Antenna device

Abstract

To provide an antenna device capable of improving broadband characteristics specific for a spiral antenna while realizing thinning in a configuration for emitting radio waves only to a front side.SOLUTION: An antenna device comprises an antenna assembly, a reflector and a plurality of kinds of patches. The antenna assembly includes a spiral antenna which emits radio waves to a front side and a rear side. The reflector includes a reflection plane opposed to the antenna assembly from the rear side and reflects radio waves, which are emitted from the spiral antenna to the rear side, on the reflection plane. The plurality of kinds of patches are formed on the reflection plane of the reflector. Regarding the plurality of kinds of patches, ratios of a dimension in a circumferential direction with respect to a dimension in a radial direction are identical to each other regardless of the kinds and areas are different for each kind.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to an antenna device.

Background Art

[0002] An antenna device in which a reflector is disposed on the rear side with respect to an antenna assembly including a spiral antenna is used. In this antenna device, the spiral antenna radiates radio waves to both the front side and the rear side, and the reflecting surface of the reflector faces the antenna assembly from the rear side. Then, the radio waves radiated from the spiral antenna to the rear side are reflected by the reflecting surface of the reflector, and the reflected radio waves are emitted from the antenna device to the front side. Thereby, it is realized that radio waves are emitted only from the antenna device to the front side.

[0003] As an antenna device that emits radio waves from a spiral antenna only to the front side as described above, there is one that uses a reflector whose reflecting surface is formed by a metasurface body. In the metasurface body used for the reflector, a plurality of patches (sector patches) formed of metal are disposed on the front surface of the dielectric substrate, and the reflecting surface of the reflector is formed by the front surface of the dielectric substrate and the plurality of patches. By forming the reflecting surface of the reflector with the metasurface body as described above, it becomes possible to ensure antenna characteristics in a wide band, and it becomes possible to ensure the wide-band characteristics inherent to the spiral antenna. Further, by forming the reflecting surface of the reflector with the metasurface body, the separation distance to the rear side from the antenna assembly to the reflecting surface of the reflector can be set to about one-tenth of the wavelength of radio waves of an appropriate frequency included in the used frequency band, and the separation distance from the antenna assembly to the reflecting surface of the reflector becomes short. Thereby, in the antenna device, it becomes possible to reduce the dimension along the front-rear direction, and it becomes possible to realize thinning.

[0004] Here, in an antenna device in which a reflecting surface of a reflector is formed by a metasurface body, if the areas of a plurality of patches arranged on the reflecting surface of the reflector are made the same or substantially the same with respect to each other, the gain, which is one of the antenna characteristics, decreases in a specific frequency range. In an antenna device provided with a spiral antenna, while realizing thinning by forming a reflecting surface with a metasurface body or the like, it is required to improve the broadband characteristics inherent to the spiral antenna.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem to be solved by the present invention is to provide an antenna device capable of improving the broadband characteristics inherent to a spiral antenna while achieving thinning in a configuration that emits radio waves only to the front side.

Means for Solving the Problems

[0008] According to an embodiment, the antenna device includes an antenna assembly, a reflector, and a plurality of types of patches. The antenna assembly includes a spiral antenna that radiates radio waves to the front side and the rear side. The reflector includes a reflecting surface that faces the antenna assembly from the rear side, and reflects the radio waves radiated from the spiral antenna to the rear side by the reflecting surface. The plurality of types of patches are formed on the reflecting surface of the reflector. In the plurality of types of patches, the ratio of the dimension along the circumferential direction to the dimension along the radial direction is the same for each other regardless of the type, and the area is different for each type.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, embodiments and the like will be described with reference to the drawings.

[0011] (First Embodiment) First, as one of the embodiments, the first embodiment will be described. FIG. 1 schematically shows the antenna device 1 according to the first embodiment in a perspective view. FIG. 2 schematically shows the antenna device 1 of FIG. 1 in an exploded perspective view.

[0012] As shown in FIGS. 1 and 2, in the antenna device 1, a virtual central axis C is defined, and the direction along the central axis C is defined as the front-rear direction (the directions indicated by the arrows C1 and C2). Further, in the antenna device 1, one side in the front-rear direction is the front side (arrow C1 side), and the side opposite to the front side is the rear side (arrow C2 side). The front side is also referred to as the front surface side, and the rear side is also referred to as the back surface side. In the antenna device 1, the axial rotation direction of the central axis C is defined as the circumferential direction (the direction indicated by the arrow A). Further, in the antenna device 1, the direction that intersects (is perpendicular or substantially perpendicular) to both the front-rear direction and the circumferential direction is defined as the radial direction. And the side facing the central axis C in the radial direction is the inner circumferential side, and the side away from the central axis C in the radial direction is the outer circumferential side.

[0013] As shown in FIGS. 1 and 2, the antenna device 1 includes an antenna assembly 2 and a reflector 3. In FIG. 2, the reflector 3 is shown in a state separated from the antenna assembly 2. The antenna assembly 2 includes a dielectric substrate 5 and a spiral antenna 6. In an example of FIG. 1, the dielectric substrate 5 is formed in a disc shape or a substantially disc shape, and the dielectric substrate 5 and the spiral antenna 6 are arranged coaxially or substantially coaxially with each other around or substantially around the central axis C. The spiral antenna 6 is formed, for example, by being printed on the dielectric substrate 5. Further, the spiral antenna 6 is formed in a thin shape, and an antenna surface that is a virtual plane or a substantially plane is defined by the spiral antenna 6. The antenna surface defined by the spiral antenna 6 is perpendicular or substantially perpendicular to the front-rear direction (central axis C) and passes through the spiral antenna 6.

[0014] Further, a feeding point 7 is formed on the spiral antenna 6, and the spiral antenna 6 is connected to a feeding unit (not shown) at the feeding point 7. Alternating current power from the feeding unit is supplied to the spiral antenna 6 via the feeding point 7. In an example of FIGS. 1 and 2, the spiral antenna 6 is a single-point feeding type in which only one feeding point 7 is provided. In the spiral antenna 6, the feeding point 7 is located at the center or substantially at the center, and the central axis C passes through the feeding point 7.

