Antenna equipment

Abstract

To provide an antenna device that ensures broadband characteristics which are characteristics unique to a spiral antenna and furthermore that can materialize thinning of an antenna.SOLUTION: An antenna device according to an embodiment includes a thin spiral antenna, a reflector, and an annular radio wave absorber. The reflector is provided on one side of two opposite radiation directions of radio waves radiated from the spiral antenna. The reflector has a reflecting surface that reflects at least a specific frequency component of radio waves emitted from the spiral antenna in the same phase as the radio waves. The radio wave absorber is provided on the annular outer peripheral surface of the reflective surface of the reflective plate or on the inside thereof.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] For example, an antenna device is known in which a reflector called an artificial magnetic material is arranged facing a thin spiral antenna. When radio waves radiated from the spiral antenna are radiated onto the reflecting surface of the reflector made of an artificial magnetic material, the phase shift of radio waves of a specific frequency is suppressed and they are reflected at 0° (in-phase).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

[0005] The problem that this invention aims to solve is to provide an antenna device that can achieve a thinner antenna while ensuring the broadband characteristics inherent to spiral antennas. [Means for solving the problem]

[0006] According to one embodiment, the antenna device comprises a thin spiral antenna, a reflector, and an annular radio wave absorber. The reflector is provided on one side of the two opposing radiation directions of the radio waves radiated from the spiral antenna. The reflector has a reflective surface that reflects radio waves of at least specific frequency components radiated from the spiral antenna in phase with the radio waves. The radio wave absorber is provided on the annular outer surface of the reflective surface of the reflector or inside it. [Brief explanation of the drawing]

[0007] [Figure 1] A schematic perspective view showing an antenna device according to the first embodiment. [Figure 2] A schematic perspective view showing the antenna assembly of the antenna device shown in Figure 1, separated from the reflector. [Figure 3] A schematic side view showing the antenna device shown in Figure 1. [Figure 4]A schematic diagram showing the vicinity of the central part of the spiral antenna of the antenna device shown in Figure 1. [Figure 5] A schematic top view of the reflector of the antenna device shown in Figure 1. [Figure 6] Enlarged view of the location indicated by the symbol VI in Figure 5. [Figure 7] A graph showing the calculated antenna gain in a certain frequency range for the antenna device according to the first embodiment and the antenna device of the comparative example. [Figure 8] A graph showing the calculated and measured radiation pattern of the comparative antenna device in a certain frequency range. [Figure 9] A graph showing the calculated and measured radiation patterns of the comparative antenna device in a frequency range different from the frequency range shown in Figure 8. [Figure 10] A graph showing the axial ratio (AR) in a certain frequency range for the antenna device according to the first embodiment and the antenna device of the comparative example. [Figure 11] A graph showing the voltage standing wave ratio (VSWR) calculated for a certain frequency range for the antenna device according to the first embodiment and the antenna device of the comparative example. [Figure 12] A schematic exploded perspective view of the antenna device according to the second embodiment. [Figure 13] A schematic perspective view of the antenna device according to the third embodiment. [Figure 14] A schematic partially exploded perspective view of the antenna device according to the fourth embodiment. [Figure 15] A schematic partially exploded perspective view of the antenna device according to the fifth embodiment. [Modes for carrying out the invention]

[0008] The following describes several embodiments of the antenna device 10 with reference to the drawings.

[0009] (First Embodiment) FIG. 1 shows a schematic perspective view of the antenna device 10 according to the present embodiment. FIG. 2 is a schematic exploded perspective view of the antenna device 10 of FIG. 1. FIG. 3 is a schematic side view of the antenna device 10. FIG. 4 is a schematic top view showing a part of a spiral arm extending from the central portion including the feeding point 24a of the spiral antenna 24 of the antenna device 10. FIG. 5 is a top view of the reflector 14 of the antenna device 10. FIG. 6 is an enlarged view of the position indicated by the reference symbol VI in FIG. 5.

[0010] As shown in FIGS. 1 to 3, the antenna device 10 according to the present embodiment includes a spiral antenna assembly 12, a reflector plate 14, an annular radio wave absorber (vibration suppression member) having radio wave absorption properties 16, and a feeding unit 18.

[0011] In the present embodiment, the spiral antenna assembly 12 includes a disk-shaped dielectric substrate 22 and a spiral antenna 24 provided on the dielectric substrate 22.

[0012] The dielectric substrate 22 is formed in a thin disk shape.

[0013] The spiral antenna 24 is printed on the dielectric substrate 22, for example. The spiral antenna 24 is thin, and in the present embodiment, a plane or a substantially plane is defined by the spiral arms of the spiral antenna 24. As shown in FIG. 4, the spiral antenna 24 has a feeding point 24a whose center is connected to the feeding unit 18, and is wound symmetrically with respect to the feeding unit 18. From the feeding point 24a of the spiral antenna 24, the spiral arms extend in two linear forms in opposite directions (for example, in the directions of 0° and 180°). The spiral antenna 24 is formed in a strip shape with a width of Wsp. Although an example in which the width Wsp of the spiral arms of the spiral antenna 24 is constant will be described, it is also suitable that the width is not constant from the feeding point 24a to the distal end and varies variously.

