Antenna device

Abstract

An antenna device comprises: a flat ground conductor plate; a first antenna element (3; 53) that has a first linear conductor which extends perpendicular to the ground conductor plate and a spiral-shaped second linear conductor which is connected to the first linear conductor and extends parallel to the ground conductor plate; a first power supply point (5; 55) that is grounded to the ground conductor plate and supplies power to the first antenna element; a second antenna element (4; 54) that has a third linear conductor which extends perpendicular to the ground conductor plate and a spiral-shaped fourth linear conductor which is connected to the third linear conductor and extends parallel to the ground conductor plate; and a second power supply point (6; 56) that is grounded to the ground conductor plate and supplies power to the second antenna element. The first antenna element and the second antenna element are arranged in plane symmetry with respect to a virtual plane perpendicular to the ground conductor plate, the first power supply point and the second power supply point are arranged in plane symmetry with respect to the virtual plane, and the electrical length at the shortest distance between the first antenna element and the second antenna element is 1 / 10 or less of the use wavelength.

Description

Antenna device

[0001] The present disclosure relates to an antenna device.

[0002] In recent years, with the development of fields such as wireless communication systems, positioning, radar, and sensing, there has been an increasing demand for high-gain antenna technology. Furthermore, as devices are becoming increasingly miniaturized in each field, there is also an increasing demand for smaller antennas. Non-Patent Document 1 teaches an antenna that attempts to meet these demands. Non-Patent Document 1 discloses an antenna in which four spiral antenna elements fed from a single feed point are arranged in a plane parallel to a ground plane (Fig. 1 in Non-Patent Document 1).

[0003] K. Hirose, M. Nakatsu, and H. Nakano, “Dual-curl antennas for broadband circular polarization,” ELECTRONICS LETTERS, July 2021, Vol. 57 No. 14

[0004] However, the antenna configuration taught in Non-Patent Document 1 has the problem that a phase shift occurs in the currents flowing in the proximity of adjacent antenna elements, and therefore, if the distance between the antenna elements is further shortened, the antenna gain decreases.

[0005] The present disclosure has been made to solve such problems, and aims to provide an antenna device that can be made smaller than conventional technologies while meeting the demand for higher gain.

[0006] One side of an antenna device according to an embodiment of the present disclosure includes a first antenna element having a flat ground conductor plate, a first linear conductor extending perpendicular to the ground conductor plate, a second linear conductor connected to the first linear conductor and extending parallel to the ground conductor plate, a first feeding point grounded to the ground conductor plate and feeding power to the first antenna element, a third linear conductor extending perpendicular to the ground conductor plate, and a fourth linear conductor connected to the third linear conductor and extending parallel to the ground conductor plate. and a second feeding point that is grounded to the ground conductor plate and feeds power to the second antenna element, wherein the first antenna element and the second antenna element are arranged symmetrically with respect to an imaginary plane perpendicular to the ground conductor plate, the first feeding point and the second feeding point are arranged symmetrically with respect to the imaginary plane, and the electrical length at the shortest distance between the first antenna element and the second antenna element is 1 / 10 or less of the wavelength used.

[0007] According to the antenna device according to the embodiment of the present disclosure, it is possible to meet the demand for high gain while being smaller in size than conventional techniques.

[0008] 5A to 5C are diagrams showing directional gains calculated by electromagnetic field simulation to confirm the effects of the antenna device according to the first embodiment. FIG. 5A is a diagram showing directional gains in the ZX plane. FIG. 5B is a diagram showing directional gains in the ZY plane. FIG. 5C is a diagram showing directional gains in the XY plane. FIG. 5A is a diagram showing directional gains in the ZX plane. FIG. 5C is a diagram showing directional gains in the XY plane. FIG. 5A is a table showing averaged values ​​of directional gains in FIGS. 5A to 5C to confirm the effects of the antenna device according to the first embodiment. FIG. 5C is a diagram showing frequency characteristics of averaged gains in the horizontal plane (ZX plane) calculated by electromagnetic field simulation to confirm the effects of the antenna device according to the first embodiment. FIG. 5B is a diagram showing current distributions calculated by electromagnetic field simulation to confirm the operations of the antenna device according to the second embodiment. FIG. 9 is an enlarged diagram showing the operations of the antenna device according to the second embodiment. 12A to 12C are diagrams showing active impedance calculated by electromagnetic field simulation to confirm the operation of the antenna device according to embodiment 2. FIG. 12A to FIG. 12C are diagrams showing directional gain calculated by electromagnetic field simulation to confirm the effects of the antenna device according to embodiment 2. FIG. 12A is a diagram showing directional gain in the ZX plane. FIG. 12B is a diagram showing directional gain in the ZY plane. FIG. 12C is a diagram showing directional gain in the XY plane. FIG. 12B is a diagram showing directional gain in the XY plane. FIG. 12C is a table showing averaged values ​​of the directional gains of FIGS. 12A to 12C to confirm the effects of the antenna device according to embodiment 2. FIG. 12C is a diagram showing the frequency characteristics of the averaged gain in the horizontal plane (ZX plane) calculated by electromagnetic field simulation to confirm the effects of the antenna device according to embodiment 2.

