Antenna Device

Abstract

To provide an antenna device that is composed of a plurality of antennas not sharing a ground plate, and that can suppress mutual interference between antennas and take even size reduction into consideration.SOLUTION: A first and a second antenna which constitute an antenna device and correspond to a common frequency band are so arranged as to form a slit having both ends made open between a first ground plate and a second ground plate that the first antenna and second antenna has respectively. The slit is so formed as to resonate in the frequency band that the first antenna and second antenna correspond to.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an antenna device made up of a plurality of antennas, which is used in a device having a communication function. [Background technology]

[0002] In recent years, wireless data communication systems such as wireless LAN, WiMAX (registered trademark), WiFi (registered trademark), and BlueTooth (registered trademark) have been adopted in a wide variety of devices, such as information terminal devices, and the demand for antennas used for these communications is increasing.

[0003] Furthermore, there are also situations where multiple antennas are mounted on one communication device in order to increase communication speed.

[0004] A problem that arises when multiple antennas are mounted on one communication device is the degradation of communication characteristics due to mutual interference between the antennas, and various methods have been proposed to suppress the mutual interference between the antennas.

[0005] As methods for reducing mutual interference between antennas, a method of providing a slit in the ground between the antennas (Patent Document 1) and a method of providing a protrusion in the ground plate between the antennas (Patent Document 2) have been proposed. However, since these methods share a ground plate between multiple antennas, it is not possible to completely prevent the phenomenon in which high-frequency current fed to one antenna flows into another antenna via the ground plate, and the effect of reducing mutual interference may be insufficient.

[0006] Although mutual interference can be reduced by eliminating the need for multiple antennas to share a ground plate, mutual interference caused by the spatial propagation of radio waves still remains. A method of providing a shielding plate between antennas has been proposed as a method for reducing mutual interference when multiple antennas do not share a ground plate (Patent Document 3).

[0007] However, the method of installing a shielding plate between antennas requires that a space for the shielding plate be secured between the antennas, and the shielding plate itself has a certain area and volume, making it difficult to miniaturize the antenna. Therefore, this method is difficult to adopt when the space for installing antennas in communications equipment is limited. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2007-13643 A [Patent Document 2] JP 2013-51644 A [Patent Document 3] JP 2015-70408 A Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present invention is to provide an antenna device that is configured with a plurality of antennas that do not share a common ground plate, and that can suppress mutual interference between the antennas while also taking into consideration miniaturization. [Means for solving the problem]

[0010] As a result of careful consideration by the inventors on the structure of the antennas and the method of arranging them within the device, they have succeeded in realizing an antenna device that is compact in size by arranging the ground plates of each antenna close to each other at a specified length and distance, thereby making it possible to suppress mutual interference caused by the spatial propagation of radio waves even without a shielding plate. Effect of the Invention

[0011] The antenna device of the present invention is expected to have the following advantages. (1) Since the antennas do not share a ground plate, mutual interference between antennas via the ground plate does not occur in principle. (2) Mutual interference caused by the spatial propagation of radio waves can be suppressed without the need for additional components such as shielding plates, which contributes to the miniaturization of antenna devices. [Brief description of the drawings]

[0012] [Figure 1] 1 shows a basic configuration of an antenna device according to the present invention. [Diagram 2] 5A and 5B are conceptual diagrams illustrating an interference suppression effect achieved by the antenna device of the present invention. [Diagram 3] 13 is a modified example of the antenna device of the present invention. [Figure 4] This is a particularly preferred variant of the antenna device according to the invention. [Diagram 5] 1 is an antenna device of a comparative example. [Figure 6] VSWR of the antenna used in Example 1. [Figure 7] 1 shows the isolation between antennas in the first embodiment. [Figure 8] VSWR of the antenna used in Example 2. [Figure 9] 13 shows the isolation between antennas in the second embodiment. [Figure 10] 13 shows the VSWR of the antenna used in the third embodiment. [Figure 11] 13 shows the isolation between antennas in the third embodiment. [Figure 12] This is the VSWR of the antenna used in the comparative example. [Figure 13] 4 shows the isolation between antennas in the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will now be described with reference to FIG.