[0014] In this embodiment, the spiral arm of the spiral antenna 24 is described as being formed in the shape of a two-wire Archimedes spiral, for example. The spiral antenna 24 can have any suitable spiral shape, such as a hyperbolic spiral. As shown in Figures 1 to 3, the outer shape of the spiral antenna 24 according to this embodiment is approximately circular.

[0015] The outer diameter of the dielectric substrate 22 of the spiral antenna assembly 12 shown in Figures 1 to 3 is the same as or larger than the outer diameter of the spiral antenna 24. The dielectric substrate 22 and the spiral antenna 24 are arranged on a common central axis, the feed section 18.

[0016] The spiral antenna 24 radiates radio waves in two normal directions N1 and N2 (see Figure 3) defined in relation to the plane of the spiral antenna 24, by being fed at the feed point 24a, which is electrically connected to the feed point 18. That is, the spiral antenna 24 forms a planar radio wave radiating surface with its spiral arms. As shown in Figure 3, the directions along the normal directions N1 and N2 of the spiral antenna 24 are the two opposite radiation directions of the radio waves radiated from the spiral antenna 24. A reflector 14 is provided on the back side (N2 side), which is one side of the normal directions N1 and N2 of the spiral antenna 24, in order to improve the antenna gain on the normal direction N1 side.

[0017] As shown in Figures 2, 3, 5, and 6, in this embodiment, the reflector 14 has a disc-shaped dielectric substrate 32, a conductive patch array 34 provided on the surface of the dielectric substrate 32, and a conductive grounding plate 36 provided on the back surface of the dielectric substrate 32.

[0018] The dielectric substrate 32 of the reflector 14 has a larger outer diameter and is thicker than the dielectric substrate 22 of the spiral antenna assembly 12. The dielectric substrate 32 is formed in a disc shape from, for example, foamed urethane and ferrite. It is preferable that the front and back surfaces of the dielectric substrate 32 are formed parallel to each other. The dielectric substrate 32 may be disc-shaped, but in this embodiment, it is assumed that a circular or donut-shaped substrate is used, in which the opening on the inner circumference is larger than that of the power supply section 18.

[0019] The material of the dielectric substrate 32 can be appropriately selected according to the frequency band used. For example, in the MHz band, a magnetic loss type dielectric such as ferrite can be used. For example, in the GHz band, a dielectric loss type dielectric such as foamed urethane or expanded polystyrene can be used. Furthermore, as in the dielectric substrate 32 of this embodiment, a combination of a magnetic loss type dielectric and a dielectric loss type dielectric can be used.

[0020] In this embodiment, the patch array 34 consists of a number of patches 34a arranged in a row, each having a shape similar to a part of the fan surface of a folding fan. The shape and size of each patch 34a are formed to be the same or approximately the same. Each patch 34a has a width Wp along the circumferential direction passing through its centroid (conductive pin 38, described later) and a length Lp along the radial direction. Preferably, the width Wp and length Lp are approximately the same (Wp / Lp ≈ 1).

[0021] Each patch 34a is formed as a thin, conductive metal plate. Each patch 34a is made of, for example, copper or a copper alloy. Each patch 34a is printed on the surface of the dielectric substrate 32, forming a single plane.

[0022] In this embodiment, the patch array 34 has a first discontinuity ring 42, a second discontinuity ring 44, and a third discontinuity ring 46, formed by a number of patches 34a. The innermost first discontinuity ring 42 is, for example, made up of 22 fan-shaped patches 34a arranged in an annular shape around the dielectric substrate 32, spaced apart by a predetermined distance δp. The second discontinuity ring 44, provided on the outer circumference side of the first discontinuity ring 42, is, for example, made up of 29 fan-shaped patches 34a arranged in an annular shape around the dielectric substrate 32, spaced apart by a predetermined distance δp. The outermost third discontinuity ring 46, provided on the outer circumference side of the second discontinuity ring 44, is, for example, made up of 35 fan-shaped patches 34a arranged in an annular shape around the dielectric substrate 32, spaced apart by a predetermined distance δp. Furthermore, each patch 34a of the first discontinuous ring 42 and each patch 34a of the second discontinuous ring 44, and each patch 34a of the second discontinuous ring 44 and each patch 34a of the third discontinuous ring 46 are separated by a predetermined distance δp in the radial direction of the dielectric substrate 32.

[0023] Furthermore, the distance δp between patches 34a along the circumferential direction of the first discontinuous ring 42, the second discontinuous ring 44, and the third discontinuous ring 46, the distance δp between patches 34a along the radial direction between the first discontinuous ring 42 and the second discontinuous ring 44, and the distance δp between patches 34a along the radial direction between the second discontinuous ring 44 and the third discontinuous ring 46 are smaller than the length Lp along the radial direction of each patch 34a, and also smaller than the width Wp along the circumferential direction of each patch 34a.

