MIMO antenna equipment

Abstract

To provide a MIMO antenna device capable of suppressing interference between antennas in a wide band and being able to be miniaturized.SOLUTION: A MIMO antenna device that performs spatial multiplex transmission includes a first dipole antenna 10 and a second dipole antenna 20. The first dipole antenna 10 is composed of a pair of first elements 11 connected to a first feeding unit 13 and arranged on a first surface 12. The second dipole antenna 20 is composed of a pair of second elements 21 connected to a second feeding unit 23 and arranged on a second surface 22 facing the first surface 12. The second dipole antenna 20 is arranged such that the second feeding unit 23 substantially overlaps with the first feeding unit 13 in the top view, and is arranged so as to intersect the first dipole antenna 10 such that the main part of the pair of second elements 21 does not overlap with the main part of the pair of first elements 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a MIMO antenna device, and more particularly to a small-sized, wideband MIMO antenna device. [Background technology]

[0002] Recently, in automobiles aiming for self-driving, wide-area communication networks using mobile phone networks are being developed to increase the capacity and speed of information transmitted. For example, MIMO (Multiple Imput Multiple Output) technology is known as a technology that performs spatial multiplexing transmission to achieve large capacity and high speed. MIMO antenna devices using multiple antenna elements generally have many design constraints, such as the need to ensure isolation by installing the antenna elements at a distance from each other. In addition, in recent years, the space for mounting antennas inside automobiles has tended to be restricted by other devices such as airbags, making it difficult to miniaturize antennas to a size that can be mounted inside the vehicle.

[0003] Also, for example, Patent Document 1 discloses a multi-band antenna device that uses multiple antenna elements in multiple frequency bands. Patent Document 1 has a structure in which a high-frequency band antenna is inserted into the same space as a low-frequency band antenna while minimizing the effect of interference between antenna elements.

[0004] Also, Patent Document 2 discloses an antenna device that has been made thin so that it can be mounted on an automobile. In Patent Document 2, a cross dipole antenna is formed on a sheet-like dielectric to support circularly polarized waves. In the first dipole antenna and the second dipole antenna that constitute the cross dipole antenna, the balanced feeder that feeds them needs to be arranged adjacent to each other without any gaps. Therefore, by arranging one antenna element of the first dipole antenna and one antenna element of the second dipole antenna on the back side of the dielectric, the balanced feeder can be arranged so that it is aligned vertically when viewed from the side. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2016-535512 [Patent Document 2] JP 2004-242277 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the antenna device in Patent Document 1 is used in base stations and repeaters, and is not designed to be compact enough to be mounted on a vehicle. In addition, no consideration is given to the effect of interference between antenna elements in a wide band when the device is compact.

[0007] In addition, the antenna device of Patent Document 2 uses a cross dipole antenna to support circular polarization, and is not usable as a MIMO antenna device. It is also not intended to suppress the influence of interference between the first dipole antenna and the second dipole antenna. Furthermore, there are many design constraints due to differences in the arrangement positions of the antenna elements of the dipole antenna and the structure of the balanced feeder, making it difficult to reduce the size.

[0008] In view of the above circumstances, the present invention provides a MIMO antenna device that can suppress interference between antennas over a wide band and can be made compact. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object of the present invention, a MIMO antenna device according to the present invention may comprise a first dipole antenna consisting of a pair of first elements connected to a first power supply portion and arranged on a first surface, and a second dipole antenna consisting of a pair of second elements connected to a second power supply portion and arranged on a second surface opposite the first surface, wherein the second dipole antenna is arranged so that the second power supply portion roughly overlaps with the first power supply portion in a top view, and is arranged crossing the first dipole antenna so that a main portion of the pair of second elements does not overlap a main portion of the pair of first elements.

[0010] Here, it is sufficient that the coaxial cables respectively connected to the first power supply portion and the second power supply portion are wired between the first surface and the second surface.

[0011] Additionally, the first dipole antenna may comprise a first bowtie antenna, and the second dipole antenna may comprise a second bowtie antenna.

[0012] The first bowtie antenna may also have a first convex element portion for adjusting antenna performance that extends from the first bowtie antenna onto the first surface.

