MIMO antenna equipment

Abstract

To provide a small and lightweight antenna device that can be used over a wide frequency range.SOLUTION: A first element and a second element are rotated approximately 90 degrees to face each other at a predetermined interval, and the whole is tilted at a predetermined angle (for example, approximately 45 degrees) and fixed to a mounting surface. Each of the elements has two arms (101A and 102A, 201A and 202B) extending away from each other from a portion to which a feed point is connected.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] The present invention relates to a thin antenna device that can be used in a wide frequency range, for example, from 698 MHz and frequencies therearound to 6 GHz and frequencies therearound. [Background technology]

[0002] In recent years, there has been an increasing demand for vehicles equipped with electronic devices to carry out communication using MIMO (Multiple-Input Multiple-Output) using frequency bands for LTE (Long Term Evolution) and 5G (5th Generation Mobile Communication System). MIMO is a communication format in which multiple antennas are used to transmit different data from each antenna and the data is received simultaneously by the multiple antennas. As an antenna device that enables such a communication format, the MIMO antenna device disclosed in Patent Document 1 is known.

[0003] The MIMO antenna device disclosed in Patent Document 1 is configured by housing multiple antennas, i.e., unbalanced and balanced antennas, in a shark fin antenna housing that is 100 mm long, 50 mm wide, and 45 mm high. The unbalanced antenna is configured by a rectangular planar etching formed in polychlorinated biphenyl. The balanced antenna is configured by two planar L-shaped arms that are symmetrically opposed to each other. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2016-504799 Summary of the Invention [Problem to be solved by the invention]

[0005] When an unbalanced antenna is made low-profile as in the MIMO antenna device disclosed in Patent Document 1, the antenna size (height) is reduced, which leads to a deterioration in VSWR (Voltage Standing Wave Ratio) and a lack of gain in the horizontal direction. In addition, when multiple antennas are housed in a small area such as a shark fin antenna housing, interference occurs between the antennas, which has an undesirable effect on the antenna characteristics. For example, in a MIMO antenna device used in LTE, the greater the isolation between the antennas, the better, but in the MIMO antenna device disclosed in Patent Document 1, it is difficult to satisfy this condition over a wide frequency band. As shown in Figures 5 to 7 of Patent Document 1, the available frequency bands are limited to multiple locations in the range of 0.6 to 3 GHz, and each band is narrow.

[0006] The main object of the present invention is to provide an antenna device that enables stable operation over a wide frequency band, and furthermore, to reduce the influence of other nearby antennas or elements. [Means for solving the problem]

[0007] An antenna device according to one embodiment of the present invention comprises a pair of first elements arranged on a first plane, and a pair of second elements arranged on a second plane parallel to the first plane, the pair of second elements having a polarization direction perpendicular to that of the pair of first elements, and each of the pair of first elements and the pair of second elements includes a portion that operates as a self-similar antenna or an antenna equivalent thereto. More specifically, each of the pair of first elements and the pair of second elements has two arms extending in directions away from each other from a base end to which a feed point can be connected, and the two arms operate as a self-similar antenna or an antenna equivalent thereto. A "self-similar antenna" is an antenna whose shape remains similar even when the scale (size ratio) is changed, such as a biconical antenna or a bowtie antenna. Effect of the Invention

[0008] The antenna device of the present invention includes a pair of first elements each including a portion that operates as a self-similar antenna or an antenna equivalent thereto, and a pair of second elements whose polarization direction is orthogonal to that of the first elements, and operates, for example, as a tapered slot antenna (a type of traveling wave antenna) in the high frequency band, which is a relatively high frequency band, and operates, for example, as a loop antenna (a type of resonant antenna) in the low frequency band, which is a relatively low frequency band. Also, in a specific frequency band in the mid-frequency band, which is a frequency band between the relatively high frequency band and the relatively low frequency band, it operates as a dipole antenna (a type of resonant antenna). Also, in the bands between the relatively high frequency band, the relatively low frequency band, and the mid-frequency band, the operation principles of those antennas are combined, that is, it operates as a composite antenna. Therefore, although it is a single antenna device, it can be stably operated over a wider frequency band than conventional antenna devices of this type. In addition, since the directions of polarization of the first and second elements are perpendicular to each other, the influence of interference and the like is reduced even when the first and second elements are close to each other, and therefore the antenna device can be made thin. [Brief description of the drawings]

