JP7680885B2 - Antenna Device - Google Patents

Description

The present invention relates to an antenna device consisting of multiple antennas, which is used in devices with communication capabilities.

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, including information terminal devices, and the demand for antennas used in these communications is increasing.

In addition, there are situations where multiple antennas are installed in one communication device to improve communication speed.

When multiple antennas are installed in one communication device, a problem occurs in that mutual interference between the antennas can degrade communication characteristics, and various methods have been proposed to suppress the mutual interference between the antennas.

Methods proposed to reduce mutual interference between antennas include providing a slit in the ground between the antennas (Patent Document 1) and providing a protrusion on the ground plate between the antennas (Patent Document 2). However, these methods share a ground plate between multiple antennas, so they cannot completely prevent the high-frequency current supplied to one antenna from flowing through the ground plate into the other antenna, and there are cases in which the effect of reducing mutual interference is insufficient.

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 (Patent Document 3) has been proposed as a method for reducing mutual interference when multiple antennas do not share a ground plate.

However, the method of installing a shield between antennas requires that a space be secured between the antennas for the shield, and the shield itself has a certain area and volume, making it difficult to miniaturize the antenna. This method is difficult to adopt when there is limited space in the communications device to install the antenna.

JP 2007-13643 A JP 2013-51644 A JP 2015-70408 A

The objective of the present invention is to provide an antenna device that is composed of multiple antennas that do not share a ground plate, and that can suppress mutual interference between the antennas while also taking into consideration miniaturization.

After extensive research into the structure of the antennas and the method of placement within the device, the inventors were able to realize an antenna device that is compact by placing the ground plates of each antenna close to each other at a specified length and distance, thereby suppressing mutual interference caused by the spatial propagation of radio waves even without the need for a shielding plate.

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 the 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 a shielding plate, which contributes to the miniaturization of the antenna device.

1 shows a basic configuration of an antenna device according to the present invention. 5A and 5B are conceptual diagrams illustrating an interference suppression effect achieved by the antenna device of the present invention. 13 is a modified example of the antenna device of the present invention. This is a particularly preferred variant of the antenna device according to the invention. 1 is an antenna device of a comparative example. 1 shows the V.S.W.R of the antenna used in Example 1. 1 shows the isolation between antennas in the first embodiment. 4 shows the V.S.W.R of the antenna used in Example 2. 13 shows the isolation between antennas in the second embodiment. This is the V.S.W.R of the antenna used in Example 3. 13 shows the isolation between antennas in the third embodiment. 4 shows the V.S.W.R of the antenna used in the comparative example. 4 shows the isolation between antennas in the comparative example.

The present invention will now be described with reference to Figure 1.

As shown in Figure 1, the antenna device 1 of the present invention has a first antenna A1 and a second antenna A2.

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 signals in any frequency band f. In FIG. 1, the first radiating element portion 21 is shown extending 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.

The second antenna A2 is composed of a 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.

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

At this time, the slit S is formed so that the first antenna A1 and the second antenna A2 resonate in the corresponding frequency band f.

In order to form the slit S so that it resonates 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.

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

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 prioritizing 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, etc., if there is a material made of a dielectric around the antenna device 1 and the antenna device 1 is affected by the wavelength shortening effect of the dielectric, the length of the slit S may be set to a value that takes into account the wavelength shortening effect.

In the present invention, the first antenna A1 and the second antenna A2 are electrically independent.
In principle, 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.

Furthermore, in the present invention, the presence of a slit S with open ends between the first ground plate 11 and the second ground plate 12 also suppresses mutual interference due to spatial propagation.

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 there is a slit S between the first ground plate 11 and the second ground plate 12 that resonates in frequency band f, slit resonance due to this high-frequency current occurs in the slit S.

When resonance occurs in the slit S, as shown in Figure 2, the slit S functions as a slit antenna that emits radio waves corresponding to the frequency band f. 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.

Between the first antenna A1 and the second antenna A2, there is a slit S that emits radio waves corresponding to the frequency band f to which both antennas A correspond. As shown in FIG. 2, the radio waves traveling from the first antenna A1 to the second antenna A2 are weakened by interference caused by the radio waves generated by the resonance of the slit S, and interference of the first antenna A1 with the second antenna A2 caused by spatial propagation is suppressed.

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 the resonance of the slit S, and interference from the second antenna A2 to the first antenna A1 caused by spatial propagation is also suppressed.

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

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

In the present invention, the first antenna A1 and the second antenna A2 are placed close 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 that occurs between the first antenna A1 and the second antenna A2.

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.

In addition, it is preferable that the slit S in the present invention has a shape with a bent portion as shown in Figures 3 and 4.

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 with a straight slit S, thereby contributing to stabilizing the mutual interference suppression effect.

In addition, 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 than a straight slit S, which contributes to miniaturization of the antenna device 1.

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 it bent into an approximately L-shape as shown in Figures 3 and 4. When forming the approximately L-shaped slit S, it can be formed by changing the shape of the ground plate 10 of one of the antennas A, such as 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 with a bent portion can be formed with little effort.

Note that the approximately L-shaped slit S refers to a slit S with a bending angle of 90° at the bend, but it does not have to be exactly 90° and some variation is allowed.

When forming the slit S into a roughly L-shape, it is preferable to set the L1:L2 ratio 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.

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

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.

In addition, in the present invention, by taking into consideration the relative positions of the radiating element portions 20 of each antenna A, it is possible to obtain a better effect of suppressing mutual interference between the antennas A.

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 angles.

By arranging the radiating element section 20 in such a positional relationship, the direction of the main axis of the directivity of the first antenna A1 and the main axis of the directivity of the second antenna A2 differ, 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.

