Dual-polarized antenna

Abstract

To provide a small and lightweight dual-polarized antenna that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear surface. [Solution] The dual-polarized antenna comprises a feed element having a loop-shaped conductor element body and four first feed lines made of conductors extending horizontally from four circumferentially equiangularly spaced positions on the element body toward a loop central axis, a ground plate disposed on the back surface of the feed element at a predetermined distance from the feed element, and four second feed lines made of conductors extending vertically from the loop central axis-side ends of the four first feed lines of the feed element toward the ground plate. Of the four second feed lines, any two second feed lines adjacent to each other in the circumferential direction around the loop central axis are connected to the ground plate, and the other two second feed lines are connected to the signal lines of the two polarized waves, respectively.

Description

[Technical Field]

[0001] The present invention relates to a dual-polarized antenna that can be used for polarized waves that are orthogonal to each other. [Background technology]

[0002] Patent document 1 describes a dual-polarized patch antenna that includes a radiating patch, a ground plate, a dielectric layer between the radiating patch and the ground plate, and a first polarization port and a second polarization port arranged on the radiating patch, and is used for polarizations that are orthogonal to each other (see Patent document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-58026 Summary of the Invention [Problem to be solved by the invention]

[0004] Dual-polarized antennas are used in radio equipment mounted on aircraft such as platforms like HAPS (High Altitude Platform Station) that can stay or fly above a certain altitude, and on aircraft like UAVs (Unmanned Aerial Vehicles) such as drones, taking into consideration the rotation and tilt of the aircraft. Radio equipment mounted on such aircraft in the air requires a small, lightweight dual-polarized antenna that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear. [Means for solving the problem]

[0005] One aspect of the present invention is a dual-polarized antenna for use with two orthogonal polarized waves. This dual-polarized antenna includes a loop-structured feed element having an element body made of a loop-shaped conductor and four first feed lines made of conductors extending horizontally from four circumferentially equiangularly spaced locations on the element body toward a loop central axis, a ground plate disposed on the back surface of the feed element at a predetermined distance from the feed element, and four second feed lines made of conductors extending vertically from the loop central axis-side ends of the four first feed lines of the feed element toward the ground plate. Any two of the four second feed lines adjacent to each other in the circumferential direction around the loop central axis are connected to the ground plate, and the other two second feed lines are connected to signal lines for the two polarized waves, respectively.

[0006] In the dual-polarized antenna, the ground plate may have one or more openings, and the openings may be formed in a portion of the ground plate facing all or part of the opening of the feed element.

[0007] The dual-polarized antenna may further comprise a parasitic element made of a conductor and arranged in front of the feed element so as to face the feed element at a predetermined distance.

[0008] The dual-polarized antenna may further include a protective member that covers and protects the feed element, the second feed line, and the parasitic element, wherein the protective member may have one or more openings. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a small and lightweight dual-polarized antenna that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear surface. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view showing an example of a dual-polarized antenna according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing an example of a dual-polarized antenna according to the embodiment. [Figure 3] FIG. 3 is an explanatory diagram showing an example of the distribution of current vectors in a feed element having a loop structure of the dual-polarized antenna of FIG. [Figure 4] FIG. 4 is an explanatory diagram showing an example of the distribution of current vectors in the second feed line of the vertical structure of the dual-polarized antenna of FIG. [Figure 5] FIG. 5 is a perspective view showing an example of a dual-polarized antenna having a ground plate without a hole according to an embodiment. [Figure 6] FIG. 6 is an explanatory diagram showing an example of electric field vectors in a vertical cross section of the dual-polarized antenna having the non-hole ground plate of FIG. [Figure 7] FIG. 7 is a perspective view showing an example of a dual-polarized antenna having a ground plate with a perforated structure according to an embodiment. [Figure 8] FIG. 8 is an explanatory diagram showing an example of electric field vectors in a vertical cross section of the dual-polarized antenna having the ground plate with the perforated structure of FIG. [Figure 9] FIG. 9 is an explanatory diagram showing an example of the distribution of current vectors in the dual-polarized antenna having the ground plate without a hole shown in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing an example of the distribution of current vectors in the dual-polarized antenna having the ground plate with the perforated structure shown in FIG. [Figure 11] FIG. 11 is a front view showing an example of the appearance of the polarized antenna according to the embodiment. [Figure 12] FIG. 12 is a right side view of the dual-polarized antenna of FIG. [Figure 13] FIG. 13 is a rear view of the dual-polarized antenna of FIG. [Figure 14] FIG. 14 is an exploded perspective view of the dual-polarized antenna of FIG. [Figure 15] FIG. 15 is a vertical cross-sectional view of the dual-polarized antenna of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that each drawing merely shows a schematic representation of the shape, size, and positional relationship to the extent that the contents of the present invention can be understood, and therefore the present invention is not limited to the shape, size, and positional relationship exemplified in each drawing. Furthermore, the numerical values exemplified below are merely preferred examples of the present invention, and therefore the present invention is not limited to the exemplified numerical values.