[0009] Various embodiments of the present disclosure will be described in detail below with reference to the drawings. In the drawings, identical or similar parts are designated by identical or similar reference numerals, and redundant explanations of such parts will be omitted. In addition, in this disclosure, the term "or" is used to mean an inclusive logical OR unless otherwise specified.

[0010] Embodiment 1. <Configuration> An antenna device 1 according to embodiment 1 of the present disclosure will be described with reference to FIGS. 1 to 7 . FIG. 1 is a diagram illustrating an example of the configuration of the antenna device 1 according to embodiment 1. In FIG. 1 , λ represents the operating wavelength, which is the free-space wavelength at the design frequency f0. As shown in FIG. 1 , the antenna device 1 according to embodiment 1 includes a ground conductor plate 2, an antenna element (first antenna element) 3, an antenna element (second antenna element) 4, a feed point (first feed point) 5, and a feed point (second feed point) 6. Note that FIG. 1 depicts an imaginary plane 70 for ease of explanation. The ground conductor plate 2 has a flat shape. The imaginary plane 70 is a plane perpendicular to the ground conductor plate 2. Both the antenna element 3 and the antenna element 4 have a spiral shape. In the example of FIG. 1 , both the antenna element 3 and the antenna element 4 have a rectangular spiral shape, and the number of spiral turns of the antenna element 3 and the antenna element 4 is equal, 7 / 4. Antenna element 3 and antenna element 4 are arranged so as to be plane-symmetric with respect to imaginary plane 70. Furthermore, feed point 5 and feed point 6 are also arranged so as to be plane-symmetric with respect to imaginary plane 70.

[0011] The antenna element 3 includes a linear conductor 3a (first linear conductor) extending perpendicular to the ground conductor plate 2, and a linear conductor 3b (second linear conductor) continuing from the linear conductor 3a and extending parallel to the ground conductor plate 2. The linear conductors 3a and 3b may be a single linear conductor as a whole, or may be formed integrally by connecting separate linear conductors. The linear conductor 3b is bent in a plane parallel to the ground conductor plate 2 so that the linear conductor 3b has a spiral shape.

[0012] Similar to the antenna element 3, the antenna element 4 includes a linear conductor 4a (third linear conductor) extending perpendicular to the ground conductor plate 2, and a linear conductor 4b (fourth linear conductor) continuing from the linear conductor 4a and extending parallel to the ground conductor plate 2. The linear conductors 4a and 4b may be a single linear conductor as a whole, or may be formed integrally by connecting separate linear conductors. The linear conductor 4b is bent in a plane parallel to the ground conductor plate 2 so that the linear conductor 4b has a spiral shape.

[0013] One end of the linear conductor 3a is connected to the ground conductor plate 2 via a feeding point 5. Also, one end of the linear conductor 4a is connected to the ground conductor plate 2 via a feeding point 6.

[0014] 2, the antenna element 3 comprises sections of sides 7 to 14. Side 7 corresponds to the linear conductor 3a. Sides 8 to 14 collectively correspond to the linear conductor 3b.

[0015] 2, the antenna element 4 includes sections 15 to 22. Side 15 corresponds to the linear conductor 4a. Sides 16 to 22 collectively correspond to the linear conductor 4b. Each of sides 7 to 22 has an electrical length equal to or less than half the wavelength.