[0013] The second bowtie antenna may also have a second convex element portion for adjusting antenna performance that extends from the second bowtie antenna onto the second surface.

[0014] In addition, the first bowtie antenna and / or the second bowtie antenna may have a side element portion for adjusting antenna performance extending from the first bowtie antenna and / or the second bowtie antenna on a side surface between the first surface and the second surface.

[0015] Furthermore, the first dipole antenna may have a first folded element portion extending from the first surface to the second surface, and the second dipole antenna may have a second folded element portion extending from the second surface to the first surface, the first folded element portion being arranged in an area within the second surface where the second dipole antenna is not arranged, and the second folded element portion being arranged in an area within the first surface where the first dipole antenna is not arranged.

[0016] Furthermore, the display may include a first substrate having a first power supply portion and a second substrate having a second power supply portion, the first substrate being disposed between the first surface and the second surface.

[0017] The first and second substrates may be formed from the front and back surfaces of a single substrate.

[0018] Furthermore, the first dipole antenna and the second dipole antenna may be arranged diagonally within the rectangular parallelepiped case. Effect of the Invention

[0019] The MIMO antenna device of the present invention has the advantage that it can suppress interference between antennas over a wide band and can be made compact. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram for explaining a MIMO antenna device of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining another example of a dipole antenna of the MIMO antenna device of the present invention. [Diagram 3] FIG. 3 is a schematic diagram for explaining a modified example of the dipole antenna of the MIMO antenna device of the present invention. [Figure 4] FIG. 4 is a graph showing the isolation characteristics versus frequency of the MIMO antenna device of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining a MIMO antenna device of the present invention, where FIG. 1(a) is a top view and FIG. 1(b) is a bb cross-sectional view. In the drawings, parts with the same reference numerals represent the same objects. As shown in the drawing, the MIMO antenna device of the present invention, which performs spatial multiplexing transmission, is mainly composed of a first dipole antenna 10 and a second dipole antenna 20. The MIMO antenna device of the present invention may be housed in, for example, a rectangular parallelepiped case 1. The case 1 may be small, for example, having a size of 60 mm×80 mm×15 mm.

[0022] The first dipole antenna 10 is composed of a pair of first elements 11. The pair of first elements 11 are arranged on a first surface 12. The first dipole antenna 10 is connected to a first power supply unit 13. The pair of first elements 11 in the illustrated example are shown to be composed of linear elements. The first dipole antenna 10 may be arranged, for example, on a first substrate 14 forming the first surface 12. The first power supply unit 13 may be arranged on the first substrate 14. The first substrate 14 may be arranged, for example, on a base 4 made of resin. The first substrate 14 may be arranged, for example, between the first surface 12 and a second surface 22 described later. A coaxial cable 2 or the like is connected to the first substrate 14, and the first substrate 14 is connected to an external device (not shown). The first substrate 12 does not necessarily have to be a flat surface, and may be a surface that is curved to some extent, such as a curved surface.

[0023] The second dipole antenna 20 is composed of a pair of second elements 21. The pair of second elements 21 are arranged on a second surface 22 facing the first surface 12. Here, facing means that the first surface 12 and the second surface 22 do not necessarily have to be parallel as shown in the figure, and may face each other at an angle to some extent as long as the first surface 12 and the second surface 22 are arranged with a certain distance between them. In addition, the second surface 22 does not necessarily have to be a flat surface, and may be a curved surface to some extent, such as a curved surface. The second dipole antenna 20 is connected to a second power supply portion 23. The pair of second elements 21 in the illustrated example are shown as being composed of linear elements. The second dipole antenna 20 may be arranged, for example, on a second substrate 24 that forms the second surface 22. In addition, the second power supply portion 23 may be arranged on the second substrate 24. The second substrate 24 may be arranged, for example, on a base 4 made of resin. The second substrate 24 may be disposed between the first surface 12 and the second surface 22, for example. The second substrate 24 is connected to a coaxial cable 3 and an external device (not shown). As shown in the figure, the second dipole antenna 20 is disposed so that the second feeder 23 is substantially overlapped with the first feeder 13 in a top view. The first feeder 13 and the second feeder 23 are disposed so that they are substantially overlapped with each other in a top view, meaning that the first feeder 13 and the second feeder 23 are disposed substantially near the center of the first dipole antenna 10 or the second dipole antenna 20 in a top view. In addition, the pair of second elements 21 are disposed so as to cross the first dipole antenna 10 so as not to overlap with the main parts of the pair of first elements 11. That is, elements of the same shape may be disposed on the first surface 12 (front surface) and the second surface 22 (back surface) facing each other to form an X-shape in a top view.

