Antenna device

Abstract

To provide a compact and lightweight antenna device that can be used over a wide frequency range.SOLUTION: A first element and a second element are rotated by approximately 90 degrees and placed opposite each other at a predetermined interval, and the entire assembly is tilted at a predetermined angle (e.g., approximately 45 degrees) and fixed to a mounting surface. Each element has two arms (101A and 102A, 201A and 202B) extending in directions away from each other from a portion where 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 thereabout to 6 GHz and frequencies thereabout. [Background technology]

[0002] In recent years, there has been an increasing demand for vehicles equipped with electronic devices to carry out MIMO (Multiple-Input Multiple-Output) communications using the frequency bands of 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 simultaneously receive the data via the multiple antennas. The MIMO antenna device disclosed in Patent Document 1 is known as an antenna device that enables such a communication format.

[0003] The MIMO antenna device disclosed in Patent Document 1 is configured by housing multiple antennas, namely, 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 on polychlorinated biphenyl. The balanced antenna is configured by two symmetrical planar L-shaped arms facing 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, resulting in a deterioration in VSWR (Voltage Standing Wave Ratio) and insufficient gain in the horizontal direction. Furthermore, housing multiple antennas in a small area such as a shark fin antenna housing causes interference 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 inter-antenna isolation, the better. However, the MIMO antenna device disclosed in Patent Document 1 has difficulty meeting this requirement across a wide frequency band. As shown in Figures 5 to 7 of Patent Document 1, the usable 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, that can 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. [Effects of the Invention]

[0008] The antenna device of the present invention includes a pair of first elements each including a portion operating as a self-similar antenna or an equivalent antenna, and a pair of second elements whose polarization direction is orthogonal to that of the first elements. Therefore, the antenna device operates as, for example, a tapered slot antenna (a type of traveling-wave antenna) in the high-frequency range, which is a relatively high frequency band, and as, for example, a loop antenna (a type of resonant antenna) in the low-frequency range, which is a relatively low frequency band. It also operates as a dipole antenna (a type of resonant antenna) in a specific frequency band in the mid-range, which is a frequency band intermediate between the relatively high frequency band and the relatively low frequency band. Furthermore, in the bands between the relatively high frequency band, the relatively low frequency band, and the mid-range, it operates in a state where the operating principles of these antennas are combined, i.e., as a composite antenna. Therefore, despite being a single antenna device, it can operate stably over a wider frequency band than conventional antenna devices of this type. Furthermore, since the polarization directions of the first element and the second element are orthogonal to each other, the effects of interference and the like are reduced even when the first element and the second element are close to each other, allowing the antenna device to be made thinner. [Brief explanation of the drawings]

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

[0010] Hereinafter, 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 with reference to the drawings. [First embodiment] The antenna device of the first embodiment is used by housing an antenna unit in a thin case that can be installed in any position, for example, in a room or vehicle. The thin case includes a case body made of a radio wave-transmitting material, for example, ABS resin, and a holding part that is appropriately shaped to fit the installation location. The case body has, for example, a rectangular prism-shaped housing with a bottom that has an internal space for housing the antenna unit, and a lid for sealing the storage space. The lid is provided on one of the four side surfaces of the housing or on one of the widest main surfaces and seals it.

[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 measuring approximately 90 mm, and a depth L3 of approximately 13 mm. As shown in FIG. 1B, the internal dimensions of case 10 are such that, for vertical side L1, the inner side L11 is approximately 87 mm, and the inner depth L31 is approximately 10 mm. After the antenna unit is housed in the case body, it is sealed with a lid. One of a plurality of holders (not shown) is attached to the mounting portion of the case body, depending on, for example, the planar shape of the dashboard.

[0012] The antenna unit housed in the case body 10 will now be described. FIGS. 2A to 2D are diagrams showing an example of the configuration of the antenna unit, 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 unit 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, with the direction of polarization perpendicular 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 using 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 feed point can be connected. This 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 first element") 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 (e.g., 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 farther from the first base end than in a region closer to the first base end. Also, the distance between each pair increases continuously or stepwise as it moves away from the first base end. That is, the distance between each pair is larger in a region farther from the first base end than in a region closer to the first base end. This is to allow each arm 101a, 102a to operate as a self-similar antenna, such as a biconical antenna or a bowtie antenna, or an equivalent.