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 linear elements that function as inverted F-shaped antennas, elements with folded structures such as U-shapes and meandering shapes, and branched elements that support multiple frequencies can be used, and a parasitic element may be provided within the antenna A to capacitively couple with the radiating element section 20 and express antenna characteristics. Figures 1 and 2 show a radiating element section 20 with a folded structure as an example.

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 with a conductive pattern on a dielectric substrate, or an antenna element that is a combination of both.

The power supply line 30 used in the present invention may be a well-known high-frequency coaxial cable with a fluororesin coating or the like. 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 with solder or by crimping.

The antenna device 1 of the present invention is used by being incorporated into a communication device.

As an embodiment of the present invention, the antenna device 1 shown in Figures 1 to 3 was created and evaluated. Below, we will describe the method of creating and evaluating the antenna device, which is common to each embodiment.

1. Preparation of an Antenna An antenna element having a ground plate 10 and a radiating element portion 20 of a predetermined shape is prepared by punching out a zinc-plated steel plate having a thickness of 0.4 mm.
In each embodiment, the basic shape of the radiating element portion 20 was the same, 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).

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.

2. Creation of the Antenna Device The first antenna A1 and the second antenna A2 created according to the above-described method for creating the 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.

3. Evaluation of the Antenna Device 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 V.S.W.R of each antenna A and the mutual interference (isolation) occurring between the first antenna A1 and the second antenna A2 were measured.

[Example 1]
As Example 1, an antenna device 1-1 of the aspect shown in Fig. 1 was created. In Example 1, the same first antenna A1-1 and second antenna A2-1 were used. The size of the ground plate 10 of each antenna A was 27 mm x 24.5 mm, and the contour sides of the 27 mm length were arranged opposite each other, and a slit S of 27 mm length and 3 mm width was formed. The external dimensions of the antenna device 1 were 27 mm x 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.

The V.S.W.R 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 V.S.W.R of the first antenna A1-1, and the dashed line indicates the V.S.W.R of the second antenna A2-1.

[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 portion 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 portion 12b is the dimension at the center in the width direction of the extension portion 12b.

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 approximately right angles, and an L-shaped slit S with a width of 3 mm is formed between the ground plates. The length of the slit S is the dimension at the center of the width of the slit S, with the horizontal portion length L1 being 9.5 mm, the vertical portion length L2 being 28.5 mm, and the total length being 38 mm. The external dimensions of the antenna device 1 are 40 mm x 54 mm.

The V.S.W.R of the antenna device 1-2 of the second embodiment is shown in Figure 8, and the isolation is shown in Figure 9. In Figure 8, the solid line indicates the V.S.W.R of the first antenna A1-2, and the dashed line indicates the V.S.W.R of the second antenna A2-2.

[Example 3]
As Example 3, an antenna device 1-3 was created as 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 portion 11b measuring 32 mm in length and 5 mm in width extended from a first ground plate 11a measuring 27 mm x 24.5 mm. The second antenna A2-3 was the same as the second antenna A2-1 used in Example 1.

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 approximately right angles, and an L-shaped slit S with a width of 3 mm is formed between the ground plates. The length of the slit S is the dimension at the center of the width of the slit S, with the horizontal portion length L1 being 28.5 mm, the vertical portion length L2 being 20.5 mm, and the total length being 49 mm. The external dimensions of the antenna device 1 are 32 mm x 56 mm.

The V.S.W.R 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 V.S.W.R of the first antenna A1-2, and the dashed line indicates the V.S.W.R of the second antenna A2-2.

[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'.

The V.S.W.R of the antenna device 1' of the comparative example is shown in Figure 12, and the isolation is shown in Figure 13. In Figure 12, the solid line indicates the V.S.W.R of the first antenna A1', and the dashed line indicates the V.S.W.R of the second antenna A2'.

The V.S.W.R of each antenna constituting the antenna device of Examples 1 to 3 and the comparative example drops near 2450 MHz (2.45 GHz), and the V.S.W.R provides sufficient performance for an antenna device used in the 2.45 GHz band.

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 approximately -12 dB near 2.45 GHz.

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

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

Furthermore, 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 with a bent portion between the antennas A, the effect of suppressing mutual interference between the antennas A is improved.

Furthermore, in the antenna device 1-3 of Example 3, 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.

The above describes an antenna device compatible with the wireless LAN band (2.45 GHz band), but 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 example described above, and various antenna configurations that have been proposed in the past can be appropriately selected and used within the scope of the concept of the present invention.

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 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.

The antenna device of the present invention can be applied to various devices with communication functions, and can be suitably used in industrial equipment used in IoT, information appliances with communication functions, automotive-related equipment, access points, etc.

1 Antenna device A Antenna A1 First antenna A2 Second antenna 10 Ground plate 11, 11a First ground plate 11b Extension portion 12, 12a of first ground plate Second ground plate 12b Extension portion 20 Radiating element portion 21 First radiating element portion 22 Second radiating element portion 30 Power supply line 31 First power supply line 32 Second power supply line S Slit P Power supply point P1 First power supply point P2 Second power supply point G Earth point G1 First earth point G2 Second earth point

Claims (7)

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 according to claim 1, wherein the first radiating element portion and the second radiating element portion have the same basic shape. An antenna device according to claim 1 or 2, characterized in that the length of the slit is approximately half the wavelength of the radio wave in the frequency band. The antenna device according to any one of claims 1 to 3, characterized in that a contour edge of the first ground plate from which the first radiating element portion extends and a contour edge of the second ground plate from which the second radiating element portion extends form a positional relationship of approximately a right angle. an extension portion extends from an opposite side of a contour side 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. a substantially L-shaped extension portion extends from an opposite side of a contour side 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. The antenna device according to claim 5 or 6, wherein 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 a range of 2:1 to 1:2.

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