[0016] The side 7 of the antenna element 3 and the side 15 of the antenna element 4 have an electrical length of 0.25 wavelengths or less. If the electrical lengths of the sides 7 and 15 are longer than 0.25 wavelengths, the directional gain on the surface parallel to the ground conductor plate 2 increases and the directional gain in the horizontal plane (ZX plane) decreases. However, by setting the electrical lengths of the sides 7 and 15 to 0.25 wavelengths or less, such a decrease in gain can be suppressed.

[0017] As an example, antenna element 3 and antenna element 4 have a rectangular folded structure in which linear conductors 3b and 4b are folded six times at right angles in the same direction in a plane parallel to ground conductor plate 2. That is, antenna element 3 has a rectangular shape with sides 8 to 14, and antenna element 4 has a rectangular shape with sides 16 to 22, because linear conductors 3b and 4b are folded six times at right angles in the same direction.

[0018] With respect to antenna element 3, side 8 is a side that extends parallel to the X-axis. Side 9 is a side that extends parallel to the Y-axis. Side 10 is a side that extends parallel to the X-axis. Side 11 is a side that extends parallel to the Y-axis. Side 12 is a side that extends parallel to the X-axis. Side 13 is a side that extends parallel to the Y-axis. Side 14 is a side that extends parallel to the X-axis. Antenna element 3 is bent at right angles at six connection points: the connection point between side 8 and side 9, the connection point between side 9 and side 10, the connection point between side 10 and side 11, the connection point between side 11 and side 12, the connection point between side 12 and side 13, and the connection point between side 13 and side 14. Antenna element 3 has multiple bent portions (connection points) bent in this way. Sides 8 to 14 have lengths such that the approximately U-shaped configuration formed by the three sides, sides 12 to 14, is located inside the rectangular shape formed by the four sides, sides 8 to 11, in the XY plane. In this disclosure, "approximately U-shaped" includes cases where one or both of the corners at the ends of the base of the U-shape are 90 degrees. For each of sides 8 to 14, the electrical length of each side (section) is equal to or less than half the wavelength used (half wavelength). Furthermore, the total electrical length of sides 7 to 14 is approximately an integer multiple of half the wavelength used (half wavelength). Here, "approximately" means within a range of 10% above or below the reference value. For example, if 1.5 wavelengths are assumed as an integer multiple of half wavelength, this means that the electrical length is within a range of 1.35 to 1.65 wavelengths.

[0019] On the other hand, with respect to antenna element 4, side 16 is a side that extends parallel to the X-axis. Side 17 is a side that extends parallel to the Y-axis. Side 18 is a side that extends parallel to the X-axis. Side 19 is a side that extends parallel to the Y-axis. Side 20 is a side that extends parallel to the X-axis. Side 21 is a side that extends parallel to the Y-axis. Side 22 is a side that extends parallel to the X-axis. Antenna element 4 is bent at right angles at six connection points: the connection point between side 16 and side 17, the connection point between side 17 and side 18, the connection point between side 18 and side 19, the connection point between side 19 and side 20, the connection point between side 20 and side 21, and the connection point between side 21 and side 22. Antenna element 4 has a plurality of bent portions (connection points) bent in this manner. Sides 16 to 22 have lengths such that the approximately U-shaped configuration formed by the three sides, sides 20 to 22, is located inside the rectangular shape formed by the four sides, sides 16 to 19, in the XY plane. The electrical length of each side (section) of sides 16 to 22 is equal to or less than half the wavelength used (half wavelength). The total electrical length of sides 15 to 22 is approximately an integer multiple of half the wavelength used (half wavelength). Here, "approximately" means that the total is within a range of 10% above or below the reference value. For example, if 1.5 wavelengths is assumed to be an integer multiple of a half wavelength, this means that the total is within a range of 1.35 to 1.65 wavelengths.

[0020] Antenna elements 3 and 4 having such a structure are arranged so as to be plane-symmetrical with respect to imaginary plane 70. In the example of Fig. 1, the shortest distance between antenna elements 3 and 4, i.e., the distance between side 10 of antenna element 3 and side 18 of antenna element 4, is 0.02 wavelengths. The electrical length of antenna element 3 and the electrical length of antenna element 4, i.e., the total electrical length of sides 7 to 14 and the total electrical length of sides 15 to 22, are approximately an integer multiple of half a wavelength.