[0015] The same is true for the two arms (e.g., 101b, 102b) of the other first element. Furthermore, 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 the 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 (e.g., 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 farther from the second base end than in a region closer to the second base end. Also, the distance between each pair increases continuously or stepwise as it moves away from the second base end. That is, the distance between each pair is larger in a region farther from the second base end than in a region closer to the second base end. This is to allow each arm 201a, 202a to operate as a self-similar antenna, such as a biconical antenna or a bowtie antenna, or an equivalent. The same is true for the two arms (e.g., 201b, 202b) of the other second element. Furthermore, 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 portion. 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 portion. The first central portion is the feed point K1 of the first element, and the second central portion is the feed point K2 of the second element. The first central portion and the second central portion 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 portions rotated approximately 90 degrees from a position directly facing the first central portions while maintaining the distance D11. Therefore, a split ring (a ring with a portion cut out and facing each other) is formed between the opposing first and second elements. The polarization directions of the first and second elements are orthogonal. That is, for example, if the polarization direction of the first element is vertical (vertical polarization), the polarization direction of the second element is horizontal (horizontal polarization). Conversely, if the polarization direction of the first element is horizontal (horizontal polarization), the polarization direction 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 rotation of the pair of second elements. Each element is a conductive plate, for example, 0.5 mm thick, and the outer edge size is a size that fits into the storage space of the case body 10 shown in Figure 1. As an example, the outer edge size of each element is approximately 87 mm x approximately 87 mm x approximately 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, approximately 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 an example structure 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 arm 201a, 202a, 201b, 202b to the tip is an open end. This tip portion is called the open end portion. Each open end portion is formed to ensure a certain area for the first element and the second element in order to ensure low frequencies (to enable use at lower frequencies). In this example, an L-shaped open end portion is shown, but the shape of the open end portion is not limited to an L-shape and may be trapezoidal, rhombus, oval, circular, triangular, or the like. The widths of the two arms 201a, 202a of one second element and the two arms 201b, 202b of the other second element increase continuously or in stages as they move away from the second base end to the open end. That is, the widths of the two arms 201a, 202a of one second element and the two arms 201b, 202b of the other second element are larger in a region far from the second base end and closer to the open end than in a region close to the second base end and far from the open end. Furthermore, 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 increases continuously or in stages as they move away from the second base end. In other words, 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 greater in the region farther from the second base end than in the region closer to the second base end. This configuration achieves the behavior of a self-similar antenna, such as a biconical antenna or a bowtie antenna, or a similar antenna. As a result, the two arms 201a, 202a of one second element and the two arms 201b, 202b of the other second element, together with the second base end, form a substantially V-shape. 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 (e.g., two arms 201a and 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 in each diagram represents frequency (MHz). The average gain is the average gain in the horizontal plane (same below). As shown in FIGS. 4A and 4B, when only the second element is used alone as an antenna, operation as a resonant antenna is dominant around 900 MHz, and operation as a non-resonant antenna is dominant above approximately 2500 MHz. Furthermore, as can be seen from FIG. 4C, the average gain is approximately -2 dBi or more from approximately 900 MHz to 4500 MHz, which is a practical level comparable to that of the MIMO antenna device disclosed in Patent Document 1.

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

[0024] Next, we will explain the antenna characteristics of the antenna unit configured as shown in Figures 2A to 2D. In this antenna unit, the second base ends of the pair of second elements are rotated approximately 90 degrees from a position directly facing the first base ends while maintaining the distance D11, and face the pair of first elements. In other words, a split ring is formed between the opposing first and second elements. This expands the frequency band to the low-frequency side, allowing the antenna to operate as a broader-bandwidth antenna. Furthermore, the polarizations of the first and second elements are orthogonal. For example, if the polarization of the first element is vertically polarized, the polarization of the second element is horizontally polarized. Conversely, if the polarization of the first element is horizontally polarized, the polarization of the second element is vertically polarized. This makes it possible to suppress mutual interference. For example, isolation is significantly improved compared to when the elements are not rotated.

[0025] An example of the characteristics of the antenna unit of the first embodiment will be described in detail below. Fig. 6A is a VSWR characteristic diagram of feed point K1, and Fig. 6B is a VSWR characteristic diagram of feed point K2. The horizontal axis in each diagram represents 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 toward the lower frequency side.

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

[0027] Fig. 8A is a diagram of the power passing characteristics from feed point K1 to feed point K2, and Fig. 8B is a diagram of the power passing characteristics 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 that represents 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 characteristics. Furthermore, S12 is an S-parameter that represents 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 characteristics. In the antenna unit of the first embodiment, the isolation between feed point K1 and feed point K2 is approximately -30 dB to approximately -70 dB over a wide band from 698 MHz and frequencies thereabout to approximately 6 GHz and higher frequencies. In other words, even though feed point K1 and feed point K2 are close to each other, interference between the antennas is extremely small.

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

[0029] Fig. 11A is a graph showing the average gain characteristics in the horizontal plane (xy plane) of feed point K1 when the antenna unit is tilted, i.e., in the state of Fig. 9B, and Fig. 11B is a graph showing the average gain characteristics in the horizontal plane (xy plane) of feed point K2 when the antenna unit is tilted, i.e., in the state of Fig. 9B. Comparing Figs. 10A and 10B, the gain in the frequency band above 5 GHz is higher for both the first and second elements than before rotation. Furthermore, the difference between the maximum and minimum gain values ​​was approximately 6 dB before rotation, but has decreased to approximately 4 dB in the rotated state. In other words, it can be seen that by fixing the antenna unit at an angle of approximately 45 degrees, the average gain can be increased while suppressing fluctuations in the average gain. Note that "approximately 45 degrees" does not necessarily mean that it is exactly 45 degrees.

[0030] Here, 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 will be described. 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 dimensions as the antenna unit of the first embodiment. The size is such that they can be accommodated in case main body 10 shown in Fig. 1.

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

[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 represents frequency (MHz). The measurement conditions for each characteristic are the same as those for the antenna unit of the first embodiment. The dashed line represents the characteristic when only the pair of first bow-tie antennas 501, 502 is present, and the solid line represents the characteristic when the pair of first bow-tie antennas 501, 502 and the pair of second bow-tie antennas 601, 602 are arranged opposite each other.

