This allows the portable terminal 1 to collectively read the wireless tags Tg within a wide reading area E1 in the direction in which the reading surface 4a is facing.

[0104] On the other hand, when a switching instruction to select the second antenna in response to a request for short-distance reading from the operator is received via the communication unit 16, power is supplied to the second antenna (antenna element 65) by the distribution unit 22, as shown in Fig. 35(A). Therefore, radio waves for short-distance reading are emitted in the direction in which the left side surface 4c is facing, as shown in a reading area E2 shown in Fig. 35(B).

[0105] This allows the mobile terminal 1 to individually read the RF tags Tg within the narrow reading area E2 when the left side surface 4c is brought close to the mobile terminal 1. For example, even when reading only one of the RF tags Tg attached to each of a large number of clothes hung on hangers, as illustrated in Fig. 36, it is possible to individually read only that RF tag Tg by simply pushing the mobile terminal 1 between the clothes so that the left side surface 4c comes into contact with the RF tag Tg.

[0106] 37(A), the antenna element 65 functioning as the second antenna for short-distance reading does not necessarily have to be provided along the outer edge 51a, and may be arranged along the lower outer edge 51b of the outer periphery of the first substrate surface 51, which is closest to the line connecting the first conductive portion 61b of the antenna element 61 and the first conductive portion 64b of the antenna element 64. Furthermore, the antenna element 65 may be arranged along the right outer edge 51c, which is closest to the line connecting the first conductive portion 63b of the antenna element 63 and the first conductive portion 64b of the antenna element 64, as in the second modified example shown in FIG.

[0107] For example, as illustrated in Figure 38, antenna element 65, which is a second antenna for short-range reading arranged along the outer edge 51b, is housed within the reading unit 4 so as to be close to and along the inner side of the bottom surface 4d of the reading unit 4, thereby making it possible to individually read wireless tags Tg within a narrow area to which the bottom surface 4d is brought close.

[0108] Furthermore, the antenna element 65 that functions as a second antenna for short-distance reading is not limited to being formed so that its longitudinal direction is linear, and may be configured as a meander line, for example, as in the third modified example illustrated in Figure 39.

[0109] [Fourth embodiment] Next, an antenna device according to a fourth embodiment of the present invention will be described with reference to the drawings. The fourth embodiment differs from the first embodiment in that, in order to easily realize polarization switching, a distribution unit 200 that functions as an antenna distribution circuit is employed instead of the distribution unit 22. Therefore, components that are substantially the same as those in the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0110] In order to output circularly polarized waves, horizontally polarized waves, and vertically polarized waves, it is necessary to feed power with various phase differences to the first conductive parts 61b to 64b, which serve as the feeding points of each of the antenna elements 61 to 64. To realize all combinations, three or more feeding patterns are required for each of the first conductive parts 61b to 64b.

[0111] For example, when it is possible to radiate a first obliquely polarized wave, a horizontally polarized wave, a circularly polarized wave, a vertically polarized wave, and a second obliquely polarized wave, conventionally, a distribution unit 400 as schematically illustrated in FIG. 40 is configured to include a single-pole five-contact switch (SP5T) 410, a single-pole four-contact switch (SP4T) 420, a single-pole four-contact switch (SP4T) 430, a distributor 440 that distributes equally, a distributor 450 that distributes with a 90-degree phase difference, and a distributor 460 that distributes with a 180-degree phase difference. In this configuration, the first output terminal 411 of the switch 410 is connected to the fourth input terminal 424 of the switch 420, the second output terminal 412 is connected to the input terminal 441 of the distributor 440, the third output terminal 413 is connected to the input terminal 451 of the distributor 450, the fourth output terminal 414 is connected to the input terminal 461 of the distributor 460, and the fifth output terminal 415 is connected to the fourth input terminal 434 of the switch 430. The distributor 440 has a first output terminal 442 connected to the first input terminal 421 of the switch 420 via a wiring 471, and a second output terminal 443 connected to the first input terminal 431 of the switch 430 via a wiring 472. The distributor 450 has a first output terminal 452 connected to the second input terminal 422 of the switch 420 via a wiring 473, and a second output terminal 453 connected to the second input terminal 432 of the switch 430 via a wiring 474. In distributor 460, first output terminal 462 is connected to third input terminal 423 of switch 420 via wiring 475, and second output terminal 463 is connected to third input terminal 433 of switch 430 via wiring 476. Switch 410 is connected to the power supply side at input terminal 416, switch 420 is connected to first conductive unit 61b at output terminal 425, and switch 430 is connected to first conductive unit 62b at output terminal 435. First conductive unit 61b is connected to first conductive unit 63b via wiring 481 that functions as a phase difference line that generates a phase difference of 180 degrees, and first conductive unit 62b is connected to first conductive unit 64b via wiring 482 that functions as a phase difference line that generates a phase difference of 180 degrees.