[0014] As shown in FIG. 1, the antenna device 1 of the present invention has a first antenna A1 and a second antenna A2.

[0015] The first antenna A1 is composed of a first ground plate 11, a first radiating element portion 21 extending from a contour side of the first ground plate 11, and a first feed line 31 connected to a first feed point P1 provided on the first radiating element portion 21, and is configured to be able to transmit or receive a signal in an arbitrary frequency band f. In Fig. 1, the first radiating element portion 21 extends perpendicularly from the contour side of the first ground plate 11, but the direction in which the first radiating element portion 21 extends is not limited to this.

[0016] The second antenna A2 is composed of the second ground plate 12, a second radiating element portion 22 extending from a contour side of the second ground plate 12, and a second feed line 32 connected to a second feed point P2 provided on the second radiating element portion 22. In principle, the second antenna A2 is configured to be able to transmit or receive signals in the frequency band f, similar to the first antenna A1. In Fig. 1, the second radiating element portion 22 extends perpendicularly from the contour side of the second ground plate 12, but the direction in which the second radiating element portion 22 extends is not limited to this.

[0017] A characteristic feature of the present invention is that first ground plate 11 and second ground plate 12 are arranged opposite each other so that a slit S with both ends open is formed between first ground plate 11 and second ground plate 12.

[0018] At this time, the slit S is formed so that the first antenna A1 and the second antenna A2 resonate in a frequency band f corresponding to each other.

[0019] In order to form the slit S so as to resonate in the frequency band f, the length of the slit S is set, in principle, to approximately half the wavelength λ of the radio waves in the frequency band f transmitted and received by the first antenna A1 and the second antenna A2.

[0020] The length of approximately half the wavelength λ does not have to be exactly half λ, and so long as half λ is used as the standard, fluctuations according to the actual usage conditions of the antenna device 1 are allowed.

[0021] The length of the slit S does not necessarily have to be set to approximately half the wavelength λ, and the length is determined by giving priority to the resonation of the slit S in the frequency band f. For example, when the antenna device 1 of the present invention is housed in a housing of a communication device or the like and a material made of a dielectric is present around the antenna device 1 and the antenna device 1 is affected by the wavelength shortening effect due to the dielectric, the length of the slit S may be set to a value taking into consideration the wavelength shortening effect.

[0022] In the present invention, the first antenna A1 and the second antenna A2 are electrically independent, In principle, the high frequency current supplied to the first antenna A1 does not flow into the second antenna A2, and vice versa, so that mutual interference between the antennas A via the ground plate 10 is suppressed.

[0023] Furthermore, in the present invention, the slit S with both ends open is provided between the first ground plate 11 and the second ground plate 12, thereby suppressing mutual interference due to spatial propagation.

[0024] When communication is performed using the antenna device 1, a high-frequency current corresponding to frequency band f also flows through the first ground plate 11 and the second ground plate 12. However, since a slit S that resonates in frequency band f is present between the first ground plate 11 and the second ground plate 12, slit resonance due to this high-frequency current occurs in the slit S.

[0025] When resonance occurs in the slit S, the slit S functions as a slit antenna that emits radio waves corresponding to the frequency band f, as shown in Figure 2. In other words, it can be said that the slit S is formed to imitate a slit antenna that can emit signals in the frequency band f.

[0026] Because there is a slit S between the first antenna A1 and the second antenna A2, which emits radio waves corresponding to the frequency band f supported by both antennas A, the radio waves traveling from the first antenna A1 to the second antenna A2 are weakened by interference from the radio waves generated by the resonance of the slit S, as shown in Figure 2, and interference between the first antenna A1 and the second antenna A2 caused by spatial propagation is suppressed.

[0027] Similarly, the radio waves traveling from the second antenna A2 to the first antenna A1 are weakened by interference from the radio waves generated by resonance of the slit S, and interference by the second antenna A2 with the first antenna A1 due to spatial propagation is also suppressed.