[0033] These measurement results show that a pair of bowtie antennas (e.g., first bowtie antennas 501, 502) can be used as a wideband antenna, and that simply arranging 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 reaches a minimum near 1000 MHz, at around 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 similarly to a self-similar antenna. However, the shape and structure of each element differ 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. In other words, the case body 10 shown in FIG. 1 can also accommodate the antenna unit of the second embodiment. For ease of explanation, the same component names and symbols will be used to describe components corresponding to those of 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 portion to which feed point K2 is connected) and the first central portion (port or portion to which 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] The pair of first elements will now be described. One first element has two arms 101c, 101d extending away from each other from a first base end. The other first element also has two arms 102c, 102d extending away from each other from the first base end. Arm 101c of one first element also extends away from the arm 102c closest to it of the other first element. Similarly, arm 101d also extends away from arm 102d. One first element and the other first element are arranged symmetrically about the first central portion, and form a roughly C-shape when viewed from the front.

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

[0038] The second elements will now be described. One second element has two arms 201c and 201d that extend away from each other from the second base end. The other second element also has two arms 202c and 202d that extend away from each other from the second base end. Arm 201c of one second element also extends away from the closest arm 202c of the other second element. Arm 201d also extends away from the closest arm 202d. One second element and the other second element are arranged symmetrically about the second central portion, and form a roughly C-shape when viewed from the front.

[0039] Each of the arms 201c, 201d, 202c, and 202d is a conductive plate having a uniform width, and its tip is an open end formed into a predetermined shape, for example, an L-shape. The open end of arm 201c faces the open end of arm 201d, and the open end of arm 202c faces the open end of arm 202d. Furthermore, bent regions 2011c, 2011d, 2021c, and 2021d are formed in a portion of each open end. The bent regions 2011c, 2011d, 2021c, and 2021d are each bent approximately 90 degrees in the thickness direction of the antenna unit, i.e., toward 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] The antenna characteristics of the antenna unit of the second embodiment are shown in Figs. 16A to 19B. Fig. 16A is a VSWR characteristic diagram at feed point K1, and Fig. 16B is a VSWR characteristic diagram at feed point K2. Fig. 17A is a radiation efficiency characteristic diagram at feed point K1, and Fig. 17B is a radiation efficiency characteristic diagram at feed point K2. The horizontal axis in each diagram represents frequency (MHz). Fig. 18A is a passing power characteristic diagram from feed point K1 of the first element to feed point K2 of the second element, and Fig. 18B is a passing power characteristic diagram from feed point K2 of the second element to feed point K1 of the first element. The vertical axis in Fig. 18A represents the above-mentioned 20Log|S21| (dB), and the vertical axis in Fig. 18B represents 20Log|S12| (dB), and the horizontal axis in each diagram represents frequency (MHz). Fig. 19A is a diagram showing the average gain characteristics in the horizontal plane (xy plane) of feed point K1 in the arrangement of Fig. 9A, and Fig. 19B is a diagram showing the average gain characteristics in the horizontal plane (xy plane) of feed point K2 in the arrangement of Fig. 9A. The horizontal axis is frequency (MHz).

[0042] Note that 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 manner similar to the self-similar antenna, but the shape and structure of each element differs from that 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. This results in long 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 the sake of convenience, the members corresponding to the antenna units in the first or second embodiment will be described using the same names and symbols.

[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 distance from the position where the second central portion (portion connected to feed point K2) and the first central portion (portion connected to feed point K1) face each other. The predetermined distance is the same as the distance D11 described in the first embodiment.

[0045] A pair of first elements will now be described. One first element has two arms 101c and 101d extending away from each other from a first base end, and the other first element has two arms 102c and 102d extending away from each other from the first base end. The widths of the two arms 101c and 101d of one first element and the two arms 102c and 102d of the other first element increase continuously or stepwise as they move away from the first base end. That is, the widths of the two arms 101c and 101d of one first element and the two arms 102c and 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. Furthermore, the opposing distance between one first element and the other first element increases continuously or stepwise as they move away from the first base end. In other words, the opposing distance between one first element and the other first element is greater in a region farther from the first base end than in a region closer to the first base end. Arm 101c of one first element also extends in a direction away from the nearest arm 102c of the other first element. This configuration achieves the operation of a self-similar antenna, such as a biconical antenna or a bowtie antenna, or an equivalent.

[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 arm 101c faces the open end of arm 101d, and the open end of arm 102c faces the open end of 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 form 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 the distance from the second base end increases. 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 greater in a region farther from the second base end than in a region closer to the second base end. The arm 201c of one second element also extends in a direction away from the closest arm 201d of the other second element. Thus, the opposing distance between the arms 201c, 202c and the arms 201d, 202d near the base end is greater than that near the open end. This configuration allows the antenna to function as a self-similar antenna, such as a biconical antenna or a bowtie antenna, or a similar antenna. As a result, the two arms 201c, 202c of one second element and the two arms 201d, 202d of the other second element are arranged 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 arm portions 201c, 201d, 202c, and 202d is an open end. The rate of change in width of each of the arm portions 201c, 201d, 202c, and 202d from near the second base end to near the open end is smaller than the rate of change in width of the first element from near the first base end to near the open end. A long-side bend region 2011c and a short-side bend region 2012c are formed in a portion of the open end of the arm portion 201c. The long-side bend region 2011c is bent 90 degrees in the thickness direction of the antenna unit, i.e., toward the nearest first element. The short-side bend region 2012c is bent 90 degrees from the long-side bend region 2011c toward the other second element, and then bent 90 degrees toward the nearest first element.