[0024] The reflector 14 forms a reflective surface 15 facing the spiral antenna assembly 12 using a dielectric substrate 32 and a patch 34a. The annular inner surface 15a and annular outer surface 15b of the reflective surface 15 are formed from the dielectric substrate 32. That is, the patch 34a is positioned so as not to protrude from the outer and inner surfaces of the dielectric substrate 32.

[0025] Each patch 34a is electrically connected to the ground plate 36 via conductive pins 38 that are arranged through the dielectric substrate 32.

[0026] When the spiral antenna 24 is viewed along the direction of radio wave radiation (normal directions N1, N2), the outer edge of the spiral antenna 24 is flush with the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14, or positioned inward from the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14. In this embodiment, it is preferable that the outer diameter of the dielectric substrate 32 of the reflector 14 is the same as or larger than the outer diameter of the dielectric substrate 22 of the spiral antenna assembly 12. When the outer diameters of the dielectric substrate 32 of the reflector 14, the dielectric substrate 22 of the spiral antenna assembly 12, and the spiral antenna 24 are the same, the outer edge of the spiral antenna 24 is flush with the outer peripheral surface 15b of the dielectric substrate 32 of the reflector 14, or positioned inward from the outer peripheral surface 15b.

[0027] Furthermore, the spiral antenna 24 and the reflector 14 of the spiral antenna assembly 12 are spaced apart. For this reason, it is preferable that the dielectric substrate 22 and the reflector 14 of the spiral antenna assembly 12 are spaced apart. The distance H1 between the spiral antenna 24 of the spiral antenna assembly 12 and the patch 34a of the reflector 14 is formed to an appropriate size. Also, the distance H2 from the top surface of the spiral antenna 24 to the bottom surface of the grounding plate 36, i.e., the thickness of the antenna device 10, is formed to an appropriate size. Distances H1 and H2 can be set as appropriate. The smaller the distance H2, the smaller the size of the antenna device 10 can be.

[0028] As shown in Figures 1 to 3, in this embodiment, the radio wave absorber 16 has a first radio wave absorbing ring 16a and a second radio wave absorbing ring 16b.

[0029] The first radio wave absorbing ring 16a is provided so as to cover the inner circumferential surface 15a of the dielectric substrate 32 of the reflector 14. The second radio wave absorbing ring 16b is provided so as to cover the outer circumferential surface 15b of the dielectric substrate 32 of the reflector 14.

[0030] The materials used for the radio wave absorbing rings 16a and 16b can be selected according to the frequency band used. Preferably, the materials used for the radio wave absorbing rings 16a and 16b are thin, so as not to affect the thickness (height) of the reflector 14 and the radial size of the reflector 14. The material of the radio wave absorbing rings 16a and 16b can be, for example, a magnetic loss type dielectric such as ferrite in the MHz band. For example, in the GHz band, a dielectric loss type dielectric such as foamed urethane or expanded polystyrene can be used. Furthermore, the material of the radio wave absorbing rings 16a and 16b can be a combination of a magnetic loss type dielectric and a dielectric loss type dielectric, as in the dielectric substrate 32 of this embodiment. Alternatively, it may be formed by mixing a magnetic loss type dielectric such as ferrite powder with synthetic rubber.

[0031] As shown in Figure 3, in this embodiment, in order to maintain a predetermined distance between the spiral antenna assembly 12 and the surface of the reflector 14, the dielectric 52 is placed between the spiral antenna assembly 12 and the surface of the reflector 14. As an example, the dielectric 52 can be a dielectric loss type dielectric such as foamed urethane or expanded polystyrene, but a magnetic loss type dielectric may also be used, or a combination of a magnetic loss type dielectric and a dielectric loss type dielectric may be used.

[0032] The radio wave absorbing ring 16b may also be configured to hold both the outer edge of the dielectric substrate 22 of the spiral antenna assembly 12 and the outer peripheral surface 15b of the reflector 14. In this case, the distance between the spiral antenna assembly 12 and the surface of the reflector 14 can be maintained at a predetermined distance, and the dielectric 52 may become unnecessary.

[0033] The feed point (tapered balun, etc.) 18 shown in Figure 2 is provided so as to penetrate the central part of the reflector 14. The feed point 18 has two conductors that are insulated from the ground plate 36 of the reflector 14 and the dielectric substrate 22 of the spiral antenna assembly 12, and are led out above the dielectric substrate 22, electrically connected to the feed point 24a at the center of the spiral antenna 24.

[0034] The spiral antenna 24 is then powered via a feed point (tapered balun, etc.) 18.

[0035] Generally, when power is supplied to the spiral antenna 24 through the feed unit 18, the spiral antenna 24 radiates radio waves in both directions perpendicular to the planar antenna surface (directions indicated by the normal directions N1 and N2 in Figure 3). The antenna characteristics of the spiral antenna 24 (antenna gain, axial ratio, voltage standing wave ratio) are very broadband. When it is necessary to radiate radio waves in a single direction forward (direction N1) from this spiral antenna 24, such a unidirectional radio wave radiation pattern can be achieved by placing a reflector 14 on the back side of the spiral antenna 24.