[0015] In an example of FIGS. 1 and 2, the spiral antenna 6 has a two-wire type including a pair of spiral arms 8. One end of each of the pair of spiral arms 8 is connected to the feeding point 7. Also, in an example of FIGS. 1 and 2, each of the pair of spiral arms 8 extends from the feeding point 7 in an Archimedean spiral shape, and the pair of spiral arms 8 are supplied with alternating current power via the feeding point 7 (central axis C).

[0016] Note that each of the pair of spiral arms 8 may extend in a spiral shape other than the Archimedean spiral shape. In an example, each of the spiral arms 8 extends in a hyperbolic spiral shape. Also, the width of each of the spiral arms 8 may be constant from the connection end to the feeding point 7 to the distal end opposite to the connection end, or may vary between the connection end to the feeding point 7 and the distal end opposite to the connection end. Also, in an example of FIGS. 1 and 2, the spiral antenna 6 emits radio waves and mainly emits right-handed circularly polarized waves. In an example, each of the spiral arms 8 of the spiral antenna 6 extends in the opposite direction to the example of FIGS. 1 and 2. In this case, the spiral antenna 6 emits radio waves and mainly emits left-handed circularly polarized waves.

[0017] Also, in an example of FIGS. 1 and 2, in the projection from the front-rear direction, the portion surrounded by the outer peripheral edge (outer periphery) of the spiral antenna 6 is circular or substantially circular. And in the projection from the front-rear direction, the outer peripheral edge of the spiral antenna 6 overlaps the outer peripheral edge of the dielectric substrate 5 or is located on the inner peripheral side with respect to the outer peripheral edge of the dielectric substrate 5. For this reason, in the projection from the front-rear direction, the entire spiral antenna 6 is located within the range surrounded by the outer peripheral edge of the dielectric substrate 5. And in the antenna assembly 2, the spiral antenna 6 does not protrude to the outer peripheral side with respect to the dielectric substrate 5.

[0018] In the spiral antenna 6, by supplying alternating current power through the feeding point 7, radio waves are radiated to the front side and the rear side. That is, in the spiral antenna 6, radio waves are radiated in both of the two normal directions with respect to the antenna surface of the spiral antenna 6. Therefore, in the antenna assembly 2, the two directions of the front side (front surface side) and the rear side (rear surface side) become the radiation directions of the radio waves from the spiral antenna 6. And the spiral antenna 6 radiates radio waves in two opposite directions to each other.

[0019] FIG. 3 shows the configuration of the reflector 3. FIG. 3 shows the state of viewing the reflector 3 from the front side. As shown in FIGS. 1 to 3 and the like, the reflector 3 includes a metasurface body 11 and a conductor 12. The reflector 3 is arranged on the rear side with respect to the antenna assembly 2. In the reflector 3, the conductor 12 is attached to the metasurface body 11 from the rear side. And the metasurface body 11 is arranged between the antenna assembly 2 and the conductor 12 in the front-rear direction. The conductor 12 serves as a grounded ground plate. Also, in the reflector 3, a reflecting surface 13 is formed by the front surface of the metasurface body 11. The reflecting surface 13 faces the front side and faces the antenna assembly 2 from the rear side.

[0020] The metasurface body 11 is formed as an artificial magnetic material and includes a dielectric substrate 15 and a patch array 16. In the metasurface body 11, the patch array 16 is arranged on the front surface of the dielectric substrate 15. And the front surface of the dielectric substrate 15 and the patch array 16 form the reflecting surface 13 of the reflector 3.

[0021] In an example of FIGS. 1 to 3, the metasurface body 11 and the conductor 12 are arranged coaxially or substantially coaxially with respect to each other around the central axis C or substantially the central axis. And the metasurface body 11 and the conductor 12 are arranged coaxially or substantially coaxially with respect to the dielectric substrate 5 and the spiral antenna 6. Also, the reflecting surface 13 is arranged coaxially or substantially coaxially with respect to the dielectric substrate 5 and the spiral antenna 6 around the central axis C or substantially the central axis.

[0022] In an example of FIGS. 1 to 3, the dielectric substrate 15 (metasurface body 11) has an outer peripheral edge 17 and an inner peripheral edge 18, and is formed in a ring shape or a donut shape. Then, the outer peripheral edge of the reflection surface 13 is formed by the outer peripheral edge 17 of the dielectric substrate 15, and the inner peripheral edge of the reflection surface 13 is formed by the inner peripheral edge 18 of the dielectric substrate 15. In one example, the inner peripheral edge 18 is not formed on the dielectric substrate 15 (metasurface body 11), and the dielectric substrate 15 may be formed in a disk shape or a substantially disk shape.

[0023] In an example of FIGS. 1 and 2, in a projection from the front-rear direction, each of the outer peripheral edge of the spiral antenna 6 and the outer peripheral edge of the dielectric substrate 5 overlaps with the outer peripheral edge 17 of the dielectric substrate 15 (metasurface body 11), or is located on the inner peripheral side with respect to the outer peripheral edge 17 of the dielectric substrate 15. Therefore, in the projection from the front-rear direction, the entire spiral antenna 6 and the dielectric substrate 5, that is, the entire antenna assembly 2 is located within the range surrounded by the outer peripheral edge 17 of the dielectric substrate 15. And the antenna assembly 2 does not protrude to the outer peripheral side with respect to the dielectric substrate 15 and the metasurface body 11.

[0024] Also, in an example of FIGS. 1 and 2, in a projection from the front-rear direction, each of the outer peripheral edge of the spiral antenna 6 and the outer peripheral edge of the dielectric substrate 5 overlaps with the outer peripheral edge of the reflection surface 13, or is located on the inner peripheral side with respect to the outer peripheral edge of the reflection surface 13. Therefore, in the projection from the front-rear direction, the entire spiral antenna 6 and the dielectric substrate 5, that is, the entire antenna assembly 2 is located within the range surrounded by the outer peripheral edge of the reflection surface 13. And the antenna assembly 2 does not protrude to the outer peripheral side with respect to the reflection surface 13.