[0112] In the distribution section 400 configured in this manner, as illustrated in FIG. 41, the switches 410, 420, and 430 are controlled by the control section 11, and the phases in the first conductive sections 61b to 64b are different, so that the radiation state can be switched to any one of horizontal polarization, vertical polarization, oblique polarization, and circular polarization.

[0113] Incidentally, the wiring 471 and the wiring 472, the wiring 473 and the wiring 474, and the wiring 475 and the wiring 476 must each be equal-length wiring. However, as can be seen from FIG. 40 , because the wirings intersect (see the dashed-line box Ep in FIG. 40 ), the wirings 471 to 476 cannot be arranged on the same board surface, necessitating a multilayer board. Because wiring on a multilayer board utilizes interlayer connections via vias, reflections due to impedance mismatch between the vias and the wiring may increase, resulting in a problem of reduced antenna performance. Furthermore, since a complex equal-length wiring design spanning between layers is required, the design becomes more difficult, increasing design costs, and the increased use of wiring such as coaxial cables also increases costs.

[0114] For this reason, this embodiment employs a distribution unit 200 schematically illustrated in Fig. 42. This distribution unit 200 is configured to include a single-pole four-contact switch (SP4T) 210, a distributor 220 that distributes with a phase difference of 90 degrees, a double-pole double-throw switch (DPDT) 230, a double-pole double-throw switch (DPDT) 240, a single-pole double-throw switch (SPDT) 250, and a single-pole double-throw switch (SPDT) 260.

[0115] In this configuration, the first output terminal 211 of the switch 210 is connected to the first input terminal 231 of the switch 230, the second output terminal 212 is connected to the first input terminal 221 of the divider 220, the third output terminal 213 is connected to the second input terminal 222 of the divider 220, and the fourth output terminal 214 is connected to the first input terminal 241 of the switch 240. The second input terminal 232 of the switch 230 is connected to the first output terminal 223 of the divider 220 via a wiring 271, the first output terminal 233 is connected to the first input terminal 251 of the switch 250 via a wiring 272, and the second output terminal 234 is connected to the second input terminal 252 of the switch 250 via a wiring 273 that functions as a phase difference line that generates a phase difference of 90 degrees with respect to the wiring 272. Switch 240 has second input terminal 242 connected to second output terminal 224 of distributor 220 via wiring 274, first output terminal 243 connected to first input terminal 261 of switch 260 via wiring 275, and second output terminal 244 connected to second input terminal 262 of switch 260 via wiring 276 functioning as a phase difference line that generates a phase difference of 90 degrees with respect to wiring 275. Switch 210 is connected to the power supply side at input terminal 215, switch 250 is connected to first conductive unit 61b at output terminal 253, and switch 260 is connected to first conductive unit 62b at output terminal 263. First conductive unit 61b is connected to first conductive unit 63b via wiring 281 functioning as a phase difference line that generates a phase difference of 180 degrees, and first conductive unit 62b is connected to first conductive unit 64b via wiring 282 functioning as a phase difference line that generates a phase difference of 180 degrees. In this configuration, the switch 210 and the distributor 220 function as a distribution circuit, the switches 230 and 250 and the wirings 272 and 273 function as a first phase circuit, and the switches 240 and 260 and the wirings 275 and 276 function as a second phase circuit.