[0028] In this way, the spatial propagation from the first antenna A1 to the second antenna A2 and the spatial propagation from the second antenna A2 to the first antenna A1 are both reduced, thereby suppressing mutual interference occurring between the first antenna A1 and the second antenna A2 due to spatial propagation.

[0029] As described above, the present invention makes it possible to suppress mutual interference without requiring additional components such as a shielding plate, and since the first antenna A1 and the second antenna A2 are positioned close to each other to form the slit S, it contributes to miniaturization of the antenna device 1.

[0030] In the present invention, the first antenna A1 and the second antenna A2 are arranged in close proximity to each other, but due to the formation of the slit S, a certain distance is ensured between the first radiating element portion 21 and the second radiating element portion 22, which also contributes to suppressing mutual interference occurring between the first antenna A1 and the second antenna A2.

[0031] The width of the slit S is set so that the slit S functions as a slit antenna, and is usually set to about 1 to 5 mm.

[0032] Moreover, the slit S in the present invention preferably has a shape having a bent portion as shown in FIGS.

[0033] When the slit S has a bent shape, radiation due to resonance of the slit S occurs in multiple directions, making it possible to reduce spatial propagation that could not be sufficiently reduced by a straight slit S, thereby contributing to stabilizing the mutual interference suppression effect.

[0034] Furthermore, when a slit S having a bent portion is formed as shown in FIG. 4, a slit S having the same length as a straight slit S can be formed in a smaller space, which contributes to miniaturization of the antenna device 1.

[0035] The shape of the slit S can be set to any shape within the scope of the technical concept of the present invention, but from the viewpoint of facilitating the manufacture of the antenna device 1, it is preferable to make the slit S bent into a substantially L-shape as shown in Figures 3 and 4. When forming the substantially L-shaped slit S, it can be formed by changing the shape of the ground plate 10 of one of the antennas A, for example by providing an extension 11b on the first ground plate 11a of the first antenna A1, as shown in Figure 4, so that the slit S having a bent portion can be formed with little effort.

[0036] Although the substantially L-shaped slit S refers to a slit S having a bending angle of 90° at the bending portion, it does not have to be strictly 90° and some variation is allowed.

[0037] When the slit S is formed in a substantially L-shape, it is preferable to set L1:L2 within the range of 2:1 to 1:2, where L1 is the length of the horizontal portion and L2 is the length of the vertical portion.

[0038] This setting is intended to use a standard L1:L2 ratio of 1:1 and not to vary significantly from the standard.

[0039] By setting L1:L2 within the above range, the resonance occurring in the slit S is stabilized, and a stable mutual interference suppression effect can be obtained.

[0040] In addition, in the present invention, by taking into consideration the positional relationship of the radiating element portions 20 of the antennas A, it is possible to obtain a better effect of suppressing mutual interference between the antennas A.

[0041] Specifically, as shown in Figures 3 and 4, it is preferable that the positional relationship between the contour side of the first ground plate 11 from which the first radiating element portion 21 extends and the contour side of the second ground plate 12 from which the second radiating element portion 22 extends is approximately right angle.

[0042] By arranging the radiating element section 20 in such a positional relationship, the main axis of the directivity of the first antenna A1 and the main axis of the directivity of the second antenna A2 will have different orientations, thereby reducing interference between the radio waves transmitted and received by each antenna A and stabilizing the effect of suppressing mutual interference between the antennas A.

[0043] The shape of the radiating element section 20 of the antenna A used in the present invention is not limited to a specific one, and various shapes can be used depending on the desired communication characteristics. In addition to a linear element that functions as an inverted F-shaped antenna, a folded structure such as a U-shape or a meandering shape, or a branched structure that supports multiple frequencies can be used, and a parasitic element may be provided in the antenna A to exhibit antenna characteristics by capacitively coupling with the radiating element section 20. In Figures 1 and 2, a radiating element section 20 having a folded structure is shown as an example.

[0044] The antenna A used in the present invention is constructed using an antenna element that is punched out of a single metal plate about 0.1 to 1 mm thick and made of nickel silver (cupronickel), copper, iron, brass, steel, etc., and molded into a single piece, an antenna element having a conductive pattern on a dielectric substrate, or an antenna element constructed by combining both.