[0025] Examples of the material for forming the dielectric substrate 15 include fluororesin-based materials, etc. An appropriate material is selected as the material for forming the dielectric substrate 15 in accordance with the frequency band to be used. For example, if the frequency band to be used is the MHz band, a magnetic type dielectric material such as ferrite can be used for the dielectric substrate 15. Also, if the frequency band to be used is the GHz band, a dielectric type dielectric material such as fluororesin-based can be used for the dielectric substrate 15. Further, it is also possible to use a combination of a magnetic type dielectric material and a dielectric type dielectric material for the dielectric substrate 15.

[0026] The patch array 16 disposed on the front surface of the dielectric substrate 15 is composed of a plurality of patches B. Each of the plurality of patches B is formed of a conductive metal, for example, formed of copper or a copper alloy, etc. Each of the patches B is a thin metal plate, and is formed, for example, by being printed on the front surface of the dielectric substrate 15. In the metasurface body 11 of the reflector 3, a reflecting surface 13 is formed by the front surface of the dielectric substrate 15 and the plurality of patches B. Each of the patches B is a fan-shaped patch that is fan-shaped or substantially fan-shaped in a projection from the front-rear direction.

[0027] In a projection from the front-rear direction, each of the plurality of patches B is disposed in a range between the outer peripheral edge and the inner peripheral edge of the reflecting surface 13, that is, in a range between the outer peripheral edge 17 and the inner peripheral edge 18 of the dielectric substrate 15. For this reason, none of the plurality of patches B protrudes to the outer peripheral side with respect to the reflecting surface 13, nor protrudes to the inner peripheral side with respect to the reflecting surface 13.

[0028] Further, each of the plurality of patches B of the patch array 16 is electrically connected to the conductor 12 via a conductive pin (not shown). The conductive pins that electrically connect each of the patches B to the conductor 12 extend through the inside of the dielectric substrate 15. Also, the reflector 3 is disposed at a distance from the spiral antenna 6 and the antenna assembly 2 toward the rear side. For this reason, the reflecting surface 13 formed by the metasurface body 11 is disposed at a distance from the spiral antenna 6 and the antenna assembly 2 toward the rear side. The distance from the antenna assembly 2 to the reflecting surface 13 toward the rear side is adjusted to an appropriate size.

[0029] Also, in the antenna device 1, the distance from the front surface of the antenna assembly 2 to the rear surface (back surface) of the conductor 12, that is, the distance from the front surface of the antenna assembly 2 to the rear surface (back surface) of the reflector 3 is adjusted to an appropriate size. By reducing the distance from the front surface of the antenna assembly 2 to the rear surface of the reflector 3, the dimensions of the antenna device 1 along the front-rear direction are reduced, and the antenna device 1 is made thinner.

[0030] < Mystery tag remains unchanged as it's not clear what it represents. Please provide more context if needed. Note that, in one example, a dielectric (not shown) is disposed in the gap between the antenna assembly 2 and the reflecting surface 13 of the reflector 3. In this case, the dielectric is formed from a dielectric loss type dielectric material such as urethane foam and styrofoam, a magnetic loss type dielectric material such as ferrite, or a combination thereof.

[0031] Also, in the antenna device 1, a power feeding portion (not shown) such as a taper balun penetrates the reflector 3 and the dielectric substrate 5 of the antenna assembly 2 in the front-rear direction. Then, the power feeding portion is connected to the feeding point 7 of the spiral antenna 6 in a state of penetrating the reflector 3 and the dielectric substrate 5. The power feeding portion penetrates the reflector 3 while being electrically insulated from the conductor 12 and the plurality of patches B of the patch array 16.

[0032] FIG. 4 shows an enlarged view of a part of the reflecting surface 13 of the reflector 3. In FIG. 4, the reflecting surface 13 is shown as viewed from the front side. As shown in FIGS. 3 and 4 and the like, the plurality of patches B of the patch array 16 are composed of a plurality of types of patches. In an example of FIGS. 3 and 4, the patch array 16 is composed of four types of patches B1 to B4. In the following description, when the type of the patch B is not particularly distinguished, it is indicated as "patch B" and the like, and when the type is distinguished, it is indicated as "patch B1" and "patch B2" and the like.

[0033] In the plurality of types of patches B, the area is different for each type. For this reason, the area of each of the patches B1 is different from the areas of each of the patches B2 to B4, and the area of each of the patches B2 is different from the areas of each of the patches B3 and B4. And the area of each of the patches B3 is different from the area of each of the patches B4. In an example of FIGS. 3 and 4, among the four types of patches B1 to B4, in ascending order of area, they are patches B1, B2, B3, and B4.

[0034] In each of the patches B, a dimension W along the circumferential direction and a dimension L along the radial direction are defined. And in each of the patches B, a ratio ε (= W / L) of the dimension W to the dimension L is defined. In the plurality of types of patches B, regardless of the type, the ratio ε is the same for each other. In one example, in each of the plurality of types of patches B, the aforementioned ratio ε is 1. In this case, in each of the patches B, the dimension L along the radial direction is the same size as the dimension W along the circumferential direction.

[0035] Due to the configuration as described above, each shape of patch B1 is a similar shape to each shape of patches B2 to B4, and each shape of patch B2 is a similar shape to each shape of patches B3 and B4. And each shape of patch B3 is a similar shape to each shape of patch B4. Among the four types of patches B1 to B4, in the order of decreasing dimension L along the radial direction, they are patches B1, B2, B3, B4, and in the order of decreasing dimension W along the circumferential direction, they are patches B1, B2, B3, B4. Note that for patches B1, B2, B3, B4, the dimension L along the radial direction is also denoted as L1, L2, L3, L4 respectively. Similarly, for patches B1, B2, B3, B4, the dimension W along the circumferential direction is also denoted as W1, W2, W3, W4 respectively.