[0009] [Figure 1A] FIG. 2 is a perspective view of a case body in which an antenna unit of the first embodiment is housed. [Figure 1B] FIG. 1B is a cross-sectional view of one side of FIG. 1A. [Figure 2A] FIG. 2 is a front view of the antenna unit according to the first embodiment. [Figure 2B] FIG. 4 is a rear view of the antenna unit according to the first embodiment. [Figure 2C] FIG. 2 is a top view of the antenna unit according to the first embodiment. [Figure 2D] FIG. 2 is a perspective view of an antenna unit according to the first embodiment. [Figure 3A] 11A and 11B are diagrams illustrating one and the other second elements. [Figure 3B] 4A to 4C are diagrams illustrating a pair of second elements. [Figure 4A] VSWR characteristic diagram of one element. [Figure 4B] Radiation efficiency characteristic diagram of one element. [Figure 4C] Average gain characteristic diagram of the antenna in the horizontal plane of FIG. 3A. [Figure 5A] VSWR characteristic diagram of two elements. [Figure 5B] Radiation efficiency characteristic diagram of two elements. [Figure 5C] Average gain characteristic diagram of the antenna in the horizontal plane of FIG. 3B. [Figure 6A] FIG. 4 is a VSWR characteristic diagram of a power supply point K1 in the first embodiment. [Figure 6B] FIG. 4 is a VSWR characteristic diagram of a power supply point K2 in the first embodiment. [Figure 7A] FIG. 4 is a radiation efficiency characteristic diagram of a feed point K1 in the first embodiment. [Figure 7B] FIG. 4 is a radiation efficiency characteristic diagram of a feed point K2 in the first embodiment. [Figure 8A] FIG. 4 is a characteristic diagram of power passing from a power feed point K1 to a power feed point K2 in the first embodiment. [Figure 8B] FIG. 4 is a characteristic diagram of power passing from a power feed point K2 to a power feed point K1 in the first embodiment. [Figure 9A] FIG. 2 is a front view of the antenna unit according to the first embodiment. [Figure 9B] FIG. 4 is a front view showing a state in which the antenna unit of the first embodiment is inclined at a predetermined angle. [Figure 10A] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K1 in the arrangement of FIG. 9A. [Figure 10B] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K2 in the arrangement of FIG. 9A. [Figure 11A] Average gain characteristic diagram in the horizontal plane of the feed point K1 in the arrangement of FIG. 9B. [Figure 11B] Average gain characteristic diagram in the horizontal plane of the feed point K2 in the arrangement of FIG. 9B. [Figure 12A] FIG. [Figure 12B] FIG. [Figure 12C]FIG. [Figure 12D] FIG. [Figure 13A] FIG. 13 is a VSWR characteristic diagram of the antenna part of the comparative example. [Figure 13B] FIG. 13B is an enlarged view of the low-frequency portion of FIG. 13A. [Figure 14A] FIG. 4 is a radiation efficiency characteristic diagram of an antenna unit of a comparative example. [Figure 14B] FIG. 14B is an enlarged view of the low-frequency portion of FIG. 14A. [Figure 15A] FIG. 11 is a front view of an antenna unit according to a second embodiment. [Figure 15B] FIG. 11 is a rear view of the antenna unit according to the second embodiment. [Figure 15C] FIG. 11 is a top view of an antenna unit according to a second embodiment. [Figure 15D] FIG. 11 is a perspective view of an antenna unit according to a second embodiment. [Figure 16A] FIG. 11 is a VSWR characteristic diagram of a power supply point K1 in the second embodiment. [Figure 16B] FIG. 11 is a VSWR characteristic diagram of a power supply point K2 in the second embodiment. [Figure 17A] FIG. 11 is a radiation efficiency characteristic diagram of a feed point K1 in the second embodiment. [Figure 17B] FIG. 11 is a radiation efficiency characteristic diagram of a feed point K2 in the second embodiment. [Figure 18A] FIG. 11 is a characteristic diagram of power passing from a power feed point K1 to a power feed point K2 in the second embodiment. [Figure 18B] FIG. 11 is a characteristic diagram of power passing from a power feed point K2 to a power feed point K1 in the second embodiment. [Figure 19A] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K1 in the arrangement of FIG. 9A. [Figure 19B] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K2 in the arrangement of FIG. 9A. [Figure 20A] FIG. 13 is a front view of an antenna unit according to a third embodiment. [Figure 20B] FIG. 11 is a top view of a long side portion of an antenna unit according to a third embodiment. [Figure 20C] FIG. 11 is a side view of a short side portion of the antenna unit according to the third embodiment. [Figure 20D] FIG. 13 is a perspective view of an antenna unit according to a third embodiment. [Figure 21A] FIG. 13 is a VSWR characteristic diagram of a power supply point K1 in the third embodiment. [Figure 21B] FIG. 13 is a VSWR characteristic diagram of a power supply point K2 in the third embodiment. [Figure 22A] FIG. 13 is a radiation efficiency characteristic diagram of a feed point K1 in the third embodiment. [Figure 22B] FIG. 13 is a radiation efficiency characteristic diagram of a feed point K2 in the third embodiment. [Figure 23A] FIG. 13 is a characteristic diagram of power passing from a power feed point K1 to a power feed point K2 in the third embodiment. [Figure 23B] FIG. 13 is a characteristic diagram of power passing from a power feed point K2 to a power feed point K1 in the third embodiment. [Figure 24A] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K1 in the arrangement of FIG. 9A. [Figure 24B] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K2 in the arrangement of FIG. 9A. [Figure 25A] FIG. 13 is a front view of an antenna unit according to a fourth embodiment. [Figure 25B] FIG. 13 is a top view of an antenna unit according to a fourth embodiment. [Figure 25C] FIG. 13 is a perspective view of an antenna unit according to a fourth embodiment. [Figure 26A] FIG. 13 is a VSWR characteristic diagram of a power supply point K1 in the fourth embodiment. [Figure 26B] FIG. 13 is a VSWR characteristic diagram of a power supply point K2 in the fourth embodiment. [Figure 27A] FIG. 13 is a radiation efficiency characteristic diagram of a feed point K1 in the fourth embodiment. [Figure 27B] FIG. 13 is a radiation efficiency characteristic diagram of a feed point K2 in the fourth embodiment. [Figure 28A] FIG. 13 is a characteristic diagram of power passing from a power feed point K1 to a power feed point K2 in the fourth embodiment. [Figure 28B] FIG. 13 is a characteristic diagram of power passing from a power feed point K2 to a power feed point K1 in the fourth embodiment. [Figure 29A] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K1 in the arrangement of FIG. 9A. [Figure 29B] 9B is a diagram showing the average gain characteristic in the horizontal plane of the feed point K2 in the arrangement of FIG. 9A. [Figure 30A]FIG. 13 is a front perspective view of an antenna unit according to a fourth embodiment. [Figure 30B] FIG. 13 is a perspective view of the rear side of the antenna unit according to the fourth embodiment. [Figure 31A] FIG. 13 is a perspective view of an antenna unit according to a sixth embodiment. [Figure 31B] FIG. 13 is a front view showing a power supply state of a first element in the sixth embodiment. [Figure 31C] FIG. 13 is a front view showing a power supply state of a second element in the sixth embodiment. [Figure 32A] FIG. 13 is a VSWR characteristic diagram of an output end of a coaxial cable F114 in the sixth embodiment. [Figure 32B] FIG. 13 is a VSWR characteristic diagram of the output end of the coaxial cable F214 in the sixth embodiment. [Figure 32C] FIG. 13 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F114 in the sixth embodiment. [Fig. 32D] FIG. 13 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F214 in the sixth embodiment. [Figure 32E] FIG. 13 is a characteristic diagram of power passing from an output end of a coaxial cable F114 to an output end of a coaxial cable F214 in the sixth embodiment. [Fig. 32F] FIG. 13 is a characteristic diagram of power passing from an output end of a coaxial cable F214 to an output end of a coaxial cable F114 in the sixth embodiment. [Fig. 32G] 32B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F114 in the arrangement of FIG. 32A. [Fig. 32H] 32B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F214 in the arrangement of FIG. 32A. [Figure 33A] FIG. 23 is a front view of a first element in the seventh embodiment. [Figure 33B] FIG. 23 is a front view of a second element in the seventh embodiment. [Figure 33C] FIG. 23 is a front view showing a power supply state of a first element in the seventh embodiment. [Figure 33D] FIG. 23 is a front view showing a power supply state of a second element in the seventh embodiment. [Figure 33E] FIG. 4 is a perspective view showing the entire state of the first element and the second element. [Figure 33F] FIG. 23 is a side view of the antenna unit according to the seventh embodiment. [Figure 34A] FIG. 13 is a VSWR characteristic diagram of the output end of the coaxial cable F114 in the seventh embodiment. [Figure 34B] FIG. 23 is a VSWR characteristic diagram of the output end of the coaxial cable F214 in the seventh embodiment. [Figure 34C] FIG. 13 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F114 in the seventh embodiment. [Fig. 34D] FIG. 23 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F214 in the seventh embodiment. [Figure 34E] FIG. 23 is a characteristic diagram of passing power from the output end of the coaxial cable F114 to the output end of the coaxial cable F214 in the seventh embodiment. [Fig. 34F] FIG. 13 is a characteristic diagram of power passing from an output end of a coaxial cable F214 to an output end of a coaxial cable F114 in the seventh embodiment. [Figure 34G] 31B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F114 in the arrangement of FIG. 31A. [Fig. 34H] FIG. 23 is a diagram showing average gain characteristics in the horizontal plane at the output end of the coaxial cable F214 in the seventh embodiment. [Figure 35A] FIG. 11 is a VSWR characteristic diagram of an output end of a coaxial cable F114 according to a modified example. [Figure 35B] FIG. 13 is a VSWR characteristic diagram of the output end of a coaxial cable F214 according to a modified example. [Figure 35C] FIG. 11 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F114 according to a modified example. [Figure 35D] FIG. 13 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F214 according to a modified example. [Figure 35E] FIG. 13 is a diagram showing passing power characteristics from an output end of a coaxial cable F114 to an output end of a coaxial cable F214 according to a modified example. [Fig. 35F] FIG. 11 is a diagram showing passing power characteristics from an output end of a coaxial cable F214 to an output end of a coaxial cable F114 according to a modified example. [Figure 35G] 31B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F114 in the arrangement of FIG. 31A. [Fig. 35H] FIG. 13 is an average gain characteristic diagram in the horizontal plane of the output end of a coaxial cable F214 according to a modified example. [Figure 36A] FIG. 23 is a perspective view showing an example of the overall configuration of an antenna unit according to an eighth embodiment. [Figure 36B] FIG. 23 is a front view showing a power supply state of a first element in the eighth embodiment. [Figure 36C] FIG. 23 is a front view showing a power supply state of a second element in the eighth embodiment. [Figure 37A] FIG. 23 is a VSWR characteristic diagram of the output end of the coaxial cable F114 in the eighth embodiment. [Figure 37B] FIG. 23 is a VSWR characteristic diagram of the output end of the coaxial cable F214 in the eighth embodiment. [Figure 37C] FIG. 23 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F114 in the eighth embodiment. [Figure 37D] FIG. 23 is a radiation efficiency characteristic diagram of an output end of a coaxial cable F214 in the eighth embodiment. [Figure 37E] FIG. 23 is a characteristic diagram of power passing from the output end of the coaxial cable F114 to the output end of the coaxial cable F214 in the eighth embodiment. [Figure 37F] FIG. 23 is a characteristic diagram of power passing from an output end of a coaxial cable F214 to an output end of a coaxial cable F114 in the eighth embodiment. [Figure 37G] 31B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F114 in the arrangement of FIG. 31A. [Fig. 37H] 31B is a diagram showing the average gain characteristic in the horizontal plane of the output end of the coaxial cable F214 in the arrangement of FIG. 31A. [Figure 38] FIG. 13 is an external view of an antenna device according to a ninth embodiment. [Figure 39] FIG. 13 is an exploded view of the antenna device according to the ninth embodiment. [Figure 40A] FIG. 4 is a perspective view of the inside of the first case body as viewed from the rear side. [Figure 40B] FIG. [Figure 40C] FIG. 4 is a perspective view of the inside of the second case body as viewed from the rear side. [Figure 40D] FIG. 4 is a front view of the inside of the second case body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, with reference to the drawings, an embodiment in which the present invention is applied to an antenna device that can be used in a wide frequency band ranging from 698 MHz and frequencies therearound to 6 GHz and frequencies therearound will be described. [First embodiment] The antenna device of the first embodiment is used by housing the antenna unit in a thin case that can be installed in any position, for example, inside a room or a vehicle. The thin case includes a case body made of a radio wave transparent material, for example, ABS resin, and a holding part that is appropriately molded according to the installation location. The case body has, for example, a bottomed rectangular prism-shaped housing having an internal space for housing the antenna unit, and a lid for sealing the housing space. The lid is provided on one of the four side surfaces of the housing, or on one of the widest main surfaces, and is sealed.

[0011] An example of the shape of the case body is shown in FIG. 1A. FIG. 1B is a cross-sectional view of one side (vertical side L1 in this example) of FIG. 1A. Case body 10 is an example of a case with vertical side L1 and horizontal side L2 both being about 90 mm, and depth L3 being about 13 mm. As shown in FIG. 1B, the internal size of case 10 is such that, for vertical side L1, inner side L11 is about 87 mm, and inner depth L31 is about 10 mm. After the antenna unit is housed in the case body, the case body is sealed with a lid. One of a plurality of holding parts (not shown) prepared according to, for example, the planar shape of the dashboard is attached to the mounting portion of the case body.

[0012] The antenna section housed in the case body 10 will be described. Figs. 2A to 2D are diagrams showing an example of the configuration of the antenna section, with Fig. 2A being a front view, Fig. 2B being a rear view of Fig. 2A, Fig. 2C being a top view, and Fig. 2D being a perspective view. For convenience, an orthogonal coordinate system with x, y, and z axes is defined. The antenna section includes a pair of first elements arranged on a first plane 100, and a pair of second elements arranged on a second plane 200 parallel to the first plane 100, the direction of polarization of which is orthogonal to that of the pair of first elements. The configurations of the pair of first elements and the pair of second elements will be described with reference to Figs. 3A and 3B.

[0013] A predetermined portion of each element (in the illustrated example, the portions where the pair of first elements and the pair of second elements are closest to each other) is a portion where a power feed point can be connected. Such a portion is called the "base end." When it is necessary to particularly distinguish between the base end of the pair of first elements and the base end of the pair of second elements, the former may be called the "first base end" and the latter the "second base end." One of the pair of first elements (for convenience, referred to as "one of the first elements") has two arms 101a, 102a extending in a direction away from the first base end, and the tip of each of the arms 101a, 102a is an open end.

[0014] The other first element of the pair (for convenience, referred to as the "other first element") also has two arms 101b, 102b extending in a direction away from the first base end, and the tip of each of the arms 101b, 102b is an open end. The width of each of the two arms (for example, 101a, 102a) of one first element increases continuously or stepwise as it moves away from the first base end. That is, the width of each is larger in a region far from the first base end than in a region close to the first base end. Also, the distance between each of the arms increases continuously or stepwise as it moves away from the first base end. That is, the distance between each of the arms increases continuously or stepwise as it moves away from the first base end. That is, the distance between each of the arms increases larger in a region far from the first base end than in a region close to the first base end. This is to allow each of the arms 101a, 102a to operate as a self-similar antenna such as a biconical antenna or a bowtie antenna, or an equivalent operation.

[0015] The same is true for the two arms (e.g., 101b, 102b) of the other first element. Moreover, the two arms (e.g., 101a, 102a) of one first element also extend in directions away from the two arms (e.g., 101b, 102b) of the other first element.

[0016] The pair of second elements also have the same shape and structure as the pair of first elements. That is, one of the pair of second elements (for convenience, referred to as one second element) has two arms 201a, 202a extending in a direction away from the second base end, and the tip of each of the arms 201a, 202a is an open end. The width of each of the two arms (for example, 201a, 202a) of one of the second elements increases continuously or stepwise as it moves away from the second base end. That is, the width of each is larger in a region far from the second base end than in a region close to the second base end. Also, the opposing distance between each of the arms increases continuously or stepwise as it moves away from the second base end. That is, the opposing distance between each of the arms is larger in a region far from the second base end than in a region close to the second base end. This is to allow each of the arms 201a, 202a to operate as a self-similar antenna such as a biconical antenna or a bowtie antenna, or an equivalent operation. The same is true for the two arms (e.g., 201b, 202b) of the other second element. Moreover, the two arms (e.g., 201a, 202a) of one second element also extend in directions away from the two arms (e.g., 201b, 202b) of the other second element.

[0017] Next, the arrangement of a pair of first elements and a pair of second elements will be described. The midpoint of the distance between the first base end of one first element and the first base end of the other first element is called the first central part. Also, the approximate midpoint of the distance between the second base end of one second element and the base end of the other second element is called the second central part. The first central part is the power feed point K1 of the first element, and the second central part is the power feed point K2 of the second element. The first central part and the second central part overlap when viewed from a plane (for example, the front or back).