[0024] In the illustrated example, the first substrate 14 and the second substrate 24 are disposed on the front and back of the base 4, respectively. However, the present invention is not limited to this, and the first substrate 14 and the second substrate 24 may be formed of the front and back surfaces of a single substrate. That is, instead of using two substrates, the front surface of a single substrate may be used as the first substrate, and the back surface of the substrate may be used as the second substrate. Also, the first dipole antenna 10 and the second dipole antenna 20 may be patterned on the first substrate 14 and the second substrate 24, respectively, by etching the copper foil of the substrate, for example. However, the present invention is not limited to this, and conductive wires or the like may be used, or the conductive wires or the like may be bent into an L-shape, for example, and disposed above the substrate.

[0025] In the illustrated example, the first dipole antenna 10 and the second dipole antenna 20 are arranged diagonally inside the rectangular parallelepiped case 1. By arranging the elements in an X-shape when viewed from above inside the case 1, it is possible to arrange the elements with longer lengths compared to when the elements are arranged in a + shape when viewed from above. However, the present invention is not limited to this, and the elements may be arranged in a + shape when viewed from above inside the case 1.

[0026] Here, when the first dipole antenna 10 and the second dipole antenna 20 are arranged in a cross-shaped (90 degrees perpendicular) in a horizontally long case, the element lengths of the first dipole antenna 10 and the second dipole antenna 20 will change. That is, when the elements are arranged in a cross-shaped manner, the element lengths can be configured to be approximately equal if the case is a square when viewed from above, but if the case is a horizontally long rectangular when viewed from above, the vertically arranged elements will be shorter than the horizontally arranged elements. Then, the resonant frequencies of the two dipole antennas will differ, and the antenna characteristics such as gain at the target frequency will differ. In a MIMO antenna device, if the antenna gain difference between the two dipole antennas becomes large, it will affect the transmission characteristics. Therefore, even if sufficient isolation can be secured between the antennas, the difference in antenna gain may deteriorate the transmission characteristics and reduce the communication speed. However, if two elements are arranged on the diagonal of a horizontally long case so as to form an X-shape when viewed from above, the first dipole antenna 10 and the second dipole antenna 20 can be configured with the same element length regardless of the crossing angle. Therefore, the antenna gains of the two dipole antennas are roughly equal, so it is possible to reduce the possibility of a decrease in communication speed. Furthermore, if two elements are arranged on the diagonal of a horizontally long case so as to form an X-shape when viewed from above, it is possible to physically lengthen the element length, making it possible to support lower frequencies.

[0027] Although it looks like a cross dipole antenna when viewed from above, the first dipole antenna 10 and second dipole antenna 20 of the MIMO antenna device of the present invention are not arranged on the same plane, nor are they intended to obtain circularly polarized waves, and therefore have a different purpose, configuration, and effect from a cross dipole antenna.

[0028] In the above illustrated example, the coaxial cables 2 and 3 are used to feed the first feeder 13 and the second feeder 23 in an unbalanced manner. In the MIMO antenna device of the present invention, the coaxial cables 2 and 3 connected to the first feeder 13 and the second feeder 23 may be wired between the first surface 12 and the second surface 22. That is, the first dipole antenna 10 and the second dipole antenna 20 are arranged so as to be positioned at the outermost side in the thickness direction, and the coaxial cables 2 and 3 are wired using the space between them. This makes it possible to make the device smaller by efficiently using a limited area. The MIMO antenna device of the present invention may use a balun or the like as necessary.

