Circularly polarized antenna

Abstract

This enables the creation of a circularly polarized antenna with an excellent axial ratio regardless of the elevation angle. [Solution] A circularly polarized antenna comprises an antenna member and an auxiliary member. The antenna member has a vertex, a base, and a circumferential surface, forming a three-dimensional shape where the vertex coincides with the center of the base when viewed from above. The antenna member comprises a radiating conductor pattern and a ground conductor pattern. The radiating conductor pattern is a three-dimensional spiral shape in which the diameter, viewed from above, progressively increases along the circumferential surface toward the outer edge of the base, with the vertex as the feed point. The ground conductor pattern is located on the base. The auxiliary member has a base wall and side walls. The ground conductor pattern of the antenna member is connected to the base wall of the auxiliary member both three-dimensionally and electrically, and a portion of the base side of the antenna member is housed in the space enclosed by the base wall and side walls.

Description

Technical Field

[0001] The present invention relates to an antenna that transmits and receives circularly polarized waves.

Background Art

[0002] Patent Document 1 describes a conical spiral antenna. The conical spiral antenna includes a linear conductor (antenna element) having a three-dimensional spiral shape. The linear conductor has a shape that extends spirally from the apex of a cone to the bottom surface so that the diameter gradually increases from the center (apex) of a circle in a plan view.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a conventional circularly polarized antenna such as the conical spiral antenna shown in Patent Document 1 has a problem that the axial ratio at a low elevation angle of the circularly polarized wave decreases.

[0005] Therefore, an object of the present invention is to realize a circularly polarized antenna having an excellent axial ratio regardless of the elevation angle.

Means for Solving the Problems

[0006] A circularly polarized antenna according to one embodiment of this invention comprises an antenna member and an auxiliary member. The antenna member has a vertex, a base, and a circumferential surface, and constitutes a three-dimensional shape in which the vertex coincides with the center of the base when viewed from above. The antenna member comprises a radiating conductor pattern and a ground conductor pattern. The radiating conductor pattern is composed of a three-dimensional spiral shape in which the diameter, when viewed from above, increases sequentially along the circumferential surface toward the outer edge of the base, with the vertex as the feed point. The ground conductor pattern is located on the base. The auxiliary member has a base wall and side walls. The ground conductor pattern of the antenna member is connected to the base wall of the auxiliary member, and a part of the base side of the antenna member is housed in the space enclosed by the base wall and side walls.

[0007] In this configuration, a three-dimensional spiral antenna is formed by the antenna components. As a result, the directional characteristics in the horizontal direction (azimuth direction) become nearly constant (the directional characteristics of the cross-section are nearly circular), and the directional characteristics in the elevation direction change smoothly with the maximum at the zenith (direction of the apex). Furthermore, the VSWR can be kept below 2.0 in the GNSS frequency band. In addition, by placing auxiliary components on the bottom side of the antenna components in a shape that surrounds the antenna components, the difference between the levels of vertical polarization and horizontal polarization at low elevation angles is suppressed. Therefore, the axial ratio of circular polarization at low elevation angles approaches 0. As a result, the directivity in the horizontal and elevation directions is excellent, and the deterioration of the axial ratio due to elevation angle is suppressed.

[0008] Furthermore, in a circularly polarized antenna according to one embodiment of this invention, with λ being the wavelength of the high-frequency signal transmitted and received by the circularly polarized antenna, it is preferable that the upper end of the side wall falls within a height range such that the length of one circumference of the ring shape, when the circumferential surface of the antenna member is viewed from the apex direction, is between 0.4λ and 2.0λ.

[0009] In this configuration, the range of high radiation intensity from the antenna component is from 0.4λ to 2.0λ. Therefore, by positioning the upper end of the side wall of the auxiliary component within this range, the axial ratio characteristics of the circularly polarized antenna are further improved.

[0010] Furthermore, in a circularly polarized antenna according to one embodiment of this invention, the antenna member is composed of a hemispherical shape, an ellipsoidal hemispherical shape based on a spheroid, a conical shape, or a three-dimensional shape based on a parabolic solid of revolution.

[0011] In this configuration, excellent radiation characteristics can be obtained by shaping the antenna components as described above.