[0018] The pair of second elements are arranged opposite the pair of first elements with the second central portion rotated approximately 90 degrees from a position directly facing the first central portion while maintaining the interval D11. Therefore, a split ring (a ring with a shape in which a part is cut out and opposed) is formed between the opposing first and second elements. In addition, the directions of polarization of the first and second elements are orthogonal to each other. That is, for example, if the direction of polarization of the first element is vertical (vertical polarization), the direction of polarization of the second element is horizontal (horizontal polarization), and conversely, if the direction of polarization of the first element is horizontal (horizontal polarization), the direction of polarization of the second element is vertical (vertical polarization). Note that "approximately 90 degrees" does not have to be exactly 90 degrees.

[0019] The size (outer edge size) connecting the outer edges of the first elements is the same as the outer edge size of the second elements. Therefore, the outer edge size is the same before and after the rotation of the pair of second elements. Each element is, for example, a conductive plate with a thickness of 0.5 mm, and the outer edge size is a size that fits into the storage space of the case body 10 in FIG. 1. As an example, the outer edge size of each element is about 87 mm x about 87 mm x about 10 mm. The distance D11 between the first plane 100 and the second plane 200 is the inner depth L31 of the case body 10, that is, about 9 mm.

[0020] Next, the element structure of each of the pair of first elements and the pair of second elements will be described in detail. Figures 3A and 3B are explanatory diagrams of a structural example of the second element. As shown in Figure 3A, the pair of second elements are configured as shown in Figure 3B by joining two arms 201a, 202a of one second element and two arms 201b, 202b of the other second element symmetrically around the second base end (feed point K2) or by integrally molding them.

[0021] The portion from each of the arms 201a, 202a, 201b, and 202b to the tip is an open end. This tip portion is called the open end portion. Each open end portion is formed mainly to ensure a certain area of ​​the first element and the second element in order to ensure low frequencies (to enable use at lower frequencies). In this example, an example in which the open end portion is formed into an L-shape is shown, but the shape of the open end portion is not limited to an L-shape and may be a trapezoid, a rhombus, an ellipse, a circle, a triangle, or the like. The width of the two arms 201a, 202a of one second element and the width of the two arms 201b, 202b of the other second element increase continuously or stepwise as they move away from the second base end to the open end. That is, the width of the two arms 201a, 202a of one second element and the width of the two arms 201b, 202b of the other second element are larger in a region far from the second base end and close to the open end than in a region close to the second base end and far from the open end. Also, the opposing distance of the two arms 201a, 202a of one second element and the opposing distance of the two arms 201b, 202b of the other second element increase continuously or stepwise as they move away from the second base end. That is, the opposing distance between the two arms 201a, 202a of one second element and the opposing distance between the two arms 201b, 202b of the other second element are larger in the area far from the second base end than in the area close to the second base end. With this configuration, the antenna operates like a self-similar antenna such as a biconical antenna or a bowtie antenna, or an equivalent thereof. As a result, the two arms 201a, 202a of one second element and the two arms 201b, 202b of the other second element form a substantially V-shape together with the second base end. The pair of first elements also have the same element structure as that shown in FIGS. 3A and 3B.

[0022] 4A to 4C show antenna characteristics when one of the second elements (for example, two arms 201a, 202a) in FIG. 3A is used alone as an antenna. FIG. 4A is a VSWR characteristic diagram, FIG. 4B is a radiation efficiency characteristic diagram, and FIG. 4C is an average gain characteristic diagram in the horizontal plane (xy plane) of the antenna in FIG. 3A. The horizontal axis of each diagram indicates frequency (MHz). The average gain is the average gain in the horizontal plane (similarly below). As shown in FIG. 4A and FIG. 4B, when only the second element is used alone as an antenna, the operation as a resonant antenna is dominant around 900 MHz, and the operation as a non-resonant antenna is dominant above about 2500 MHz. Also, as can be seen from FIG. 4C, the average gain is about -2 dBi or more at about 900 MHz to 4500 MHz, which is a practical level that is comparable to the MIMO antenna device disclosed in Patent Document 1.

[0023] 5A to 5C show antenna characteristics when a pair of second elements shown in FIG. 3B is operated as an antenna. FIG. 5A is a VSWR characteristic diagram, FIG. 5B is a radiation efficiency characteristic diagram, and FIG. 5C is an average gain characteristic diagram in the horizontal plane (xy plane) of the antenna in FIG. 3B. The horizontal axis in each case indicates frequency (MHz). As can be seen from FIG. 5A to FIG. 5C, when a pair of second elements is operated as an antenna, the VSWR, radiation efficiency, and average gain (dBi) at a frequency of about 1500 MHz are significantly improved compared to when one second element shown in FIG. 3A is used. Similar antenna characteristics are obtained for a pair of first elements.

[0024] Next, the antenna characteristics of the antenna unit configured as shown in Figs. 2A to 2D will be described. In this antenna unit, the second base end of the pair of second elements faces the pair of first elements in a state where the second base end is rotated approximately 90 degrees from a position directly facing the first base end while maintaining the interval D11. That is, a split ring is formed between the opposing first and second elements. Therefore, the frequency band is expanded to the low frequency side, and it is possible to operate as a wider band antenna. In addition, the polarization of the first and second elements is orthogonal. For example, if the polarization of the first element is vertically polarized, the polarization of the second element is horizontally polarized, and conversely, if the polarization of the first element is horizontally polarized, the polarization of the second element is vertically polarized. Therefore, it is possible to suppress mutual interference. For example, the isolation is significantly improved compared to the case where there is no rotation.

[0025] An example of the characteristics of the antenna unit of the first embodiment will be specifically described below. Fig. 6A is a VSWR characteristic diagram of the feed point K1, and Fig. 6B is a VSWR characteristic diagram of the feed point K2. The horizontal axis in each case is frequency (MHz). According to the antenna unit of the first embodiment, the frequency band that can be used as a received wave or a transmitted wave is expanded to the lower frequency side.

[0026] Fig. 7A is a radiation efficiency characteristic diagram of the feed point K1, and Fig. 7B is a radiation efficiency characteristic diagram of the feed point K2. The horizontal axis in each case is frequency (MHz). In the antenna unit of the first embodiment, the radiation efficiency at around 698 MHz is about 0.85 (about 0.17 in the example of Fig. 4B, and about 0.3 in the example of Fig. 5B). It can be seen that the usable frequency is expanded in the direction of lower frequencies.

[0027] Fig. 8A is a diagram showing the power passing characteristic from feed point K1 to feed point K2, and Fig. 8B is a diagram showing the power passing characteristic from feed point K2 to feed point K1. The vertical axis of Fig. 8A is 20Log|S21| (dB), and the vertical axis of Fig. 8B is 20Log|S12| (dB), and the horizontal axis of each is frequency (MHz). S21 is an S parameter representing the transmission coefficient from feed point K1 of the first element to feed point K2 of the second element, and 20Log|S21| is the decibel representation of the power passing characteristic. Moreover, S12 is an S parameter representing the transmission coefficient from feed point K2 of the second element to feed point K1 of the first element, and 20Log|S12| is the decibel representation of the power passing characteristic. In the antenna unit of the first embodiment, the isolation between the feed point K1 and the feed point K2 is about -30 dB to about -70 dB or less over a wide band from 698 MHz and frequencies around it to about 6 GHz and higher frequencies. In other words, even though the feed point K1 and the feed point K2 are close to each other, interference between the antennas is extremely small.

[0028] The antenna unit in the first embodiment is installed on the Z plane, which is vertically above the XY plane that is parallel to the earth. The inventors verified how much the antenna characteristics change when the antenna unit is tilted by a specified angle on the Z plane. FIG. 9A is a front view of the antenna unit of this embodiment, and is the same as FIG. 2A. FIG. 9B is a diagram showing a state in which the antenna unit is tilted at a predetermined angle θ, for example, approximately 45 degrees counterclockwise. FIG. 10A is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K1 in the arrangement of FIG. 9A, and FIG. 10B is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K2 in the arrangement of FIG. 9A. The vertical axis is average gain (dBi) and the horizontal axis is frequency (MHz). In the pair of first elements, for example, the average gain is about 1 dBi near 698 MHz, and about -3 dBi near 6 GHz. The range of gain fluctuations at frequencies between these frequencies is also smaller than those in FIG. 4C and FIG. 5C. In the pair of second elements, for example, the average gain is about -2 dBi near 698 MHz, and about -2 dBi near 6 GHz. The range of average gain fluctuations at frequencies between these frequencies is also smaller than those in FIG. 4C and FIG. 5C.

[0029] Fig. 11A is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K1 when the antenna unit is tilted, i.e., in the state of Fig. 9B, and Fig. 11B is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K2 when the antenna unit is in the state of Fig. 9B. In comparison with Figs. 10A and 10B, the gains in the frequency band of 5 GHz or more are higher for both the first and second elements than before rotation. Also, the difference between the maximum and minimum values ​​of the gain was about 6 dB before rotation, but is reduced to about 4 dB in the rotated state. In other words, it can be seen that by fixing the antenna unit at an angle of about 45 degrees, it is possible to suppress the fluctuation of the average gain while increasing the average gain. Note that "approximately 45 degrees" does not necessarily mean that it is exactly 45 degrees.

[0030] Here, in order to explain the characteristic operation of the antenna unit of the first embodiment, a comparative antenna unit having a similar structure to the antenna unit of the first embodiment will be explained. Fig. 12A is a front view of the comparative antenna unit, Fig. 12B is a rear view, Fig. 12C is a top view, and Fig. 12D is a perspective view. The comparative antenna unit includes a pair of first bowtie antennas and a pair of second bowtie antennas that have the same frequency, material, and length and width size as the antenna unit of the first embodiment. The size is such that they can be accommodated in the case body 10 shown in Fig. 1.

[0031] A pair of first bowtie antennas 501, 502 are each a semicircular plate with its diameter portion facing outward on the first surface 500. A pair of second bowtie antennas 601, 602 are each a semicircular plate with its diameter portion facing outward on the second surface 600. Each bowtie antenna faces the other while maintaining a distance D11, with the closest arc portions (for example, arc portions to which feed points K1, K2 are connected) rotated approximately 90 degrees from their respective positions facing directly opposite each other.