[0012] The antenna according to the embodiment described herein is a dual-polarized antenna (dual-polarized loop antenna) that can be used for two mutually orthogonal polarized waves (for example, horizontally polarized and vertically polarized waves). The dual-polarized antenna of this embodiment is a small and lightweight dual-polarized antenna that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear surface by including a loop-structured feed element and a ground plate with a perforated or non-perforated structure. In particular, the dual-polarized antenna of this embodiment is suitable for radio equipment mounted on platforms such as HAPS, which can stay or fly in the air at a predetermined altitude, or on aircraft such as UAVs (Unmanned Aerial Vehicles) such as drones.

[0013] 1 and 2 are a plan view and a perspective view, respectively, showing an example of a dual-polarized antenna 10 according to an embodiment. The dual-polarized antenna 10 may be a transmitting / receiving antenna, or may be a transmitting antenna or a receiving antenna. Radio waves to be transmitted or received by the dual-polarized antenna 10 are, for example, microwaves, millimeter waves, or submillimeter waves of 300 MHz or higher.

[0014] 1 and 2, a dual-polarized antenna (hereinafter simply referred to as "antenna") 10 includes a feed element 100 and a ground plate 120. The feed element 100 has an element body 110 made of a loop-shaped conductor, and four first feed lines 111, 112, 113, and 114 made of a conductor such as metal. The feed element 100 has a four-fold rotationally symmetric loop structure centered on a loop central axis A in the z-axis direction in the drawings.

[0015] The element body 110 is, for example, a hollow disk disposed parallel to the illustrated xy plane and having an opening 101 therein. The loop shape of the element body 110 may be any shape, such as the circle shown in the figure. The loop shape of the element body 110 may be an ellipse, a triangle, a rectangle, or a polygon with pentagons or more. The perimeter (loop length) of the element body 110 may be one wavelength (1λ) or approximately one wavelength of the target radio wave. Here, "λ" is the wavelength of the target radio wave in free space (the same applies below). The element body 110 may be formed from a wire, plate, tube, or the like made of a conductor such as metal. The cross section of the element body 110 may be any shape, such as a rectangle. The cross section of the element body 110 may be a circle, an ellipse, a triangle, or a polygon with pentagons or more.

[0016] The first feed lines 111, 112, 113, and 114 are each a horizontally structured feed line extending from four locations at equal angular intervals (90 degrees or approximately 90 degrees) around the circumferential direction of the element body 110 in the horizontal direction (x and y directions in the figure) toward the loop central axis A. The first feed lines 111, 112, 113, and 114 may be formed of a wire, plate, pipe, or the like made of a conductor such as metal. The cross sections of the first feed lines 111, 112, 113, and 114 may have any shape, such as a rectangle. The cross sections of the first feed lines 111, 112, 113, and 114 may also be circular, elliptical, triangular, or polygonal with pentagons or more sides.

[0017] The element body 110 and the first power supply lines 111, 112, 113, and 114 may be integrally molded from the same member, or the element body 110 and the first power supply lines 111, 112, 113, and 114 may be molded as separate members and then joined at four points spaced at equal angles (90 degrees or approximately 90 degrees) around the circumference of the element body 110.