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

[0050] By forming these bent regions 2011c, 2012c, 2021c, 2022c, 2011d, 2012d, 2021d, and 2022d, the overall size can be reduced while maintaining the antenna performance that would be achieved if these regions were not formed. Also, because a pair of first elements and a pair of second elements form a split ring, the usable frequency band can be expanded to the lower frequency side.

[0051] The antenna characteristics of the antenna unit of the third embodiment are shown in Figures 21A to 24B. Figure 21A is a VSWR characteristic diagram at feed point K1, and Figure 21B is a VSWR characteristic diagram at feed point K2. Figure 22A is a radiation efficiency characteristic diagram at feed point K1, and Figure 22B is a radiation efficiency characteristic diagram at feed point K2. The horizontal axis in each diagram represents frequency (MHz). Figure 23A is a passing power characteristic diagram from feed point K1 of the first element to feed point K2 of the second element, and Figure 23B is a passing power characteristic diagram from feed point K2 of the second element to feed point K1 of the first element. The vertical axis in Figure 23A is 20Log|S21| (dB), and the vertical axis in Figure 23B is 20Log|S12| (dB), and the horizontal axis in each diagram represents frequency (MHz). Fig. 24A is a diagram showing the 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 the average gain characteristics in the horizontal plane (xy plane) of the feed point K2 in the arrangement of Fig. 9A. The horizontal axis represents 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 manner similar to that of a self-similar antenna, but the shape and structure of each element differ from those of the antenna unit of the first embodiment. However, for ease of explanation, the same component names and symbols will be used for components corresponding to those of 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 according to the fourth embodiment has the same basic structure as the antenna unit according to the first embodiment. The spacing between the pair of first elements and the pair of second elements and the outer edge size are also the same as those of the antenna unit according to the first embodiment. The antenna unit of the fourth embodiment differs from the antenna unit 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, the antenna unit of the fourth embodiment does not have the split ring described above.

[0054] The antenna characteristics of the antenna unit of the fourth embodiment are shown in Figures 26A to 29B. Figure 26A is a VSWR characteristic diagram at feed point K1, and Figure 26B is a VSWR characteristic diagram at feed point K2. Figure 27A is a radiation efficiency characteristic diagram at feed point K1, and Figure 27B is a radiation efficiency characteristic diagram at feed point K2. The horizontal axis in each diagram represents frequency (MHz). Figure 28A is a passing power characteristic diagram from feed point K1 of the first element to feed point K2 of the second element, and Figure 28B is a passing power characteristic diagram from feed point K2 of the second element to feed point K1 of the first element. The vertical axis in Figure 28A is 20Log|S21| (dB), and the vertical axis in Figure 28B is 20Log|S12| (dB), and the horizontal axis in each diagram represents frequency (MHz). Fig. 29A is a diagram showing the average gain characteristics in the horizontal plane (xy plane) of feed point K1 in the arrangement of Fig. 9A, and Fig. 29B is a diagram showing the average gain characteristics in the horizontal plane (xy plane) of 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. The antenna unit of the fifth embodiment is similar to the antenna unit of the first embodiment in the positional relationship between a pair of first elements and a pair of second elements, and in the shape, structure, and size of each element, but differs from the antenna unit of the first embodiment in the way in which each pair of elements is combined. In addition, the form of the feed point is specified. For convenience, the same component names and symbols will be used for components corresponding to those of the antenna unit of the first embodiment.

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

[0058] In addition, the first feeder F11, which has a ferrite core wound around it, is connected to the first central feed point, and the second feeder F21, which has a ferrite core wound at an angle that differs by approximately 90 degrees from that of the first feeder F11, is connected to the second central feed point. This suppresses leakage current in the low-frequency range where resonance occurs, such as 698 MHz, and stabilizes and improves 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 to this. One element may be a different size from the other as long as they have a portion that operates as a self-similar antenna or an equivalent antenna, the directions of polarization are orthogonal to each other, and the shape allows the area of ​​the overlapping portion to be small.

[0060] In the first, second, fourth, and fifth embodiments, examples were described in which the pair of first elements and the pair of second elements were substantially V-shaped or substantially C-shaped, but they may also be substantially D-shaped, substantially U-shaped, substantially semicircular, substantially semi-elliptical, substantially triangular, or substantially rectangular. Furthermore, these embodiments were described assuming a configuration in which two feeding points are provided, but a configuration in which only one feeding point is provided may also be used. Because the first element and the second element are electrically connected, the same operation as when two feeding points are provided is possible. 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. Furthermore, 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 when used as an antenna.

[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, thereby suppressing mutual interference between the elements and enabling a thinner antenna device. Furthermore, since 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, reception or transmission can be performed over a wide frequency band, enabling stable operation over a wide frequency band.

[0062] 12A to 12D , when the pair of second bow-tie antennas 601, 602 are arranged facing the pair of first bow-tie antennas 501, 502 in a state rotated approximately 90 degrees from a state in which they are directly facing the pair of first bow-tie antennas 501, 502, a conductor is interposed around the periphery between the elements of the first bow-tie antennas 501, 502 and the second bow-tie antennas 601, 602. On the other hand, by arranging the pair of second elements in the antenna unit 12 of the first to fifth embodiments so as to face the pair of first elements while being rotated approximately 90 degrees from the state where they are directly facing each other, the overlapping area between the elements when the two elements are brought close to each other is reduced, that is, 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, fluctuations in reactance can be suppressed and impedance is stabilized, thereby achieving a wide bandwidth.