[0021] Feed point 5 and feed point 6 are excited with equal amplitude and in phase. Feed point 5 is located at a corner of the antenna area, which is a rectangular parallelepiped of the smallest dimensions that can accommodate antenna elements 3 and 4. The expression "located at a corner" includes being located within a range of 0.03 wavelengths from the corner. Feed point 6 is located symmetrically to feed point 5 with respect to an imaginary plane 70 perpendicular to ground conductor plate 2.

[0022] <Operation> Next, the operation of the antenna device 1 according to the first embodiment will be described with reference to Fig. 2 to Fig. 4. Fig. 2 shows the current distribution calculated by an electromagnetic field simulation when the feed points 5 and 6 of the antenna device 1 according to the first embodiment are excited with equal amplitude and in-phase.

[0023] 2, it can be seen that the currents flowing through sides 8, 10, 12, 14, 16, 18, 20, and 22 extending in the X-axis direction are relatively large, while the currents flowing through sides 9, 11, 13, 17, 19, and 21 extending in the Y-axis direction are relatively small. It can be seen that the currents flowing through sides 8, 10, 16, and 18 are particularly large. By setting the electrical length of each side to a half wavelength or less, it is possible to increase the currents flowing through sides extending in the X-axis direction while decreasing the currents flowing through sides extending in the Y-axis direction. This causes the multiple directions in which strong currents flow on the antenna device 1 to coincide in the X-axis direction, resulting in high directional gain in the Z direction.

[0024] Fig. 3 is an enlarged view of sides 10, 14, 18, and 22 in Fig. 2. Of the four sides extending in the X-axis direction, the current flowing through sides 10 and 18 is large, but it can be seen that antenna elements 3 and 4 have plane-symmetric shapes with respect to an imaginary plane 70 perpendicular to ground conductor plate 2, and that by exciting feed points 5 and 6 with equal amplitude and in phase, currents flow in the same direction through sides 10 and 18. As a result, large currents flow through sides 10 and 18, and the currents reinforce each other in phase, so the overall current distribution through sides 10, 14, 18, and 22 can be viewed as the sum of the currents flowing through sides 10 and 18.

[0025] As described above, the antenna device 1 according to the first embodiment has a current distribution similar to that of a three-element array antenna, because the currents flowing are in phase and large at three locations: 1) side 8, 2) side 16, and 3) the positions when sides 10 and 18 are viewed together. This narrows the directivity in the ZY plane and increases the directional gain in the horizontal plane (ZX plane).

[0026] 1, sides 10 and 18 are close to each other at a distance of 0.02 wavelengths, but if the distance between sides 10 and 18 is 0.1 wavelengths (1 / 10 wavelengths) or less, the effect of adding the currents of sides 10 and 18 can be obtained, and the desired effect can be achieved. Note that the distance between sides 10 and 18 is longer than 0 wavelengths to prevent short-circuiting.

[0027] FIG. 4 shows the active impedance of the antenna device 1 according to the first embodiment calculated by electromagnetic field simulation. Here, antenna element 3 and antenna element 4 have a symmetrical structure, and feed point 5 and feed point 6 are excited with equal amplitude and in-phase, so the active impedances of antenna element 3 and antenna element 4 are equal. Therefore, FIG. 4 shows only the active impedance of antenna element 3 when feed point 5 is used as the reference plane. Note that, because feed point 5 and feed point 6 are excited with equal amplitude and in-phase, the active impedance can be calculated as the sum of reflection and coupling. According to the antenna device 1 according to the first embodiment, the electrical length of the antenna is adjusted to be an integer multiple of a half wavelength at the design frequency (f0), and the active impedance is set to a high impedance. This reduces the current flowing through the ground conductor plate 2, causing the ground conductor plate 2 to function as a reflector, thereby increasing the directional gain in the horizontal plane (ZX plane).

