Antenna device and method for designing antenna device

Abstract

To provide an antenna device capable of adjusting the radiation state of radio waves while suppressing the increase in size.SOLUTION: An antenna device 10 has a dipole-type antenna element 20 extending in the Z-axis direction and a pair of unpowered elements 25a, 25b, each of which is installed on both sides of the antenna element 20 in a direction intersecting the Z-axis direction, for example, in the X-axis direction orthogonal to the Z-axis direction. Slots 26a and 26b, which are elongated openings, are formed in each of the pair of unpowered elements 25a and 25b.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an antenna device and a method for designing an antenna device. [Background technology]

[0002] Patent Document 1 shows an omnidirectional antenna including a dielectric substrate whose length direction is perpendicular to the ground, and two parasitic elements disposed at positions away from the front and back surfaces of the dielectric substrate in the vertical direction of the substrate surface. A half-wave dipole antenna extending in the length direction is formed on one side of the dielectric substrate in the width direction, and an earth plane is formed on the other side of the dielectric substrate in the width direction. The earth plane acts as a reflector and thus affects the directivity of the dipole antenna in the horizontal plane. The two parasitic elements adjust the directivity in this horizontal plane by guiding radio waves from the dipole antenna. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-311511 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a dipole antenna is provided that extends in the vertical direction, the radiation state of radio waves in the horizontal plane of the dipole antenna, i.e., the radiation direction and radiation intensity, can be adjusted by placing a parasitic element near the dipole antenna in the horizontal direction. In this case, the effect of adjusting the radiation state can be enhanced by determining the vertical length of the parasitic element based on an integer multiple of the half wavelength of the radio waves.

[0005] On the other hand, for example, an antenna device for a mobile communication base station may radiate radio waves in multiple frequency bands, i.e., multiple wavelengths. In particular, in such a case, in order to effectively adjust the radiation state of radio waves in multiple frequency bands, it may be necessary to install multiple parasitic elements with different lengths, etc. As a result, there is a risk that the antenna size will increase.

[0006] An object of the present invention is to provide an antenna device capable of adjusting the radiation state of radio waves while suppressing an increase in size.

[0007] The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0008] An antenna device according to an embodiment includes a dipole antenna element extending in a first direction, and a first parasitic element and a second parasitic element respectively disposed on both sides of the antenna element in a second direction intersecting the first direction. A slot is formed in each of the first parasitic element and the second parasitic element. Effect of the Invention

[0009] To briefly explain the effect obtained by a representative embodiment of the invention disclosed in this application, in an antenna device, it becomes possible to adjust the radiation state of radio waves while suppressing an increase in size. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view showing an example of a basic configuration of an antenna device according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram for explaining an example of the operation of a parasitic element in which a slot is formed in FIG. [Diagram 3] 2 is a schematic diagram illustrating an example of the operation of the antenna device of FIG. 1. [Figure 4]2 is a perspective view showing an example of the configuration of a main part of an entire antenna device to which the basic configuration of FIG. 1 is applied. [Diagram 5] 5 is a diagram showing the results of verifying the directivity on the horizontal plane in the antenna device of FIG. 4. [Figure 6] 4 is a flow chart showing an example of a method for designing the antenna device according to the first embodiment. [Figure 7] 11 is a perspective view showing an example of a basic configuration of an antenna device according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiment, the same members are generally designated by the same reference numerals, and the repeated description will be omitted.

[0012] (Embodiment 1) <Basic configuration of antenna device> Fig. 1 is a perspective view showing an example of a basic configuration of an antenna device according to a first embodiment. In the specification, as shown in Fig. 1, a direction (second direction) that intersects with the Z-axis direction (first direction) as a reference and that is perpendicular to the Z-axis direction is defined as an X-axis direction (fourth direction). A direction that is perpendicular to the Z-axis direction (first direction) and also perpendicular to the X-axis direction (fourth direction) is defined as a Y-axis direction (third direction). For example, the Z-axis direction is perpendicular to the ground, and the X-axis and Y-axis directions are horizontal to the ground.

[0013] The antenna device 10 shown in Fig. 1 includes an antenna element 20 and a pair of parasitic elements 25a, 25b. The antenna element 20 is a dipole-type element extending in the Z-axis direction. An AC power source 21 of a predetermined frequency band is fed between the two poles of the antenna element 20. This causes the antenna element 20 to emit vertically polarized waves, i.e., radio waves whose electric field oscillates in the Z-axis direction. The length L1 of the antenna element 20 in the Z-axis direction is determined to reflect the wavelength of the radio waves, specifically, half the wavelength.