[0036] In an example such as FIGS. 3 and 4, in the patch array 16, a plurality of each of the four types of patches B1 to B4 are provided. Also, on the reflecting surface 13, a plurality of patch rows Q are formed by a plurality of types of patches B. In an example such as FIGS. 3 and 4, four patch rows Q1 to Q4 are formed as the patch rows Q. In each of the patch rows Q, a plurality of patches B are arranged along the circumferential direction (the direction around the axis of the central axis C). Also, in each of the patch rows Q, a plurality of patches B are arranged over the entire circumference in the circumferential direction.

[0037] On the reflecting surface 13, a plurality of patch rows Q are arranged side by side in the radial direction. In an example such as FIGS. 3 and 4, on the reflecting surface 13, a plurality of patch rows Q are arranged concentrically with the central axis C as the center or substantially the center. And the four patch rows Q1 to Q4 are arranged in the order of patch rows Q1, Q2, Q3, Q4 from the inner circumferential side to the outer circumferential side.

[0038] In each of the patch rows Q, a plurality of patches B having the same area and type with respect to each other are arranged along the circumferential direction. In an example such as FIGS. 3 and 4, in the patch row Q1, only a plurality of patches B1 are arranged along the circumferential direction, and in the patch row Q2, only a plurality of patches B2 are arranged along the circumferential direction. And in the patch row Q3, only a plurality of patches B3 are arranged along the circumferential direction, and in the patch row Q4, only a plurality of patches B4 are arranged along the circumferential direction. In an example such as FIG. 3, 16 patches B1 are arranged in the patch row Q1, 22 patches B2 are arranged in the patch row Q2, 29 patches B3 are arranged in the patch row Q3, and 35 patches B4 are arranged in the patch row Q4, respectively.

[0039] Due to the configuration as described above, in the four patch rows Q1 to Q4, the areas and types of the plurality of patches B to be arranged are different from each other. And in each of the plurality of patch rows Q, the areas and types of the plurality of patches B to be arranged are different from those of the patch rows Q adjacent in the radial direction. For example, in the patch row Q1, the patch row Q2 arranged adjacent to the outer peripheral side has different areas and types of the patches B to be arranged. And in the patch row Q3, the patch row Q2 arranged adjacent to the inner peripheral side and the patch row Q4 arranged adjacent to the outer peripheral side have different areas and types of the patches B to be arranged. Also, in an example such as FIGS. 3 and 4, the patch rows Q arranged on the outer peripheral side have larger-area patches B arranged. For this reason, in the innermost patch row Q1, the patch B1 having the smallest area among the patches B1 to B4 is arranged. And in the outermost patch row Q4, the patch B4 having the largest area among the patches B1 to B4 is arranged.

[0040] In each of the plurality of patch columns Q, the plurality of patches B are arranged along the circumferential direction at a constant circumferential pitch Pw. And in each of the patch columns Q, the patches B adjacent to each other in the circumferential direction are arranged with an interval dw. In each of the patch columns Q, the sum of the dimension W of the patch B along the width direction and the interval dw becomes the circumferential pitch Pw. Here, in the patch columns Q1, Q2, Q3, Q4, let the intervals between the patches B adjacent to each other in the circumferential direction be dw1, dw2, dw3, dw4, respectively. In the patch columns Q1, Q2, Q3, Q4, the circumferential pitch Pw in the arrangement of the plurality of patches B is W1 + dw1, W2 + dw2, W3 + dw3, W4 + dw4, respectively.

[0041] Also, in an example such as FIGS. 3 and 4, the circumferential pitch Pw in the arrangement of the plurality of patches B is the same size for the plurality of patch columns Q with respect to each other. For this reason, in the four patch columns Q1 to Q4, the circumferential pitch Pw is the same size with respect to each other. That is, in the patch columns Q1 to Q4, the plurality of patches B are arranged at the same circumferential pitch Pw with respect to each other. Therefore, for the patch columns Q1 to Q4, the relationship of W1 + dw1 = W2 + dw2 = W3 + dw3 = W4 + dw4 = Pw holds.

[0042] Here, for the four types of patches B1 to B4, as described above, the patches are B1, B2, B3, B4 in ascending order of the dimension W along the circumferential direction, and the relationship of W4 > W3 > W2 > W1 holds with respect to the dimension W along the circumferential direction. For this reason, since the circumferential pitch Pw is the same size for the plurality of patch columns Q with respect to each other, with respect to the interval dw between the patches B adjacent to each other in the circumferential direction, the relationship of dw1 > dw2 > dw3 > dw4 holds. Therefore, in an example such as FIGS. 3 and 4, the closer the patch column Q is to the outer peripheral side, the smaller the interval dw between the patches B adjacent to each other in the circumferential direction.

[0043] Further, on the reflecting surface 13, a plurality of patch rows Q are arranged side by side in the radial direction at a constant radial pitch Pl. And on the reflecting surface 13, the patch rows Q adjacent to each other in the radial direction are arranged with an interval dl. Here, let dlk be the interval dl between the patch row Qk and the patch row Qk+1 arranged adjacent to the outer peripheral side of the patch row Qk. In an example such as FIGS. 3 and 4, k is any natural number greater than or equal to 1 and less than or equal to 3. And the interval dl1 between the patch rows Q1 and Q2, the interval dl2 between the patch rows Q2 and Q3, and the interval dl3 between the patch rows Q3 and Q4 are respectively defined.

[0044] In an example of FIGS. 3 and 4, the sum of the interval dlk between the patch rows Qk and Qk+1 and the dimension Lk+1 along the radial direction of the patch Bk+1 arranged in the patch row Qk+1 is the radial pitch Pl. And the radial pitch Pl is constant as described above. Therefore, in an example of FIGS. 3 and 4, the relationship of dl1 + L2 = dl2 + L3 = dl4 + L4 = Pl holds.

[0045] Also, in the four types of patches B1 to B4, as described above, in the order of decreasing dimension L along the radial direction, they are the patches B1, B2, B3, B4, and regarding the dimension W along the radial direction, the relationship of L4 > L3 > L2 > L1 holds. Therefore, since the radial pitch Pl is constant, regarding the interval dl between the patch rows Q adjacent to each other in the radial direction, the relationship of dl1 > dl2 > dl3 holds.