[0116] In the distribution section 200 configured in this manner, as illustrated in FIG. 43, each switch 210, 230, 240, 250, 260 is controlled by the control section 11, and the phases in each of the first conductive sections 61b to 64b are different, so that the radiation state can be switched to any one of horizontal polarization, vertical polarization, diagonal polarization, and circular polarization.

[0117] In particular, in this embodiment, as can be seen from FIG. 42, the wirings 271 to 276 do not cross each other, so even if the wirings 271 and 274 are configured as equal-length wirings, the wirings 272 and 275 are configured as equal-length wirings, or the wirings 273 and 276 are configured as equal-length wirings, the wirings 271 to 276 can be arranged on the same substrate surface, thereby reducing wiring costs.

[0118] As a first modification of this embodiment, when obliquely polarized waves are not emitted, a distribution unit 300 as shown in Fig. 44 may be employed. The distribution unit 300 is configured to include the above-mentioned distributor 220 and switches 250 and 260, a single-pole double-throw switch (SPDT) 310, and a single-pole double-throw switch (SPDT) 320.

[0119] In this configuration, the switch 310 has an input terminal 311 connected to the first output terminal 223 of the divider 220 via a wiring 331, a first output terminal 312 connected to the first input terminal 251 of the switch 250 via a wiring 332, and a second output terminal 313 connected to the second input terminal 252 of the switch 250 via a wiring 333 that functions as a phase difference line that generates a phase difference of 90 degrees with respect to the wiring 332. The switch 320 has an input terminal 321 connected to the second output terminal 224 of the divider 220 via a wiring 334, a second output terminal 323 connected to the first input terminal 261 of the switch 260 via a wiring 335, and a first output terminal 322 connected to the second input terminal 262 of the switch 260 via a wiring 336 that functions as a phase difference line that generates a phase difference of 90 degrees with respect to the wiring 335. Divider 220 is connected to the power supply side at first input terminal 221, and is connected to a 50 Ω termination resistor at second input terminal 222. In this configuration, divider 220 functions as a distribution circuit, switches 310 and 250 and wirings 332 and 333 function as a first phase circuit, and switches 320 and 260 and wirings 335 and 336 function as a second phase circuit.

[0120] In the distribution section 300 configured in this manner, as illustrated in Figure 45, each switch 310, 320, 250, 260 is controlled by the control section 11, and since the phases in each of the first conductive sections 61b to 64b are different, the radiation state can be switched to any one of horizontal polarization, vertical polarization, and circular polarization.

[0121] In addition, the distribution unit 200 or distribution unit 300, which is a characteristic configuration of this embodiment, is not limited to being adopted as a distribution unit for the antenna device 40, but may also be adopted, for example, as a distribution unit for the antenna device 40a or a distribution unit for the antenna device 100, or as a distribution unit for an antenna device of another configuration.

[0122] [Fifth embodiment] Next, an antenna device according to a fifth embodiment of the present invention will be described with reference to the drawings. The fifth embodiment differs from the first embodiment mainly in that a stress dispersing shape is provided for the second conductive portion of each antenna element. Therefore, the same reference numerals are used for components that are substantially the same as those in the first embodiment, and descriptions thereof will be omitted.

[0123] Generally, antenna elements mounted on antenna substrates are made of thin conductive plates to reduce weight and costs. Because of this structure, if a mobile terminal equipped with an antenna device is subjected to an impact, such as being dropped, stress is concentrated at the soldered connection points on the substrate surface of the antenna element, which is deflected by the impact. Repeated stress concentrations can cause the antenna element to break at the connection points.