[0032] Fig. 13A is a VSWR characteristic diagram of the antenna unit of the comparative example, and Fig. 13B is an enlarged view of the low frequency portion of Fig. 13A. Fig. 14A is a radiation efficiency characteristic diagram of the antenna unit of the comparative example, and Fig. 14B is an enlarged view of the low frequency portion of Fig. 14A. The horizontal axis in each case is frequency (MHz). The measurement conditions for each characteristic are the same as those for the antenna unit of the first embodiment. The dashed line indicates the characteristic when only the pair of first bowtie antennas 501, 502 is provided, and the solid line indicates the characteristic when the pair of first bowtie antennas 501, 502 and the pair of second bowtie antennas 601, 602 are arranged opposite each other.

[0033] These measurement results show that even a pair of bowtie antennas (for example, the first bowtie antennas 501, 502) can be used as a wideband antenna, and that simply placing one pair of bowtie antennas and the other pair of bowtie antennas facing each other with their closest arcs rotated approximately 90 degrees from their directly opposite positions while maintaining the distance D11 can result in a decrease in both VSWR and radiation efficiency. Particularly in the low frequency range, the VSWR is at a minimum near 1000 MHz, at about 6, and the radiation efficiency is also 0.5 or less.

[0034] [Second embodiment] Next, a second embodiment of the present invention will be described. The antenna unit of the second embodiment is similar to the antenna unit of the first embodiment in that it includes a pair of first elements and a pair of second elements whose polarization directions are orthogonal to each other, and each element includes a portion that operates in accordance with a self-similar antenna, but the shape and structure of each element are different from those of the antenna unit of the first embodiment. However, the size of the antenna unit of the second embodiment is similar to that of the antenna unit of the first embodiment. That is, the case body 10 shown in FIG. 1 can also accommodate the antenna unit of the second embodiment. For convenience of explanation, the same member names and the same reference numerals are used for members corresponding to the antenna unit of the first embodiment.

[0035] Fig. 15A is a front view of the antenna unit according to the second embodiment, Fig. 15B is a rear view, Fig. 15C is a top view, and Fig. 15D is a perspective view. The antenna unit of the second embodiment has a pair of first elements and a pair of second elements. The pair of second elements face the pair of first elements in a state rotated approximately 90 degrees while maintaining a predetermined distance D11 from a position where the second central portion (port or part to which the feed point K2 is connected) and the first central portion (port or part to which the feed point K1 is connected) face each other. The outer edge size of the antenna unit is the same before and after the rotation.

[0036] A pair of first elements will be described. One first element has two arms 101c, 101d extending from a first base end in a direction away from each other. The other first element also has two arms 102c, 102d extending from a first base end in a direction away from each other. The arm 101c of one first element also extends in a direction away from the nearest arm 102c of the other first element. Similarly, the arm 101d also extends in a direction away from the arm 102d. One first element and the other first element are disposed symmetrically about the first central portion, and are substantially C-shaped when viewed from the front.

[0037] Each of the arms 101c, 101d, 102c, and 102d is a conductive plate having a uniform width, and the tip of the arm is an open end formed into a predetermined shape, for example, an L-shape. The open end of the arm 101c faces the open end of the arm 101d, and the open end of the arm 102c faces the open end of the arm 102d. In addition, bent regions 1011c, 1011d, 1021c, and 1021d are formed in a part of each open end. The bent regions 1011c, 1011d, 1021c, and 1021d are bent at approximately 90 degrees in the thickness direction of the antenna unit, that is, in the direction of the second element described later. This is to reduce the overall size while maintaining performance.

[0038] The second element will be described. One second element has two arms 201c, 201d extending from the second base end in a direction away from each other. The other second element also has two arms 202c, 202d extending from the second base end in a direction away from each other. The arm 201c of one second element also extends in a direction away from the nearest arm 202c of the other second element. The arm 201d also extends in a direction away from the nearest arm 202d. One second element and the other second element are arranged symmetrically with respect to the second central portion, and are substantially C-shaped when viewed from the front.

[0039] Each of the arms 201c, 201d, 202c, and 202d is a conductive plate having a uniform width, and the tip of the arm is an open end formed into a predetermined shape, for example, an L-shape. The open end of the arm 201c faces the open end of the arm 201d, and the open end of the arm 202c faces the open end of the arm 202d. In addition, bent regions 2011c, 2011d, 2021c, and 2021d are formed in a part of each open end. The bent regions 2011c, 2011d, 2021c, and 2021d are bent at approximately 90 degrees in the thickness direction of the antenna unit, i.e., in the direction of the first element. This is to reduce the overall size while maintaining performance.

[0040] Furthermore, like the antenna section of the first embodiment, the antenna section of the second embodiment also has split rings formed therein, so that the usable frequency band can be expanded to the lower frequency side.

[0041] Antenna characteristics of the antenna unit of the second embodiment are shown in Figs. 16A to 19B. Fig. 16A is a VSWR characteristic diagram of the feed point K1, and Fig. 16B is a VSWR characteristic diagram of the feed point K2. Fig. 17A is a radiation efficiency characteristic diagram of the feed point K1, and Fig. 17B is a radiation efficiency characteristic diagram of the feed point K2. The horizontal axis of each diagram is frequency (MHz). Fig. 18A is a passing power characteristic diagram from the feed point K1 of the first element to the feed point K2 of the second element, and Fig. 18B is a passing power characteristic diagram from the feed point K2 of the second element to the feed point K1 of the first element. The vertical axis of Fig. 18A is the above-mentioned 20Log|S21| (dB), and the vertical axis of Fig. 18B is 20Log|S12| (dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 19A is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K1 in the arrangement of Fig. 9A, and Fig. 19B is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K2 in the arrangement of Fig. 9A. The horizontal axis is frequency (MHz).

[0042] The bent regions 1011c, 1011d, 1021c, 1021d, 2011c, 2011d, 2021c, and 2021d may also be provided in the antenna unit of the first embodiment. It has been confirmed that the average gain in the horizontal plane (xy plane) is stably increased by fixing the antenna unit of the second embodiment at an angle of approximately 45 degrees on the Z plane as shown in FIG. 10B.

[0043] [Third embodiment] Next, a third embodiment of the present invention will be described. The antenna unit of the third embodiment is similar to the antenna units of the first and second embodiments in that it includes a pair of first elements and a pair of second elements whose polarization directions are orthogonal to each other, and each element includes a self-similar antenna or a portion that operates in a similar manner, but the shape and structure of each element are different from those of the antenna unit of the first embodiment. One of the features of the antenna unit of the third embodiment is that the shape, structure, and size of the first element are different from the shape, structure, and size of the second element. The outer edge size of the antenna unit is rectangular when viewed from the front. Therefore, there are long sides and short sides. The antenna case 10 shown in Figures 1A and 1B is also a rectangular parallelepiped with relatively large long sides. However, for ease of explanation, the members corresponding to the antenna units in the first and second embodiments will be described using the same member names and reference numerals.

[0044] 20A is a front view of the antenna unit according to the third embodiment, FIG. 20B is a side view of the long side portion, FIG. 20C is a side view of the short side portion, and FIG. 20D is a perspective view. The antenna unit of the third embodiment has a pair of first elements and a pair of second elements. The pair of second elements face the pair of first elements in a state rotated approximately 90 degrees while maintaining a predetermined interval from a position where the second center portion (a portion to which the feed point K2 is connected) and the first center portion (a portion to which the feed point K1 is connected) face each other. The predetermined interval is the same as the interval D11 described in the first embodiment.

[0045] A pair of first elements will be described. One first element has two arms 101c, 101d extending from the first base end in a direction away from each other, and the other first element has two arms 102c, 102d extending from the first base end in a direction away from each other. The two arms 101c, 101d of one first element and the two arms 102c, 102d of the other first element each have a width that increases continuously or stepwise as they move away from the first base end. That is, the widths of the two arms 101c, 101d of one first element and the two arms 102c, 102d of the other first element are larger in a region farther from the first base end than in a region closer to the first base end. Also, the facing distance between one first element and the other first element increases continuously or stepwise as they move away from the first base end. That is, the distance between one first element and the other first element is greater in a region far from the first base end than in a region close to the first base end. The arm 101c of one first element also extends in a direction away from the nearest arm 102c of the other first element. With this configuration, the antenna operates like a self-similar antenna such as a biconical antenna or a bowtie antenna, or an equivalent thereof.

[0046] The tip of each of the arms 101c, 102c, 101d, and 102d is an open end. Each open end is formed into a predetermined shape, for example, an L-shape. The open end of the arm 101c faces the open end of the arm 101d, and the open end of the arm 102c faces the open end of the arm 102d. As a result, the two arms 101c and 101d of one first element and the two arms 102c and 102d of the other first element are arranged symmetrically with respect to the first central portion, and each has a substantially C-shape when viewed from the front.

[0047] Next, a pair of second elements will be described. The opposing distance between the two arms 201c, 202c of one second element and the two arms 201d, 202d of the other second element increases continuously or stepwise as they move away from the second base end. That is, the opposing distance between the two arms 201c, 202c of one second element and the two arms 201d, 202d of the other second element is larger in a region far from the second base end than in a region close to the second base end. The arm 201c of one second element also extends in a direction away from the arm 201d closest to the other second element. In this way, the opposing distance between the arms 201c, 202c and the arms 201d, 202d is larger near the open end compared to near the base end. With this configuration, a self-similar antenna such as a biconical antenna or a bowtie antenna or an equivalent operation is performed. As a result, the two arms 201c, 202c of one second element and the two arms 201d, 202d of the other second element are disposed symmetrically with respect to the second central portion, and each form a substantially C-shape when viewed from the front.

[0048] The tip of each of the arms 201c, 201d, 202c, and 202d is an open end. The rate of change in width of each of the arms 201c, 201d, 202c, and 202d from the vicinity of the second base end to the vicinity of the open end is smaller than the rate of change in width of the first element from the vicinity of the first base end to the vicinity of the open end. A long side bend region 2011c and a short side bend region 2012c are formed in a part of the open end of the arm 201c. The long side bend region 2011c is bent 90 degrees in the thickness direction of the antenna unit, i.e., in the direction of the nearest first element. The short side bend region 2012c is bent 90 degrees from the long side bend region 2011c in the direction of the other second element, and then bent 90 degrees in the direction of the nearest first element.

[0049] The open ends of the other arms 202c, 201d, and 202d are also formed with folding regions of the same structure as the open end of arm 201c. That is, a portion of arm 202c is formed with folding region 2021c on the long side and folding region 2022c on the short side. A portion of arm 201d is formed with folding region 2011d on the long side and folding region 2012d on the short side. A portion of arm 202d is formed with folding region 2021d on the long side and folding region 2022d on the short side.

[0050] By forming these bent regions 2011c, 2012c, 2021c, 2022c, 2011d, 2012d, 2021d, and 2022d, it is possible to reduce the overall size while maintaining the antenna performance when they are not formed. In addition, a pair of first elements and a pair of second elements form a split ring, so that the usable frequency band can be expanded to the low frequency side.