[0063] The antenna unit can be housed in a radio wave-transmitting case (case body 10) with dimensions of 90 mm in length and width 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 Figures 16A to 19B, the antenna units of the first and second embodiments have stable and excellent antenna characteristics across the low to high frequency bands of LTE and 5G, and can therefore be used as antenna devices for domestic and overseas use without any design changes.

[0065] By increasing the width with increasing distance from the feed point K1 (K2), the VSWR, especially in the high-frequency range, is reduced, radiation efficiency and average gain are increased, and fluctuations in these can be suppressed. Furthermore, by configuring a pair of first elements and a pair of second elements, and further by rotating the pair of second elements approximately 90 degrees from a state directly facing the pair of first elements and arranging both elements closely, the opposing ends of the elements are electrically connected to each other, forming a loop and enabling a broader bandwidth in the low-frequency range around 698 MHz. This configuration expands the low-frequency side of the usable frequency band, which was difficult to achieve with conventional antenna devices, thereby achieving a wider usable frequency band.

[0066] The two arms (e.g., 101a and 101b) each have a tip formed into a predetermined shape that corresponds to the shape of the installation site, which increases the degree of freedom in element shape while ensuring the required element area for each arm. The "required element area" is determined by the resonant frequency of the split ring, which expands the low-frequency band.

[0067] A portion of the region of one of the two arms (e.g., 101c, 101d) farthest from the power supply point (e.g., K1) is bent toward the opposing other arm (e.g., 201c, 201d), so that the frequency band can be expanded toward the lower frequency side without changing the vertical and horizontal size 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 practical antenna characteristics when a pair of bowtie antennas rotated approximately 90 degrees from each other are used as wideband antennas, spaced 40 mm or more apart. In addition, 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 extend the frequency to a lower frequency of approximately 450 MHz while maintaining the performance of the antenna of each embodiment, this can be achieved by enlarging the size of the antenna unit when viewed from the front or back (outer edge size) in accordance with the wavelength ratio without changing the spacing D11 between the antenna units. Note that, although the performance of the antenna will be inferior to that of the antenna of these embodiments, it is also possible to extend the frequency to a lower frequency of approximately 450 MHz by appropriately adjusting the width of the arm portion 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 will be described that has a configuration that takes into consideration the operational effects of the antenna units of the first to fifth embodiments as well as simplification of the element manufacturing process. The antenna unit has a pair of first elements and a pair of second elements, their relative positions, and a power supply system that 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 to describe components that correspond to those of 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 the power supply state of a pair of first elements, and Fig. 31C is a front view showing the power supply state of a pair of second elements. This antenna unit is sized to be housed in a box-shaped resin case (for example, case 10 shown in Figs. 1A and 1B) that is 60 mm long in the z direction, 80 mm long in the x direction, and 15 mm long in the y direction.

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

[0072] The base end regions 101e and 102e correspond to the partial regions of the arms including the portions where 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, while 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 each of the front and back surfaces of a single substrate PB1, and are then conductively connected to each other by a plurality of conductive via holes 1011e in this example. In this example, the substrate PB1 is configured as a substantially rectangular PCB (Printed Circuit Board; the same applies below). The base end regions 102e are also printed in a strip shape on each of the front and back surfaces of the substrate PB1, and are then conductively connected to each other by a plurality of conductive via holes 1021e. The portion where the two base end regions 101e, 102e are closest to each other is the first central portion (the portion or port to which the feed point K1 is connected). A signal line F111 of a coaxial cable F114, which is an example of a feeder, is conductively connected to the base end region 102e. A ground line F112 of the coaxial cable F114 is conductively connected to the base end region 101e. This allows the pair of first elements to function as two dipole antennas. Furthermore, 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] 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. In order to increase the gain in the low frequency band around 698 GHz, it is common to increase the size of the antenna unit, but by attaching the ferrite core F113, it is possible to reduce the size of the antenna unit while maintaining the gain in the low frequency band. Here, in the coaxial cable F114, the connection point with the first element is a feeding point K1, and the end opposite to the feeding point K1 is an output end. Furthermore, 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 ground line F112 of the coaxial cable are directly connected to the board areas 101e and 102e formed on the board PB1, thereby simplifying the overall configuration of the antenna unit.

[0075] The extension regions 101f, 101g, 102f, and 102g are metal plates that are approximately 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 each have an open end near the tip. The open end is composed of first end portions 1011f, 1011g, 1021f, and 1021g that are trapezoidal on a plane perpendicular to the substrate PB1, and second end portions 1012f, 1012g, 1022f, and 1022g that are bent onto a plane parallel to the substrate PB1 and have an approximately triangular shape. The second end portions 1012f, 1012g, 1022f, and 1022g are approximately triangular in shape to maintain a self-similar shape, maintain constant impedance, and improve antenna performance (VSWR, radiation efficiency, and gain).

[0076] To avoid coupling between the opposing second ends 1012f, 1012g and 1022f, 1022g, portions of the triangular tips may be removed to form a shape closer to a trapezoid. Each end has a width that increases toward the tip of its extension region. By forming the second ends 1012f, 1012g, 1022f, 1022g into a substantially triangular shape, the antenna unit as a whole maintains a similar shape, maintaining constant impedance and improving antenna characteristics, particularly VSWR. The two extension regions 101f, 101g of one first element and the two extension regions 102f, 102g of the other first element are symmetrically arranged about the first central portion, and each form a substantially C-shape when viewed from the front (y-axis direction).