[0045] The feeder line 30 used in the present invention may be a well-known high-frequency coaxial cable with a fluororesin coating, etc. The inner conductor or outer conductor of this high-frequency coaxial cable may be connected to a predetermined location on the antenna A by fixing it by soldering or by crimping.

[0046] The antenna device 1 of the present invention is used in a form incorporated in a communication device. EXAMPLES

[0047] As an embodiment of the present invention, an antenna device 1 shown in Figures 1 to 3 was fabricated and evaluated. A method for fabricating and evaluating the antenna device, which is common to each embodiment, will be described below.

[0048] 1. Creating an antenna An antenna element having a ground plate 10 and a radiating element portion 20 of a predetermined shape is created by punching out a zinc-plated steel plate having a thickness of 0.4 mm. In each embodiment, the radiating element portion 20 had the same basic shape having a folded structure, and the detailed dimensions were set so as to function as an antenna capable of transmitting or receiving radio waves in the wireless LAN band (2.45 GHz band, wavelength λ≒122 mm).

[0049] As the power supply line 30, a coaxial cable composed of an inner conductor, a fluororesin (PFA) insulator, an outer conductor, and a PFA jacket was prepared. The tip of the coaxial cable was stripped in a step, and the inner conductor was soldered to a predetermined location of the radiating element portion 20 to form a feeding point P. An external conductor was soldered to a predetermined location on the ground plate 10 to form an earth point G, completing the antenna A. Furthermore, a well-known coaxial cable connector is provided on the other side of the coaxial cable so that it can be connected to a high-frequency circuit.

[0050] 2. Creating an antenna device The first antenna A1 and the second antenna A2, which were created according to the above-described method for creating antenna A, were fixed onto a resin substrate so that the first ground plate 11 and the second ground plate 12 faced each other to form a slit S, completing the antenna device 1. The length of the slit S was set to a dimension that would cause resonance in the slit S, taking into consideration the wavelength shortening effect due to the presence of the resin substrate.

[0051] 3. Antenna device evaluation A high-frequency signal in the 2.45 GHz band was fed to each of the first antenna A1 and the second antenna A2, and the VSWR of each antenna A and the mutual interference (isolation) occurring between the first antenna A1 and the second antenna A2 were measured.

[0052] [Example 1] As Example 1, an antenna device 1-1 of the aspect shown in FIG. 1 was created. In Example 1, the first antenna A1-1 and the second antenna A2-1 were the same. The size of the ground plate 10 of each antenna A was 27 mm × 24.5 mm, and the contour sides of the 27 mm length were arranged opposite to each other, and a slit S of 27 mm length and 3 mm width was formed. The outer dimensions of the antenna device 1 were 27 mm × 52 mm. The radiating element portion 20 extended perpendicularly to the ground plate 10 from the contour side of the ground plate 10 opposite to the contour side that constitutes the slit S.

[0053] The VSWR of the antenna device 1-1 of the first embodiment is shown in Fig. 6, and the isolation is shown in Fig. 7. In Fig. 6, the solid line indicates the VSWR of the first antenna A1-1, and the dashed line indicates the VSWR of the second antenna A2-1.

[0054] [Example 2] As Example 2, an antenna device 1-2 was created in the manner shown in Fig. 3. In Example 2, the first antenna A1-2 used was the same as the first antenna A1-1 used in Example 1. The second antenna A2-2 was based on the second antenna A2-1 used in Example 1, and had a structure in which an L-shaped extension part 12b with a length of 27 mm and a width of 5 mm was extended from a second ground plate 12a with a size of 27 mm x 24.5 mm. The length of the extension part 12b is the dimension at the center in the width direction of the extension part 12b.