[0028] Next, the effects of the antenna device 1 according to the first embodiment will be described with reference to FIGS. 5 to 7. FIGS. 5A to 5C show the directional gain (dBi) of the antenna device 1 according to the first embodiment calculated by electromagnetic field simulation. FIG. 5A shows the directional gain in the ZX plane, FIG. 5B shows the directional gain in the ZY plane, and FIG. 5C shows the directional gain in the XY plane. The values ​​of Eθ and EΦ are displayed as calculation results in each figure. Here, when the vector from the origin to the observation point is defined as the observation vector, θ represents the angle of separation of the observation vector from the Z axis, and Φ represents the angle of separation of the vector obtained by projecting the observation vector onto the XY plane from the X axis. The following descriptions of θ and Φ are also used with the same definitions. The table in FIG. 6 also shows the averaged values ​​of the directional gains in FIGS. 5A to 5C. The averaged value is the average of all angles obtained by adding the power of each component of the true values ​​of Eθ and EΦ. The results in FIGS. 5 and 6 reveal that the directional gain in the ZX plane is the highest.

[0029] FIG. 7 shows the frequency characteristics of the averaged gain in the horizontal plane (ZX plane) of the antenna device 1 according to the first embodiment, and it can be seen that the averaged gain in the horizontal plane is maximum at the design frequency (f0).

[0030] Although the antenna elements 3 and 4 have been described as having a rectangular folded structure in which the linear conductors 3b and 4b are folded six times at right angles in the same direction in a plane parallel to the ground conductor plate 2, the number of folds does not have to be six. Also, in Fig. 1, the electrical length of the linear conductors 3b and 4b of the antenna element 3 in the direction perpendicular to the ground conductor plate 2 (Z direction) is set to 0.07 wavelengths, but the electrical length in the Z direction may be 0.25 wavelengths or less. If the electrical length in the Z direction is greater than 0.25 wavelengths, the directivity in the plane parallel to the ground conductor plate 2 will be increased, resulting in a decrease in directional gain in the horizontal plane (ZX plane).

[0031] The bending angle of antenna elements 3 and 4 may be an acute angle or an obtuse angle, or may be a curved shape. The dimensions of ground conductor plate 2 may be different from those shown in Fig. 1, and the shape may be any shape other than rectangular.

[0032] Second Embodiment. <Configuration> Next, an antenna device 51 according to a second embodiment of the present disclosure will be described with reference to FIGS. 8 to 14 . FIG. 8 is a diagram illustrating an example of the configuration of the antenna device 51 according to the second embodiment. As shown in FIG. 8 , the antenna device 51 includes an antenna element 53 and an antenna element 54. In short, the number of spiral turns of the antenna elements 53 and 54 is equal, greater than 3 / 4 and less than 4 / 4. In the example of FIG. 8 , the antenna elements 53 and 54 have a C-shaped spiral shape in which the linear conductor 53 b of the antenna element 53 and the linear conductor 54 b of the antenna element 54 are bent three times at right angles along the same direction in a plane parallel to the ground conductor plate 52. This will be described in more detail below.

[0033] In FIG. 8 , λ is the wavelength used, which is the free-space wavelength at the design frequency f0. As shown in FIG. 1 , the antenna device 51 according to the second embodiment includes a ground conductor plate 52, an antenna element (first antenna element) 53, an antenna element (second antenna element) 54, a feed point (first feed point) 55, and a feed point (second feed point) 56. Note that FIG. 8 depicts an imaginary plane 71 for ease of explanation. The ground conductor plate 52 has a flat shape. The imaginary plane 71 is a plane perpendicular to the ground conductor plate 52. Both the antenna element 53 and the antenna element 54 have a spiral shape. In the example of FIG. 8 , both the antenna element 53 and the antenna element 54 have a rectangular spiral shape, and the number of turns of the spiral of the antenna element 53 and the antenna element 54 is equal, greater than 3 / 4 and less than 4 / 4. The antenna element 53 and the antenna element 54 are arranged symmetrically with respect to the imaginary plane 71. The feed point 55 and the feed point 56 are also arranged symmetrically with respect to the imaginary plane 71 .

[0034] The antenna element 53 includes a linear conductor 53a extending perpendicular to the ground conductor plate 52 and a linear conductor 53b continuing from the linear conductor 53a and extending parallel to the ground conductor plate 52. The linear conductors 53a and 53b may be a single linear conductor as a whole, or may be formed integrally by connecting separate linear conductors. The linear conductor 53b is bent in a plane parallel to the ground conductor plate 52 so that the linear conductor 53b has a spiral shape.