[0012] Furthermore, in a circularly polarized antenna according to one embodiment of this invention, the radiating conductor pattern has at least one of the following shapes: an Archimedes spiral shape, a logarithmic spiral shape, or a helical shape.

[0013] In this configuration, excellent radiation characteristics can be obtained by shaping the radiating conductor pattern as described above.

[0014] Furthermore, in a circularly polarized antenna according to one embodiment of this invention, the radiating conductor pattern is configured in a 4-wire fractional winding shape.

[0015] This configuration allows for the transmission and reception of circularly polarized waves with excellent axial ratio characteristics. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is an external perspective view of a circularly polarized antenna according to an embodiment of the present invention. [Figure 2] Figure 2 is an exploded perspective view of a circularly polarized antenna according to an embodiment of the present invention. [Figure 3] Figure 3 is a schematic side view (side cross-sectional view) showing the configuration of a circularly polarized antenna according to an embodiment of the present invention. [Figure 4] Figure 4(A) is a graph showing an example of the horizontal directivity of a circularly polarized antenna according to an embodiment of the present invention, and Figure 4(B) is a graph showing an example of the vertical directivity of this circularly polarized antenna. [Figure 5] Figure 5 is a graph showing an example of the VSWR frequency characteristics of a circularly polarized antenna according to an embodiment of the present invention. [Figure 6]FIG. 6(A), FIG. 6(B), and FIG. 6(C) are perspective views schematically showing derivative examples of the antenna member of the circularly polarized antenna according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0017] The circularly polarized antenna according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of the circularly polarized antenna according to an embodiment of the present invention. FIG. 2 is an exploded perspective view of the circularly polarized antenna according to an embodiment of the present invention. FIG. 3 is a side view (side cross-sectional view) schematically showing the configuration of the circularly polarized antenna according to an embodiment of the present invention.

[0018] As shown in FIGS. 1, 2, and 3, the circularly polarized antenna 10 includes an antenna member 20 and an auxiliary member 30.

[0019] The antenna member 20 includes a plurality of radiation conductor patterns 21 - 24 (radiation conductor pattern 21, radiation conductor pattern 22, radiation conductor pattern 23, radiation conductor pattern 24) and a ground conductor pattern 29.

[0020] The radiation conductor patterns 21, radiation conductor pattern 22, radiation conductor pattern 23, and radiation conductor pattern 24 have the same shape. The length (electrical length) of each of the radiation conductor patterns 21, radiation conductor pattern 22, radiation conductor pattern 23, and radiation conductor pattern 24 is the same and is set based on the wavelength λ of the high-frequency signal transmitted and received by the circularly polarized antenna 10. Here, the wavelength λ of the high-frequency signal corresponds to, for example, the frequency representing the frequency band in which a desired gain is to be obtained by the circularly polarized antenna 10, and corresponds to the center frequency of the frequency band or the frequency at which the most gain is to be obtained in the frequency band.

[0021] The radiation conductor pattern 21 has a power feeding end PF21 at one end in the extending direction and a ground connection end ED21 at the other end. The radiation conductor pattern 21 has a shape that gradually widens along the direction extending from the power feeding end PF21 to the ground connection end ED21.

[0022] The radiation conductor pattern 22 has a power feeding end PF22 at one end in the extending direction and a ground connection end ED22 at the other end. The radiation conductor pattern 22 has a shape that gradually widens along the direction extending from the power feeding end PF22 to the ground connection end ED22.

[0023] The radiation conductor pattern 23 has a power feeding end PF23 at one end in the extending direction and a ground connection end ED23 at the other end. The radiation conductor pattern 23 has a shape that gradually widens along the direction extending from the power feeding end PF23 to the ground connection end ED23.

[0024] The radiation conductor pattern 24 has a power feeding end PF24 at one end in the extending direction and a ground connection end ED24 at the other end. The radiation conductor pattern 24 has a shape that gradually widens along the direction extending from the power feeding end PF24 to the ground connection end ED24.

[0025] The ground conductor pattern 29 is circular or polygonal.

[0026] The antenna member 20 is formed into a three-dimensional shape by a plurality of radiation conductor patterns 21 - 24 and the ground conductor pattern 29. Specifically, the antenna member 20 is formed into an elliptical hemispherical shape based on an elliptical rotating body. At this time, the elliptical hemispherical shape is a shape obtained by cutting the elliptical rotating body with a plane parallel to the short dimension direction and passing through the center of the rotating body.

