Directional antenna

Abstract

A directional antenna includes a substrate, a power-supply radiating element, paired non-power-supply radiating elements, and a metal plate. The power-supply radiating element is formed on the front surface of the substrate to be along the vertical direction. The power-supply radiating element receives electric power from the power-supplying portion. The paired non-power-supply radiating elements are provided along the vertical direction and oppose each other across the power-supply radiating element in a horizontal direction which is a direction along the front surface of the substrate on the horizontal plane, when viewed in a front-rear direction. A part of the metal plate is provided behind a part of the power-supply radiating element. The metal plate is not provided behind the paired non-power-supply radiating elements. The 3 dB beam width of the directional antenna on the horizontal plane is equal to or greater than 180 degrees including the range forward of the directional antenna.

Claims

1. A directional antenna comprising: a substrate which is arranged such that a front surface and a rear surface extend along a vertical direction which is orthogonal to a horizontal plane, such that a direction from the rear surface of the substrate toward the front surface of the substrate is a forward direction and a direction from the front surface of the substrate to the rear surface of the substrate is a rearward direction on the horizontal plane, a power-supply radiating element which is provided on the front surface of the substrate to extend along the vertical direction and the power-supply radiating element receives electric power, at least paired non-power-supply radiating elements which extend along the vertical direction, oppose each other across the power-supply radiating element in a horizontal direction which is a direction along the front surface of the substrate on the horizontal plane when viewed in a front-rear direction which is orthogonal to the horizontal direction and the vertical direction, and do not receive the electric power, and a metal plate which is provided on the rear surface of the substrate, at least a part of the metal plate being provided behind at least a part of the power-supply radiating element and the metal plate being not provided behind the non-power-supply radiating elements, wherein a 3 dB beam width on the horizontal plane is equal to or greater than 180 degrees including a range forward of the directional antenna when the power-supply radiating element is excited in response to power supply and the at least paired non-power-supply radiating elements are excited on account of an influence of excitation of the power-supply radiating element.

2. The directional antenna according to claim 1, wherein the paired non-power-supply radiating elements are provided on the front surface of the substrate.

3. The directional antenna according to claim 1, wherein the power-supply radiating element is a patch antenna, and the paired non-power-supply radiating elements are dipole antennas, respectively.

4. The directional antenna according to claim 2, wherein the power-supply radiating element is a patch antenna, and the paired non-power-supply radiating elements are dipole antennas, respectively.

5. The directional antenna according to claim 1, the directional antenna being mounted on a straddled vehicle.

6. The directional antenna according to claim 2, the directional antenna being mounted on a straddled vehicle.

7. The directional antenna according to claim 3, the directional antenna being mounted on a straddled vehicle.

8. The directional antenna according to claim 4, the directional antenna being mounted on a straddled vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B are schematic representations of a directional antenna of an embodiment. FIG. 1A shows a front surface of a substrate, whereas FIG. 1B shows a rear surface of the substrate.

(2) FIG. 2 shows an example of a simulation result of horizontal plane directivities of the directional antenna of the embodiment.

(3) FIG. 3 shows an example of a measurement result of horizontal plane directivities of the directional antenna of the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The following will describe a directional antenna 1 of an embodiment of the present teaching with reference to the schematic representation in FIGS. 1A and 1B. As shown in FIGS. 1A and 1B, the directional antenna 1 includes a substrate 10, a power-supply radiating element 20, paired non-power-supply radiating elements 30, and a metal plate 40.

(5) The substrate 10 is a printed board formed to be flat in shape. The substrate 10 is made of a dielectric material having flexibility. The substrate 10 has a front surface 10a shown in FIG. 1A and a rear surface 10b shown in FIG. 1B. As shown in FIGS. 1A and 1B, the substrate 10 is arranged such that the front surface 10a and the rear surface 10b are along the vertical direction which is orthogonal to the horizontal plane. The vertical direction is indicated by arrows labeled “orthogonal direction” in FIGS. 1A and 1B. The horizontal plane is parallel to the horizontal direction which is along the front surface 10a of the substrate 10 indicated by the arrows labeled “horizontal direction” in FIGS. 1A and 1B, and when flat, the substrate 10 forms a plane that is parallel to the orthogonal direction and the horizontal direction. In FIGS. 1A and 1B, a direction from the rear surface 10b of the substrate 10 toward the front surface 10a that is orthogonal to the front surface 10a is a forward direction (indicated by F in the figures). Meanwhile, a direction from the front surface 10a of the substrate 10 toward the rear surface 10b that is orthogonal to the rear surface 10b is a rearward direction (indicated by B in the figures). The signs F and B in the figures indicate the forward and rearward directions, respectively.