[0051] Antenna characteristics of the antenna unit of the third embodiment are shown in Figs. 21A to 24B. Fig. 21A is a VSWR characteristic diagram of the feed point K1, and Fig. 21B is a VSWR characteristic diagram of the feed point K2. Fig. 22A is a radiation efficiency characteristic diagram of the feed point K1, and Fig. 22B is a radiation efficiency characteristic diagram of the feed point K2. The horizontal axis of each diagram is frequency (MHz). Fig. 23A is a passing power characteristic diagram from the feed point K1 of the first element to the feed point K2 of the second element, and Fig. 23B is a passing power characteristic diagram from the feed point K2 of the second element to the feed point K1 of the first element. The vertical axis of Fig. 23A is 20Log|S21| (dB), and the vertical axis of Fig. 23B is 20Log|S12| (dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 24A is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K1 in the arrangement of Fig. 9A, and Fig. 24B is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K2 in the arrangement of Fig. 9A. The horizontal axis is frequency (MHz).

[0052] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described. The antenna unit of the fourth embodiment is similar to the antenna unit of the first embodiment in that it includes a pair of first elements and a pair of second elements whose polarization directions are orthogonal to each other, and each element includes a self-similar antenna or a portion that operates in a similar manner, but the shape and structure of each element are different from those of the antenna unit of the first embodiment. However, for ease of explanation, the same member names and symbols are used for members corresponding to the antenna unit of the first embodiment.

[0053] Fig. 25A is a front view of the antenna unit according to the fourth embodiment, Fig. 25B is a top view, and Fig. 25C is a perspective view. The antenna unit of the fourth embodiment has the same basic structure as the antenna unit of the first embodiment. The interval between the pair of first elements and the pair of second elements and the outer edge size are also similar to those of the antenna unit of the first embodiment. The antenna section of the fourth embodiment differs from the antenna section of the first embodiment in that the open end of the arm of the first element is electrically connected to the open end of the arm of the adjacent second element, and in that in the illustrated example, they are integrally molded to form a loop shape including a portion that operates as a self-similar antenna or an antenna equivalent thereto. Therefore, in the antenna section of the fourth embodiment, the above-mentioned split ring is not formed.

[0054] Antenna characteristics of the antenna unit of the fourth embodiment are shown in Figs. 26A to 29B. Fig. 26A is a VSWR characteristic diagram of the feed point K1, and Fig. 26B is a VSWR characteristic diagram of the feed point K2. Fig. 27A is a radiation efficiency characteristic diagram of the feed point K1, and Fig. 27B is a radiation efficiency characteristic diagram of the feed point K2. The horizontal axis of each diagram is frequency (MHz). Fig. 28A is a passing power characteristic diagram from the feed point K1 of the first element to the feed point K2 of the second element, and Fig. 28B is a passing power characteristic diagram from the feed point K2 of the second element to the feed point K1 of the first element. The vertical axis of Fig. 28A is 20Log|S21|(dB), and the vertical axis of Fig. 28B is 20Log|S12|(dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 29A is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K1 in the arrangement of Fig. 9A, and Fig. 29B is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the feed point K2 in the arrangement of Fig. 9A. The horizontal axis is frequency (MHz).

[0055] [Fifth embodiment] Next, a fifth embodiment of the present invention will be described. In the antenna section of the fifth embodiment, the positional relationship between a pair of first elements and a pair of second elements, and the shape, structure, and size of each element are similar to those of the antenna section of the first embodiment, but the way in which each pair of elements is combined is different from that of the antenna section of the first embodiment. In addition, the form of the power supply point is embodied. For convenience, the same member names and the same reference numerals are used for members corresponding to the antenna section of the first embodiment.

[0056] FIG. 30A is a perspective view showing a configuration example of the antenna unit according to the fifth embodiment, and FIG. 30B is a perspective view seen from the rear side of FIG. 30A. In the first embodiment, one first element and the other first element are two inverted V-shaped elements symmetrical with respect to the first central portion, but in the antenna unit according to the fifth embodiment, one first element of the pair is composed of two arms 101a and 101b, and the other first element is composed of two arms 102a and 102b, thereby forming two approximately C-shaped elements symmetrical with respect to the first central portion. The same is true for the pair of second elements. That is, one second element is composed of two arms 201a and 201b, and the other second element is composed of two arms 202a and 202b, thereby forming two approximately C-shaped elements symmetrical with respect to the second central portion.

[0057] Even with such a combination of elements, the polarization directions of signals that can be received or transmitted by a pair of first elements and a pair of second elements are orthogonal, and each element includes a portion that operates as a self-similar antenna or an antenna equivalent thereto, so that the same effects as those of the first embodiment can be achieved.

[0058] In addition, the first feeder F11 with a wound ferrite core is connected to the first central feed point, and the second feeder F21 with the ferrite core wound at an angle of approximately 90 degrees different from that of the first feeder F11 is connected to the second central feed point. This makes it possible to suppress leakage current in the low frequency range where resonance occurs, such as 698 MHz, and stabilize and improve the radiation characteristics. In addition, L11 and L21 in Figs. 30A and 30B indicate coaxial cables that are examples of the feeders F11 and F21, respectively.

[0059] [Variation 1] In the first, second, fourth and fifth embodiments, the first element and the second element have been described as having the same shape, structure and size, but this is not limited thereto. As long as they have a portion that operates as a self-similar antenna or an antenna equivalent thereto, the directions of polarization are orthogonal to each other, and the shape allows the area of ​​the overlapping portion to be small, one element may be a different size from the other.

[0060] In the first, second, fourth and fifth embodiments, the pair of first elements and the pair of second elements are generally V-shaped or generally C-shaped, but they may be generally D-shaped, generally U-shaped, generally semicircular, generally semi-elliptical, generally triangular or generally rectangular. In these embodiments, the configuration is described assuming that the power supply points are provided at two locations, but they may be provided at only one location. The first and second elements are electrically connected, so they can operate in the same way as when they are provided at two locations. In the first embodiment, an example was described in which the antenna characteristics were improved by installing the antenna unit at an angle of approximately 45 degrees on the Z plane, but the antenna units of the second to fifth embodiments may also be installed at a similar angle. Moreover, not only the pair of first elements or the pair of second elements, but also one arm or two arms constituting each element may be installed at a similar angle.

[0061] [Effects of the antenna devices according to the first to fifth embodiments] In the antenna unit of the first to fifth embodiments, the pair of first elements and the pair of second elements are arranged so that the directions of polarization are orthogonal to each other, so that mutual interference between the elements is suppressed and the antenna device can be made thinner. In addition, each of the pair of first elements and the pair of second elements includes a portion that operates as a self-similar antenna or an antenna equivalent thereto, so that reception or transmission can be performed over a wide frequency band, enabling stable operation over a wide frequency band.

[0062] In addition, each of the pair of first elements and the pair of second elements has two arms extending in a direction away from each other from a base end to which a power feed point can be connected, so that the elements can be made smaller. As in the comparative example antenna unit shown in Figures 12A to 12D, when the pair of second bowtie antennas 601, 602 are arranged facing the pair of first bowtie antennas 501, 502 in a state rotated approximately 90 degrees from a state directly facing the pair of first bowtie antennas 501, 502, a conductor is interposed around the periphery between the elements of the first bowtie antennas 501, 502 and the second bowtie antennas 601, 602. On the other hand, by disposing the pair of second elements in the antenna unit 12 of the first to fifth embodiments facing the pair of first elements in a state rotated by approximately 90 degrees from a state in which they face each other, the overlapping area between the elements when the two elements are brought close to each other becomes small. In other words, a configuration is achieved in which no conductor is present around the first and second elements. Therefore, since no scatterers are introduced between the two elements, the reactance fluctuation can be suppressed and the impedance is stabilized, thereby realizing a wide bandwidth.

[0063] The antenna unit can be housed in a radio wave-transmitting case (case body 10) with vertical and horizontal dimensions of 90 mm and a thickness of 13 mm or less, making it possible to realize an antenna device that houses two antennas that is small and thin, suppresses interference, and has excellent isolation. This antenna device can be installed, for example, anywhere in a vehicle or anywhere inside a room and can be used for MIMO using LTE or 5G frequency bands.

[0064] Furthermore, as shown in Figures 6A to 8B and 16A to 19B, the antenna units of the first and second embodiments have stable and excellent antenna characteristics over the low to high frequency bands of LTE and 5G, and can be used as antenna devices for domestic and overseas use without any design changes.

[0065] By increasing the width as it moves away from the feeding point K1 (K2), the VSWR in particular on the high frequency side is reduced, the radiation efficiency and the average gain are increased, and the fluctuations of these can be suppressed. In addition, by configuring a pair of first elements and a pair of second elements, and further by rotating the pair of second elements by approximately 90 degrees from the state where they face the pair of first elements, facing the pair of first elements, and arranging both elements close to each other, the opposing ends of the opposing elements are electrically connected to each other to form a loop, making it possible to broaden the low frequency band around 698 MHz. With such a configuration, for example, the low frequency side of the usable frequency band is expanded, which was difficult to achieve with a conventional antenna device, and a wider usable frequency band is realized.

[0066] The two arms (e.g., 101a and 101b) have their tips molded into a predetermined shape determined according to the shape of the installation site, so that the required element area can be secured for each arm while increasing the degree of freedom of the element shape. The "required element area" is determined by the resonant frequency of the split ring that expands the low-frequency band.

[0067] Since a portion of the area of ​​one of the two arms (e.g., 101c, 101d) that is farthest from the power supply point (e.g., K1) is bent toward the opposing other arm (e.g., 201c, 201d), the frequency band can be expanded to the lower side without changing the vertical and horizontal side sizes and thickness of the entire antenna unit (and the case body 10).

[0068] In addition, the comparative example antenna unit described in the first embodiment can obtain antenna characteristics at a practical level when a pair of bowtie antennas rotated approximately 90 degrees from each other are used as wideband antennas with a distance of 40 mm or more. In the first to fifth embodiments, an example was described in which the minimum LTE frequency was set to 698 MHz, but in order to expand the frequency to a lower frequency of approximately 450 MHz while maintaining the performance of the antenna in each embodiment, this can be achieved by expanding the size (outer edge size) of the antenna unit as viewed from the front or back in accordance with the wavelength ratio without changing the spacing D11 between the antenna units. Note that, although the performance of the antenna is inferior to that of the embodiments, it is also possible to expand the frequency to a lower frequency of approximately 450 MHz by appropriately adjusting the width of the arm and the area of ​​the portion corresponding to the open end without changing the size (outer edge size) of the antenna unit.