[0046] In an example, the circumferential pitch Pw in the arrangement of the plurality of patches B in each patch row Q is the same size as the radial pitch Pl. Also, in an example, the circumferential pitch Pw in each patch row Q is the same size as the radial pitch Pl, and for each of the plurality of types of patches B, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is 1. However, in any case, for the plurality of types of patches B, the ratio of the dimension W along the circumferential direction to the dimension L along the radial direction is the same for each other regardless of the type, and the area is different for each type.

[0047] In this embodiment, as described above, when AC power from the power supply unit is supplied to the spiral antenna 6, radio waves are radiated from the spiral antenna 6 to the front side and the rear side. In the antenna device 1, the reflector 3 reflects the radio waves radiated from the spiral antenna 6 to the rear side, with the reflecting surface 13. Then, the radio waves reflected by the reflecting surface 13 are emitted from the antenna device 1 to the front side. As a result, it is realized that radio waves are emitted only from the antenna device 1 to the front side. That is, it becomes possible to emit the radio waves from the spiral antenna 6 only in one direction.

[0048] Also, in this embodiment, the reflecting surface 13 of the reflector 3 is formed by the metasurface body 11. In the metasurface body 11, the reflecting surface 13 is formed by arranging a patch array 16 composed of a plurality of patches (sector patches) B on the front surface of the dielectric substrate 15. By forming the reflecting surface 13 of the reflector 3 with the metasurface body 11 as described above, it becomes possible to ensure antenna characteristics such as gain, axial ratio, input impedance, VSWR (voltage standing wave radio), and antenna efficiency over a wide band, and to ensure the wide-band characteristics inherent in the spiral antenna 6. That is, even in a configuration where radio waves are emitted only to the front side, wide-band characteristics can be ensured.

[0049] Also, by forming the reflecting surface 13 of the reflector 3 with the metasurface body 11 that becomes an artificial magnetic material as described above, in the reflecting surface 13, the incident radio waves (electromagnetic waves) are reflected in the same phase without shifting the phase, at least in a specific frequency component. As a result, at least for a specific frequency component, the phase of the radio waves incident on the reflecting surface 13 formed from the metasurface body 11 is the same as the phase of the reflected wave from the reflecting surface 13. Such a phenomenon is also shown in Non-Patent Document 1.

[0050] Here, unlike this embodiment, it is assumed that a reflector and a reflecting surface are formed from a general metal or the like. In this case, the distance from the antenna assembly to the reflecting surface of the reflector on the rear side is set to about one-quarter of the wavelength of an appropriate radio wave included in the frequency band to be used, and it is necessary to prevent the radio wave radiated from the spiral antenna from being canceled by the reflected wave from the reflecting surface. On the other hand, in this embodiment, in the reflecting surface 13 formed by the metasurface body 11, radio waves are reflected at least for specific frequency components without a phase shift. Therefore, even if the distance from the antenna assembly 2 to the reflecting surface 13 of the reflector 3 on the rear side is made shorter than one-quarter of the wavelength of an appropriate radio wave included in the frequency band to be used, it is possible to prevent the radio wave radiated from the spiral antenna 6 from being canceled by the reflected wave from the reflecting surface 13.

[0051] Therefore, in this embodiment, it is possible to shorten the distance from the antenna assembly 2 to the reflecting surface 13 of the reflector 3 on the rear side. In one example, the distance from the antenna assembly 2 to the reflecting surface 13 can be set to about one-tenth of the wavelength of an appropriate radio wave included in the frequency band to be used. As a result, in the antenna device 1, it is possible to reduce the dimension along the front-rear direction, and it is possible to realize a thinner profile.

[0052] Also, in this embodiment, the patch array 16 arranged on the reflecting surface 13 is composed of a plurality of types of patches B. And in the plurality of types of patches B, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is the same for each other regardless of the type, and the area is different for each type. By configuring the plurality of types of patches B as described above, in the antenna device 1, a decrease in the gain (antenna gain), which is one of the antenna characteristics, in a specific frequency range can be effectively suppressed. By suppressing the decrease in the gain in the specific frequency range, the broadband characteristics inherent to the spiral antenna 6 are improved.

[0053] Here, as verification related to the embodiment, for each of the antenna device 1 having the configuration of the present embodiment and the antenna device having the configuration of the comparative example, antenna characteristics including gain were calculated. In the calculation of the antenna characteristics, the dimensions and dielectric constant, etc. of each component of the antenna device were appropriately set. At this time, for example, the dimensions and dielectric constant, etc. were set with reference to Non-Patent Document 1. Also, in any configuration of the embodiment and the comparative example, a configuration was adopted in which the reflecting surface of the reflector is formed from the metasurface body, and the reflecting surface was formed by arranging a plurality of patches on the front surface of the dielectric substrate. Then, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction was made the same for all the patches arranged on the reflecting surface, and the ratio ε was made 1 for all the patches.

[0054] However, in the configuration of the embodiment, a plurality of types of patches having different areas from each other were arranged on the reflecting surface, and the plurality of types of patches were arranged on the reflecting surface in the same arrangement as an example in FIGS. 3 and 4. For this reason, in each of the four patch rows in the configuration of the embodiment, a plurality of patches having the same area and type as each other were arranged along the circumferential direction. And in the four patch rows, the areas and types of the plurality of patches to be arranged were made different from each other, and patches having a larger area were arranged in the patch row arranged on the outer peripheral side. Also, in the configuration of the embodiment, the circumferential pitch Pw in the arrangement of the plurality of patches was made the same size in the four patch rows, and the circumferential pitch Pw in the arrangement of the plurality of patches in each of the patch rows was made the same size as the radial pitch Pl.