(6) As shown in FIG. 1A, the power-supply radiating element 20 is formed on the front surface 10a of the substrate 10. The power-supply radiating element 20 is a patch antenna. The power-supply radiating element 20 includes a patch portion 21, a power-supplying portion 22, and a stub portion 23. The patch portion 21 is formed to be a flat plate which is substantially square in shape, other than a cutout portion 21a to be described in further detail later. The maximum length Lp in the vertical direction of the patch portion 21 is substantially identical with the maximum width Wp in the horizontal direction. The term “substantially identical” means having a variation of five (5) percent or less, in the example shown in FIG. 1A. The patch portion 21 is provided with a cutout portion 21a at the center of one end portion in the vertical direction. The cutout portion 21a is rectangular in shape and has the length Lc in the vertical direction and the length We in the horizontal direction. The cutout portion 21a of the patch portion 21 is connected to the power-supplying portion 22, or in other words, the power-supplying portion 22 is connected to the patch portion 21 at the cutout portion 21a. The power-supplying portion 22 extends from the patch portion 21 to one end, in the vertical direction, of the front surface 10a of the substrate 10. The patch portion 21 receives electric power from the power-supplying portion 22. The stub portion 23 is provided to adjust the phase of the power-supply radiating element 20. The stub portion 23 is formed behind the power-supplying portion 22 (or, in other words, between the power-supplying portion 22 and the substrate 10) and extends along the horizontal direction. The stub portion 23 is formed such that the length Ls from the power-supplying portion 22 to one end in the horizontal direction is longer than the length of the stub portion 23 in the vertical direction. The stub portion 23 is separated from one end portion, or edge, of the patch portion 21 by the distance Ds in the vertical direction.

(7) The paired non-power-supply radiating elements 30 are constituted by a non-power-supply radiating element 30a and a non-power-supply radiating element 30b. The non-power-supply radiating element 30a and the non-power-supply radiating element 30b are identical in shape. Each of the non-power-supply radiating element 30a and the non-power-supply radiating element 30b is rectangular in shape and has the length Ld in the vertical direction and the length Wd in the horizontal direction. Each of the non-power-supply radiating element 30a and the non-power-supply radiating element 30b is arranged so that the length Ld in the vertical direction is longer than the length Wd in the horizontal direction. The paired non-power-supply radiating elements 30 are dipole antennas. The paired non-power-supply radiating elements 30 are formed on the front surface 10a of the substrate 10 and extend along the vertical direction. In other words, the paired non-power-supply radiating elements 30 are provided on the front surface 10a of the substrate 10 to be parallel to the power-supply radiating element 20. The non-power-supply radiating element 30a and the non-power-supply radiating element 30b are provided on the front surface 10a of the substrate 10 to be parallel to each other. The paired non-power-supply radiating elements 30 oppose each other across the power-supply radiating element 20 in the horizontal direction when viewed in the front-rear direction which is orthogonal to the horizontal direction and the vertical direction. Each of the non-power-supply radiating element 30a and the non-power-supply radiating element 30b is separated from the power-supply radiating element 20 by the distance Dd in the horizontal direction. No power is supplied to the paired non-power-supply radiating elements 30.

(8) As shown in FIG. 1B, the metal plate 40 is provided on apart of the rear surface 10b of the substrate 10. The metal plate 40 is formed to be a flat plate. The metal plate 40 is provided at the center in the horizontal direction of the rear surface 10b of the substrate 10 to have the length Wg in the horizontal direction. The metal plate 40 is formed to extend from first end portion to second end portion in the horizontal direction of the rear surface 10b of the substrate 10. The metal plate 40 is made of metal which reflects electromagnetic waves. As shown in FIG. 1A, the length Wg of the metal plate 40 in the horizontal direction is arranged to be shorter than the maximum length Wp in the horizontal direction of the patch portion 21 of the power-supply radiating element 20. This arrangement allows electromagnetic waves excited by the power-supply radiating element 20 to be radiated laterally from the substrate 10. In this specification, lateral directions from the power-supply radiating element 20 are equivalent to directions away from the power-supply radiating element 20 in the horizontal direction. A part of the metal plate 40 is provided behind a part of the power-supply radiating element 20. The metal plate 40 is not provided behind the paired non-power-supply radiating elements 30.