[0035] Similar to the antenna element 53, the antenna element 54 includes a linear conductor 54a extending perpendicular to the ground conductor plate 52 and a linear conductor 54b continuing from the linear conductor 54a and extending parallel to the ground conductor plate 52. The linear conductors 54a and 54b may be a single linear conductor as a whole, or may be separate linear conductors connected together to form an integrated structure. The linear conductor 54b is bent in a plane parallel to the ground conductor plate 52 so that the linear conductor 54b has a spiral shape.

[0036] One end of the linear conductor 53a is connected to the ground conductor plate 52 via a feeding point 55. One end of the linear conductor 54a is connected to the ground conductor plate 52 via a feeding point 56.

[0037] 9, the antenna element 53 includes sections of sides 57 to 61. Side 57 corresponds to the linear conductor 53a. Sides 58 to 61 collectively correspond to the linear conductor 53b.

[0038] 9, the antenna element 54 includes sections 62 to 66. The side 62 corresponds to the linear conductor 54a. The sides 63 to 66 collectively correspond to the linear conductor 54b. Each of the sides 57 to 66 has an electrical length equal to or less than half a wavelength.

[0039] The side 57 of the antenna element 53 and the side 63 of the antenna element 54 have an electrical length of 0.25 wavelengths or less. If the electrical lengths of the sides 57 and 63 are longer than 0.25 wavelengths, the directional gain on the surface parallel to the ground conductor plate 52 increases, and the directional gain in the horizontal plane (ZX plane) decreases. However, by setting the electrical lengths of the sides 57 and 63 to 0.25 wavelengths or less, such a decrease in gain can be suppressed.

[0040] As an example, antenna element 53 and antenna element 54 have a square C-shaped folded structure in which linear conductors 53b and 54b are folded three times at right angles in the same direction in a plane parallel to ground conductor plate 52. That is, antenna element 53 and antenna element 54 have linear conductors 53b and 54b folded three times at right angles in the same direction, so that antenna element 53 has a square shape with sides 58 to 61, and antenna element 54 has a square C shape with sides 63 to 66.

[0041] With respect to antenna element 53, side 58 is a side that extends parallel to the X-axis. Side 59 is a side that extends parallel to the Y-axis. Side 60 is a side that extends parallel to the X-axis. Side 61 is a side that extends parallel to the Y-axis. Antenna element 53 is bent at right angles at three connection points: the connection point between sides 58 and 59, the connection point between sides 59 and 60, and the connection point between sides 60 and 61. Antenna element 53 has multiple bent portions (connection points) bent in this manner. For each of sides 58 to 61, the electrical length of each side (section) is half the wavelength used (half wavelength) or less. Furthermore, the total electrical length of sides 57 to 61 is approximately an integer multiple of half the wavelength used (half wavelength). Here, "approximately" means within a range of 10% above or below a reference value. For example, if 1.0 wavelength is assumed as an integer multiple of half wavelength, this means that the wavelength is within the range of 0.9 to 1.1 wavelength.

[0042] On the other hand, with respect to antenna element 54, side 63 is a side that extends parallel to the X-axis. Side 64 is a side that extends parallel to the Y-axis. Side 65 is a side that extends parallel to the X-axis. Side 66 is a side that extends parallel to the Y-axis. Antenna element 54 is bent at right angles at three connection points: the connection point between side 63 and side 64, the connection point between side 64 and side 65, and the connection point between side 65 and side 66. Antenna element 54 has multiple bent portions (connection points) bent in this manner. For each of sides 63 to 66, the electrical length of each side (section) is half the wavelength used (half wavelength) or less. Furthermore, the total electrical length of sides 62 to 66 is approximately an integer multiple of half the wavelength used (half wavelength). Here, "approximately" means within a range of 10% above or below a reference value. For example, if 1.0 wavelength is assumed as an integer multiple of half wavelength, this means that the wavelength is within the range of 0.9 to 1.1 wavelength.

[0043] Antenna elements 53 and 54 having such a structure are arranged so as to be plane-symmetrical with respect to imaginary plane 71. In the example of Fig. 8, the shortest distance between antenna elements 53 and 54, i.e., the distance between side 60 of antenna element 53 and side 65 of antenna element 54, is 0.03 wavelengths. The electrical length of antenna element 53 and the electrical length of antenna element 54, i.e., the total electrical length of sides 57 to 61 and the total electrical length of sides 62 to 66, are approximately an integer multiple of half a wavelength.