[0077] Next, the pair of second elements will be described. One of the pair of second elements has a base end region 201e whose base end is formed in a convex shape toward the base end of the other second element (in the 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 convex shape toward the base end of the 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 a substrate PB2 that is disposed on a plane parallel to the substrate PB1 and tilted approximately 90 degrees around 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 regions 201e are printed in strips on the front and back surfaces of the substrate PB2, and are then electrically connected to each other by a plurality of conductive via holes 2011e. The base end regions 202e are also printed in strips on the front and back surfaces of the substrate PB2, and are then electrically connected to each other by a plurality of conductive via holes 2021e.

[0079] The portion 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 feed point K2 is connected). A signal line F211 of a coaxial cable F214, which is an example of a feeder, is conductively connected to the base end region 202e. A 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 function 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. Furthermore, the base end regions 201e and 202e, the extension regions 201f and 201g, and the extension regions 202f and 202g function as two tapered slot antennas. Here, in the coaxial cable F214, the connection point with the second element is a feed point K2, and the end opposite to the feed point K2 is an output end.

[0080] The extension regions 201f, 201g, 202f, and 202g are metal plates perpendicular to the substrate PB2 and have widths in the direction of the first element, and are each made of sheet metal. The extension regions 201f, 201g, 202f, and 202g each have an open end near its tip. The open end is composed of first end portions 2011f, 2011g, 2021f, and 2021g that are trapezoidal on a plane perpendicular to the substrate PB2, and second end portions 2012f, 2012g, 2022f, and 2022g that are bent onto a plane parallel to the substrate PB2 and form a substantially triangular shape. The same applies to the second element; a portion of the triangular end may be removed to form a shape closer to a trapezoid. The width of each end portion 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 arranged symmetrically around the second central portion, and each form an approximately 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 second end 1012f, 1012g, 1022f, 1022g of the first element and the first end 2021f, 2021g, 2011f, 2011g and second end 2022f, 2022g, 2012f, 2012g of the adjacent second element. In other words, both regions are non-conductive but capacitively coupled. This allows the pair of first elements and the pair of second elements to function as a loop antenna. This split ring serves to extend the usable frequency band of the antenna toward the lower frequency range.

[0082] In the antenna unit of the sixth embodiment, similar to the antenna units of the previous embodiments, a pair of first elements are tilted at approximately 90 degrees relative to a pair of second elements, so that the directions of polarization of signals that can be received or transmitted are orthogonal to each other, and some or all of the elements function as self-similar antennas or equivalent antennas.

[0083] Furthermore, when a self-similar antenna or an element that operates similarly to it is made of sheet metal, it is required that the width around the base end where the feed point is connected be as narrow as possible. This makes it difficult to achieve. 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 electrically connected, respectively, making it easy to fabricate.

[0084] Furthermore, 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 conductive via holes 1011e, 1021e, 2011e, and 2021e. Therefore, radiation resistance and inductance are increased compared to when they are formed with only one print, improving radiation efficiency. Note that a partial region of at least one of the pair of first elements and the pair of second elements may be formed on the substrates PB1 and PB2. Furthermore, the base end regions 101e, 102e, 201e, and 202e may be formed on only one surface of the substrates PB1 and PB2. In this case, the conductive via holes 1011e, 1021e, 2011e, and 2021e are unnecessary.

[0085] Next, the antenna characteristics of the antenna of the sixth embodiment will be described. Figure 32A is a VSWR characteristic diagram of the output end of coaxial cable F114, and Figure 32B is a VSWR characteristic diagram of the output end of coaxial cable F214. Figure 32C is a radiation efficiency characteristic diagram of the output end of coaxial cable F114, and Figure 32D is a radiation efficiency characteristic diagram of the output end of coaxial cable F214. The horizontal axis in each diagram represents frequency (MHz). Figure 32E is a passing power characteristic diagram from the output end of coaxial cable F114 to the output end of coaxial cable F214, and Figure 32F is a passing power characteristic diagram from the output end of coaxial cable F214 to the output end of coaxial cable F114. The vertical axis in Figure 32E is 20Log|S21| (dB), and the vertical axis in Figure 32F is 20Log|S12| (dB), and the horizontal axis in each diagram represents frequency (MHz). Fig. 32G is a diagram showing the 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 the 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 in low frequencies such as 698 MHz and frequencies around it.

[0087] Note that the configuration in which the antenna unit is configured with 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 besides those shown in Figures 31A to 31C. For example, the above configuration can also be applied to antenna units of other configurations configured with one first element and one second element.

[0088] [Seventh embodiment] In the seventh embodiment, as an application of the sixth embodiment, an example will be described in which each element of the antenna unit is created by printing on a substrate. 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 the power supply state of the pair of first elements, and Fig. 33D is a front view showing the power supply state of the pair of second elements. Fig. 33E is a perspective view for explaining the overall state of the first and second elements, and Fig. 33F is a side view of the antenna unit. Here, the substrate 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 components used in the previous embodiments will be described using the same reference numerals.

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

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

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

[0092] As shown in Fig. 33C, a signal line F111 of a coaxial cable F114 is conductively connected to the base end of one of the first elements. 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 function 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 a feeding point K1, and the end opposite to the feeding point K1 is an output end.