[0018] The ground plate 120 is disposed on the back surface of the feed element 100, facing the feed element 100 at a predetermined distance. The separation distance (gap) between the ground plate 120 and the feed element 100 is, for example, 0.06λ or approximately 0.06λ. The ground plate 120 functions as a reflecting element (reflector) that reflects target radio waves in the direction of the directivity (front direction) of the feed element 100. The ground plate 120 is disposed parallel to the illustrated xy plane, i.e., parallel or nearly parallel to the element body 110. The ground plate 120 is formed, for example, from a plate-shaped member made of a conductor such as metal. The outer shape of the ground plate 120 may be any shape, such as a rectangle. The outer shape of the ground plate 120 may be circular, elliptical, triangular, or polygonal with pentagons or more. The ground plate 120 may have through-holes (holes) as openings, as described below.

[0019] In addition to the element body 110 and the ground plate 120, the antenna 10 further includes four second feed lines 131, 132, 133, and 134 made of a conductor such as metal. The second feed lines 131, 132, 133, and 134 extend vertically from the loop central axis side end of each of the four first feed lines in the feed element 100 toward the ground plate 120. The second feed lines 131, 132, 133, and 134 are vertical feed lines concentrated around the loop central axis A.

[0020] In the antenna 10 of this embodiment, of the four second feed lines 131, 132, 133, and 134, any two second feed lines 133 and 134 that are adjacent to each other in the circumferential direction centered on the loop central axis A are connected to the ground plate 120. The other two second feed lines 131 and 132 are connected to a signal line of a first polarized wave (horizontal polarization) and a signal line of a second polarized wave (vertical polarization), respectively, via feed ports 141 and 142 that are arranged on the ground plate 120 in an electrically insulated state.

[0021] 1 and 2, the horizontally structured first feed lines 111 and 113 and the opposing vertically structured second feed lines 131 and 133 are feed lines for a first polarization (horizontal polarization). The horizontally structured first feed lines 112 and 114 and the opposing vertically structured second feed lines 132 and 134 are feed lines for a second polarization (vertical polarization).

[0022] FIG. 3 is an explanatory diagram showing an example of current vector distribution in the loop-structured feed element 100 of the dual-polarized antenna 10 of FIG. 1. FIG. 3 shows the results of computer simulation calculations of current vectors when feeding vertically (V) polarized waves at multiple points set throughout the element body 110 and first feed lines 111-114 of the feed element 100. When transmitting and receiving vertically (V) polarized radio waves, for example, as shown in FIG. 3, upward currents I1-I4 are generated in the left and right ends of the loop-shaped element body 110 and the first feed lines 112 and 114. This results in the formation of a vertically polarized electric field parallel to the yz plane in the figure. At this time, the currents flowing in the upper and lower ends of the loop-shaped element body 110 and the first feed lines 111 and 113 are small, thereby reducing the impact on the transmission and reception of horizontally (H) polarized radio waves.

[0023] On the other hand, when transmitting and receiving horizontally (H) polarized radio waves, a current is generated in the horizontal direction in the figure at the upper and lower ends of the loop-shaped element body 110 and in the first feed lines 111 and 113. This generates a horizontally polarized electric field parallel to the xz plane in the figure. At this time, the current flowing in the left and right ends of the loop-shaped element body 110 and the first feed lines 112 and 114 is small, so the influence on the transmission and reception of vertically (V) polarized radio waves can be reduced.

[0024] FIG. 4 is an explanatory diagram showing an example of the distribution of current vectors in the vertically structured second feed lines 131, 132, 133, and 134 of the dual-polarized antenna 10 of FIG. 2. FIG. 4 shows the results of computer simulation calculations of current vectors when feeding vertically (V) polarized waves at multiple points set throughout the vertically structured second feed lines 131-134. When transmitting and receiving vertically (V) polarized radio waves, for example, as shown in FIG. 4, a downward current I5 is generated in the second feed line 132, and an upward current I6 is generated in the second feed line 134. In other words, opposite-phase currents flow in the opposing second feed lines 132 and 134. This allows vertically (V) polarized currents to flow through the left and right ends of the loop-shaped element body 110 and the first feed lines 112 and 114, respectively, while suppressing unwanted radiation in the lateral direction of the antenna. At this time, the current flowing through the other second feed lines 131 and 133 is small, so that the influence on transmission and reception of horizontally (H) polarized radio waves can be reduced.