[0069] [Sixth embodiment] Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, an antenna unit having a configuration that takes into consideration the operational effects of the antenna units of the first to fifth embodiments as well as the simplification of the element manufacturing process will be described. The antenna unit has a pair of first elements and a pair of second elements, their relative positions, and a power supply system, which are generally similar to those of the antenna units of the first to fifth embodiments. For convenience, the same component names and symbols will be used for members corresponding to the antenna units of the embodiments described so far.

[0070] Fig. 31A is a perspective view of the antenna unit in the sixth embodiment, Fig. 31B is a front view showing a pair of first elements in a power supply state, and Fig. 31C is a front view showing a pair of second elements in a power supply state. This antenna unit is sized to be housed in a box-shaped resin case (for example, case 10 shown in Figs. 1A and 1B) with a length of 60 mm in the z direction, a length of 80 mm in the x direction, and a length of 15 mm in the y direction.

[0071] Referring to Figures 31A to 31C, of ​​a pair of first elements, one first element has a base end region 101e which is a first region whose base end is formed in an arch shape toward the base end of the other first element (in the x-axis direction), an extension region 101f which is a second region which is conductively connected to one end of the base end region 101e, and another extension region 101g which is conductively connected to the other end of the base end region 101e. The other first element also has a base end region 102e whose base end is formed in a convex shape toward the base end of one of the first elements, an extension region 102f electrically connected to one end of the base end region 102e, and another extension region 102g electrically connected to the other end of the base end region 102e. The conductive connection can be realized by solder connection or conductive via holes. Both regions may also be electrically connected by using conductive screws, bolts, and nuts, conductive adhesives, or conductive wires.

[0072] The base end regions 101e and 102e correspond to the partial regions of the arms including the portions to which the power feed points are connected in the embodiments described above, i.e., the regions near the first base end or the second base end. The extension regions 101f, 101g, 102f, and 102g correspond to the remaining regions of the partial regions of the arms in the embodiments described above.

[0073] The base end regions 101e are printed in a strip shape on the front and back sides of a single substrate PB1, and are then conductively connected to each other through a plurality of conductive via holes 1011e in this example. The substrate PB1 is formed of a PCB (Printed Circuit Board; the same applies below) having a substantially rectangular shape in this example. The base end regions 102e are also printed in a strip shape on the front and back sides of the substrate PB1, and are then conductively connected to each other through a plurality of conductive via holes 1021e. The portion where the two base end regions 101e and 102e are closest to each other is the above-mentioned first center portion (the portion or port to which the feeding point K1 is connected). The signal line F111 of the coaxial cable F114, which is an example of a feeding feeder, is conductively connected to the base end region 102e. The ground line F112 of the coaxial cable F114 is conductively connected to the base end region 101e. As a result, the pair of first elements operate as two dipole antennas. Moreover, the base end regions 101e and 102e, the extension regions 101f and 101g, and the extension regions 102f and 102g function as two tapered slot antennas.

[0074] In addition, a ferrite core F113 is attached to the coaxial cable F114, which makes it possible to block current leaking from the outer sheath of the coaxial cable F114. Also, in order to increase the gain in the low frequency band around 698 GHz, it is common to increase the size of the antenna part, but by attaching the ferrite core F113, it is possible to reduce the size of the antenna part while maintaining the gain in the low frequency band. Here, in the coaxial cable F114, the connection point with the first element is defined as a feed point K1, and the end opposite to the feed point K1 is defined as an output end. In addition, while an impedance matching circuit is generally provided on a printed circuit board, the antenna of this embodiment does not require an impedance matching circuit, and the signal line F111 and the ground line F112 of the coaxial cable are directly connected to the board areas 101e and 102e formed on the board PB1, thus simplifying the overall configuration of the antenna unit.

[0075] The extension regions 101f, 101g, 102f, and 102g are metal plates that are almost perpendicular to the substrate PB1 and have a width in the direction of the second element, and are each made of sheet metal. The extension regions 101f, 101g, 102f, and 102g have open ends near their tips. The open ends are composed of first ends 1011f, 1011g, 1021f, and 1021g that are trapezoidal on a plane perpendicular to the substrate PB1, and second ends 1012f, 1012g, 1022f, and 1022g that are bent on a plane parallel to the substrate PB1 and are approximately triangular. The second ends 1012f, 1012g, 1022f, and 1022g are approximately triangular in order to maintain a self-similar shape, keep the impedance constant, and improve antenna performance (VSWR, radiation efficiency, and gain).

[0076] In order to avoid bonding with the opposing second end portions 1012f, 1012g and 1022f, 1022g, a part of the tip of the triangle may be cut off to make it closer to a trapezoid. The width of each end portion increases toward the tip of the extension region. By making the second end portions 1012f, 1012g, 1022f, 1022g approximately triangular, the antenna portion as a whole maintains a similar shape, and the impedance is made constant, making it possible to improve the antenna characteristics, especially the VSWR. The two extension regions 101f, 101g of one first element and the two extension regions 102f, 102g of the other first element are arranged symmetrically with respect to the first central portion, and each has an approximately C-shape when viewed from the front (y-axis direction).

[0077] Next, the pair of second elements will be described. Of the pair of second elements, one second element has a base end region 201e whose base end is formed in a curved shape in the direction of the base end of the other second element (z-axis direction), an extension region 201f conductively connected to one end of the base end region 201e, and another extension region 201g conductively connected to the other end of the base end region 201e. The other second element also has a base end region 202e whose base end is formed in a curved shape in the direction of the base end of one second element, an extension region 202f conductively connected to one end of the base end region 202e, and another extension region 202g conductively connected to the other end of the base end region 202e.

[0078] The base end region 201e is formed on the substrate PB2, which is disposed on a plane parallel to the substrate PB1 and tilted at approximately 90 degrees from the first central portion. The substrate PB2 is a substantially rectangular PCB whose long sides extend in a direction perpendicular to the substrate PB1. The base end region 201e is printed in a strip shape on each of the front and back surfaces of the substrate PB2, and then conductively connected to each other by a plurality of conductive via holes 2011e. The base end region 202e is also printed in a strip shape on each of the front and back surfaces of the substrate PB2, and then conductively connected to each other by a plurality of conductive via holes 2021e.

[0079] The part where the two base end regions 201e and 202e are closest to each other is the second center portion (the portion or port to which the power feed point K2 is connected) described above. The signal line F211 of the coaxial cable F214, which is an example of a power feeder, is conductively connected to the base end region 202e. The ground line F212 of the coaxial cable F214 is conductively connected to the base end region 201e. This allows the pair of second elements to operate as two dipole antennas or two tapered slot antennas. A ferrite core F213 is attached to the coaxial cable F214. Its function is the same as that of the first element. In addition, the base end regions 201e and 202e, the extension regions 201f and 201g, and the extension regions 202f and 202g operate as two tapered slot antennas. Here, in the coaxial cable F214, the connection point with the second element is defined as a feed point K2, and the end opposite to the feed point K2 is defined as an output end.

[0080] The extension regions 201f, 201g, 202f, and 202g are metal plates that are perpendicular to the substrate PB2 and have a width in the direction of the first element, and are each made of sheet metal. The vicinity of the tip of the extension regions 201f, 201g, 202f, and 202g is an open end. The open end is composed of a first end 2011f, 2011g, 2021f, and 2021g that is trapezoidal on a plane perpendicular to the substrate PB2, and a second end 2012f, 2012g, 2022f, and 2022g that is bent on a plane parallel to the substrate PB2 and is substantially triangular. The same is true for the second element, where a part of the tip of the triangle may be cut off to form a shape close to a trapezoid. The width of each end increases toward the tip of the respective extension region. The two extension regions 201f, 201g of one second element and the two extension regions 202f, 202g of the other second element are disposed symmetrically about the second central portion, and each form a substantially C-shape when viewed from the front (y-axis direction).

[0081] A split ring is formed between the first end 1011f, 1011g, 1021f, 1021g and the second end 1012f, 1012g, 1022f, 1022g of the first element and the first end 2021f, 2021g, 2011f, 2011g and the second end 2022f, 2022g, 2012f, 2012g of the nearest second element. That is, both areas are non-conductive but capacitively coupled. As a result, the pair of first elements and the pair of second elements as a whole operate in accordance with a loop antenna. This split ring plays a role in expanding the usable frequency band of the antenna part to the low frequency side.

[0082] In the antenna unit of the sixth embodiment, similarly to the antenna units of the embodiments described so far, a pair of first elements are inclined at approximately 90 degrees to a pair of second elements, so that the directions of polarization of receivable or transmittable signals are orthogonal to each other, and part or all of each element operates as a self-similar antenna or an antenna equivalent thereto.

[0083] In addition, when a self-similar antenna or an element that operates similarly to the self-similar antenna is made of sheet metal, it is required that the width around the base end where the power supply point is connected be as narrow as possible. Therefore, it is difficult to realize. However, the antenna unit of the sixth embodiment is configured such that the base end regions 101e, 102e, 201e, and 202e are formed by printing on the substrates PB1 and PB2, and the base end region 101e and the extension regions 101f and 101g, the base end region 102e and the extension regions 102f and 102g, the base end region 201e and the extension regions 201f and 201g, and the base end region 202e and the extension regions 202f and 202g are conductively connected, respectively, making it easy to create the antenna unit.

[0084] In addition, the base end regions 101e, 102e, 201e, and 202e are formed by conductively connecting two prints formed on the front and back surfaces of the substrates PB1 and PB2, respectively, with the conductive via holes 1011e, 1021e, 2011e, and 2021e, so that the radiation resistance and inductance are increased and the radiation efficiency is improved compared to the case where only one print is formed. Note that a part of the region of at least one element of the pair of first elements and the pair of second elements may be formed on the substrates PB1 and PB2. In addition, the base end regions 101e, 102e, 201e, and 202e may be formed only on one surface of the substrates PB1 and PB2. In this case, the conductive via holes 1011e, 1021e, 2011e, and 2021e are not necessary.

[0085] Next, the antenna characteristics of the antenna of the sixth embodiment will be described. Fig. 32A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Fig. 32B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Fig. 32C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Fig. 32D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis of each diagram is frequency (MHz). Fig. 32E is a passing power characteristic diagram from the output end of the coaxial cable F114 to the output end of the coaxial cable F214, and Fig. 32F is a passing power characteristic diagram from the output end of the coaxial cable F214 to the output end of the coaxial cable F114. The vertical axis of Fig. 32E is 20Log|S21|(dB), and the vertical axis of Fig. 32F is 20Log|S12|(dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 32G is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F114 in the arrangement of Fig. 31A, and Fig. 32H is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F214. The horizontal axis is frequency (MHz).