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

[0094] The other second element has two arms 202j, 202k extending in directions away from each other from a base end to which a feed point can be connected. Arm 202j has a region 2021j whose width increases with increasing distance from the base end and an open end 2022j that is linearly cut out from another corner of substrate PB3 toward the center of substrate PB3. Arm 202k has a region 2021k whose width increases with increasing distance from the base end and an open end 2022k that is linearly cut out from another corner of substrate PB3 toward the center of 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 electrically connected to the base end of one of the second elements. The ground line F212 of the coaxial cable F214 is electrically connected to the base end of the other second element. This allows the pair of second elements to function 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 a feed point K2, and the end opposite to the feed point K2 is an output end.

[0096] 33E, a split ring is formed between the open end (e.g., open end 1012j) of the arm of the first element on the front surface of the substrate PCB3 and the open end (e.g., open end 2012j) of the arm of the nearest second element on the back surface of the substrate PCB3. Therefore, the first element and the second element are not conductive, but are capacitively coupled and operate 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 in each diagram represents 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 in Fig. 34E is 20Log|S21| (dB), and the vertical axis in Fig. 34F is 20Log|S12| (dB), and the horizontal axis in each diagram represents frequency (MHz). Fig. 34G is a diagram showing the 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 the 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, the antenna is extremely thin, with a thickness of just 0.8 mm plus the printed portion, and is a square antenna with a side length of 87 mm, but it can be used and put into practical use at low frequencies such as around 698 MHz. Although the seventh embodiment has been described as having 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 thereof, it is also possible to implement a configuration using two substrates. That is, a pair of first elements may be formed as a conductive pattern on a first surface of one substrate, and a pair of second elements may be formed as a conductive pattern on a second surface of the other substrate opposite the first surface, with the conductive patterns being electrically connected by conductive through holes or the like.

[0099] [Modification of the Seventh Embodiment] In the seventh embodiment, an example was described in which there is no electrical continuity (a split ring is formed) 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 it on the back surface of the substrate PB3. Therefore, below, as a modified example, a configuration will be described in which there is electrical continuity 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 it on the back surface of the substrate PB3. The electrical continuity 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 it on the back surface of the substrate PB3 can be achieved by, for example, soldering, a conductive via hole, or the like.

[0100] Antenna characteristics of the antenna unit of a modified example of the seventh embodiment are shown in Figures 35A to 35H. The measurement conditions are the same as those of the seventh embodiment. Figure 35A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Figure 35B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Figure 35C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Figure 35D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis in each figure represents frequency (MHz). Figure 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 Figure 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 in Figure 35E is 20Log|S21| (dB), and the vertical axis in Figure 35F is 20Log|S12| (dB), and the horizontal axis in each figure represents frequency (MHz). Fig. 35G is a diagram showing the 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 the 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 nearest 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, which has a configuration in which the open end of a first element on the front surface of the substrate is electrically connected to the open end of a second element on the rear surface of the substrate. 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 the power supply state of a pair of first elements, and Fig. 36C is a front view showing the power supply state of a pair of second elements.

[0103] The difference from the antenna part of the sixth embodiment is that there is no split ring between the open end of the first element on the surface of the substrate and the open end of the second element on the back surface of the substrate, that is, 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 that 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 Figures 37A to 37H. The measurement conditions are the same as those of the sixth embodiment. Figure 37A is a VSWR characteristic diagram of the output end of the coaxial cable F114, and Figure 37B is a VSWR characteristic diagram of the output end of the coaxial cable F214. Figure 37C is a radiation efficiency characteristic diagram of the output end of the coaxial cable F114, and Figure 37D is a radiation efficiency characteristic diagram of the output end of the coaxial cable F214. The horizontal axis in each figure represents frequency (MHz). Figure 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 Figure 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 in Figure 37E is 20Log|S21| (dB), and the vertical axis in Figure 37F is 20Log|S12| (dB), and the horizontal axis in each figure represents frequency (MHz). Figure 37G is a diagram showing the average gain characteristics in the horizontal plane (xy plane) of the output end of the coaxial cable F114 in the arrangement of Figure 31A, and Figure 37H is a diagram showing the 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 nearest 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 antenna unit is incorporated 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-transmitting plastic and, as shown in the front, back, plan, bottom, right side, and left side views of FIG. 38 and the exploded view of FIG. 39, is composed of a substantially rectangular first case body 10a and a second case body 10b whose internal storage space is sealed at their open ends. 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. 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, as viewed from the inside. FIG. 40D is a front view of the inside of the first case body 10a. The first case body 10a has four screw receiving bosses 10a1 to 10a4 with threaded screw receiving holes. Sealing is performed by inserting a screw 10c into the back of the second case body 10b and tightening it, but adhesive can also be used. The dimensions of the first case body 10a and the second case body 10b when sealed, excluding the exposed coaxial cables F114 and F214, are 60 mm in length, 80 mm in width, and 15 mm in thickness.

[0107] The antenna unit housed in each case body 10a, 10b has a modified shape, etc., of the antenna unit 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 of the pair of first elements on the substrate PB1. 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-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. The claws PB1a-PB1d are then passed through the through holes, and the vicinity of their tips is bent on the base end regions 101e, 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 may be fixed to the base end regions 101e and 102e by soldering.