[0029] The MIMO antenna device of the present invention, configured as described above, can suppress interference between the first dipole antenna 10 and the second dipole antenna 20 over a wide band. In addition, since interference between the antennas can be suppressed, the device can be housed in a small case. Therefore, the device can be miniaturized to a size that can be stored in, for example, the instrument panel of a vehicle.

[0030] Next, another example of the dipole antenna of the MIMO antenna device of the present invention will be described with reference to FIG. 2. FIG. 2 is a schematic diagram for explaining another example of the dipole antenna of the MIMO antenna device of the present invention, where FIG. 2(a) is a top view and FIG. 2(b) is a bb cross-sectional view. In the figure, parts with the same reference numerals as in FIG. 1 represent the same objects. In the example of FIG. 1, a dipole antenna composed of linear elements is shown, but in the example of FIG. 2, a first dipole antenna 10 composed of a first bowtie antenna 10' is shown. In addition, the second dipole antenna 20 is also composed of a second bowtie antenna 20'. That is, it has a structure in which two bowtie antennas are arranged crossing each other in a top view. Generally, bowtie antennas are antennas having a self-complementary structure, but the bowtie antennas 10' and 20' in the illustrated example have a structure close to a self-complementary structure. As in the illustrated example, the pair of first elements 11 do not have to have a symmetrical shape, and the pair of second elements 21 do not have to have a symmetrical shape. Furthermore, the bowtie antenna 10' and the bowtie antenna 20' do not have to have a symmetrical shape. The first bowtie antenna 10' and the second bowtie antenna 20' as shown in the illustrated example may be provided as a conductive plate-like body made of sheet metal, a conductive film, or a substrate formed by sputtering, or plated by a laser direct structuring technique.

[0031] The first bowtie antenna 10' is disposed on the first surface 12. In the illustrated example, the surface of the base 4 constitutes the first surface 12. A first substrate 14 having a first power feed portion 13 is fixed to the base 4. The first bowtie antenna 10' is connected to the first power feed portion 13. In the example shown in FIG. 2(a), the element on the lower left side is the ground side element, and the element on the upper right side is the hot side element. Therefore, the first power feed portion 13 on the upper right side is connected to the signal line of the first substrate 14, and the first power feed portion 13 on the lower left side is connected to the ground of the first substrate 14.

[0032] The second bowtie antenna 20' is disposed on a second surface 22 opposite to the first surface 12. In the illustrated example, the back surface of the base 4 constitutes the second surface 22. A second substrate 24 having a second power supply 23 is fixed to the base 4. The second bowtie antenna 20' is connected to the second power supply 23. In the example shown in FIG. 2(a), the lower right element on the back surface side (indicated by a dotted line) is the ground side element, and the upper left element on the back surface side is the hot side element. Therefore, the lower right second power supply 23 is connected to the signal line of the second substrate 24, and the upper left second power supply 23 is connected to the ground of the second substrate 24. The main part of the second bowtie antenna 20' is disposed so as to cross the first bowtie antenna 10' without overlapping with the main part of the first bowtie antenna 10'. Here, the main part of the antenna means a tip side part of the element that is somewhat away from the power supply. It should be noted that there is no problem if the main parts of each antenna overlap to some extent as long as the antenna performance is within an acceptable range.

[0033] The illustrated example also has a first convex element 15 extending from the first bowtie antenna 10'. The first convex element 15 extends on the first surface 12 and is used to adjust the antenna performance. That is, the shape of the first bowtie antenna 10' can be changed using the first convex element 15 to adjust the antenna performance such as frequency characteristics. The shape and position of the first convex element 15 are not limited to those in the illustrated example and may be appropriately determined while observing the antenna performance.

[0034] Similarly, the second bowtie antenna 20′ may also be provided with a second convex element portion 25 for adjusting antenna performance extending from the second bowtie antenna 20′ onto the second surface 22. The shape and position of the second convex element 25 are not limited to those in the illustrated example, and may be appropriately determined while taking into account the antenna performance.

[0035] By using such a bowtie antenna, the MIMO antenna device of the present invention can achieve a wider bandwidth than a linear element.