[0086] As can be seen from these antenna characteristics, the antenna unit is ultra-compact, with a length in the z direction of less than 60 mm, a length in the x direction of less than 80 mm, and a length in the y direction of less than 15 mm, yet it can be used and put into practical use at low frequencies, such as 698 MHz and frequencies therearound.

[0087] The configuration in which the antenna unit is composed of a base end region formed on a substrate and an extension region made of sheet metal and electrically coupled to each other can be applied to other configurations than those shown in Figures 31A to 31C. For example, the above configuration can be applied to other configurations of antenna units composed of one first element and one second element.

[0088] [Seventh embodiment] In the seventh embodiment, an example in which each element of the antenna part is created by printing on a board will be described as an application of the sixth embodiment. FIG. 33A is a front view of a pair of first elements in the seventh embodiment, FIG. 33B is a front view of a pair of second elements, FIG. 33C is a front view showing a power supply state of the pair of first elements, and FIG. 33D is a front view showing a power supply state of the pair of second elements. FIG. 33E is a perspective view for explaining the state of the first element and the second element as a whole, and FIG. 33F is a side view of the antenna part. Here, the board is assumed to be a square PCB with a thickness of 0.8 mm and a side length of 87 mm. For convenience, the same components as the antenna parts used in the previous embodiments will be described with the same reference numerals.

[0089] The antenna section of the seventh embodiment is formed by printing a pair of first elements on one surface (front surface) of a substrate PB3 having a planar front and back surfaces, and printing a pair of second elements whose polarization direction is perpendicular to that of the pair of first elements on the other surface (back surface) of the substrate PB3.

[0090] 33A, one of the pair of first elements has two arms 101j, 101k that extend in directions away from each other from a base end to which a feed point can be connected. The arm 101j has a region 1011j whose width increases with distance from the base end and an open end 1012j that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. The arm 101k has a region 1011k whose width increases with distance from the base end and an open end 1012k that is cut out in a straight line from one corner of the substrate PB3 toward the center of the substrate PB3.

[0091] The other first element has two arms 102j and 102k that extend away from each other from a base end to which a feed point can be connected. The arm 102j has a region 1021j whose width increases with distance from the base end and an open end 1022j that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. The arm 102k has a region 1021k whose width increases with distance from the base end and an open end 1022k that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. Each element of the pair of first elements operates as a self-similar antenna or an antenna equivalent thereto.

[0092] A signal line F111 of a coaxial cable F114 is conductively connected to the base end of one of the first elements as shown in Fig. 33C. A ground line F112 of the coaxial cable F114 is conductively connected to the base end of the other first element. This allows the pair of first elements to operate as two dipole antennas or two tapered slot antennas. A ferrite core F113 is attached to the coaxial cable F114. Here, in the coaxial cable F114, the connection point with the first element is defined as a feed point K1, and the end opposite to the feed point K1 is defined as an output end.

[0093] 33B, one of the pair of second elements has two arms 201j, 201k that extend in directions away from each other from a base end to which a feed point can be connected. The arm 201j has a region 2011j whose width increases with distance from the base end and an open end 2012j that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. The arm 201k has a region 2011k whose width increases with distance from the base end and an open end 2012k that is cut out in a straight line from one corner of the substrate PB3 toward the center of the substrate PB3.

[0094] The other second element has two arms 202j, 202k that extend away from each other from a base end to which a feed point can be connected. The arm 202j has a region 2021j whose width increases with distance from the base end and an open end 2022j that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. The arm 202k has a region 2021k whose width increases with distance from the base end and an open end 2022k that is cut out in a straight line from another corner of the substrate PB3 toward the center of the substrate PB3. Each element of the pair of second elements operates as a self-similar antenna or an antenna equivalent thereto.

[0095] As shown in Fig. 33D, the signal line F211 of the coaxial cable F214 is conductively connected to the base end of one of the second elements. The ground line F212 of the coaxial cable F214 is conductively connected to the base end of the other second element. This allows the pair of second elements to operate as two dipole antennas. A ferrite core F213 is attached to the coaxial cable F214. Here, in the coaxial cable F214, the connection point with the second element is defined as a feed point K2, and the end opposite to the feed point K2 is defined as an output end.

[0096] 33E, a split ring is formed between an open end (e.g., open end 1012j) of an arm of a first element on the front surface of the substrate PCB3 and an open end (e.g., open end 2012j) of an arm of a second element located closest to the front surface of the substrate PCB3. Therefore, the first element and the second element are not conductive, but are capacitively coupled and also function as a loop antenna.

[0097] The antenna characteristics of the antenna unit of the seventh embodiment will be described. Fig. 34A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Fig. 34B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Fig. 34C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Fig. 34D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis of each is frequency (MHz). Fig. 34E is a passing power characteristic diagram from the output end of the coaxial cable F114 to the output end of the coaxial cable F214, and Fig. 34F is a passing power characteristic diagram from the output end of the coaxial cable F214 to the output end of the coaxial cable F114. The vertical axis of Fig. 34E is 20Log|S21|(dB), and the vertical axis of Fig. 34F is 20Log|S12|(dB), and the horizontal axis of each is frequency (MHz). Fig. 34G is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F114 in the arrangement of Fig. 31A, and Fig. 34H is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F214. The horizontal axis is frequency (MHz).

[0098] As can be seen from these antenna characteristics, as shown in Figure 33F, although the antenna is extremely small, with a thickness of just 0.8 mm plus the printed portion, and a square shape with a side length of 87 mm, it can be used and put into practical use at low frequencies such as around 698 MHz. In the seventh embodiment, a configuration in which the first elements are formed on the front surface of one substrate and the second elements are formed on the back surface of the substrate has been described, but the present invention can also be implemented using a configuration in which two substrates are used. That is, a pair of first elements may be formed on a first surface of one substrate as a conductive pattern, and a pair of second elements may be formed on a second surface of the other substrate opposite to the first surface as a conductive pattern, and the conductive patterns may be made conductive by conductive through holes or the like.

[0099] [Modification of the Seventh Embodiment] In the seventh embodiment, an example was described in which the open end (e.g., open end 1012j) of the arm of the first element on the front surface of the substrate PB3 and the open end (e.g., open end 2012j) of the arm of the second element closest to the back surface of the substrate PB3 are not electrically connected (a split ring is formed). Therefore, hereinafter, as a modified example, a configuration in which the open end (e.g., open end 1012j) of the arm of the first element on the front surface of the substrate PB3 and the open end (e.g., open end 2012j) of the arm of the second element closest to the back surface of the substrate PB3 are electrically connected is described. The electrical connection between the open end (e.g., open end 1012j) of the arm of the first element on the front surface of the substrate PB3 and the open end (e.g., open end 2012j) of the arm of the second element closest to the back surface of the substrate PB3 can be realized by, for example, soldering, a conductive via hole, or the like.

[0100] Antenna characteristics of the antenna unit of the modified example of the seventh embodiment are shown in Figs. 35A to 35H. The measurement conditions are the same as those of the seventh embodiment. Fig. 35A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Fig. 35B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Fig. 35C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Fig. 35D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis of each diagram is frequency (MHz). Fig. 35E is a passing power characteristic diagram from the output end of the coaxial cable F114 to the output end of the coaxial cable F214, and Fig. 35F is a passing power characteristic diagram from the output end of the coaxial cable F214 to the output end of the coaxial cable F114. The vertical axis of Fig. 35E is 20Log|S21| (dB), and the vertical axis of Fig. 35F is 20Log|S12| (dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 35G is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F114 in the arrangement of Fig. 31A, and Fig. 35H is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F214. The horizontal axis is frequency (MHz).

[0101] As can be seen from the VSWR characteristics of these antennas, when comparing the case where the open ends of the adjacent arms are made conductive with the case where they are made non-conductive as in the antenna section of the seventh embodiment, it can be seen that the band of the antenna of the seventh embodiment is expanded below approximately 1 GHz.

[0102] [Eighth embodiment] In the eighth embodiment, an antenna unit of the sixth embodiment will be described, in which an open end of a first element on the front surface of the board is electrically connected to an open end of a second element on the rear surface of the board. Fig. 36A is a perspective view showing an example of the overall configuration of the antenna unit of the eighth embodiment, Fig. 36B is a front view showing a power supply state of a pair of first elements, and Fig. 36C is a front view showing a power supply state of a pair of second elements.

[0103] The difference from the antenna portion of the sixth embodiment is that there is no split ring between the open end of the first element on the front surface of the substrate and the nearby open end of the second element on the back surface of the substrate, in other words, the first ends of the nearest open ends are conductive to each other, and there are no second ends 1012f, 1012g, 1022f, 1022g of the first element which are bent onto a plane parallel to the substrate PB1 to form an approximately triangular shape, and no second ends 2012f, 2012g, 2022f, 2022g of the second element.

[0104] The antenna characteristics of the antenna unit of the eighth embodiment are as shown in Figs. 37A to 37H. The measurement conditions are the same as those of the sixth embodiment. Fig. 37A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Fig. 37B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Fig. 37C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Fig. 37D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis of each diagram is frequency (MHz). Fig. 37E is a passing power characteristic diagram from the output end of the coaxial cable F114 to the output end of the coaxial cable F214, and Fig. 37F is a passing power characteristic diagram from the output end of the coaxial cable F214 to the output end of the coaxial cable F114. The vertical axis of Fig. 37E is 20Log|S21| (dB), and the vertical axis of Fig. 37F is 20Log|S12| (dB), and the horizontal axis of each diagram is frequency (MHz). Fig. 37G is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F114 in the arrangement of Fig. 31A, and Fig. 37H is a diagram showing average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F214. The horizontal axis is frequency (MHz).

[0105] As can be seen from the VSWR characteristics of these antennas, when comparing the antenna unit of the eighth embodiment, in which the open ends of the adjacent arms are conductive, with the antenna unit of the sixth embodiment, in which the open ends are non-conductive, it can be seen that the band of the antenna of the eighth embodiment is expanded below approximately 1 GHz.

[0106] [Ninth embodiment] In the ninth embodiment, the structure of incorporating the antenna unit into the case and the power supply system will be described in detail. Here, the combined case shown in Figs. 38 to 40 will be described, instead of the case 10 shown in Figs. 1A and 1B. This case is made of radio wave permeable plastic, and is composed of a first case body 10a and a second case body 10b, which are substantially rectangular in shape and have their internal storage spaces sealed at their open ends, as shown in Figs. 38 and 39, which are front, rear, plan, bottom, right and left side views, respectively. Fig. 40A is a perspective view of the inside of the first case body 10a with a pair of first elements fixed thereto, as viewed from the rear side, and Fig. 40B is a front view of the inside of the first case body 10a. Fig. 40C is a perspective view of the inside of the second case body 10B with a pair of second elements fixed thereto, and Fig. 40D is a front view of the inside of the first case body 10a. The first case body 10a is formed with four screw receiving bosses 10a1 to 10a4 with screw receiving members threaded therein. Sealing is performed by inserting the screw 10c from the rear face of the second case body 10b and tightening it with the screw, but adhesive can also be used. The size of the first case body 10a and the second case body 10b when sealed is 60 mm on the long side, 80 mm on the short side, and 15 mm in thickness, excluding the exposed coaxial cables F114 and F214.