[0025] On the other hand, when transmitting and receiving horizontally (H) polarized radio waves, a downward current is generated in one of the second feed lines 131, 133, and an upward current is generated in the other. That is, opposite-phase currents flow in the opposing second feed lines 131, 133. This allows horizontally (H) polarized current to flow through the upper and lower ends of the loop-shaped element body 110 and the first feed lines 111, 113, respectively, while suppressing unwanted radiation in the lateral direction of the antenna. At this time, the current flowing through the other second feed lines 132, 134 is small, thereby reducing the impact on the transmission and reception of vertically (V) polarized radio waves.

[0026] As described above, the antenna 10 of this embodiment is an antenna with a linear loop structure, and therefore can be made lighter than a planar patch antenna.

[0027] Furthermore, according to the antenna 10 of this embodiment, the loop length (perimeter) of the element body 110 of the power supply element 100 can be set to one wavelength (1λ) or approximately one wavelength of the target radio wave, and the area is smaller than that of a patch antenna, which has a circumference of 2λ (for example, it can be reduced to 1 / π of the area of a patch antenna), making it possible to reduce the size.

[0028] Furthermore, according to the antenna 10 of this embodiment, the feed lines 111-114, 131-134 for vertically (V) polarized waves and horizontally (H) polarized waves can be arranged at the center inside the loop-shaped feed element 100, thereby reducing the influence of coupling between polarized waves on the feed element 100 and realizing shared use of vertically (V) polarized waves and horizontally (H) polarized waves.

[0029] Furthermore, according to the antenna 10 of this embodiment, an axially symmetrical vertically structured feed element is configured that connects the second feed lines 133, 134 extending toward the center inside the loop-shaped feed element 100 to the ground plate 120. This allows opposite-phase currents to flow through the opposing second feed lines 132, 134 for vertically (V) polarized waves, and opposite-phase currents to flow through the opposing second feed lines 131, 133 for horizontally (H) polarized waves. This suppresses the inverted-F mode (the operating mode of an inverted-F antenna) and the vertical electric field (e.g., the electric field along a plane including the z-axis in the figure), thereby suppressing unwanted radiation in the horizontal direction of the antenna 10 (e.g., the direction perpendicular to the z-axis in the figure) and improving the antenna gain.

[0030] In the antenna 10 of this embodiment, the ground plate 120 may be a non-perforated ground plate with no openings, or a perforated ground plate with one or more openings. In particular, a configuration using a perforated ground plate can further improve the gain of the antenna 10 and also improve the FB ratio (front-to-back ratio) of the antenna 10, as will be described below.

[0031] Fig. 5 is a perspective view showing an example of a dual-polarized antenna 10 having a disk-shaped ground plate 120 without a hole according to an embodiment. In Fig. 5, parts (components) common to those in Figs. 1 and 2 are designated by the same reference numerals, and descriptions thereof will be omitted. Fig. 6 shows the results of calculations, using a computer simulation, of electric field vectors at multiple points set in the entire surrounding space in a longitudinal cross section (BB cross section) of the dual-polarized antenna 10 having the ground plate 120 without a hole in Fig. 5. As shown in Fig. 6, when the ground plate 120 without a hole is used, unwanted radiation is likely to occur in the space behind the outer edge of the ground plate 120 of the antenna 10 due to a fringing electric field Ef.

[0032] FIG. 7 is a perspective view showing an example of a dual-polarized antenna having a disk-shaped ground plate 120 with a perforated structure according to an embodiment. Note that in FIG. 7, the same components as those in FIGS. 1 and 2 are designated by the same reference numerals, and their description will be omitted. In FIG. 7, the ground plate 120 has a perforated structure with a plurality of rectangular openings 121, 122, 123, and 124 formed in a portion facing a part of the opening 101 of the feed element 100. The openings 121, 122, 123, and 124 in the ground plate 120 contribute to reducing the weight of the ground plate 120. Furthermore, by using both the feed element 100 with a loop structure and the perforated ground plate 120, the entire antenna 10 can have a perforated structure, thereby improving the wind load of the antenna 10 itself.

[0033] The opening (hole) of the ground plate 120 may be formed in a portion that faces the entire opening 101 of the feed element. The shape of the opening (hole) of the ground plate 120 may be rectangular as shown in the figure, or may be circular.