[0036] In the above illustrated examples, the first dipole antenna 10 and the second dipole antenna 20 are described as examples using linear elements or sheet metal elements, but the present invention is not limited to this. For example, elements may be patterned on a circuit board by etching or the like.

[0037] Next, a modified example of the dipole antenna of the MIMO antenna device of the present invention will be described with reference to FIG. 3. FIG. 3 is a schematic diagram for explaining a modified example of the dipole antenna of the MIMO antenna device of the present invention, in which FIG. 3(a) is a top view, FIG. 3(b) is a partially sectional front view, and FIG. 3(c) is a lateral side view. In the figures, parts with the same reference numerals as in FIG. 1 represent the same objects. The dipole antenna of the illustrated example is basically based on the bowtie antenna as shown in FIG. 2. As shown in FIG. 3, the first bowtie antenna 10' and the second bowtie antenna 20' are examples of deformations obtained by appropriately combining the above-mentioned convex elements for adjusting the antenna performance. However, the present invention is not limited to this, and any shape may be used as long as it is a bowtie antenna in principle.

[0038] In this example, as shown in FIG. 3(b), the first bowtie antenna 10' has a first side element 16 for adjusting antenna performance extending from the first bowtie antenna 10' on a side surface between the first surface 12 and the second surface 22. Specifically, the first side element 16 extends laterally from the pair of first elements 11 so as to be bent 90 degrees along the side surface of the base 4. Similarly, the second bowtie antenna 20' has a second side element 26 for adjusting antenna performance extending from the second bowtie antenna 20' on a side surface between the first surface 12 and the second surface 22. Specifically, the second side element 26 extends laterally from the pair of second elements 21 so as to be bent 90 degrees along the side surface of the base 4.

[0039] The illustrated example shows an example in which the first side element 16 and the second side element 26 are inserted into and fixed to the insertion portion 5 provided on the base 4. As a result, the dipole antenna is fixed to the base 4 together with the bowtie antenna which is integrally provided by sheet metal processing or the like.

[0040] By using the side space in this way, it is possible to extend the antenna length of the bowtie antenna using the side elements 16 and 26. This makes it possible to adjust the antenna performance near the lower limit frequency of the dipole antenna. Note that the first side element 16 and the second side element 26 are not limited to those formed by bending the bowtie antenna by 90 degrees as described above. For example, the side elements may be arranged on the inside or outside of a case or the like that covers the MIMO antenna device, and the side elements may be configured to be electrically connected to the bowtie antenna.

[0041] Also, as shown in FIG. 3(a), the second dipole antenna 20 may be configured to have a second folded element portion 27 extending from the second surface 22 to the first surface 12. The second folded element portion 27 is configured to further extend the pair of second elements 21 arranged on the second surface 22 onto the first surface 12. The second folded element portion 27 may have any shape that allows the antenna performance to be appropriately adjusted, for example, one of them may be L-shaped and the other may be triangular as shown in the figure, or may have the same shape. Also, as shown in FIG. 3(c), the second folded element portion 27 and the second element 21 may be electrically connected by the second side surface connection portion 28. The second side surface connection portion 28 may be provided by sheet metal processing or the like integrally with the second element 21 and the second folded element portion 27 using a conductive plate-like body. Also, the second folded element portion 27 and the second element 21 may be connected using a through hole, wiring, or the like.

[0042] Similarly, the first dipole antenna 10 may be configured to further include a first folded element portion 17 extending from the first surface 12 to the second surface 22. The first folded element portion 17 is configured to further extend the pair of first elements 11 arranged on the first surface 12 onto the second surface 22. The first folded element portion 17 may also have any shape that allows the antenna performance to be appropriately adjusted, and for example, one may be L-shaped and the other may be triangular as shown in the figure, or may have the same shape. The first folded element portion 17 and the first element 11 may also be electrically connected by the first side surface connection portion 18.

[0043] As shown in the figure, the second folded element portion 27 may be disposed in an area of ​​the first surface 12 where the first dipole antenna 10' is not disposed. Similarly, the first folded element portion 17 may be disposed in an area of ​​the second surface 22 where the second dipole antenna 20' is not disposed. By disposing them in this manner, it is possible to adjust the antenna performance near the lower limit frequency of the dipole antenna while efficiently utilizing the limited area in the case 1.