[0107] The antenna section housed in each case body 10a, 10b is a modified version of the antenna section of the sixth embodiment. That is, a pair of through holes is formed at both ends or near both ends of the base end region 101e on the substrate PB1 of the pair of first elements. A pair of through holes is also formed at both ends or near both ends of the base end region 102e on the substrate PB1. Metal claws PB1a to PB1d are integrally formed at the base ends of the extension regions 101f, 101g, 102f, and 102g made of sheet metal, and pass through the through holes. Then, the claws PB1a to PB1d are passed through the through holes, and the vicinity of the tip is bent on the base end regions 101e and 102e of the substrate PB1. As a result, the extension regions 101f, 101g, 102f, and 102g are fixed in a conductively connected state to the base end regions 101e and 102e on the substrate PB1. At this point, the claws PB1a to PB1d and the base end regions 101e and 102e may be fixed by soldering.

[0108] As described above, the substrate PB1 is not provided with an impedance matching circuit, and the signal line and the ground line of the coaxial cable F114 are directly connected to one of the base end regions 101e and 102e. The coaxial cable F114 is connected to one end of the short side of the first case body 10a. It is fixed together with the ferrite core F113 on the near side.

[0109] The first end portions 1011f, 1011g, 1021f, and 1021g and the second end portions 1012f, 1012g, 1022f, and 1022g are formed into shapes that conform to the bottom and side surfaces of the first case body 10a, respectively. The length of the substrate PB1 and the lengths of the extension regions 101f, 101g, 102f, and 102g are longer than the configurations corresponding to each configuration in the second element. On the other hand, the lengths of the portions (post-branching regions) where the extension regions 101f, 101g, 102f, and 102g branch off from the base end regions 101e and 102e and extend away from them are shorter than the configurations corresponding to each configuration in the second element. As mentioned above, the opposing second ends 1012f, 1012g and 1022f, 1022g of the second ends 1012f, 1012g and a portion of the tip portion of the second ends 1022f, 1022g are shaped close to a trapezoid by adjusting the capacitive and inductive properties to ensure the desired frequency band.

[0110] The pair of second elements are also accommodated in the second case body 10b with a similar structure. That is, a pair of through holes is formed at both ends or near both ends of the base end region 201e on the substrate PB2 in the pair of second elements. A pair of through holes is also formed at both ends or near both ends of the base end region 202e on the substrate PB2. Metal claws PB2a to PB2d that penetrate the through holes are integrally formed at the base ends of the extension regions 201f, 201g, 202f, and 202g made of sheet metal. Then, after the claws PB2a to PB2d penetrate the through holes, the vicinity of the tips is bent on the base end regions 201e and 202e of the substrate PB2. As a result, the extension regions 201f, 201g, 202f, and 202g and the base end regions 201e and 202e on the substrate PB2 are fixed in a conductively connected state. At this point, the claws PB2a to PB2d and the base end regions 201e and 202e may be fixed by soldering.

[0111] The substrate PB1 is not provided with an impedance matching circuit, and the signal line and ground line of the coaxial cable F214 are directly connected to one of the base end regions 201e and 202e. The coaxial cable F214 is fixed to the short side of the second case body 10a closer to the other end together with the ferrite core F213. This makes the closest distance to the coaxial cable F114 as long as possible.

[0112] The first ends 2011f, 2011g, 2021f, 2021g and the second ends 2012f, 2012g, 2022f, 2022g are formed in a shape that follows the bottom and side surfaces of the first case body 10b, respectively. As described above, the second ends 1012f, 1012g and the tip portions of the second ends 1022f, 1022g facing each other among the second ends 1012f, 1012g, 1022f, 1022g are shaped like a trapezoid by adjusting the capacitive and inductive properties to ensure a desired frequency band. Note that, among the pair of first elements and the pair of second elements, the nearest open end portion (for example, the second end 1012f and the second end 2022f) is non-conductive and acts as a split ring. In other words, it is capacitively coupled and also operates as a loop antenna.

[0113] As described above, the antenna unit of this embodiment operates according to different operating principles or in a state where these different operating principles are combined depending on the frequency band used. For example, in a frequency band in which the first ends 1011f, 1011g, 1021f, 1021g and the second ends 1012f, 1012g, 1022f, 1022g of the pair of first elements and the first ends 2011f, 2011g, 2021f, 2021g and the second ends 2012f, 2012g, 2022f, 2022g of the pair of second elements are capacitively coupled, the pair of first elements and the pair of second elements as a whole operate in accordance with a loop antenna (operation A).

[0114] Also, the pair of first elements and the pair of second elements each operate as two dipole antennas (operation B). In this case, the longer the length of the portions of the two extension regions 101f, 101g and the extension regions 102f, 102g made of sheet metal that branch off from the base end regions 101e, 102e and extend away from them, the more the antenna characteristics (VSWR, etc.) in the mid-frequency range shift to the low-frequency side. In other words, the band in which the antenna characteristics are stable expands.

[0115] Furthermore, the base end regions 101e and 102e, the extension regions 101f and 101g, and the extension regions 102f and 102g operate as two tapered slot antennas (operation C). In this case, the longer the length of the two extension regions 101f and 101g and the extension regions 102f and 102g that extend while facing the length of the substrates PB1 and PB2, the closer the antenna characteristics (VSWR, etc.) of the high frequency band to the antenna characteristics of the low frequency band. In other words, the band in which the antenna characteristics are stable is expanded. In this way, an antenna device having one antenna unit mainly operates as a loop antenna in the low frequency band, mainly operates as a dipole antenna in the mid frequency band, and mainly operates as a tapered slot antenna in the high frequency band. Also, in the intermediate band, it operates as a composite antenna in which these operating principles are combined. In other words, from the low frequency band to the mid frequency band, it mainly operates as a composite antenna that combines the operating principles of a loop antenna and a dipole antenna, and from the mid frequency band to the high frequency band, it mainly operates as a composite antenna that combines the operating principles of a dipole antenna and a tapered slot antenna.

[0116] The coaxial cable F114 connected to the pair of first elements and the coaxial cable F214 connected to the pair of second elements are fixed at the furthest positions in the first case body 10a and the second case body 10b, and are used while remaining spaced apart even outside the cases. This makes it possible to suppress mutual interference caused by unnecessary radio waves resulting from currents flowing through the outer sheaths of the coaxial cables F114 and F214. If the ferrite cores F113 and F213 are not provided on the coaxial cables F114 and F214, the radiation efficiency will decrease at the lowest frequency side of the band, but operation is possible. Therefore, in applications where a decrease in radiation efficiency at the low frequency band can be tolerated, the coaxial cables F114 and F214 may be used without the ferrite cores F113 and F213.

[0117] In the ninth embodiment, the first element and the second element are each provided with a port for power supply, and the coaxial cables F114, F214 are connected to each of the ports for power supply. In other words, an antenna device having an antenna unit according to the ninth embodiment has ports, and the coaxial cables F114, F214 for power supply are connected to each of the two ports. However, the antenna device can be operated even when power is supplied from a single coaxial cable by providing a branch circuit or the like. In this case, it is sufficient to remove the coaxial cable connected to one of the two ports.

[0118] Although the length of the substrates PB1 and PB2 and the lengths of the extension regions 101f, 101g, 102f, 102g, 201f, 201g, 202f, and 202g are different between the pair of first elements and the pair of second elements, this is not limited to the above. For example, when the shape of the first cases 10a and 10b is substantially square, these lengths may be the same.

Claims

1. A MIMO antenna device for use in a vehicle, which performs spatial multiplexing transmission, a first dipole antenna having a pair of first elements connected to a first feeding portion and disposed on a first plane; a second dipole antenna having a pair of second elements connected to a second feeding portion and disposed on a second plane opposite to the first plane, the second dipole antenna is disposed such that the second power supply portion substantially overlaps with the first power supply portion in a plan view, the pair of second elements are arranged in a state rotated by a predetermined angle while maintaining a predetermined interval from a position where a second center of the second dipole antenna coincides with a first center of the first dipole antenna, MIMO antenna device.

2. The MIMO antenna device according to claim 1 , wherein coaxial cables connected to the first feeding portion and the second feeding portion, respectively, are routed between the first plane and the second plane.

3. the first dipole antenna comprises a first bowtie antenna; 3. The MIMO antenna arrangement of claim 1 or 2, wherein the second dipole antenna comprises a second bowtie antenna.

4. The MIMO antenna apparatus of claim 3 , wherein the first element extends from the first bowtie antenna onto the first plane and includes a shape that adjusts capacitive and inductive properties.

5. The MIMO antenna apparatus according to claim 3 or 4, wherein the second element extends from the second bowtie antenna onto the second plane and includes a shape that adjusts capacitive and inductive properties.

6. A MIMO antenna device as described in any of claims 3 to 5, wherein at least one of the first bowtie antenna and the second bowtie antenna has an element portion for adjusting capacitive and inductive properties extending from at least one of the first bowtie antenna and the second bowtie antenna between the first plane and the second plane.

7. The first bowtie antenna includes a bent region extending from the first bowtie antenna and bent 90 degrees in a thickness direction of the MIMO antenna device, or 6. The MIMO antenna device according to claim 3, wherein the second bowtie antenna includes another bent region extending from the second bowtie antenna and bent at 90 degrees in a thickness direction of the MIMO antenna device.

8. The first dipole antenna has a first folded element extending from the first plane to the second plane, the second dipole antenna has a second folded element extending from the second plane to the first plane; the first folded element is disposed in an area in the second plane where the second dipole antenna is not disposed, the second folded element is disposed in an area in the first plane where the first dipole antenna is not disposed; 7. The MIMO antenna device according to claim 1.

9. a first substrate having the first power supply portion; The MIMO antenna apparatus according to claim 1 , further comprising: a second substrate having the second feeding portion.

10. 9. The MIMO antenna device according to claim 1, wherein the first element is formed on a front surface of a single substrate, and the second element is formed on a rear surface of the single substrate.

11. 11. The MIMO antenna device according to claim 1, wherein the first dipole antenna and the second dipole antenna are disposed diagonally within a case.

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