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

[0109] The first ends 1011f, 1011g, 1021f, and 1021g and the second ends 1012f, 1012g, 1022f, and 1022g are formed into shapes that follow the bottom and side surfaces of the first case body 10a, respectively. The lengths of the substrate PB1 and the extension regions 101f, 101g, 102f, and 102g are longer than the corresponding components in the second element. Meanwhile, the lengths of the portions (post-branch regions) of the extension regions 101f, 101g, 102f, and 102g that branch off from the base end regions 101e and 102e and extend away from them are shorter than the corresponding components in the second element. As mentioned above, a portion of the tip portions of the opposing second ends 1012f, 1012g and 1022f, 1022g of the second ends 1012f, 1012g and second ends 1022f, 1022g has a shape 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 housed in the second case body 10b with a similar structure. That is, a pair of through holes is formed at or near both ends of the base end region 201e of each of the pair of second elements on the substrate PB2. A pair of through holes is also formed at 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 passing through the through holes, the claws PB2a to PB2d are bent near their tips on the base end regions 201e and 202e of the substrate PB2. This fixes the extension regions 201f, 201g, 202f, and 202g to the base end regions 201e and 202e on the substrate PB2 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 does not include 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 maximizes the distance to the coaxial cable F214.

[0112] The first ends 2011f, 2011g, 2021f, and 2021g and the second ends 2012f, 2012g, 2022f, and 2022g are molded into shapes that conform to the bottom and side surfaces of the first case body 10b, respectively. As described above, portions of the tip portions of the opposing second ends 1012f, 1012g, 1022f, and 1022g of the second ends 1012f, 1012g and 1022f, 1022g are shaped like trapezoids by adjusting the capacitive and inductive properties to ensure the desired frequency band. Note that the nearest open ends of the pair of first elements and the pair of second elements (e.g., the second ends 1012f and 2022f) are non-conductive and function as split rings. In other words, they are capacitively coupled and function as loop antennas.

[0113] As described above, the antenna unit of this embodiment operates on different operating principles or a combination of these different operating principles depending on the frequency band being used. For example, in a frequency band in which the first ends 1011f, 1011g, 1021f, 1021g and second ends 1012f, 1012g, 1022f, 1022g of the pair of first elements and the first ends 2011f, 2011g, 2021f, 2021g and 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 similar to a loop antenna (operation A).

[0114] Furthermore, 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 lengths of the portions of the two extension regions 101f, 101g and 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 lengths of the two extension regions 101f and 101g and the extension regions 102f and 102g, which extend opposite to the length of the substrates PB1 and PB2, the closer the antenna characteristics (VSWR, etc.) in the high frequency range to those in the low frequency range. In other words, the bandwidth over which the antenna characteristics are stable expands. In this way, an antenna device having one antenna unit mainly operates as a loop antenna in the low frequency band, mainly as a dipole antenna in the mid frequency band, and mainly as a tapered slot antenna in the high frequency band. Furthermore, in the intermediate frequency band, it operates as a composite antenna that combines these operating principles. That is, 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 jackets of the coaxial cables F114 and F214. If the coaxial cables F114, F214 are not provided with the ferrite cores F113, F213, the radiation efficiency will decrease at the lowest frequency of the band, but operation will still be possible. Therefore, in applications where a decrease in radiation efficiency at the low frequency band can be tolerated, the coaxial cables F114, F214 may be used without the ferrite cores F113, F213.

[0117] In the ninth embodiment, the first element and the second element each have a power feeding port, and coaxial cables F114 and F214 are connected to the respective power feeding ports. In other words, an antenna device including the antenna unit of the ninth embodiment has ports, and coaxial cables F114 and F214 for power feeding are connected to the two ports, respectively. However, by providing a branch circuit or the like, the antenna device can operate even when power is fed by a single coaxial cable. In this case, it is sufficient to remove the coaxial cable connected to one of the two ports.

[0118] Although the case where the lengths 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 has been described, this is not limited to this. For example, if the shape of the first cases 10a and 10b is approximately square, these lengths may be the same.

Claims

1. An antenna device for use in a vehicle, comprising: a first element disposed on a first plane; a second element disposed on a second plane; a substrate electrically connected to the first element and the second element, one surface of which is the first plane on which the first element is formed, and the other surface of which is the second plane on which the second element is formed; Each of the first element and the second element has a base end and at least two arms extending away from each other from the base end, the first element and the second element face each other with the base end portion as a center, and each element includes a portion that operates as a self-similar antenna; Antenna device.

2. a power supply point that allows power to be supplied to the first element and the second element; The feed point is formed on the substrate and connected to the base end portion. The antenna device according to claim 1 .

3. the two arms of the first element extend in directions away from the base end, the two arms of the second element extend in directions away from the base end, a distance between the first element and the second element in one plane is larger in a region away from the base end than in a region close to the base end; The antenna device according to claim 1 .

4. The two arms of the first element and the two arms of the second element each have a width greater at a portion away from the base end than at a portion closer to the base end. The antenna device according to claim 1 .

5. the two arms of the first element and the two arms of the second element each have an open end, As a result, together with the base end portion, the shape is one of a substantially C-shape, a substantially D-shape, a substantially U-shape, a substantially V-shape, a substantially semicircular shape, a substantially semi-elliptical shape, a substantially triangular shape, and a substantially rectangular shape. The antenna device according to claim 1 .

6. The first element and the second element are symmetrical with respect to the base end portion. The antenna device according to claim 1 .

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