[0044] Feed point 55 and feed point 56 are excited with equal amplitude and in phase. Feed point 55 is located at a corner of the antenna area, which is a rectangular parallelepiped of the smallest dimensions that can accommodate antenna elements 53 and 54. The expression "located at a corner" includes being located within a range of 0.03 wavelengths from the corner. Feed point 56 is located symmetrically to feed point 55 with respect to an imaginary plane 71 that is perpendicular to ground conductor plate 52.

[0045] <Operation> Next, the operation of antenna device 51 according to embodiment 2 will be described with reference to Figures 9 to 11. Figure 9 shows the current distribution calculated by electromagnetic field simulation when feed point 55 and feed point 56 of antenna device 51 according to embodiment 2 are excited with equal amplitude and in phase.

[0046] 9 shows that the currents flowing through sides 58, 60, 63, and 65 are relatively large. By setting the electrical length of each side to a half wavelength or less, the current flowing through sides extending in the X-axis direction can be increased, while the current flowing through sides extending in the Y-axis direction can be reduced. As a result, the multiple directions in which strong currents flow on antenna device 51 coincide with each other in the X-axis direction, and the directional gain in the Z direction is increased.

[0047] 10 is an enlarged view of sides 60 and 65 in Fig. 9. It can be seen that antenna elements 53 and 54 have plane-symmetric shapes with respect to an imaginary plane 71 perpendicular to ground conductor plate 52, and that by exciting feed points 55 and 56 with equal amplitude and in-phase, currents flow in the same direction in sides 60 and 65. As a result, large currents flow in sides 60 and 65 and reinforce each other in-phase, so the overall current distribution in sides 60 and 65 can be regarded as the sum of the currents flowing in sides 60 and 65.

[0048] As described above, antenna device 51 according to the second embodiment has a current distribution similar to that of a three-element array antenna, because the currents flowing are in phase and large at three locations: 1) side 58, 2) side 63, and 3) the positions when sides 60 and 65 are viewed together. This narrows the directivity in the ZY plane and increases the directional gain in the horizontal plane (ZX plane).

[0049] 8, sides 60 and 65 are close to each other at a distance of 0.03 wavelengths, but if the distance between sides 60 and 65 is 0.1 wavelengths (1 / 10 wavelengths) or less, the effect of adding the currents of sides 60 and 65 can be obtained, and the desired effect can be achieved. Note that the distance between sides 60 and 65 is longer than 0 wavelengths to prevent short-circuiting.

[0050] FIG. 11 shows the active impedance of the antenna device 51 according to the second embodiment, calculated by electromagnetic field simulation. Here, the antenna elements 53 and 54 have a symmetrical structure, and the feed points 55 and 56 are excited with equal amplitude and in-phase, so the active impedances of the antenna elements 53 and 54 are equal. Therefore, FIG. 11 shows only the active impedance of the antenna element 53 when the reference plane is the feed point 55. Note that the feed points 55 and 56 are excited with equal amplitude and in-phase, so the active impedance can be calculated as the sum of reflection and coupling. According to the antenna device 51 according to the second embodiment, the electrical length of the antenna is adjusted to be an integer multiple of a half wavelength at the design frequency (f0), and the active impedance is set to a high impedance. This reduces the current flowing through the ground conductor plate 52, causing the ground conductor plate 52 to function as a reflector, thereby increasing the directional gain in the horizontal plane (ZX plane).

[0051] Next, the effects of the antenna device 51 according to the second embodiment will be described with reference to FIGS. 12 to 14. FIGS. 12A to 12C show the directional gain (dBi) of the antenna device 51 according to the second embodiment calculated by electromagnetic field simulation. FIG. 12A shows the directional gain in the ZX plane, FIG. 12B shows the directional gain in the ZY plane, and FIG. 12C shows the directional gain in the XY plane. The values ​​of Eθ and EΦ are displayed as calculation results in each figure. The table in FIG. 13 also shows the average values ​​of the directional gains in FIGS. 12A to 12C. The average value is the average value of all angles obtained by power-adding the true values ​​of each component of Eθ and EΦ. The results in FIGS. 12 and 13 reveal that the directional gain in the ZX plane is the highest.