[0036] Furthermore, by using the reflector 14 according to this embodiment, unlike reflectors formed from general metals, the distance from the spiral antenna 24 can be reduced compared to arranging a metal conductor at approximately 1 / 4 wavelength of the appropriate frequency of the radio wave. In this embodiment, the reflector 14 is made of, for example, an artificial magnetic material (artificial magnet) that reflects the incident radio wave (electromagnetic wave) at the same phase (0°) without shifting the phase of a specific frequency component. At a specific frequency component, the phase of the radio wave incident on the reflective surface 15 of the artificial magnetic material and the reflected wave from the reflective surface 15 of the artificial magnetic material are in phase at the reflective surface 15 (see Non-Patent Literature 2). Therefore, even if the reflective surface 15 of the reflector 14 is at a distance shorter than 1 / 4 wavelength of the appropriate frequency of the radio wave relative to the spiral antenna 24, for example, at a distance of about 1 / 10 wavelength of the appropriate frequency of the radio wave, or even shorter, the radio waves radiated from the spiral antenna 24 are prevented from being canceled out by the reflected wave from the reflective surface 15. In this embodiment, the spiral antenna 24, i.e., the spiral antenna assembly 12, and the surface (reflective surface 15) of the reflector 14 can be brought closer together, for example, to a distance of about 1 / 10 of a wavelength, or even shorter. Therefore, by positioning the reflective surface 15 of the reflector 14 at a distance shorter than 1 / 4 of a wavelength of the radio wave of a suitable frequency from the spiral antenna 24, the antenna device 10 can be miniaturized. For example, the entire antenna device 10 can be made thinner by the difference between about 1 / 4 of a wavelength and about 1 / 10 of a wavelength of the radio wave of a suitable frequency.

[0037] Furthermore, when using such a reflector 14, the phase of the radio waves radiated from the spiral antenna 24 may shift in certain frequency components when reflected by the reflective surface 15 of the reflector 14, as described above.

[0038] Figure 7 shows an example of calculating the antenna gain performance using the antenna device 10 according to this embodiment, and an example of calculating the antenna gain performance using the antenna device of the comparative example, in a specific frequency range (2 GHz to 11 GHz). The antenna device of the comparative example differs from the antenna device 10 according to this embodiment in that it lacks the radio wave absorbing rings 16a and 16b. The antenna device of the comparative example is the same as the antenna device 10 according to this embodiment in all other structural aspects, except for the lack of the radio wave absorbing rings 16a and 16b. Here, the dimensions, dielectric constant, etc., of each part of the antenna device 10 were set appropriately (see, for example, Table I and Table II of Non-Patent Document 2).

[0039] As is clear from Figure 7, the antenna gain (dBi) of the comparative example antenna device showed dips around frequencies of 3.5 GHz, 5.3 GHz, 8.5 GHz, and 10.2 GHz. Therefore, it can be said that the gain of the comparative example antenna device decreased in a certain frequency range. Consequently, even when using a reflector 14 made of artificial magnetic material, it is assumed that it is difficult to maintain the inherent broadband characteristics of the spiral antenna 24 depending on the configuration of the dielectric substrate 32 of the reflector 14 and the patch array 34.

[0040] On the other hand, as shown in Figure 7, the antenna gain of the antenna device 10 according to this embodiment did not experience the gain drop at the aforementioned frequencies compared to the antenna device of the comparative example, and a generally constant gain was obtained over the wide bandwidth inherent to the spiral antenna 24.

[0041] The drop in antenna gain at a specific frequency in the comparative example antenna device, as described above, is presumed to be caused by a phase difference between the radio waves radiated from the spiral antenna 24 and the radio waves reflected by the reflective surface 15 of the reflector 14 at certain frequencies, resulting in the radio waves canceling each other out.

[0042] Generally, the radiation pattern of a spiral antenna 24 in the forward direction (direction of the normal direction N1) shows that the radiation pattern of radio waves in the direction normal to the plane formed by the spiral antenna 24 (0°) is larger than that of other angles. In the radiation pattern of the comparative example antenna device in the forward direction (direction of the normal direction N1), as shown by the solid line in Figure 8, at a certain frequency (GHz band), the radiation pattern of radio waves in the direction normal to the plane formed by the spiral antenna 24 (0°, N1 direction) was observed to decrease compared to the radiation pattern of radio waves shifted by, for example, ±30° (see Fig. 8(a) of Non-Patent Literature 2). As shown by the solid line in Figure 9, at a different frequency (GHz band) than the example shown by the solid line in Figure 8, the radiation pattern of radio waves in the direction normal to the plane formed by the spiral antenna 24 (0°, N1 direction) was observed to decrease compared to the radiation pattern of radio waves shifted by, for example, ±20° (see Fig. 8(b) of Non-Patent Literature 2).