[0034] Figure 8 shows the results of computer simulation calculations of electric field vectors at multiple points set throughout the surrounding space in the longitudinal cross section (CC cross section) of the dual-polarized antenna having the perforated ground plate 120 of Figure 7. As shown in Figure 8, when the perforated ground plate 120 is used, an electric field Ec that is out of phase with the fringing electric field is generated in the central space behind the ground plate 120 of the antenna 10, suppressing unwanted radiation into the space behind the antenna 10. As a result, the gain of the antenna 10 can be further improved, and the FB ratio (front-to-back ratio) of the antenna 10 can also be improved.

[0035] Fig. 9 is an explanatory diagram showing an example of the distribution of current vectors in the dual-polarized antenna 10 having the holeless disk-shaped ground plate 120 of Fig. 5. In Fig. 9, the ground plate 120 has no openings (holes), and therefore image currents I7 and I8 corresponding to the currents I1 and I2 flowing through the first feed lines 112 and 114 so as to form, for example, a vertically polarized electric field flow dispersedly in the ground plate 120, making it difficult to achieve the effect of canceling the fringing electric field described above.

[0036] 10 is an explanatory diagram showing an example of the distribution of current vectors in the dual-polarized antenna 10 having the perforated ground plate 120 shown in FIG. 7. In FIG. 10, the ground plate 120 has openings (holes) 121, 122, 123, and 124 in a portion facing the opening 101 of the feed element 100. Therefore, image currents I7 and I8 corresponding to currents I1 and I2 flowing through the first feed lines 112 and 114 to form a vertically polarized electric field, for example, are concentrated in the linear ground portion (portion facing the first feed lines 112 and 114) of the ground plate 120 that is symmetrical to the first feed lines 112 and 114, thereby enhancing the effect of canceling the fringing electric field. As a result, the gain of the antenna 10 can be further improved, and the front-to-back ratio (FB ratio) of the antenna 10 can also be further improved.

[0037] 11, 12, and 13 are a front view, a right side view, and a rear view, respectively, showing an example of the appearance of a polarized antenna 10 according to another embodiment. FIG. 14 is an exploded perspective view of the polarized antenna 10 of FIG. 11. FIG. 15 is a longitudinal cross-sectional view (D-D cross-sectional view) of the polarized antenna 10 of FIG. 11. In FIGS. 11 to 15, parts (components) common to those in FIGS. 1, 2, 5, and 7 are designated by the same reference numerals, and description thereof will be omitted. Furthermore, the antenna 10 of this embodiment has pin-shaped second feed lines (vertical feed lines) 131 to 134, but the second feed lines (vertical feed lines) 131 to 134 are omitted in the perspective view of FIG. 14 for convenience of illustration.

[0038] 11 to 15, dual-polarized antenna 10 further includes: a hollow, disk-shaped parasitic element 150 made of a conductor such as metal and arranged in front of and facing feed element 100 at a predetermined distance; and a radome 155 as a protective member arranged to cover feed element 100 and parasitic element 150. The distance (gap) between parasitic element 150 and feed element 100 is, for example, 0.01λ or approximately 0.01λ.

[0039] The parasitic element 150 is electromagnetically coupled to the feed element 100, thereby expanding the frequency band. The overall shape of the parasitic element 150 is a loop similar to that of the element body 110 of the feed element 100. The outer and inner diameters of the parasitic element 150 are smaller than those of the element body 110 of the feed element 100, respectively.

[0040] The radome 155 functions as a protective member that protects the feed element 100, the second feed lines (vertical feed lines) 131, 132, 133, and 134, and the parasitic element 150. The radome 155 also functions as a housing (protective case) for the antenna 10. The radome 155 is made of a material that has good transparency to target radio waves. For example, the radome 155 is made of a material with a low relative permittivity to suppress reflection of radio waves on its surface, or a material with a low dielectric loss tangent to suppress attenuation of radio waves due to dielectric loss during transmission. The radome 155 may be made of, for example, glass fiber or fluororesin.

[0041] The radome 155 may have one or more openings to allow wind to pass through in order to improve wind loading on the antenna 10 .