[0052] FIG. 13 shows the frequency characteristics of the averaged gain in the horizontal plane (ZX plane) of the antenna device 51 according to the second embodiment, and it can be seen that the averaged gain in the horizontal plane is maximum at the design frequency (f0).

[0053] Although the antenna elements 53 and 54 have been described as having a rectangular folded structure in which the linear conductors 53b and 54b are folded three times at right angles in the same direction in a plane parallel to the ground conductor plate 52, the number of folds does not have to be three. Also, in Figure 8, the electrical length of the linear conductors 53b of the antenna element 53 and the linear conductors 54b of the antenna element 54 in the direction perpendicular to the ground conductor plate 52 (Z direction) is set to 0.09 wavelengths, but the electrical length in the Z direction may be 0.25 wavelengths or less. Furthermore, if the electrical length in the Z direction is greater than 0.25 wavelengths, the directivity in the plane parallel to the ground conductor plate 52 will be increased, resulting in a decrease in directional gain in the horizontal plane (ZX plane).

[0054] The bending angle of the antenna elements 53 and 54 may be an acute angle or an obtuse angle, or the antenna elements may be bent in a curved shape. The dimensions of the ground conductor plate 52 may be different from those shown in FIG. 8, and the shape may be any shape other than a rectangle.

[0055] It is possible to combine the embodiments, and to modify or omit each embodiment as appropriate.

[0056] The antenna device of the present disclosure can be used as an antenna device in various fields such as wireless communication systems where high gain and miniaturization are required.

[0057] 1 Antenna device, 2 Ground conductor plate, 3 Antenna element, 3a Linear conductor, 3b Linear conductor, 4 Antenna element, 4a Linear conductor, 4b Linear conductor, 5 Feed point, 6 Feed point, 7-22 Side, 51 Antenna device, 52 Ground conductor plate, 53 Antenna element, 53a Linear conductor, 53b Linear conductor, 54 Antenna element, 54a Linear conductor, 54b Linear conductor, 55 Feed point, 56 Feed point, 57-66 Side, 70 Virtual plane, 71 Virtual plane.

Claims

1. A first antenna element having a flat ground conductor plate, a first linear conductor extending perpendicular to the ground conductor plate, and a second linear conductor of a spiral shape that is continuous with the first linear conductor and extends parallel to the ground conductor plate; a first feeding point grounded to the ground conductor plate and feeding power to the first antenna element; a third linear conductor extending perpendicular to the ground conductor plate; and a second antenna element having a fourth linear conductor of a spiral shape that is continuous with the third linear conductor and extends parallel to the ground conductor plate; a second feeding point grounded to the ground conductor plate and feeding power to the second antenna element, wherein the first antenna element and the second antenna element are arranged symmetrically with respect to a virtual plane perpendicular to the ground conductor plate, the first feeding point and the second feeding point are arranged symmetrically with respect to the virtual plane, and the electrical length at the shortest distance between the first antenna element and the second antenna element is 1 / 10 or less of the operating wavelength. Antenna device.

2. The antenna device according to claim 1, wherein the second linear conductor and the fourth linear conductor have a plurality of bent portions bent at right angles along the same direction a plurality of times in a plane parallel to the ground conductor plate.

3. The electrical length of all sections between adjacent bent portions of the second linear conductor is 1 / 2 or less of the operating wavelength, and the electrical length of all sections between adjacent bent portions of the fourth linear conductor is 1 / 2 or less of the operating wavelength. The antenna device according to claim 2.

4. The sum of the electrical lengths of the first linear conductor and the second linear conductor is an integer multiple of 1 / 2 of the operating wavelength, and the sum of the electrical lengths of the third linear conductor and the fourth linear conductor is an integer multiple of 1 / 2 of the operating wavelength. The antenna device according to any one of claims 1 to 3.

5. The first feeding point and the second feeding point are excited with equal amplitude and in phase. The antenna device according to any one of claims 1 to 4.

6. The first feeding point is located at a corner of an antenna region that is a rectangular parallelepiped with the minimum dimensions in which the first antenna element and the second antenna element are accommodated, and the second feeding point is located at another corner of the antenna region. The antenna device according to any one of claims 1 to 5.

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