[0027] The bottom surface BF20 of the antenna member 20 is formed by the plane that cuts the elliptical rotating body. The apex TP20 of the antenna member 20 is formed by the end point facing the bottom surface BF20 of the elliptical hemispherical shape. The apex TP20 overlaps the center of the bottom surface BF20 when the antenna member 20 is viewed from a direction orthogonal to the apex TP20. The peripheral surface SF20 of the antenna member 20 is formed by the surface connecting the apex TP20 and the bottom surface BF20 in the elliptical hemispherical shape.

[0028] As a result, the antenna member 20 is configured such that the diameter (circumference) viewed from a direction perpendicular to the vertex TP20 gradually increases from the vertex TP20 towards the base surface BF20.

[0029] Multiple radiating conductor patterns 21, 22, 23, and 24 are arranged along the circumferential surface SF20 (so as to constitute the circumferential surface SF20). More specifically, the feed ends PF21 of radiating conductor pattern 21, PF22 of radiating conductor pattern 22, PF23 of radiating conductor pattern 23, and PF24 of radiating conductor pattern 24 are arranged near the vertex TP20, but not directly connected to each other.

[0030] Viewed in the direction of the line connecting the center point of vertex TP20 and base BF20 (hereinafter referred to as "viewed from the base"), feed ends PF21 and PF23 are positioned at an angle of 180° around vertex TP20. Viewed from the base, feed ends PF22 and PF24 are positioned at an angle of 180° around vertex TP20. Feed end PF22 is positioned at an angle of 90° clockwise relative to feed end PF21 in the viewed from the base. Feed end PF24 is positioned at an angle of 90° clockwise relative to feed end PF23 in the viewed from the base.

[0031] The feeding phase is reversed by 180° between feeding terminals PF21 and PF23, and by 180° between feeding terminals PF22 and PF24. In addition, the feeding phase of feeding terminal PF21 lags behind feeding terminal PF22 by 90°.

[0032] Multiple radiating conductor patterns 21, 22, 23, and 24 are arranged on the circumferential surface SF20 in a counterclockwise spiral shape when viewed from below, starting from their respective feed ends PF21, PF22, PF23, and PF24. In this arrangement, the spacing between radiating conductor pattern 21 and radiating conductor pattern 22, between radiating conductor pattern 22 and radiating conductor pattern 23, between radiating conductor pattern 23 and radiating conductor pattern 24, and between radiating conductor pattern 24 and radiating conductor pattern 21 is always the same.

[0033] The multiple radiating conductor patterns 21, 22, 23, and 24 are spiral in shape, making approximately 1.5 turns.

[0034] The ground connection terminals ED21, ED22, ED23, and ED24 of the multiple radiating conductor patterns 21, 22, 23, and 24 are positioned on the outer edge of the bottom surface BF20. The multiple ground connection terminals ED21, ED22, ED23, and ED24 are positioned at 90° intervals when viewed from the bottom.

[0035] The ground conductor pattern 29 is positioned on the bottom surface BF20. In this configuration, the center of the ground conductor pattern 29 coincides with the center of the bottom surface BF20. The outer edge of the ground conductor pattern 29 coincides with the outer edge of the bottom surface BF20.

[0036] Multiple ground connection terminals ED21, ED22, ED23, and ED24 are connected to the outer edge of the ground conductor pattern 29.

[0037] The auxiliary member 30 has a bottom wall 31 and side walls 32. The auxiliary member 30 is made of a conductor. The bottom wall 31 is circular or polygonal. The diameter of the bottom wall 31 is larger than the diameter of the bottom surface BF20 of the antenna member 20, and is approximately the same as the diameter of the bottom surface BF20.

[0038] The side wall 32 is cylindrical. The side wall 32 is positioned along the outer edge of the bottom wall 31. The side wall 32 connects to the bottom wall 31.

[0039] In this configuration, the auxiliary member 30 is surrounded by a bottom wall 31 and side walls 32, and has an internal space 300 that is open on the side opposite the bottom wall 31.

[0040] The antenna member 20 is placed in the internal space 300 of the auxiliary member 30. The ground conductor pattern 29 on the bottom surface BF20 of the antenna member 20 contacts the bottom wall 31 of the auxiliary member 30, connecting them both three-dimensionally and electrically.