[0042] 11 to 15, a radome 155 has a convex portion 157 formed in a convex shape in the main directivity direction of the antenna 10, and a flange portion 156 formed on the circumferential portion of the convex portion. Four through-holes 156a for mounting an antenna are formed in the flange portion 156 at four positions in four-fold rotational symmetry around the loop central axis A. A ground plate 120 is attached to the back surface of the flange portion 156 of the radome 155. Four through-holes 120a for mounting an antenna that correspond to the through-holes 156a for mounting an antenna in the flange portion 156 are formed in the ground plate 120 at four positions in four-fold rotational symmetry around the loop central axis A.

[0043] The parasitic element 150 and the fed element 100 are attached to the inner surface of the protrusion 157 of the radome 155. The outer peripheral edge of the element body 110 of the fed element 100 is supported by the inner peripheral surface of the protrusion 157 of the radome 155. The inner edges of the first feed lines 111 to 114 are supported by the outer peripheral surface of a boss 158 formed in the center of the radome 155. The center portion of the ground plate 120 is supported by a support member 165 attached to the boss 158 of the radome 155.

[0044] The second feed lines (vertical feed lines) 131-134 are attached by passing through through holes in a support member 165 that is attached to a boss portion 158 of the radome 155. One end (upper end in FIG. 15) of each of the second feed lines 131-134 is connected to an end of the first feed lines 111-114 of the feed element 100 that faces the central axis. The other end (lower end in FIG. 15) of two of the four second feed lines 131-134, the second feed lines 131 and 132, are connected to two feed ports 141 that are insulated and attached to corresponding positions on the ground plate 120. The other end (lower end in FIG. 15) of the remaining two second feed lines 133 and 134 are directly connected to the ground plate 120.

[0045] A support member 165 is attached to the end of a boss portion 158 of a radome 155 having a parasitic element 150 and a fed element 100, and a ground plate 120 is attached via the support member 165. A bolt 160 serving as a fixing member is attached so as to pass through a central through-hole 159 of the boss portion 158 of the radome 155, a central through-hole 166 of the support member 165, and a central through-hole 125 of the ground plate 120, and a nut 161 serving as a fixing member is attached to the tip of the bolt 160 and tightened. This allows the assembly of a small and lightweight antenna 10 in which the fed element 100 having the first feed lines 111-114, the ground plate 120, the second feed lines 131-134, the parasitic element 150, and the radome 155 are positioned in their predetermined positions.

[0046] As described above, according to this embodiment, it is possible to provide a small and lightweight dual-polarized antenna 10 that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear surface.

[0047] Furthermore, the present invention can provide a small, lightweight, dual-polarized antenna that can achieve high antenna gain while suppressing unnecessary radio wave radiation to the rear, making it suitable as an antenna for radio equipment mounted on HAPS, UAVs, and other devices in the sky. This can therefore contribute to achieving Goal 9 of the Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote industry, innovation and infrastructure." [Explanation of symbols]

[0048] 10: Dual-polarized antenna 100: Feed element 101: Opening 110: Element body 111~114: First feeder line 120: Ground plate 120a: Through hole 121~124: Opening 125: Central through hole 131~134: Second feeder line 141: Power supply port 142: Power supply port 150: Parasitic element 155:Radome 156: Flange part 156a: Through hole 157: Convex part 158: Boss Department 159: Central through hole 160: Bolt 161: Nut 165: Support member 166: Central through hole

Claims

1. A dual-polarized antenna that is used for two mutually orthogonal polarized waves, a feed element having an element body made of a loop-shaped conductor and four first feed lines made of conductors extending laterally from four locations at equal angular intervals around the circumferential direction of the element body toward a central axis of the loop; a ground plate disposed on the rear surface of the feed element at a predetermined distance from the feed element, the ground plate reflecting a target radio wave toward the feed element; four second feed lines each made of a conductor extending in a vertical direction from an end of each of the four first feed lines in the feed element on the loop central axis side toward the ground plate; a parasitic element made of a hollow disk-shaped conductor, which is arranged in front of the feed element so as to face the feed element at a predetermined distance and which is electromagnetically coupled with the feed element to expand the frequency band; any two of the four second feed lines adjacent to each other in a circumferential direction around the loop central axis are connected to the ground plate, and the other two second feed lines are connected to the signal lines of the two polarized waves via feed ports that are arranged on the ground plate in an electrically insulated state; having directivity in a direction from the ground plate to the feeding element; A dual-polarized antenna characterized by:

2. 2. The dual-polarized antenna of claim 1, The polarized-wave dual-antenna is characterized in that the ground plate is a perforated ground plate having one or more openings that improve the gain of the polarized-wave dual-antenna and the FB ratio (front-to-back ratio) of the polarized-wave dual-antenna.