[0043] The reflector 14 described above is provided on the back side of the spiral antenna 24 in this embodiment and comparative example. The reflector 14 is made of an artificial magnetic material (artificial magnet) that has a structure that reflects the incident radio waves (electromagnetic waves) in the same phase without shifting the phase of specific frequency components. However, while adopting a reflector 14 made of an artificial magnetic material in the antenna device 10 can realize the inherent broadband characteristics of the spiral antenna 24, depending on the structure of the reflector 14 made of an artificial magnetic material (the dimensions of the patch array 34 and the number of layers (the same as the size of the dielectric substrate 32)), an unacceptable decrease in antenna gain may occur. As shown in Figure 7, in the antenna device of the comparative example, it is assumed that the reflector 14 causes a phase shift in the reflected radio waves at a certain frequency. In the antenna gain of the antenna device of the comparative example in Figure 7, this phase shift is thought to have caused a drop in antenna gain at a certain frequency.

[0044] The antenna device 10 according to this embodiment has a ring-shaped radio wave absorber 16. The radio wave absorbing rings 16a and 16b of the radio wave absorber 16 absorb radio waves that are out of phase with respect to the radio waves radiated from the spiral antenna 24 that are reflected by the reflector 14, and can suppress the radiation of radio waves reflected by the reflector 14.

[0045] Furthermore, the radio wave absorbing rings 16a and 16b according to this embodiment suppress vibrations of appropriate frequencies, such as generating a vibration damping effect on the reflector 14, and work to suppress resonance of the reflector 14, for example. For this reason, the radio wave absorber 16 (radio wave absorbing rings 16a and 16b) is used as an annular vibration suppression member (resonance suppression member) that suppresses vibrations of the reflector 14, such as resonance. Therefore, by using the radio wave absorbing rings 16a and 16b, it is assumed that the antenna gain from 2 GHz to 11 GHz can be made less variable for each frequency, and a stable antenna gain can be obtained. In other words, the antenna device 10 according to this embodiment can maintain the inherent broadband characteristics of the spiral antenna 24 even when using the same reflector 14 as the antenna device of the comparative example.

[0046] Figure 10 shows an example of calculating the axial ratio (AR) of the antenna device 10 according to this embodiment and the antenna device of the comparative example in a specific frequency range (2 GHz to 11 GHz). Generally, it is considered that the characteristics as circular polarization are good when the axial ratio is 3 dB or less. The axial ratio of the antenna device 10 according to this embodiment and the antenna device of the comparative example are both 3 dB or less in the frequency band range from 2 GHz to 11 GHz, which is substantially the same. Furthermore, the antenna device 10 according to this embodiment maintained a stable axial ratio level of 3 dB or less at frequencies above 3 GHz, for example, compared to the antenna device of the comparative example. Therefore, it can be said that the antenna device 10 according to this embodiment has substantially the same characteristics as, or better than, the antenna device of the comparative example.

[0047] Figure 11 shows a calculation example of the voltage standing wave ratio (VSWR) characteristics of the antenna device 10 according to this embodiment and the antenna device of a comparative example in a specific frequency range (2 GHz to 11 GHz). It can be seen that, similar to the axial ratio characteristics shown in Figure 10, broadband characteristics (voltage standing wave ratio of 2 or less) are obtained for the voltage standing wave ratio characteristics, regardless of the presence or absence of the radio wave absorption rings 16a and 16b.

[0048] As described above, the antenna device 10 according to this embodiment includes a reflector 14 provided on one side of the two opposite radiation directions of the radio waves radiated from the spiral antenna 24, and having a reflective surface 15 that reflects at least specific frequency components of radio waves radiated from the spiral antenna 24 in the same phase as those radio waves. In this embodiment, for example, an artificial magnetic material can be used as the reflector 14. Therefore, the distance between the spiral antenna assembly 12 including the spiral antenna 24 and the reflector 14 can be made smaller than 1 / 4 wavelength, such as about 1 / 10 wavelength, or even shorter, which is shorter than 1 / 4 wavelength of the wavelength corresponding to a specific frequency of the radio waves. Therefore, the antenna device 10 can be made thinner. Furthermore, an annular radio wave absorber 16 is provided on the annular outer surface 15b or inside the dielectric substrate 32 of the reflector 14. In this embodiment, the annular radio wave absorber 16 is provided on the annular outer surface 15b and the annular inner surface 15a of the dielectric substrate 32 of the reflector 14, which are concentric with respect to the central axis. As a result, the radio wave absorber 16 can absorb radio waves that are out of phase with respect to the radio waves radiated from the spiral antenna 24 and reflected by the reflector 14, thereby suppressing the radiation of radio waves reflected by the reflector 14. In addition, the radio wave absorber 16 (radio wave absorbing rings 16a, 16b) is used as an annular vibration suppression member (resonance suppression member) to suppress vibration of the reflector 14, such as resonance. Therefore, it is possible to suppress the drop in antenna gain of the spiral antenna 24 in an appropriate frequency band. In other words, the antenna device 10 according to this embodiment can maintain the inherent broadband characteristics of the spiral antenna 24.

[0049] The reflector 14 is positioned on the back side of the spiral antenna 24, which is one side of the normal directions N1 and N2 of the spiral antenna 24, where the radio waves radiated from the spiral antenna 24 are located. When the spiral antenna 24 is viewed along the direction of radio wave radiation (the direction of the normal directions N1 and N2), the outer edge of the spiral antenna 24 is flush with the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14, or positioned inside the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14. As a result, a greater antenna gain can be obtained due to the reflection of radio waves by the reflecting surface 15 of the reflector 14.