[0055] On the other hand, in the configuration of the comparative example, only one type of patch was arranged on the reflecting surface. Therefore, for all the patches arranged on the reflecting surface, the areas were made the same with respect to each other. And for all the patches arranged on the reflecting surface, the dimension W along the circumferential direction was made the same with respect to each other, and the dimension L along the radial direction was made the same with respect to each other. Note that also in the configuration of the comparative example, similar to the configuration of the embodiment, on the reflecting surface, four patch rows were arranged side by side in the radial direction. And the number of patches arranged in each of the four patch rows was made the same with respect to each other in the configuration of the comparative example and the configuration of the embodiment. Also, in the configuration of the comparative example, the above-described circumferential pitch Pw and radial pitch Pl were set to the same magnitude as that of the configuration of the embodiment.

[0056] FIG. 5 shows an example of the calculation results of the gain characteristics (relationship) with respect to frequency for each of the antenna device 1 having the configuration of the embodiment and the antenna device having the configuration of the comparative example. FIG. 6 shows an enlarged view of the range surrounded by the frame α1 in the example of FIG. 5. In FIGS. 5 and 6, the horizontal axis represents the frequency in units of GHz, and the vertical axis represents the gain in units of dBi. In FIG. 5, the relationship of the gain with respect to the frequency in the frequency range of 2 GHz or more and 11 GHz or less is shown, and in FIG. 6, the frequency range of 4 GHz or more and 7 GHz or more in FIG. 5 is enlarged and shown. Also, in FIGS. 5 and 6, the change in the gain in the configuration of the embodiment is shown by a solid line, and the change in the gain in the configuration of the comparative example is shown by a broken line.

[0057] Also, in the verification, in both the configuration of the embodiment and the configuration of the comparative example, the spiral antenna was configured to mainly radiate a right-handed circularly polarized wave as a radio wave. Therefore, in FIGS. 5 and 6, the gain for the right-handed circularly polarized wave is shown. Also, in FIGS. 5 and 6, the gain in the direction where the angle θ is 0° is shown. Here, the angle θ is an angle defined in an antenna device that emits radio waves only to the front side. And the front side corresponds to the direction where the angle θ is 0°, and the rear side corresponds to the direction where the angle θ is 180°.

[0058] As a result of calculating the gain in the verification, as shown in FIGS. 5 and 6, in the configuration of the comparative example, the gain decreased in each of the frequency ranges of 4.5 GHz and its vicinity, and 6.3 GHz and its vicinity. On the other hand, in the configuration of the embodiment, the decrease in gain was suppressed in any of the two frequency ranges where the gain decreased in the configuration of the comparative example. That is, in the configuration of the embodiment, the gain was improved compared to the configuration of the comparative example in each of the frequency ranges of 4.5 GHz and its vicinity, and 6.3 GHz and its vicinity. For this reason, in a plurality of types of patches, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is made the same for each other regardless of the type, and the area is made different for each type, so that the decrease in gain in a specific frequency range is appropriately suppressed.

[0059] Also, in the verification, for each of the antenna device 1 having the configuration of the embodiment and the antenna device having the configuration of the above-described comparative example, as antenna characteristics, the respective characteristics of the axial ratio with respect to frequency and the input impedance Zin were calculated. FIG. 7 shows an example of the calculation result of the characteristic (relationship) of the axial ratio with respect to frequency for each of the antenna device 1 having the configuration of the embodiment and the antenna device having the configuration of the comparative example. In FIG. 7, the horizontal axis represents the frequency in units of GHz, and the vertical axis represents the axial ratio in units of dB. FIG. 7 shows the relationship of the axial ratio with respect to frequency in the frequency range of 2 GHz or more and 11 GHz or less, and shows the axial ratio in the direction where the angle θ is 0°. Also, in FIG. 7, the change in the axial ratio in the configuration of the embodiment is indicated by a solid line, and the change in the axial ratio in the configuration of the comparative example is indicated by a broken line.

[0060] Here, regarding the axial ratio, when the axial ratio is 3 dB or less, it is considered that the characteristics as circularly polarized waves are good. As a result of calculating the axial ratio in the verification, as shown in FIG. 7, in the frequency range of 2 GHz or higher and 11 GHz or lower, the frequency bands where the axial ratio becomes 3 dB or less are substantially common to each other in the configuration of the embodiment and the configuration of the comparative example. That is, the characteristics of the axial ratio with respect to frequency showed the same tendency in the configuration of the embodiment and the configuration of the comparative example. Therefore, in the configuration in which a plurality of types of patches having different areas are provided with respect to each other, and the configuration in which only one type of patch is provided, the characteristics of the input impedance Zin with respect to frequency showed the same tendency.

[0061] FIG. 8 shows an example of the calculation results of the characteristics (relationships) of the input impedance Zin with respect to frequency for each of the antenna device 1 having the configuration of the embodiment and the antenna device having the configuration of the comparative example. In FIG. 8, the horizontal axis represents the frequency in units of GHz, and the vertical axis represents the input impedance Zin in units of Ω. In FIG. 8, the relationship of the input impedance Zin with respect to frequency in the frequency range of 2 GHz or higher and 11 GHz or lower is shown. And in FIG. 8, the characteristics with respect to frequency are shown for each of the real component Rin and the imaginary component Xin of the input impedance Zin. Also, in FIG. 8, the changes in the real component Rin and the imaginary component Xin of the input impedance Zin in the configuration of the embodiment are shown by solid lines, and the changes in the real component Rin and the imaginary component Xin of the input impedance Zin in the configuration of the comparative example are shown by broken lines.

[0062] As a result of calculating the input impedance Zin in the verification, as shown in FIG. 8, in the frequency range of 2 GHz or higher and 11 GHz or lower, the characteristics of each of the real component Rin and the imaginary component Xin of the input impedance Zin with respect to frequency showed the same tendency in the configuration of the embodiment and the configuration of the comparative example. Therefore, in the configuration in which a plurality of types of patches having different areas are provided with respect to each other, and the configuration in which only one type of patch is provided, the characteristics of the input impedance Zin with respect to frequency showed the same tendency.

[0063] As described above, as a result of the calculations in the verification, in the configuration of the embodiment, compared with the configuration of the comparative example, the gain reduction in a specific frequency range is appropriate, and antenna characteristics other than the gain, such as the axial ratio and the input impedance Zin, have the same tendency as the configuration of the comparative example. Therefore, in the configuration of the embodiment, the broadband characteristics inherent to the spiral antenna are improved compared with the configuration of the comparative example.