[0055] In Example 2, the first antenna A1 and the second antenna A2 are arranged so that the contour side of the first ground plate 11 from which the first radiating element portion 21 extends and the contour side of the second ground plate 12 from which the second radiating element portion 22 extends are positioned at a substantially right angle, and an L-shaped slit S having a width of 3 mm is formed between the ground plates. The length of the slit S, measured at the center of the width direction of the slit S, is set to 9.5 mm for the horizontal portion length L1, 28.5 mm for the vertical portion length L2, and 38 mm for the total length. The external dimensions of the antenna device 1 are 40 mm x 54 mm.

[0056] The VSWR of the antenna device 1-2 of the second embodiment is shown in Fig. 8, and the isolation is shown in Fig. 9. In Fig. 8, the solid line indicates the VSWR of the first antenna A1-2, and the dashed line indicates the VSWR of the second antenna A2-2.

[0057] [Example 3] As Example 3, an antenna device 1-3 was created in the manner shown in Fig. 4. In Example 3, the first antenna A1-3 was based on the first antenna A1-1 used in Example 1, and had a structure in which a linear extension part 11b with a length of 32 mm and a width of 5 mm was extended from a first ground plate 11a with a size of 27 mm x 24.5 mm. The second antenna A2-3 was the same as the second antenna A2-1 used in Example 1.

[0058] In Example 3, the first antenna A1 and the second antenna A2 are arranged so that the contour side of the first ground plate 11 from which the first radiating element portion 21 extends and the contour side of the second ground plate 12 from which the second radiating element portion 22 extends are positioned at a substantially right angle, and an L-shaped slit S having a width of 3 mm is formed between the ground plates. The length of the slit S, measured at the center of the width direction of the slit S, is set to 28.5 mm for the horizontal portion length L1, 20.5 mm for the vertical portion length L2, and 49 mm for the total length. The external dimensions of the antenna device 1 are 32 mm x 56 mm.

[0059] The VSWR of the antenna device 1-3 of the third embodiment is shown in Fig. 10, and the isolation is shown in Fig. 11. In Fig. 10, the solid line indicates the VSWR of the first antenna A1-2, and the dashed line indicates the VSWR of the second antenna A2-2.

[0060] [Comparative Example] As a comparative example, an antenna device 1' shown in Fig. 5 was created. The antenna device 1' of the comparative example is an antenna device 1-2 of Example 2 in which the extension portion 11b is omitted, and sufficient resonance does not occur in the slit S' between the ground plates 10'.

[0061] The VSWR of the antenna device 1' of the comparative example is shown in Fig. 12, and the isolation is shown in Fig. 13. In Fig. 12, the solid line indicates the VSWR of the first antenna A1', and the dashed line indicates the VSWR of the second antenna A2'.

[0062] The VSWR of each of the antennas constituting the antenna devices of Examples 1 to 3 and the comparative example drops near 2450 MHz (2.45 GHz), and the VSWR provides sufficient performance for an antenna device used in the 2.45 GHz band.

[0063] On the other hand, when the isolation of each antenna device was checked, the isolation between antennas A' in antenna device 1' of the comparative example was about -12 dB in the vicinity of 2.45 GHz.

[0064] In comparison with the antenna device 1' of the comparative example, the isolation between the antennas A in the antenna device 1-1 of the embodiment 1 in which a linear slit S is provided between the antennas A is approximately -17 dB in the vicinity of 2.45 GHz, which is an improved value compared to the comparative example.

[0065] From the above, it was confirmed that by providing a slit S whose length is set so that resonance occurs between the antennas A, mutual interference between the antennas A can be suppressed.

[0066] In addition, in the antenna device 1-2 of Example 2 in which an L-shaped slit S is provided between the antennas A, the isolation between the antennas A is reduced to approximately -19 dB, which is slightly improved compared to Example 1. From this result, it was confirmed that by providing a slit S having a bent portion between the antennas A, the effect of suppressing mutual interference between the antennas A is improved.

[0067] Furthermore, in the antenna device 1-3 of the third embodiment in which an L-shaped slit S is provided between the antennas A and the ratio L1:L2 of the length L1 of the horizontal part of the slit S to the length L2 of the vertical part is set to 1.39:1, close to 1:1, the isolation between the antennas A was reduced to approximately -23 dB. It was confirmed that by providing a slit S with a bent part between the antennas A and taking into consideration the dimensional ratio of the horizontal part to the vertical part, interference between the antennas A can be more effectively suppressed.