[0041] Here, the height of the antenna member 20 (distance between the apex TP20 and the base BF20) is greater than the height of the side wall 32 of the auxiliary member 30. In this case, as shown in Figure 3, it is preferable that the upper end EU32 of the side wall 32 falls within the following range.

[0042] The height at which the circumference of the ring-shaped area when the circumferential surface SF20 of the antenna member 20 is viewed from below is 0.4λ is defined as H1, and the height at which it is 2.0λ is defined as H2. It is preferable that the upper end EU32 of the side wall 32 falls within the range between heights H1 and H2.

[0043] With this configuration, the circularly polarized antenna 10 achieves the following characteristics. Figure 4(A) is a graph showing an example of the horizontal directivity of a circularly polarized antenna according to an embodiment of the present invention, and Figure 4(B) is a graph showing an example of the vertical directivity of this circularly polarized antenna. In Figures 4(A) and 4(B), the solid line and the dashed line represent the intensity of vertical polarization, one of which represents the intensity of horizontal polarization, and the other represents the intensity of horizontal polarization. Figure 5 is a graph showing an example of the frequency characteristics of the VSWR of a circularly polarized antenna according to an embodiment of the present invention.

[0044] The antenna member 20 of the circularly polarized antenna 10 has an elliptical hemispherical shape in which the diameter viewed from the bottom increases from the apex TP20 to the bottom surface BF20, forming a three-dimensional spiral shape with four fractional turns. Furthermore, the circularly polarized antenna 10 includes an auxiliary member 30 that accommodates a portion of the antenna member 20 on the bottom surface BF20 side.

[0045] As a result, the horizontal (azimuth) directivity characteristics of the circularly polarized antenna 10 become nearly constant (the directivity characteristics of the cross-section are circular) due to the configuration of the antenna member 20 (see Figure 4(A)). Furthermore, the configuration of the antenna member 20 allows the circularly polarized antenna 10 to reduce the difference in intensity between vertical and horizontal polarization (see Figure 4(A)).

[0046] Furthermore, the configuration of the antenna member 20 allows the directional characteristics of the circularly polarized antenna 10 in the vertical direction (elevation direction) to change smoothly, with the maximum at the zenith (direction of the apex) (see Figure 4(B)). In addition, the configuration of the antenna member 20 allows the circularly polarized antenna 10 to approach 0 in terms of axial ratio at high elevation angles (see Figure 4(B)).

[0047] Furthermore, by having both the antenna member 20 and the auxiliary member 30, the VSWR of the circularly polarized antenna 10 can be reduced to less than 2.0 in the GNSS frequency band FBW (GNSS) (see Figure 5).

[0048] Furthermore, the circularly polarized antenna 10 can achieve an axial ratio of approximately 0 at low elevation angles through the configuration of the auxiliary member 30 (see Figure 4(B)).

[0049] Thus, the circularly polarized antenna 10 has an excellent axial ratio regardless of the elevation angle, has approximately the same level of directivity in all directions, has directivity that changes smoothly according to the elevation angle, and can transmit and receive high-frequency signals with low loss in the GNSS frequency band.

[0050] The antenna components of a circularly polarized antenna may have the following shapes:

[0051] Figures 6(A), 6(B), and 6(C) are schematic perspective views showing derivative examples of antenna members for a circularly polarized antenna according to an embodiment of the present invention.

[0052] In Figure 6(A), the external shape of antenna member 20A is a hemispherical shape. In Figure 6(B), the external shape of antenna member 20B is a cone shape. In Figure 6(C), the external shape of antenna member 20C is a three-dimensional shape based on a parabolic solid of revolution.

[0053] Even with the shapes of antenna members 20A, 20B, and 20C, the same effects and advantages as the circularly polarized antenna 10 using the antenna member 20 described above can be achieved.

[0054] Furthermore, if the shape of the antenna member is such that it has a vertex TP20 and the circumference length increases sequentially from the vertex TP20 toward the base BF20 (a shape in which the diameter increases sequentially), then the same effects as the circularly polarized antenna 10 described above can be obtained.

[0055] Furthermore, if the multiple radiating conductor patterns of a circularly polarized antenna are composed of at least one of the following shapes: Archimedes spiral, logarithmic spiral, or helical, the circularly polarized antenna can obtain the effects described above.