[0124] To suppress this, conventionally, structures have been adopted that add dedicated parts to suppress the vibration of the antenna element, or that increase the rigidity of the antenna element by increasing the thickness of the plate material, etc. However, such structures not only hinder the miniaturization and weight reduction of the antenna device, but also increase manufacturing costs, and depending on the structure, there is a possibility that the antenna performance may be degraded.

[0125] For this reason, the antenna element 70 employed in this embodiment is characterized in that a notch is provided in a portion of the second conductive part away from the substrate connection portion using solder or the like as a shape for stress dispersion, thereby suppressing stress concentration at the substrate connection portion.

[0126] Since the four antenna elements employed in this embodiment have the same shape, the antenna element 70 shown in FIG. 46 will be used as an example for explanation. 46, antenna element 70 includes a main body 71 arranged to extend in a strip shape (longitudinal shape) along ground layer 52, a first conductive part 72 connected to one longitudinal end of main body 71 and fed with power via distribution part 22, and a second conductive part 73 connected to the other longitudinal end of main body 71 and having an open end. Similar to each of antenna elements 61 to 64, antenna element 70 is formed by integrally molding main body 71, first conductive part 72, and second conductive part 73 by subjecting a conductive member to sheet metal processing or the like.

[0127] Like each of the antenna elements 61 to 64, each antenna element 70 is arranged so that the longitudinal direction of the main body portion 71 is aligned with four straight lines L1 to L4 that extend radially from a predetermined reference point P1c at equal angles toward the four corners of the first substrate surface 51.

[0128] The first conductive portion 72 and the second conductive portion 73 are each approximately perpendicular to the ground layer 52 (first substrate surface 51) and are arranged in the positional relationship of the above-mentioned first distance D1 and second distance D2, similar to each of the first conductive portions 61b to 64b and each of the second conductive portions 61c to 64c.

[0129] In order to improve antenna characteristics, the first conductive portion 72 is formed so that slits 72a that narrow both left and right ends are provided downward, except for the upper end portion that is continuous with the main body portion 71.

[0130] The second conductive portion 73 is formed so that a pair of notches 74a, 74b are provided as a shape for dispersing stress at a position approximately midway between the main body portion 71 and the first substrate surface 51. The second conductive portion 73 is divided by a line connecting the notches 74a and 74b into a main body side portion 73a that is continuous with the main body portion 71 and a substrate surface side portion 73b that is provided with a pair of substrate connection portions 73c, and a bent portion 75 is formed so that it is continuous by bending at the edge of the substrate surface side portion 73b on the side of the notch 74a as a shape for dispersing stress and increasing rigidity.

[0131] Next, the effect of suppressing stress concentration by the antenna element 70 according to this embodiment will be described with reference to FIGS. In a conventional configuration employing an antenna element 80 in which the pair of notches 74a, 74b and the bent portion 75 are not provided in the second conductive portion 83, when the antenna device is dropped or subjected to an impact, as can be seen in Fig. 47(A), the deflection becomes large at the portion of the second conductive portion 83 that is on the main body portion 81 side, causing stress to concentrate at both substrate connection portions 83c. As a result, excessive stress is repeatedly concentrated at both substrate connection portions 83c, which may cause the antenna element 80 to break at both substrate connection portions 83c.

[0132] In contrast, in antenna element 70 according to this embodiment, when an impact such as that caused by being dropped is applied to the antenna device, stress is dispersed by the pair of notches 74a, 74b and bent portion 75, and therefore, as can be seen in Fig. 47(B), deflection is relatively small at main body side portion 73a of second conductive part 73. In this way, stress concentration is suppressed by the pair of notches 74a, 74b and bent portion 75, so it is possible to realize an antenna device that can improve resistance to impacts such as those caused by being dropped without hindering reductions in size, weight, cost, etc.