[0014] A pair of parasitic elements (first and second parasitic elements) 25a, 25b are not fed and are installed on both sides of the antenna element 20 in a direction (second direction) intersecting the Z axis, for example, the X axis direction (fourth direction). That is, the angle between the line connecting the center points of the pair of parasitic elements 25a, 25b and the Z axis direction is, for example, 90°. However, the angle is not necessarily limited to 90°. Each of the parasitic elements 25a, 25b is, for example, a conductive plate having a surface consisting of the Z axis direction and the Y axis direction. The length of each of the parasitic elements 25a, 25b in the Z axis direction is L0, and the width of each of the parasitic elements 25a, 25b in the Y axis direction is W0. The parasitic elements 25a, 25b play a role in adjusting the radiation state of the radio wave, for example, the radiation direction and radiation intensity.

[0015] Specifically, the size of each of the parasitic elements 25a, 25b, particularly the length L0 in the Z-axis direction and the distance D0 in the X-axis direction between each of the parasitic elements 25a, 25b and the antenna element 20, are appropriately determined to reflect the wavelength of the radio wave, specifically, half the wavelength. Then, depending on the length L0, the distance D0, etc., the parasitic elements 25a, 25b can function as a reflecting element that reflects the radio wave from the antenna element 20, or as a waveguide element that guides the radio wave from the antenna element 20. As a result, it becomes possible to adjust the radiation direction and radiation intensity of the radio wave from the antenna device 10 so as to satisfy predetermined required specifications.

[0016] On the other hand, the antenna element 20 may radiate radio waves in multiple frequency bands, for example, radio waves in a first frequency band and radio waves in a second frequency band that is a higher frequency band than the first frequency band. In this case, it may be difficult to appropriately adjust the radiation state of radio waves in multiple frequency bands using a pair of parasitic elements 25a, 25b. As a countermeasure, for example, it may be possible to install multiple pairs of parasitic elements 25a, 25b each having a different length L0. However, in this case, the size of the antenna device 10 may increase, and there may be a possibility that the installation space for the new parasitic elements may not be sufficiently secured.

[0017] 1, the parasitic elements 25a and 25b are formed with slots 26a and 26b, which are elongated openings. The slots 26a and 26b extend in a direction tilted at a predetermined angle from the Z-axis direction to the Y-axis direction, and have a length L2 in the extension direction and a width W2 in a direction perpendicular to the extension direction. The slots 26a and 26b can radiate radio waves in a predetermined frequency band according to the length L2. By causing interference between the radio waves radiated from the slots 26a and 26b and the radio waves radiated from the antenna element 20, it becomes possible to adjust the radiation state of the radio waves from the antenna device 10.

[0018] That is, when the antenna device 10 of Fig. 1 is used, the radiation state of radio waves in, for example, a first frequency band can be adjusted by the parasitic elements 25a and 25b. Furthermore, the radiation state of radio waves in, for example, a second frequency band can be adjusted by the slots 26a and 26b. This makes it possible to adjust the radiation state of radio waves in multiple frequency bands by installing a pair of parasitic elements 25a and 25b with the slots 26a and 26b formed therein, without installing multiple pairs of parasitic elements. As a result, it becomes possible to adjust the radiation state of radio waves while suppressing an increase in the size of the antenna device 10.

[0019] <Slot details> Fig. 2 is a schematic diagram for explaining an example of the operation of parasitic element 25 in Fig. 1 in which slot 26 is formed. As shown in Fig. 2, when parasitic element 25 receives radio waves from antenna element 20, current I flows through parasitic element 25. When the radio waves from antenna element 20 are vertically polarized waves, that is, radio waves vibrating in the Z-axis direction, the direction of current I is also the Z-axis direction. In this case, slot 26 is formed so as to extend in a direction inclined by angle θ toward the Y-axis direction, in other words, in a direction rotated by angle θ around the X-axis direction as the rotation axis.

[0020] By forming the slot 26 so as to block the current I in this way, an electric field E is generated inside the slot 26 in the direction of the width W2 of the slot 26. This electric field E causes radio waves to be emitted from the slot 26. The intensity of the electric field E generated in the slot 26 can be adjusted by the angle θ and width W2 of the slot 26. The polarization direction of the radio waves can also be adjusted by the angle θ of the slot 26. Furthermore, the frequency of the radiated radio waves can be adjusted by the length L2 of the slot 26. The length L2 of the slot is determined, for example, to reflect the wavelength, specifically, half the wavelength, of the radio waves radiated by the antenna element 20, and is also determined to reflect the wavelength shortening rate, etc.