[0050] Therefore, according to this embodiment, it is possible to provide an antenna device 10 that can achieve a thin profile while ensuring the broadband characteristics which are an inherent characteristic of the spiral antenna 24.

[0051] In this embodiment, an example was described in which a radio wave absorbing ring 16a is placed on the inner circumferential surface 15a of the reflective surface 15 of the reflector 14, and a radio wave absorbing ring 16b is placed on the outer circumferential surface 15b of the reflective surface 15 of the reflector 14. That is, an example was described in which a radio wave absorbing ring 16a is placed on the inner circumferential surface 15a, which is the inner edge of the reflective surface 15 of the reflector 14, and a radio wave absorbing ring 16b is placed on the outer circumferential surface 15b, which is the outer edge of the reflective surface 15 of the reflector 14. For example, another radio wave absorbing ring made of the same material as the radio wave absorbing rings 16a and 16b may be placed at an appropriate position between the inner circumferential surface 15a and the outer circumferential surface 15b of the reflective surface 15 of the reflector 14. In this case, the appearance of the other radio wave absorbing ring may be such that it is sandwiched between dielectric substrates 32 formed separately on the inside and outside, or embedded in the dielectric substrate 32 of the reflector 14. In this case, the other radio wave absorbing ring is preferably formed as an annular body that is point-symmetric with respect to the feed point 24a of the spiral antenna 24, or axis-symmetric with respect to the axis of the feed point 18, such as an annular ring centered on the feed point 18. That is, in the antenna device 10 according to this embodiment, the other radio wave absorbing ring is circular in shape centered on the feed point 24a of the spiral antenna 24, and is formed to divide the reflective surface 15 of the reflector 14 into an inner annular region and an outer annular region.

[0052] In the antenna device 10 of this embodiment, the spiral antenna 24 has a two-wire Archimedean spiral shape, with wires extending in two directions from the feed point 24a at the center of the spiral antenna 24. For example, a one-wire spiral antenna 24 with one end as the feed point can be used. In this case, the feed point of the spiral antenna 24 may be located at one end of the center, or conversely, at the other end that is pathwise furthest from the center.

[0053] In the antenna device 10 of this embodiment, an example has been described in which a single-feed spiral antenna 24 is used, in which power is supplied from the feed unit 18 to the feed point 24a at the center of the spiral antenna 24. Although not shown, a double-feed spiral antenna 24 may also be used as the spiral antenna of the antenna device 10 according to this embodiment, for example, in which a pair of feed points are provided at equidistant positions along the spiral arm, away from the center of the spiral antenna 24.

[0054] (Second Embodiment) The antenna device 10 according to the second embodiment will be described with reference to Figure 12. The antenna device 10 according to this embodiment is a modified example of the antenna device 10 according to the first embodiment, and the same reference numerals are used for the same components or components having the same function as those described in the first embodiment, and detailed explanations are omitted.

[0055] As shown in Figure 12, in this embodiment, the antenna device 10 includes a spiral antenna assembly 12, a reflector 14, a radio wave absorber 16, and a power supply unit 18.

[0056] The reflector 14 is formed in multiple layers stacked spaced apart along the direction of radio wave radiation, which is along the normal directions N1 and N2 shown in Figure 3 of the spiral antenna 24. In this embodiment, the reflector 14 consists of two layers: a first reflector 14a and a second reflector 14b. The first reflector 14a and the second reflector 14b differ from the reflector 14 described in the first embodiment in the number of discontinuous rings along the radial direction of the patch array 34, i.e., the number of patches 34a, but their other structures are formed to be similar to those of the reflector 14 described in the first embodiment. The first reflector 14a and the second reflector 14b are formed to be, for example, the same size, and the feed unit 18 is arranged on the central axis. The first reflector 14a and the second reflector 14b are spaced apart by an appropriate distance along the central axis (the axial direction of the feed unit 18). The distance between the first reflector 14a and the second reflector 14b is maintained using a material with a dielectric constant close to that of air, such as foamed resin. Alternatively, the distance between the first reflector 14a and the second reflector 14b can be maintained by directly holding them with radio wave absorbing rings 16a and 16b.

[0057] The antenna device 10 according to this embodiment has radio wave absorbing rings 16a and 16b of annular radio wave absorbers 16 provided on a first reflector 14a and a second reflector 14b, which are formed of, for example, an artificial magnetic material. The radio wave absorbing ring 16a covers the inner circumferential surfaces 15a of the first reflector 14a and the second reflector 14b. The radio wave absorbing ring 16b covers the outer circumferential surfaces 15b of the first reflector 14a and the second reflector 14b. In other words, these radio wave absorbing rings 16a and 16b are provided spanning the first reflector 14a and the second reflector 14b, respectively.

[0058] Furthermore, the radio wave absorbing rings 16a and 16b according to this embodiment can absorb radio waves that are out of phase with respect to the radio waves radiated from the spiral antenna 24 that are reflected by the reflectors 14a and 14b, and can suppress the radiation of radio waves reflected by the reflector 14.