[0044] Moreover, the first folded element portion 17 and the second folded element portion 27 may also be appropriately inserted into the insertion portion 5 provided on the side surface of the base portion 4 and fixed thereto.

[0045] In the MIMO antenna device of the present invention, the antennas on the first surface 12 and the second surface 22 can be formed completely symmetrically, so when two ports (two antennas) are not required, it is possible to simply make it into a one-port antenna device by removing one of the antennas. Also, for example, in the above illustrated example, the MIMO antenna device is described as using two dipole antennas, but the present invention is not limited to this, and it is also possible to increase the number of ports while suppressing interference between antennas by adding further dipole antennas and arranging them crosswise so that the main parts of the elements do not overlap.

[0046] 4 is a graph of the isolation characteristics versus frequency of the MIMO antenna device of the present invention. In the graph, the horizontal axis is frequency and the vertical axis is isolation. The gray line indicates the desired specifications, and a level below this is considered to be good isolation. As shown in the graph, the MIMO antenna device of the present invention can ensure good isolation characteristics over a wide band.

[0047] It should be noted that the MIMO antenna device of the present invention is not limited to the above-mentioned illustrated examples, and various modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0048] 1 case 2 Coaxial Cable 3 Coaxial Cable 4 base 5 Insertion section 10 First dipole antenna 10' First Bowtie Antenna 11 First Element 12 Front page 13 First power supply section 14 First board 15 First convex element 16 First side element 17 First folded element part 18 First side connection part 20 Second dipole antenna 20' Second Bowtie Antenna 21 2nd Element 22 Side 2 23 Second power supply section 24 Second board 25 Second convex element part 26 Second side element 27 Second folded element part 28 Second side connection

Claims

1. A MIMO antenna device that performs spatial multiplexing transmission, the MIMO antenna device comprising: a first dipole antenna including a pair of first elements connected to a first feeding portion and disposed on a first surface; a second dipole antenna consisting of a pair of second elements connected to a second power supply portion and arranged on a second surface opposite to the first surface, the second dipole antenna being arranged so that the second power supply portion substantially overlaps with the first power supply portion in a top view, and being arranged to cross the first dipole antenna such that a main portion of the pair of second elements does not overlap a main portion of the pair of first elements; Coaxial cables connected to the first power supply unit and the second power supply unit are wired between the first surface and the second surface, respectively. A MIMO antenna device.

2. 2. The MIMO antenna apparatus according to claim 1, wherein the first dipole antenna comprises a first bowtie antenna, and the second dipole antenna comprises a second bowtie antenna.

3. 3. The MIMO antenna device according to claim 2, wherein the first bowtie antenna has a first convex element portion for adjusting antenna performance extending from the first bowtie antenna onto a first surface.

4. 4. The MIMO antenna device according to claim 2, wherein the second bowtie antenna has a second convex element portion for adjusting antenna performance extending from the second bowtie antenna onto a second surface.

5. 5. A MIMO antenna device according to claim 2, wherein the first bowtie antenna and / or the second bowtie antenna has a side element portion for adjusting antenna performance extending from the first bowtie antenna and / or the second bowtie antenna on a side surface between the first surface and the second surface.

6. In the MIMO antenna device according to any one of claims 1 to 5, the first dipole antenna has a first folded element portion extending from a first surface to a second surface; the second dipole antenna has a second folded element portion extending from the second surface to the first surface, the first folded element portion is disposed in an area in the second plane where the second dipole antenna is not disposed, the second folded element portion is disposed in an area within the first plane where the first dipole antenna is not disposed; A MIMO antenna device.

7. 7. The MIMO antenna device according to claim 1, further comprising: a first substrate having a first power supply portion and a second substrate having a second power supply portion, the first substrate being disposed between the first surface and the second surface.

8. 8. The MIMO antenna device according to claim 7, wherein the first substrate and the second substrate are formed from the front and back surfaces of a single substrate.

9. 9. The MIMO antenna device according to claim 1, wherein the first dipole antenna and the second dipole antenna are disposed on diagonals within a rectangular parallelepiped case.

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