[0021] Fig. 3 is a schematic diagram for explaining an example of the operation of the antenna device of Fig. 1. Fig. 3 shows the radiation state of radio waves radiated from the antenna device 10 in a horizontal plane, i.e., a plane consisting of the X-axis direction and the Y-axis direction. In general, in addition to radio waves called a main lobe 30 oriented in an intended direction, here approximately in the Y-axis direction, radio waves called a side lobe 31 oriented in an unintended direction, here approximately in the X-axis direction, are radiated from the antenna element 20. Of these, it is usually desired that the side lobe 31 be suppressed to a predetermined radiation intensity or less.

[0022] Therefore, slots 26a, 26b formed in parasitic elements 25a, 25b are made to radiate radio waves in the same frequency band as the radio waves radiated from antenna element 20. As a result, the radio waves radiated from slots 26a, 26b interfere with the radio waves of side lobe 31 radiated from antenna element 20. Here, for example, by appropriately adjusting length L2, width W2 and angle θ of slot 26 so as to generate interference that weakens the radio waves, it is possible to suppress side lobe 31.

[0023] <Overall configuration of antenna device> Fig. 4 is a perspective view showing an example of the configuration of the main parts of the entire antenna device to which the basic configuration of Fig. 1 is applied. The antenna device 10a shown in Fig. 4 is, for example, an antenna device for a base station of a mobile communication, and has an elongated shape extending in the Z-axis direction, i.e., in a direction perpendicular to the ground. The antenna device 10a includes a base substrate 35 having a surface consisting of the Z-axis direction and the X-axis direction, and a plurality of antenna units 40[1], 40[2], 40[3], ... which are sequentially installed in the Z-axis direction on the base substrate 35. In the specification, the plurality of antenna units 40[1], 40[2], 40[3], ... are collectively referred to as antenna unit 40.

[0024] The antenna unit 40 includes a pair of parasitic elements 25a, 25b, two antenna elements 20a, 20b, and a parasitic element 36. The pair of parasitic elements 25a, 25b are disposed at both ends of the antenna device 10a in the X-axis direction, in other words, in the width direction of the antenna device 10a. Slots 26a, 26b are formed in the parasitic elements 25a, 25b, respectively, as in the case of FIG. 1, etc.

[0025] The parasitic element 36 is disposed midway between the pair of parasitic elements 25a, 25b in the X-axis direction. In the X-axis direction, the antenna element 20a is disposed between the parasitic element 25a and the parasitic element 36, and the antenna element 20b is disposed between the parasitic element 36 and the parasitic element 25b. Each of the two antenna elements 20a, 20b radiates radio waves in a predetermined frequency band, and a radio wave obtained by combining the two radio waves is radiated from the antenna unit 40. The two antenna elements 20a, 20b collectively correspond to the antenna element 20 in FIG. 1.

[0026] The base substrate 35 includes a reflector on the installation surface of the antenna elements. The reflector reflects radio waves emitted from the antenna elements 20a and 20b. Although not shown, the base substrate 35 includes wiring for supplying AC power to the antenna elements 20a and 20b. In FIG. 4, the antenna unit 40 includes the antenna elements 20a and 20b for vertical polarization, but may also include an antenna element for horizontal polarization, for example, an antenna element extending in the X-axis direction. The antenna device 10a in FIG. 4 may also include a phase shifter for adjusting the phase of AC power to the multiple antenna elements 20a and 20b arranged in the Z-axis direction in order to control the tilt angle in the vertical plane consisting of the Z-axis direction and the Y-axis direction.

[0027] Such an antenna device for a mobile communication base station may support multiple frequency bands, such as the 1.5 GHz band and the 2.0 GHz band. For each frequency band, there may be required specifications for the radiation direction in a horizontal plane consisting of the X-axis and Y-axis directions, i.e., directivity, and for the radiation intensity of the side lobe. For example, when focusing on only one frequency band, it is possible to meet the required specifications by adjusting the size of the pair of parasitic elements 25a and 25b and also the size of the parasitic element 36.

[0028] However, when focusing on multiple frequency bands, it may be difficult to simultaneously satisfy the required specifications for each frequency band with a pair of parasitic elements 25a, 25b. If multiple pairs of parasitic elements are provided in antenna unit 40 as a countermeasure, this may lead to an increase in costs. Furthermore, in the case of an antenna device for a mobile communication base station, the size, particularly in the X-axis direction and Y-axis direction, may be limited from the standpoint of mechanical strength taking into account wind pressure loads, etc. In this case, providing multiple pairs of parasitic elements may itself be difficult in terms of installation space.