[0064] Also, in the present embodiment, a radio wave absorber or the like is not attached to the metasurface body 11 that forms the reflecting surface 13. For this reason, in the antenna device 1, a phenomenon in which radio waves are absorbed by a radio wave absorber in a specific frequency range does not occur. Therefore, a decrease in antenna efficiency, which is one of the antenna characteristics, in a specific frequency range is effectively suppressed. As a result, the broadband characteristics inherent to the spiral antenna 6 are further improved.

[0065] Also, in an example of the present embodiment, in each of the plurality of patch rows Q, a plurality of patches B are arranged along the circumferential direction at a constant circumferential pitch Pw, and the circumferential pitch Pw has the same size for the plurality of patch rows Q. And the plurality of patch rows Q are arranged side by side in the radial direction at a constant radial pitch Pl. By arranging the plurality of patches B on the reflecting surface 13 in this way, the configuration of the embodiment is realized without greatly changing the arrangement and configuration of the plurality of patches B from the configuration in which only one type of patch, such as the configuration of the comparative example described above, is provided. Therefore, it is possible to improve the broadband characteristics inherent to the spiral antenna 6 without greatly changing the arrangement and configuration of the plurality of patches B from the configuration in which only one type of patch is provided.

[0066] (Modification example) FIG. 9 schematically shows the antenna device 1 according to the first modification example in an exploded perspective view. In FIG. 9, the reflector 3 is shown in a state separated from the antenna assembly 2. In the above-described embodiments and the like, in the projection from the front-rear direction, the portion surrounded by the outer peripheral edge (outer periphery) of the spiral antenna 6 is circular or substantially circular. In this modification example, as shown in FIG. 9, in the projection from the front-rear direction, the portion surrounded by the outer peripheral edge of the spiral antenna 6 is polygonal. In an example of FIG. 9, in the projection from the front-rear direction, the portion surrounded by the outer peripheral edge of the spiral antenna 6 is square or substantially square.

[0067] Also, in the above-described embodiment, the spiral antenna 6 is of a two-wire type and a single-point feeding type, but it is not limited thereto. In a certain modification example, the spiral antenna 6 is of a single-wire type having only one spiral arm 8. In this case, in the spiral antenna 6, the spiral arm 8 extends spirally, for example, from the central portion (central axis C) of the antenna assembly 2. In this modification example, a feeding point is formed at one end of the spiral arm 8. Therefore, in the spiral arm 8, a feeding point is formed at one end located at the central portion of the antenna assembly 2 or at the distal end on the side opposite to the central portion.

[0068] Also, in another certain modification example, in the spiral antenna 6, a pair of spiral arms 8 are provided and a pair of feeding points are formed, and the spiral antenna 6 is of a two-point feeding type. In this case, corresponding feeding points are provided one by one for the pair of spiral arms 8. In this modification example, each of the pair of spiral arms 8 is connected to one of the corresponding pair of feeding points at the end closer to the central portion of the antenna assembly 2. And alternating current power is supplied to each of the pair of spiral arms 8 through one of the pair of feeding points to which it is connected.

[0069] Here, even if the configuration of the antenna assembly 2 is changed as in the above-described modification example including the first modification example, the reflector 3 including the metasurface body 11 has the same configuration as in the above-described embodiment and the like. For this reason, in any of the above-described modification examples, in a plurality of types of patches B, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is the same for each other regardless of the type, and the area is different for each type. Therefore, any of the modification examples exhibits the same operations and effects as in the first embodiment and the like. That is, in any of the modification examples, in a specific frequency range, a decrease in the gain, which is one of the antenna characteristics, is effectively suppressed, and the broadband characteristics inherent to the spiral antenna 6 are improved.

[0070] Also, in the above-described embodiment and the like, in the reflector 3, the metasurface body 11 has a single-layer structure, but it is not limited thereto. In a certain modification example, two or more layers of metasurface bodies 11 are provided on the reflector 3, and in the reflector 3, two or more layers of metasurface bodies 11 are laminated in the front-rear direction. In this modification example, each of the two or more layers of metasurface bodies 11 has the same configuration as the metasurface body 11 in the above-described embodiment and the like. For this reason, in each of the two or more layers of metasurface bodies 11, a reflecting surface is formed by the front surface of the dielectric substrate 15 and the patch array 16. And in each reflecting surface 13 of the two or more layers of metasurface bodies 11, a plurality of types of patches B are arranged in the same manner as in the above-described embodiment and the like.

[0071] Even in this modification example in which two or more layers of metasurface bodies 11 are laminated, a plurality of types of patches B are arranged on each reflecting surface 13 of the metasurface body 11. And in the plurality of types of patches B, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is the same for each other regardless of the type, and the area is different for each type. Therefore, this modification example also exhibits the same operations and effects as in the first embodiment and the like. That is, even in this modification example, in a specific frequency range, a decrease in the gain, which is one of the antenna characteristics, is effectively suppressed, and the broadband characteristics inherent to the spiral antenna 6 are improved.

[0072] Also, in the first embodiment and the like, in the plurality of patch rows Q formed on the reflecting surface 13, the patches B having a larger area are arranged in the patch row Q disposed on the outer peripheral side, but it is not limited thereto. FIG. 10 schematically shows a reflector 3 of the antenna device 1 according to the second modification in a perspective view. As shown in FIG. 10, in this modification, as in the example of FIGS. 3 and 4, four patch rows Q1 to Q4 are arranged on the reflecting surface 13 of the metasurface body 11. The patch rows Q1 to Q4 are arranged in the order of patch rows Q1, Q2, Q3, Q4 from the inner peripheral side to the outer peripheral side.