[0059] Furthermore, the radio wave absorbing rings 16a and 16b according to this embodiment suppress vibrations at appropriate frequencies, such as generating a vibration damping effect on the reflectors 14a and 14b, and work to suppress resonance of the reflectors 14a and 14b. For this reason, the radio wave absorber 16 (radio wave absorbing rings 16a and 16b) is used as annular vibration suppression member (resonance suppression member) that suppresses vibrations, such as resonance, of the reflectors 14a and 14b. Therefore, by using the radio wave absorbing rings 16a and 16b, it is assumed that the antenna gain from 2 GHz to 11 GHz can be made less variable for each frequency, and a stable antenna gain can be obtained. In other words, the antenna device 10 according to this embodiment can maintain the inherent broadband characteristics of the spiral antenna 24 even when using the same reflectors 14a and 14b as the antenna device of the comparative example.

[0060] Furthermore, the axial ratio (see Figure 10) and voltage standing wave ratio (see Figure 11) of the antenna device 10 according to this embodiment can be good, as described in the first embodiment, regardless of whether reflectors 14a and 14b are used and whether or not radio wave absorbing rings 16a and 16b are present.

[0061] In this embodiment, the antenna device 10 has been described as having two layers, consisting of a first reflector 14a and a second reflector 14b, but it is also preferable to use more reflectors, such as three layers.

[0062] According to the antenna device 10 of this embodiment, similar to the antenna device 10 described in the first embodiment, it is possible to achieve a thinner design while ensuring the broadband characteristics which are inherent characteristics of the spiral antenna 24.

[0063] (Third embodiment) The antenna device 10 according to the third embodiment will be described with reference to Figure 13. The antenna device 10 according to this embodiment is a modified version of the antenna device 10 according to the first and second embodiments, and the same reference numerals are used for the same components or components having the same function as those described in the first and second embodiments, and detailed descriptions are omitted.

[0064] In this embodiment, the outer circumferential surface 15b of the reflective surface 15 of the reflector plate 14 of the antenna device 10 is formed as a regular polygon such as a square. In this embodiment, the patch 34a is not shaped like a part of the fan surface of the fan described in the first embodiment, but is formed in a rectangular shape such as a roughly square. The inner circumferential surface 15a of the reflective surface 15 of the reflector plate 14 is preferably formed as a roughly square, although it is not shown. In addition, the inner circumferential surface 15a of the reflective surface 15 of the reflector plate 14 may be formed in a regular polygon shape or a circular shape.

[0065] As described above, the radio wave absorbing ring 16a may or may not be provided on the inner circumferential surface 15a of the reflective surface 15 of the reflector 14. Conversely, if a radio wave absorbing ring 16a is provided on the inner circumferential surface 15a of the reflective surface 15 of the reflector 14, then a radio wave absorbing ring 16b may or may not be provided on the outer circumferential surface 15b of the reflective surface 15 of the reflector 14.

[0066] Similar to the spiral antenna assembly 12 described in the first embodiment, the dielectric substrate 22 of the spiral antenna assembly 12 has a circular shape, and the spiral antenna 24 has a roughly circular shape.

[0067] When the spiral antenna 24 is viewed along the direction of radio wave radiation (the normal directions N1 and N2 shown in Figure 3), the outer edge of the spiral antenna 24 is flush with the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14, or positioned inward from the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14. Therefore, the size of the reflecting surface 15 of the reflector 14 is such that the entire outer edge of the spiral antenna assembly 12 is positioned inward from the outer peripheral surface 15b of the reflecting surface 15. The feed point 18 (see Figure 2) penetrates the centroid of the reflecting surface 15 of the reflector 14. The feed point 18 is electrically connected to and fed to the feed point at the center of the spiral antenna 24.

[0068] Furthermore, the regular polygonal reflectors 14, such as squares, shown in Figure 13 may also be formed in multiple layers, such as two layers, as described in the reflectors 14a and 14b in the second embodiment.

[0069] According to the antenna device 10 of this embodiment, similar to the antenna device 10 described in the first and second embodiments, it is possible to achieve a thinner design while ensuring the broadband characteristics that are inherent to the spiral antenna 24.

[0070] (Fourth Embodiment) The antenna device 10 according to the fourth embodiment will be described with reference to Figure 14. The antenna device 10 according to this embodiment is a modified version of the antenna device 10 according to the first to third embodiments, and the same reference numerals are used for members that are the same as or have the same function as those described in the first to third embodiments, and detailed explanations are omitted.

[0071] As shown in Figure 14, the antenna device 10 according to this embodiment further includes a concave body 20 in addition to the antenna device 10 described in the third embodiment. The reflector 14 and the radio wave absorber 16 are housed in the cavity 20a of the concave body 20. In this embodiment, the cavity 20a of the concave body 20 is formed in a rectangular shape to match the outer shapes of the reflector 14 and the radio wave absorber 16. The concave body 20 is formed, for example, in the shape of a bottomed cylinder. The concave body 20 is preferably made of a metal material such as aluminum, copper, or stainless steel.