[0029] 2, in the example of FIG. 4, the size of the pair of parasitic elements 25a, 25b, particularly the length L0 in the Z-axis direction, is determined to reflect the wavelength, specifically half the wavelength, of the radio waves in the lower frequency band (first frequency band) radiated by the antenna elements 20a, 20b. As an example, the length L0 of the parasitic elements 25a, 25b is about 90 mm to 110 mm, and the width W0 is about 10 mm to 20 mm. Such parasitic elements 25a, 25b mainly make it possible to adjust the radiation state of the radio waves in the lower frequency band, that is, the directivity and side lobes.

[0030] Moreover, the length L2 in the extension direction of the slots 26a, 26b formed in the parasitic elements 25a, 25b is determined to reflect the wavelength, more specifically, half the wavelength, of the radio waves of the higher frequency band (second frequency band) radiated by the antenna elements 20a, 20b. As an example, the length L2 of the slots 26a, 26b is determined to be about 45 mm to 55 mm after reflecting the wavelength shortening rate and the like in the half wavelength of the radio waves of the higher frequency band. Moreover, the width W2 of the slots 26a, 26b is determined to be about 1 mm to 4 mm. Furthermore, the angle θ of the slots 26a, 26b is determined to be about 10° to 15°.

[0031] Such slots 26a and 26b mainly allow adjustment of the radiation state of radio waves in the higher frequency band, i.e., the directivity and side lobes. In particular, the slot antenna realized by the slots 26a and 26b may affect a narrower frequency band than the parasitic elements 25a and 25b. Therefore, it becomes possible to adjust the radiation state of radio waves in a certain narrow frequency band and suppress the influence on other frequency bands.

[0032] <Test results of antenna characteristics> Fig. 5 is a diagram showing the results of verifying the directivity in the horizontal plane of the antenna device of Fig. 4. Fig. 5 shows the results of the verification at target frequency B included in the higher frequency band, and at non-target frequency A (frequency A<frequency B). Non-target frequency A is a frequency that is about 100 MHz away from target frequency B. Fig. 5 also shows a comparison at each frequency between the case where slots 26a, 26b are formed in parasitic elements 25a, 25b and the case where they are not formed.

[0033] In Fig. 5, at the non-target frequency A, the relative strength of the side lobes does not change much between when the slots 26a, 26b are formed and when they are not (see d1 in Fig. 5). On the other hand, at the target frequency B, the relative strength of the side lobes is smaller when the slots 26a, 26b are formed than when the slots 26a, 26b are not formed (see d2 in Fig. 5). In this way, by forming the slots 26a, 26b, it is possible to adjust the radiation state of the radio wave in a certain narrow frequency band, and in detail, it is possible to suppress the relative strength of the side lobes.

[0034] <Antenna device design method> Fig. 6 is a flow diagram showing an example of a design method of the antenna device according to the first embodiment. In Fig. 6, first, the length L1 of the antenna element 20 is determined so as to reflect the wavelength of radio waves in a required frequency band (step S101). Next, the size (L0 × W0) of the pair of parasitic elements 25a, 25b is determined so as to reflect the wavelength of radio waves in the lower frequency band (step S102).

[0035] Next, the length L2 of the slots 26a, 26b is determined to reflect the wavelength of the radio wave of the higher frequency band (step S103). Then, the slots 26a, 26b having the length L2 determined in step S103 are formed in the pair of parasitic elements 25a, 25b (step S104). At this time, the slots 26a, 26b are formed so as to extend in the extension direction of the antenna element 20, i.e., in a direction inclined at an angle θ to the Y-axis direction with respect to the Z-axis direction.

[0036] Next, the antenna element 20 and the pair of parasitic elements 25a, 25b are placed at a predetermined interval D0 (step S105). Then, while performing a simulation, each parameter is fine-tuned to meet a predetermined required specification (step S106). In step S106, in particular, the size (L0×W0) of the parasitic elements 25a, 25b in step S102, the length L0 and angle θ of the slots 26a, 26b in steps S103 and S104, or the width W0 of the slots 26a, 26b are fine-tuned.