(9) The resonance frequency of the directional antenna 1 is determined by the maximum length Lp in the vertical direction of the patch portion 21 of the power-supply radiating element 20 and the length Ld in the vertical direction of each of the paired non-power-supply radiating elements 30 (i.e., the non-power-supply radiating element 30a and the non-power-supply radiating element 30b). The input impedance of the directional antenna 1 is determined by the length Lc in the vertical direction of the cutout portion 21a of the power-supply radiating element 20, the length Wc in the horizontal direction of the cutout portion 21a of the power-supply radiating element 20, the length Ls in the horizontal direction of the stub portion 23, and the distance Ds in the vertical direction between the stub portion 23 and the patch portion 21. The horizontal plane directivities of the directional antenna 1 are determined by the distance Dd in the horizontal direction between the power-supply radiating element 20 and each of the paired non-power-supply radiating elements 30, the length Wd in the horizontal direction of each of the paired non-power-supply radiating elements 30, and the length Wg in the horizontal direction of the metal plate 40. It is therefore possible to adjust the directivity range of the directional antenna 1 by adjusting these design parameters described above. For example, the resonance frequency is changed when the length of each of the paired non-power-supply radiating elements 30 in the vertical direction is changed relative to the power-supply radiating element 20. The design parameters Lp, Lc, Wc, Dd, Wd, Wg, Ld, Ls, and Ds can be determined by a multi-objective genetic algorithm which gives a Pareto solution.

(10) An example of a simulation result of the horizontal plane directivities of the directional antenna 1 is shown in FIG. 2. Furthermore, an example of a result of the horizontal plane directivities of an experimentally-manufactured directional antenna 1 is shown in FIG. 3. FIG. 2 and FIG. 3 show the intensities of electromagnetic waves on the horizontal plane of the directional antenna 1. The directional antenna 1 is provided at the center of each of FIG. 2 and FIG. 3, and the horizontal axis (±90°) in each figure indicates the horizontal direction of the directional antenna 1. The forward direction of the directional antenna 1 is a direction toward 0° from the center, and the rearward direction of the directional antenna 1 is a direction toward 180° from the center in FIG. 2 and FIG. 3. The lateral directions of the directional antenna 1 are directions toward ±90° from the center in FIG. 2 and FIG. 3. In this specification, the lateral directions of the directional antenna 1 are equivalent to directions away from the directional antenna 1 in the horizontal direction. A range forward of the directional antenna 1 is a range between −90° and 90° including 0° in FIG. 2 and FIG. 3.

(11) In the simulation shown in FIG. 2, the relative permittivity of the substrate 10 was 2.16, the dielectric loss of the substrate 10 was 0.0005, the thickness of the substrate 10 was 0.8 mm, and the operating frequency of the substrate 10 was 5.9 GHz. This substrate 10 was mounted along a cylindrical curved surface with the relative permittivity of 3.0, thickness of 2.5 mm, and radius of 12.5 cm, and the design parameters were optimized. The design parameters after the optimization were Lp=17.6 mm, Lc=3.5 mm, Wc=5.5 mm, Dd=9.0 mm, Wd=5.0 mm, Wg=13.0 mm, Ld=13.6 mm, Ls=4.2 mm, and Ds=3.0 mm. An objective function in the simulation was executed as maximization of the minimum gain in the coverage, minimization of the difference between the maximum gain and the minimum gain in the coverage, and minimization of a back lobe level (a rearward radiation level of the directional antenna 1).

(12) As the simulation result in FIG. 2 shows, the 3 dB beam width which is the communication available range of electromagnetic waves on the horizontal plane of the directional antenna 1 falls within the range between angles S1 and S2 in the figure (i.e., from about −135° to about 135°). In other words, the 3 dB beam width of the directional antenna 1 on the horizontal plane is equal to or greater than 180 degrees including the range forward of the directional antenna 1. S3 in the figure indicates an angle at which the intensity of the electromagnetic waves is the highest. The simulation result in FIG. 3 shows that the back lobe is restrained while the lateral radiations are sufficient in the directional antenna 1.

(13) The experimentally-manufactured directional antenna 1 shown in FIG. 3 uses the same design parameters as the directional antenna 1 used in the simulation shown in FIG. 2. As the measurement result in FIG. 3 shows, the 3 dB beam width which is the communication available range of electromagnetic waves on the horizontal plane of the directional antenna 1 is equal to or greater than 180 degrees including the range forward of the directional antenna 1. It is noted that the back lobe in the measurement result in FIG. 3 is large on account of a mounting jig to which the directional antenna 1 is attached.

(14) Because of the arrangement above, the directional antenna 1 of the present embodiment exerts the following effects.