3. 3. The dual-polarized antenna of claim 2, a ground plate having an opening formed in a portion thereof facing all or part of the opening of the feed element;

4. In the dual-polarized antenna of claim 1, 2 or 3, A dual-polarized antenna, characterized in that the separation distance between the parasitic element and the feed element is 0.01λ or approximately 0.01λ (λ: wavelength of the target radio wave).

5. 4. The dual-polarized antenna according to claim 1, 2 or 3, 10. The dual-polarized antenna according to claim 9, further comprising a protective member that covers and protects the feed element, the second feed line, and the parasitic element.

6. In the dual-polarized antenna of claim 5, the protective member has a cylindrical convex portion having a disk-shaped front cover portion at an end portion on a front side in the direction of directivity and an open rear side, a flange portion formed on a circumferential portion on the rear side of the convex portion, and a boss portion formed along a central axis inside the convex portion, the parasitic element and the fed element are mounted on an inner wall of the front cover of the protruding portion of the protective member, with the parasitic element and the fed element positioned in this order from the front side; the ground plate is attached to a rear surface side of the flange portion of the protection member, and a central portion of the ground plate is supported by a support member attached to the boss portion of the protection member, the four second feed lines are attached in a state in which their front side ends are connected to the central axis side ends of the four first feed lines and the second feed lines pass through through holes of the support member attached to the boss portion, the ground plate is fixed to the protective member by a fixing member attached so as to pass through a central through-hole of the boss portion of the protective member, a central through-hole of the support member, and a central through-hole of the ground plate; A dual-polarized antenna characterized by:

7. A dual-polarized antenna shared by two mutually orthogonal polarized waves, a feed element having an element body made of a loop-shaped conductor and four first feed lines made of conductors extending laterally from four locations at equal angular intervals around the circumferential direction of the element body toward a central axis of the loop; a ground plate disposed on the rear surface of the feed element at a predetermined distance from the feed element, the ground plate reflecting a target radio wave toward the feed element; four second feed lines each made of a conductor extending in a vertical direction from an end of the four first feed lines in the feed element on the loop central axis side toward the ground plate, any two of the four second feed lines adjacent to each other in a circumferential direction around the loop central axis are connected to the ground plate, and the other two second feed lines are connected to the signal lines of the two polarized waves via feed ports that are arranged on the ground plate in an electrically insulated state; having directivity in a direction from the ground plate to the feed element, The ground plate is a perforated ground plate having one or more openings that improve the gain of the dual-polarized antenna and the front-to-back ratio (FB ratio) of the dual-polarized antenna. A dual-polarized antenna characterized by:

8. The dual-polarized antenna of claim 7, a ground plate having an opening formed in a portion thereof facing all or part of the opening of the feed element;

9. The polarized antenna of claim 7 or 8, The dual-polarized antenna further comprises a protective member that covers and protects the feed element and the second feed line.

10. The dual-polarized antenna of claim 9, the protective member has a cylindrical convex portion having a disk-shaped front cover portion at an end portion on a front side in the direction of directivity and an open rear side, a flange portion formed on a circumferential portion on the rear side of the convex portion, and a boss portion formed along a central axis inside the convex portion, the power supply element is positioned and attached to an inner wall of the front cover portion of the protrusion of the protection member, the ground plate is attached to a rear surface side of the flange portion of the protection member, and a central portion of the ground plate is supported by a support member attached to the boss portion of the protection member, the four second feed lines are attached in a state in which their front side ends are connected to the central axis side ends of the four first feed lines and the second feed lines pass through through holes of the support member attached to the boss portion, the ground plate is fixed to the protective member by a fixing member attached so as to pass through a central through-hole of the boss portion of the protective member, a central through-hole of the support member, and a central through-hole of the ground plate; A dual-polarized antenna characterized by:

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