[0037] <Major Effects of the First Embodiment> As described above, by using the antenna device according to the first embodiment, it is typically possible to adjust the radiation state of radio waves while suppressing an increase in size. In particular, it is possible to adjust the radiation state of radio waves, for example, the relative strength of side lobes, in a plurality of frequency bands, without adding new parasitic elements. As a result, it is possible to reduce costs, and furthermore, it is possible to satisfy the antenna size restrictions required for antenna devices for mobile communication base stations, etc.

[0038] (Embodiment 2) <Basic configuration of antenna device> Fig. 7 is a perspective view showing an example of the basic configuration of an antenna device according to embodiment 2. In antenna device 10b shown in Fig. 7, unlike the configuration example of Fig. 1, a pair of parasitic elements 25a, 25b each have a plurality of slots formed therein. In this example, parasitic element 25a has two slots 26a1, 26a2 formed therein, and parasitic element 25b has two slots 26b1, 26b2 formed therein.

[0039] For example, when the two slots 26a1, 26a2 are made to have the same shape and size, it may be possible to adjust the radiation state of radio waves in a certain frequency band more finely than in the case of Fig. 1. In this case, referring to Fig. 2, the angle θ of the extension direction of the two slots 26a1, 26a2 may be made different. Also, the length L2 of the extension direction of the two slots 26a1, 26a2 may be set to different sizes. In this case, it may be possible to individually adjust the radiation state of radio waves in two frequency bands according to the length L2.

[0040] <Major Effects of the Second Embodiment> As described above, by using the antenna device of the second embodiment, it is possible to obtain the same effects as those described in the first embodiment. Furthermore, there are cases where it is possible to more flexibly adjust the radiation state of radio waves while suppressing an increase in the size of the antenna device.

[0041] The invention made by the present inventor has been specifically described above based on the embodiments, but the present invention is not limited to the above-mentioned embodiments and can be modified in various ways without departing from the gist of the invention. For example, the above-mentioned embodiments have been described in detail to easily explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

[0042] For example, in Fig. 1, one antenna element 20 radiates radio waves in multiple frequency bands, but multiple antenna elements may radiate radio waves in multiple frequency bands, respectively. The planar directions of parasitic elements 25a and 25b are not necessarily limited to the Z-axis direction and the Y-axis direction as shown in Fig. 1, and in some cases may be directions slightly rotated around at least one of the X-axis direction, the Y-axis direction, and the Z-axis direction as the rotation axis based on the arrangement in Fig. 1. [Explanation of symbols]

[0043] 10 Antenna device 20, 20a, 20b Antenna elements 21 AC power supply 25, 25a, 25b Parasitic elements 26,26a,26a1,26a2,26b,26b1,26b2 Slots 30 Main Lobe 31 Side lobe 35 Base Board 36 Parasitic element 40 Antenna unit L0, L1, L2 Length W0, W2 width D0 interval E Electric field I current

Claims

1. a dipole antenna element extending in a first direction and radiating radio waves in a first frequency band and radio waves in a second frequency band that is a higher frequency band than the first frequency band; a first parasitic element and a second parasitic element respectively disposed on both sides of the antenna element in a second direction intersecting the first direction; Equipped with a slot is formed in each of the first parasitic element and the second parasitic element; the sizes of the first parasitic element and the second parasitic element are determined in accordance with a wavelength of radio waves in the first frequency band; each of the first parasitic element and the second parasitic element is formed of a conductive plate having a surface that is in the first direction and the third direction, where a direction perpendicular to the first direction and the second direction is defined as a third direction; The slot is formed so as to extend in a direction inclined from the first direction to the third direction, and a length of the slot in the extension direction is determined so as to reflect a wavelength of radio waves in the second frequency band. Antenna device.

2. 2. The antenna device according to claim 1, a plurality of the slots are formed in each of the first parasitic element and the second parasitic element; Antenna device.

3. A method for designing an antenna device, comprising the steps of: The antenna device comprises: a dipole antenna element extending in a first direction and radiating radio waves in a first frequency band and radio waves in a second frequency band that is a higher frequency band than the first frequency band; a first parasitic element and a second parasitic element respectively disposed on both sides of the antenna element in a second direction intersecting the first direction; Equipped with determining sizes of the first parasitic element and the second parasitic element in accordance with a wavelength of radio waves in the first frequency band; determining a length of a slot formed in each of the first parasitic element and the second parasitic element in accordance with a wavelength of radio waves in the second frequency band; The slot is defined to extend in a direction inclined from the first direction to the third direction, where a direction perpendicular to the first direction and the second direction is defined as a third direction. A method for designing an antenna device.

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