(15) The substrate 10 is arranged such that the front surface 10a and the rear surface 10b extend along the vertical direction which is orthogonal to the horizontal plane. Power is supplied to the power-supply radiating element 20 on the front surface 10a of the substrate 10 whereas no power is supplied to the paired non-power-supply radiating elements 30 opposing each other across the power-supply radiating element 20 in the horizontal direction. The power-supply radiating element 20 is excited in response to power supply. The paired non-power-supply radiating elements 30 are excited on account of an influence of the excitation of the power-supply radiating element 20. In this way, the power-supply radiating element 20 and the paired non-power-supply radiating elements 30 function as antennas. The directional antenna 1 of the present embodiment is able to prevent the occurrence of power supply loss.

(16) The metal plate 40 is provided behind at least a part of the power-supply radiating element 20. This prevents electric waves from the power-supply radiating element 20 from being radiated rearward from that part of the power-supply radiating element 20. To put it differently, the electric waves from the power-supply radiating element 20 are radiated in the forward direction and the lateral directions from the power-supply radiating element 20. The directional antenna 1 of the present embodiment is able to prevent unnecessary radiation of electric waves from the power-supply radiating element 20, and to obtain forward and lateral directivities from the power-supply radiating element 20. The metal plate 40 is not provided behind the paired non-power-supply radiating elements 30. The paired non-power-supply radiating elements 30 are therefore able to radiate electric waves in wide angles on the horizontal plane. In other words, with the directional antenna 1 of the present teaching, the intensities of electric waves are sufficient in the lateral directions of the directional antenna 1. In the directional antenna 1 of the present embodiment, the 3 dB beam width which is the communication available range of electromagnetic waves is equal to or greater than 180 degrees on the horizontal plane. Even if a metal or a person exists behind the directional antenna 1 of the present embodiment, an influence on the radiation characteristics is avoided in the directional antenna 1 by adjusting the directivity range.

(17) Furthermore, the power-supply radiating element 20 and the paired non-power-supply radiating elements 30 are provided on the surface of the same substrate 10. For this reason, the directional antenna 1 can be formed as a single printed board, for example. The directional antenna 1 can therefore be easily formed.

(18) Furthermore, the power-supply radiating element 20 is a patch antenna which is suitable as an antenna with directional characteristics. The paired non-power-supply radiating elements 30 are dipole antennas suitable as an antenna with non-directional characteristics. This arrangement makes it possible to further secure forward and lateral directivities of the directional antenna 1.

(19) The directional antenna 1 of the present embodiment is therefore able to have directivity covering a wide range by adjustment of the range of directivity.

(20) Preferred embodiments of the present teaching have been described above. However, the present teaching is not limited to the above-described embodiments, and various changes can be made within the scope of the claims. Further, modifications described below may be used in combination as needed.

(21) The directional antenna of the present teaching may be variously arranged on condition that, in regard to the horizontal plane directivities, the 3 dB beam width is equal to or greater than 180 degrees including the range forward of the directional antenna.

(22) The substrate 10 of the embodiment above is made of a dielectric material having flexibility. Alternatively, the substrate of the present teaching may be made of a dielectric material not having flexibility. The substrate 10 of the embodiment above is formed to be a flat plate. Alternatively, the substrate of the present teaching may be a plate with a curved surface. In other words, the directional antenna of the present teaching may be, for example, mounted on a substrate formed of a dielectric having a curved surface.

(23) The length Wg of the metal plate 40 of the embodiment above in the horizontal direction is arranged to be shorter than the maximum length Wp in the horizontal direction of the patch portion 21 of the power-supply radiating element 20. Alternatively, the directional antenna of the present teaching may be arranged such that the length in the horizontal direction of the metal plate is identical with the length in the horizontal direction of the power-supply radiating element. Alternatively, the directional antenna of the present teaching may be arranged such that the length in the horizontal direction of the metal plate maybe longer than the length in the horizontal direction of the power-supply radiating element.

(24) The paired non-power-supply radiating elements 30 of the directional antenna 1 of the embodiment above are constituted by the two non-power-supply radiating elements 30a and 30b. Alternatively, in the directional antenna of the present teaching, two or more paired non-power-supply radiating elements may be provided. For example, the directional antenna may include four non-power-supply radiating elements.

(25) The directional antenna of the present teaching may be mounted on a straddled vehicle. The straddled vehicle is, for example, a motorcycle. The directional antenna of the present teaching can be provided at, for example, the front surface of the vehicle body cover of the straddled vehicle. The directional antenna of the present teaching is preferably provided at a position where a metal or a human does not oppose the front surface or a side surface of the power-supply radiating element. The directional antenna of the present teaching may be mounted on a vehicle which is not a straddled vehicle. The directional antenna of the present teaching may be used for vehicle-to-vehicle communication and road-to-vehicle communication.

REFERENCE SIGNS LIST

(26) 1 directional antenna 10 substrate 20 power-supply radiating element 30 non-power-supply radiating element 40 metal plate