[0072] The cavity 20a of the concave body 20 can be formed in a circular or polygonal shape to match the outer shapes of the reflector 14 and the radio wave absorber 16. The cavity 20a supports the radio wave absorber 16 when the radio wave absorber 16 is provided on the outer surface 15b of the reflector 14, and supports the outer surface 15b of the reflector 14 when the radio wave absorber 16 is provided in a position inside the outer surface 15b of the reflector 14.

[0073] According to the antenna device 10 of this embodiment, similar to the antenna device 10 described in the first, second, and third embodiments, it is possible to achieve a thinner design while ensuring the broadband characteristics that are inherent to the spiral antenna 24.

[0074] (Fifth embodiment) The antenna device 10 according to the fifth embodiment will be described with reference to Figure 15. The antenna device 10 according to this embodiment is a modified version of the antenna device 10 according to the first to fourth embodiments, and the same reference numerals are used for members that are the same as or have the same function as those described in the first to fourth embodiments, and detailed explanations are omitted.

[0075] As shown in Figure 15, the spiral antenna assembly 12 of the antenna device 10 according to this embodiment has a substantially rectangular spiral antenna 124, rather than a substantially circular spiral antenna 24. In Figure 15, the spiral antenna 124 is an example formed from wire or the like, and is not provided on the dielectric substrate 22 described in the first embodiment. It is also preferable that the spiral antenna 124 is provided on the dielectric substrate 22 described in the first embodiment by printing or the like.

[0076] When the spiral antenna 124 is viewed along the direction of radio wave radiation (normal directions N1, N2), the outer edge of the spiral antenna 124 is flush with the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14, or positioned inward from the outer peripheral surface 15b of the reflecting surface 15 of the reflector 14. In this embodiment, it is preferable that the outer diameter of the dielectric substrate 32 of the reflector 14 is the same as or larger than the length of the diagonal of the spiral antenna 124. When the diagonal lengths of the dielectric substrate 32 of the reflector 14 and the spiral antenna 124 are the same, the outer edge of the spiral antenna 124 is flush with the outer peripheral surface 15b of the dielectric substrate 32 of the reflector 14, or positioned inward from the outer peripheral surface 15b.

[0077] In this embodiment, the spiral antenna 124 has a roughly square shape, but it can be formed as an appropriate roughly regular polygon, such as a roughly regular pentagon or a roughly regular hexagon.

[0078] According to the antenna device 10 of this embodiment, similar to the antenna device 10 described in the first embodiment, it is possible to achieve a thinner design while ensuring the broadband characteristics which are inherent characteristics of the spiral antenna 124.

[0079] According to the antenna device of at least one embodiment described above, it is possible to achieve a thin profile while ensuring the broadband characteristics that are inherent to spiral antennas.

[0080] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0081] 10... Antenna device, 12... Spiral antenna assembly, 14... Reflector, 15... Reflecting surface, 15a... Inner surface, 15b... Outer surface, 16... Radio wave absorber, 16a, 16b... Radio wave absorbing ring, 18... Feed point, 22... Dielectric substrate, 24... Spiral antenna, 24a... Feed point, 32... Dielectric substrate, 34... Patch array, 34a... Patch, 36... Grounding plate, 38... Conductive pin, 42, 44, 46... Discontinuous ring.

Claims

1. A thin spiral antenna, A reflector is provided on one side of the two opposing radiation directions of the radio waves radiated from the spiral antenna, and has a reflective surface that reflects radio waves of at least specific frequency components radiated from the spiral antenna in the same phase as the radio waves. An annular radio wave absorber provided on the annular outer surface or inside thereof of the reflective surface of the reflector, An antenna device having the following features.

2. The outer edge of the spiral antenna and the outer circumferential surface of the reflector are formed in the shape of a substantially regular polygon or a substantially circular shape, respectively. When the spiral antenna is viewed along the direction of radiation of the radio waves, the outer edge of the spiral antenna is flush with the outer peripheral surface of the reflecting surface of the reflector, or positioned inward from the outer peripheral surface of the reflecting surface of the reflector. The antenna device according to claim 1.

3. The reflective surface of the reflector is located inside the outer peripheral surface and includes an annular inner peripheral surface that defines the reflective surface between it and the outer peripheral surface. The aforementioned radio wave absorber is A first radio wave absorbing ring is provided on the outer circumferential surface of the reflective surface of the reflector, A first radio wave absorbing ring is provided on the inner circumferential surface of the reflective surface of the reflector. An antenna device according to claim 1 or claim 2, having the following features.

4. The reflector is formed in multiple layers that are stacked spaced apart along the direction of radiation of the radio waves. The radio wave absorber is provided across the multiple layers of reflectors, The antenna device according to claim 1 or claim 2.

5. The antenna device according to claim 1 or claim 2, having a cavity that supports at least one of the reflector and the radio wave absorber.

6. A spiral antenna defined as a plane, A reflector is provided on one side of the normal direction defined in two directions on the plane of the spiral antenna, and reflects radio waves of at least specific frequency components radiated from the spiral antenna in the same phase as the radio waves. An annular vibration suppressing member provided on the annular outer surface of the reflector or on the inside thereof, which suppresses vibration of the reflector; An antenna device having the following features.

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