[0056] Furthermore, the circularly polarized antenna configuration described above is not limited to RHCP (Reverse Helicopter Power Pack) configurations, but can also be applied to LHCP (Low Helicopter Power Pack) configurations by reversing the phase difference between the spiral direction and the feed point.

[0057] (1) An antenna member comprising: a radiation conductor pattern having a vertex, a base, and a circumferential surface, the vertex converging with the center of the base when viewed from above, and the radiating conductor pattern having a three-dimensional spiral shape in which the diameter when viewed from above gradually increases along the circumferential surface toward the outer edge of the base, with the vertex as the feed point; and a ground conductor pattern arranged on the base; A circularly polarized antenna comprising a bottom wall and side walls, wherein the ground conductor pattern of the antenna member is connected three-dimensionally and electrically to the bottom wall, and an auxiliary member is provided in the space enclosed by the bottom wall and the side walls, within which a portion of the bottom surface of the antenna member is housed.

[0058] (2) The circularly polarized antenna described in (1), Let λ be the wavelength of the high-frequency signal transmitted and received by the circularly polarized antenna. The upper end of the side wall falls within a height range such that the length of one circumference of the ring formed by viewing the circumferential surface of the antenna member from the direction of the vertex is between 0.4λ and 2.0λ, thus forming a circularly polarized antenna.

[0059] (3) A circularly polarized antenna as described in (1) or (2), The antenna member is composed of a hemispherical shape, an ellipsoidal hemispherical shape based on a spheroid, a conical shape, or a three-dimensional shape based on a parabolic solid of revolution. Circularly polarized antenna.

[0060] (4) A circularly polarized antenna as described in any of (1) to (3), The radiating conductor pattern is a circularly polarized antenna having at least one of an Archimedean spiral shape, a logarithmic spiral shape, or a helical shape.

[0061] (5) A circularly polarized antenna as described in any of (1) to (4), The aforementioned radiating conductor pattern is composed of a 4-wire fractional winding shape. Circularly polarized antenna. [Explanation of Symbols]

[0062] 10: Circular Polarization Antenna 20, 20A, 20B, 20C: Antenna components 21-24: Radiating Conductor Pattern 29: Ground conductor pattern 30: Auxiliary member 31: Bottom wall 32: Side wall 300: Interior space BF20: Bottom ED21, ED22, ED23, ED24: Ground connection terminal EU32:Top end FBW: Frequency Bandwidth H1, H2: Height PF21, PF22, PF23, PF24: Feeding end SF20: Peripheral surface TP20: Vertex

Claims

1. An antenna member comprising: a radiation conductor pattern having a vertex, a base, and a circumferential surface, the vertex converging with the center of the base when viewed from above, and the radiating conductor pattern having a three-dimensional spiral shape in which the diameter when viewed from above gradually increases along the circumferential surface toward the outer edge of the base, with the vertex as the feed point; and a ground conductor pattern disposed on the base. A circularly polarized antenna comprising a bottom wall and side walls, wherein the ground conductor pattern of the antenna member is connected three-dimensionally and electrically to the bottom wall, and an auxiliary member is provided in the space enclosed by the bottom wall and the side walls, within which a portion of the bottom surface of the antenna member is housed.

2. A circularly polarized antenna according to claim 1, Let λ be the wavelength of the high-frequency signal transmitted and received by the circularly polarized antenna. The upper end of the side wall falls within a height range such that the length of the circumference of the ring formed by viewing the circumferential surface of the antenna member from the direction of the vertex is between 0.4λ and 2.0λ. Circularly polarized antenna.

3. A circularly polarized antenna according to claim 1, The antenna member is composed of a hemispherical shape, an ellipsoidal hemispherical shape based on a spheroid, a conical shape, or a three-dimensional shape based on a parabolic solid of revolution. Circularly polarized antenna.

4. A circularly polarized antenna according to claim 1, The radiating conductor pattern has at least one of the following shapes: an Archimedean spiral, a logarithmic spiral, or a helical shape. Circularly polarized antenna.

5. A circularly polarized antenna according to claim 1, The aforementioned radiating conductor pattern is composed of a four-wire fractional winding shape. Circularly polarized antenna.

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