[0073] However, in this modification, in the patch row Q1, only a plurality of patches B4 are arranged along the circumferential direction, and in the patch row Q2, only a plurality of patches B3 are arranged along the circumferential direction. In the patch row Q3, only a plurality of patches B2 are arranged along the circumferential direction, and in the patch row Q4, only a plurality of patches B1 are arranged along the circumferential direction. Therefore, in this modification, the patches B having a larger area are arranged in the patch row Q disposed on the outer peripheral side.

[0074] FIG. 11 schematically shows a reflector 3 of the antenna device 1 according to the third modification in a perspective view. As shown in FIG. 11, also in this modification, on the reflecting surface 13 of the metasurface body 11, the patch rows Q1, Q2, Q3, Q4 are arranged in order from the inner peripheral side to the outer peripheral side. However, in this modification, in the patch row Q1, only a plurality of patches B3 are arranged along the circumferential direction, and in the patch row Q2, only a plurality of patches B1 are arranged along the circumferential direction. In the patch row Q3, only a plurality of patches B4 are arranged along the circumferential direction, and in the patch row Q4, only a plurality of patches B2 are arranged along the circumferential direction. Therefore, in this modification, in each of the patch rows Q, the areas and types of the plurality of patches B arranged are randomly changed from the patch rows Q adjacent in the radial direction.

[0075] In either the second modification example of FIG. 10 or the third modification example of FIG. 11, in each of the plurality of patch rows Q, a plurality of patches B having the same area and type with respect to each other are arranged along the circumferential direction, similar to the first embodiment and the like. And in each of the plurality of patch rows Q, the areas and types of the plurality of patches B to be arranged are different from those of the patch rows Q adjacent in the radial direction.

[0076] Also, in the above-described embodiments and the like, although the configuration is such that four (four rows) of patch rows Q are arranged in the circumferential direction, the number of patch rows Q arranged in the circumferential direction may be two or three, or may be five or more. However, regardless of the number of patch rows Q arranged in the circumferential direction, in each of the plurality of patch rows Q, a plurality of patches B having the same area and type with respect to each other are arranged along the circumferential direction. And in each of the plurality of patch rows Q, the areas and types of the plurality of patches B to be arranged are different from those of the patch rows Q adjacent in the radial direction.

[0077] Also, in the above-described embodiment, on the reflecting surface 13, four types of patches B1 to B4 having different areas from each other are arranged. As long as the patch array 16 arranged on the reflecting surface 13 is composed of a plurality of types of patches B having different areas from each other, the number of types of patches B arranged on the reflecting surface 13 may be two or three, or may be five or more. In a modification example, only two types of patches B1 and B2 having different areas from each other are arranged on the reflecting surface 13. And on the reflecting surface 13, a patch row Q in which only the patch B1 is arranged in the circumferential direction and a patch row Q in which only the patch B2 is arranged in the circumferential direction are alternately arranged in the radial direction.

[0078] Also, in a modification example, on the reflecting surface 13, a plurality of patch rows are arranged side by side in the circumferential direction. And in each of the plurality of patch rows, a plurality of patches B having the same area and type with respect to each other are arranged along the radial direction. And in each of the plurality of patch rows, the areas and types of the plurality of patches B to be arranged are different from those of the patch rows adjacent in the circumferential direction.

[0079] Here, even if the arrangement of the plurality of types of patches B on the reflecting surface 13 of the metasurface body 11 is changed as in the above-described modification examples including the second modification example and the third modification example, a plurality of types of patches B are arranged on the reflecting surface 13 of the metasurface body 11 in the same manner as in the above-described embodiments and the like. And in any of the above-described modification examples, among the plurality of types of patches B, the ratio ε of the dimension W along the circumferential direction to the dimension L along the radial direction is the same for each other regardless of the type, and the area is different for each type. Therefore, in any of the modification examples, the same operations and effects as in the first embodiment and the like are exhibited. That is, in any of the modification examples, in a specific frequency range, the decrease in the gain, which is one of the antenna characteristics, is effectively suppressed, and the broadband characteristics inherent in the spiral antenna 6 are improved.

[0080] According to at least one of these embodiments or examples, a plurality of types of patches are formed on the reflecting surface of the reflector, and in the plurality of types of patches, the ratio of the dimension along the circumferential direction to the dimension along the radial direction is the same for each other regardless of the type, and the area is different for each type. Thereby, in a configuration that emits radio waves only to the front side, it is possible to provide an antenna device capable of realizing thinning while improving the broadband characteristics inherent in the spiral antenna.

[0081] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0082] 1…Antenna device, 2…Antenna assembly, 3…Reflector, 6…Spiral antenna, 11…Metasurface body, 16…Patch array, B (B1~B4)…Patch, Q (Q1~Q4)…Patch row, W (W1~W4)…Dimension, L (L1~L4)…Dimension, Pw…Circumferential pitch, Pl…Radial pitch.

Claims

1. An antenna assembly comprising a spiral antenna that radiates radio waves to the front side and the rear side, a reflector having a reflecting surface facing the antenna assembly from the rear side, the reflector reflecting the radio waves radiated from the spiral antenna to the rear side with the reflecting surface, a plurality of types of patches formed on the reflecting surface of the reflector, wherein the ratio of the dimension along the circumferential direction to the dimension along the radial direction is the same for each other regardless of the type, and a plurality of types of patches having different areas for each type, An antenna device comprising the above.

2. On the reflecting surface, a plurality of patch rows are arranged side by side in the radial direction by the plurality of types of patches, In each of the plurality of patch rows, a plurality of patches among the plurality of types of patches are arranged along the circumferential direction, The antenna device according to Claim 1.

3. In each of the plurality of patch rows, the plurality of patches are arranged along the circumferential direction with a constant circumferential pitch, The circumferential pitch in the arrangement of the plurality of patches is the same size for each of the plurality of patch rows, The plurality of patch rows are arranged side by side in the radial direction with a constant radial pitch, The antenna device according to Claim 2.

4. In each of the plurality of patch rows, a plurality of patches having the same area and type for each other are arranged along the circumferential direction, In each of the plurality of patch rows, the area and type of the plurality of patches to be arranged are different from those of the patch rows adjacent in the radial direction, The antenna device according to Claim 2 or 3.

Images