[0133] In particular, in this embodiment, the pair of notches 74a, 74b are located approximately midway between the main body portion 71 and the first substrate surface 51. As a result, as illustrated in FIG. 48(A), not only are the notches 74a, 74b able to easily absorb vibration, but also, since they are located away from the substrate connection portion 73c, they can effectively disperse stress when an impact or the like occurs. On the other hand, in a configuration in which the notches 74a, 74b are located near the main body portion 71, as illustrated in FIG. 48(B), the range in which vibration can be absorbed is narrow, and stress dispersion is limited. Furthermore, in a configuration in which the notches 74a, 74b are located near the first substrate surface 51, as illustrated in FIG. 48(C), they are close to the substrate connection portion 73c, and therefore, stress cannot be effectively dispersed. Note that in FIG. 48, for ease of explanation, hatching is applied to areas where stress above a predetermined value occurs when an impact or the like occurs, and the hatching pitch is reduced as the stress increases.

[0134] The stress dispersion shape provided in the second conductive portion 73 is not limited to the above-described pair of notches 74a, 74b, and may alternatively be, for example, only notch 74a or only notch 74b as in a first modified example illustrated in Fig. 49(A). Further, other stress dispersion shapes provided in the second conductive portion 73 may include gentle notches 74c, 74d as in a second modified example illustrated in Fig. 49(B), or an internal notch (opening) 74e as in a third modified example illustrated in Fig. 49(C).

[0135] Furthermore, the shape provided in the second conductive portion 73 for increasing rigidity while dispersing stress is not limited to the above-described bent portion 75, and for example, a bent portion continuing to the edge of the substrate surface side portion 73b on the side of the cutout 74b may be used. Furthermore, the shape provided in the second conductive portion 73 for increasing rigidity while dispersing stress may be a highly rigid shape such as a rib continuing to the substrate surface side portion 73b.

[0136] The characteristic configuration of this embodiment, in which the second conductive portion of each antenna element is provided with a shape for stress dispersion, is not limited to being adopted in an antenna device in which each antenna element is arranged along four straight lines L1 to L4 extending radially from a predetermined reference point P1c, but may also be adopted, for example, in an antenna device in which each antenna element is arranged along the outer edge of the antenna substrate 50.

[0137] The present invention is not limited to the above-described embodiments and modifications, and may be embodied as follows, for example. (1) The antenna device according to the present invention is not limited to being used in a gun grip type portable terminal 1, but may also be used in a portable terminal formed in a substantially flat plate shape, for example. Furthermore, the antenna device according to the present invention is not limited to being used in a portable terminal that functions as an information code reader that optically reads information codes in addition to a wireless tag reader that reads wireless tags Tg, but may also be used in a portable terminal that has only the function of a wireless tag reader, or in a portable terminal that has other functions.

[0138] 1. Mobile devices 11 Control section 20. Wireless tag processing unit 22,200,300 Distribution Department 40, 40a Antenna device 50 Antenna board 50a Dielectric layer 51 First board surface 52 Ground layer (antenna ground) 61~64,65,70 Antenna elements 61a~64a,71 Main body 61b~64b,72 1st conductive part 61c~64c,73 Second conductive part 74a~74d Notch 75 Bend 100 Antenna device 110 Antenna board 112 Ground layer (antenna ground) 120 antenna elements 121 Main body 121a~121d Outer edge 131a~134a 1st extension section 131b~134b 2nd extension section 141~144 Feed element D1 First distance D2 2nd distance Fs composite radio wave L1~L4 straight line Lc1~Lc4 Perpendicular bisector P1c reference point P2c center point

Claims

1. four antenna elements; an antenna substrate on which the four antenna elements can be arranged; An antenna device comprising: The antenna substrate has an antenna ground that extends in a plane on an outer layer or an inner layer, and a dielectric layer is provided along one or both sides of the antenna ground, and a surface of the dielectric layer when viewed in a plane is defined as a first substrate surface, and the four antenna elements are respectively arranged on the first substrate surface, The phase of the power supplied to the four antenna elements is controllable for each of the antenna elements; the antenna element is made by folding a plate-like conductive material, and includes a main body portion arranged along the antenna ground, a first conductive portion connected to one end of the main body portion in the longitudinal direction and receiving power supply with controlled power phase, and a second conductive portion connected to the other end of the main body portion in the longitudinal direction and having an open end; The four antenna elements are arranged such that the longitudinal direction of the main body is aligned with four straight lines extending radially at equal angles from a predetermined reference point on the substrate surface, and a first distance between the first conductive portion and the predetermined reference point is longer than a second distance between the second conductive portion and the predetermined reference point.