[0068] Although an antenna device compatible with the wireless LAN band (2.45 GHz band) has been described above, this is merely one example of the present invention, and it goes without saying that the present invention can be applied to antenna devices compatible with other bands as long as they are within the scope of the concept of the present invention. In particular, the specific configuration of the antenna used in the antenna device is not limited to the above-mentioned example, and various antenna configurations proposed in the past can be appropriately selected and used within the scope of the concept of the present invention.

[0069] Furthermore, the number of antennas constituting the antenna device of the present invention is not limited to two, and an antenna device may be constructed using three or more antennas. When using three or more antennas, it is not necessarily necessary to form slits between the ground plates of all the antennas, and a slit may be formed only between the ground plates of two selected antennas depending on the desired performance of the antenna device. [Industrial Applicability]

[0070] The antenna device of the present invention can be applied to various devices with communication functions, and can be suitably used in industrial devices used in IoT, information appliances with communication functions, automobile-related devices, access points, and the like. [Explanation of symbols]

[0071] 1 Antenna device A Antenna A1 First Antenna A2 Second Antenna 10 Ground plate 11, 11a First ground plate 11b Extension of first ground plate 12, 12a Second ground plate 12b Extension of second ground plate 20 Radiating element section 21 First radiating element section 22 Second radiating element section 30 Power supply line 31 First power supply line 32 Second power supply line S slit P Feeding point P1 First power supply point P2 Second power supply point G Earth Point G1 First Earth Point G2 Second Earth Point

Claims

1. An antenna device having a first antenna and a second antenna, The first antenna and the second antenna do not share a ground plate; the first antenna is composed of a first ground plate, a first radiating element portion extending from a contour side of the first ground plate perpendicular to the first ground plate, and a first feed line connected to a first feed point provided on the first radiating element portion; the second antenna is composed of a second ground plate, a second radiating element portion extending from a contour side of the second ground plate perpendicular to the second ground plate, and a second feed line connected to a second feed point provided on the second radiating element portion, The first antenna and the second antenna transmit or receive radio waves in a common frequency band, the first ground plate and the second ground plate are disposed opposite to each other so that a slit having both ends open is formed between the first ground plate and the second ground plate; The antenna device is characterized in that the slit is formed so as to resonate and function as a slit antenna that radiates radio waves corresponding to the frequency band.

2. The antenna device as described in claim 1, characterized in that the basic shapes of the first radiating element portion and the second radiating element portion are the same.

3. 3. The antenna device according to claim 1, wherein the length of the slit is approximately half the wavelength of a radio wave in the frequency band.

4. An antenna device as described in any one of claims 1 to 3, characterized in that the positional relationship between the contour edge of the first ground plate from which the first radiating element portion extends and the contour edge of the second ground plate from which the second radiating element portion extends is approximately right angle.

5. An extension portion extends from an opposite side of a contour edge of the first ground plate from which the first radiating element portion extends, 5. The antenna device according to claim 4, wherein an opposite side of the contour side of the first ground plate faces one side of the second ground plate, and an opposite side of the contour side of the second ground plate faces one side of the extension, thereby forming a slit bent in a substantially L-shape with both ends open between the first ground plate and the second ground plate.

6. A substantially L-shaped extension portion extends from an opposite side of a contour edge of the second ground plate from which the second radiating element portion extends, 5. The antenna device according to claim 4, wherein an opposite side of the contour side of the first ground plate faces one side of the second ground plate and one side of the extending portion, and one side of the first ground plate faces another side of the extending portion, thereby forming a slit bent in a substantially L-shape with both ends open between the first ground plate and the second ground plate.

7. An antenna device as described in claim 5 or 6, characterized in that when the length of the horizontal portion of the approximately L-shaped slit is L1 and the length of the vertical portion is L2, L1:L2 is within the range of 2:1 to 1:2.

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