2. 2. The antenna device according to claim 1, wherein when the four antenna elements are arranged in a circumferential direction as a first antenna element, a second antenna element, a third antenna element, and a fourth antenna element, the antenna device switches between radiating horizontally polarized waves and radiating vertically polarized waves depending on whether the phase of the power supplied to the first antenna element and the second antenna element is made to differ by 180 degrees from the phase of the power supplied to the third antenna element and the fourth antenna element or the phase of the power supplied to the first antenna element and the fourth antenna element is made to differ by 180 degrees from the phase of the power supplied to the second antenna element and the third antenna element.

3. 3. The antenna device according to claim 2, wherein the antenna device switches between two types of diagonally polarized radiation, depending on whether the phase of the power supplied to the second antenna element is different from the phase of the power supplied to the fourth antenna element by 180 degrees without supplying power to the first antenna element and the third antenna element, or whether the phase of the power supplied to the first antenna element is different from the phase of the power supplied to the third antenna element by 180 degrees without supplying power to the second antenna element and the fourth antenna element.

4. 4. The antenna device according to claim 3, wherein a phase of the power supplied to the first antenna element is set to 0 degrees, power is supplied to the second antenna element with a phase difference of 90 degrees, power is supplied to the third antenna element with a phase difference of 180 degrees, and power is supplied to the fourth antenna element with a phase difference of 270 degrees, thereby radiating circularly polarized waves.

5. an antenna element having a rectangular body; an antenna substrate on which an antenna ground is provided and on which the antenna element is disposed so that the main body is aligned with the antenna ground; An antenna device comprising: the phase of the power fed to the antenna element via four feed elements is controllable for each of the feed elements; The antenna device is characterized in that the four feeding elements are arranged so that their connection positions with the main body are point-symmetrical with respect to the center point of the main body and are located on the perpendicular bisectors of the four outer edges that constitute the outer periphery of the main body.

6. When the four feed elements are arranged in the circumferential direction as a first feed element, a second feed element, a third feed element, and a fourth feed element, 6. The antenna device according to claim 5, wherein radiation of two types of obliquely polarized waves is switched between a case where the phase of the power supplied to the first feed element and the fourth feed element is made to differ by 180 degrees from a phase of the power supplied to the second feed element and the third feed element, and a case where the phase of the power supplied to the first feed element and the second feed element is made to differ by 180 degrees from a phase of the power supplied to the third feed element and the fourth feed element.

7. 7. The antenna device according to claim 6, wherein the antenna device switches between radiating a horizontally polarized wave and radiating a vertically polarized wave depending on whether the phase of the power fed to the second feed element is made to differ by 180 degrees from the phase of the power fed to the fourth feed element without feeding power to the first feed element and the third feed element, or whether the phase of the power fed to the first feed element is made to differ by 180 degrees from the phase of the power fed to the third feed element without feeding power to the second feed element and the fourth feed element.

8. 8. The antenna device according to claim 7, wherein a phase of the power fed to the first feed element is set to 0 degrees, power is fed to the second feed element with a phase difference of 90 degrees, power is fed to the third feed element with a phase difference of 180 degrees, and power is fed to the fourth feed element with a phase difference of 270 degrees, thereby radiating circularly polarized waves.

9. 6. The antenna device according to claim 5, wherein the antenna element further comprises four first extension portions extending from four corners of the main body portion so as to be orthogonal to the antenna ground.

10. the antenna element further includes four second extension portions extending from the first extension portion so as to be parallel to the antenna ground, The antenna device according to claim 9 , wherein the four second extension portions are arranged point-symmetrically with respect to a center point of the main body portion.

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