JP7526149B2 - Antenna with reflector - Google Patents

Description

The present invention relates to an antenna with a reflector that can be used as an omnidirectional antenna formed by combining multiple antennas.

For example, a conventional transmitting antenna system for broadcasting is a collection of reflector-equipped antennas with twin loop antennas or dipole antennas as radiating elements. The collection generally comprises multiple reflector-equipped antennas arranged on three or more surfaces at equal intervals on the same circumference. Such multiple reflector-equipped antennas are arranged, for example, at 120° intervals when arranged on three surfaces, and at 90° intervals when arranged on four surfaces. Conventional collections of reflector-equipped antennas are adjusted so that the combined directivity of the multiple reflector-equipped antennas arranged on each surface is omnidirectional, and are often installed on the top of steel towers.

Figure 8A is a side view showing an example of a conventional reflector-equipped antenna assembly 100 that can be attached to the top of a steel tower. Here, the conventional reflector-equipped antenna assembly 100 has four reflector-equipped antennas 110 arranged on four sides at equal intervals on the circumference of the pole section 120. Figure 8B is a top view of the conventional reflector-equipped antenna assembly 100 shown in Figure 8A as seen from the top of the steel tower. Referring to Figure 8B, the conventional reflector-equipped antenna assembly 100 has four reflector-equipped antennas 110 arranged on four sides at equal intervals (i.e., 90° intervals) on the circumference of the pole section 120 with an attachment radius r. Here, the attachment radius r shown in Figure 8B means the distance from the center of the pole section 120 to the back of each reflector-equipped antenna 110 (i.e., the reflector). Note that it is desirable for the attachment radius r to be as small as possible so as to be omnidirectional.

Figure 9 is a schematic diagram showing the structure and radiation directivity of reflector-equipped antenna 110 constituting conventional reflector-equipped antenna assembly 100 shown in Figures 8A and 8B. Here, reflector-equipped antenna 110 comprises radiating element 300 with feeding point 301, and reflector 2 arranged parallel to radiating element 300 (a dipole antenna element) at a predetermined distance by a support (not shown). Here, the predetermined distance is often set to λ/4 (a quarter wavelength) where λ is the wavelength radiated from reflector-equipped antenna 110. Note that although a dipole element is described as the radiating element in Figure 9, the same applies to a twin loop element.

The radiation directivity of the reflector-equipped antenna 110 will be described using a schematic diagram of the radiation directivity of the reflector-equipped antenna 110 in Fig. 9. Here, the radiation directivities _300a1 and _300a2 of the reflector-equipped antenna 110 when there is no reflector 2 (i.e., the radiation directivity of the radiating element 300) are shown by dashed lines. As shown in Fig. 9, the radiation directivities _300a1 and _300a2 shown by dashed lines are symmetrical with respect to the feeding point 301 of the radiating element 300. In addition, the radiation directivities 300'a1 and 300'a2 of the electric image element 300' when the radiation directivity of the electric image element 300' of the radiating element 300 caused by the reflector ₂ is taken into consideration are shown by dashed and dotted lines. As shown in Fig. 9, the radiation directivities _300'a1 and _300'a2 shown by _dashed and dotted lines are symmetrical with respect to the electric image element 300'.

Further, in Fig. 9, the radiation directivities _300S1 and _300S2 of the reflector-equipped antenna 110 as a whole, which are a combination of the above two radiation directivities (i.e., taking into account the influence of the reflector 2), are shown by thick dashed lines. Here, the radiation directivities _300S1 and _300S2 shown by the thick dashed lines are a combination of the radiation directivities _300a1 and _300a2 shown by dashed lines and the radiation directivities _300'a1 and _300'a2 shown by dashed lines. In this way, the radiation directivities _300S1 and _300S2 shown by the thick dashed lines are dominated by radiation directivities directed forward from the radiating element 300, and have flat phase directivities based on the vicinity of the feeding point 301 of the radiating element 300. Here, the radiation reference point _300S0 of the reflector-equipped radiating element 300 as a whole is shown by a black dot. The radiation reference point _300S0 indicated by the black dot is generally located a little closer to the reflector 2 than the radiating element 300. Fig. 10 shows a conventional antenna with a reflector in which a radiating element (dual loop element) in which one-wavelength loop elements (loop elements) are installed symmetrically above and below the feed point and connected by a balanced line is used as the radiating element 300 arranged at a predetermined distance (about a quarter wavelength) from the reflector 2. Here, the radiating element 300 includes dual loop elements _302a1 and _302a2 equipped with a feed point 301.

Next, referring to Fig. 11, calculation results of horizontal plane directivity when the structure shown in Fig. 10 is used as the assembly 100 of antennas with reflectors of Fig. 8A and Fig. 8B in a calculation implementation model and the mounting radius r is changed from 250 mm to 500 mm will be described. Here, Fig. 11 shows the horizontal plane directivity (20 log E/E ₀ (dB)) of the assembly 100 of antennas with reflectors when the mounting radius r is 300 mm, 350 mm, 400 mm, and 450 mm. In Fig. 1, when the mounting radius r is 450 mm, comparing the 0° (maximum) direction with the 30° (minimum) direction, it can be seen that the directivity deviation is about -6 dB in the ±30° direction.

Next, in Figure 12, the dashed line shows the calculation results of the directivity deviation when the mounting radius r is changed from 250 mm to 500 mm in the conventional reflector-equipped antenna assembly 100 of Figure 8. Referring to Figure 12, it can be seen that in the conventional reflector-equipped antenna assembly 100, the directivity deviation increases as the mounting radius r is increased.

Here, an example of a method for improving the above-mentioned directivity deviation is the antenna described in Patent Document 1. Patent Document 1 employs an antenna having three or more radiating elements arranged adjacent to each other in the horizontal direction with a predetermined opening angle instead of each reflector-equipped antenna 110 of the reflector-equipped antenna assembly 100 shown in Figures 8A and 8B. In other words, Patent Document 1 focuses on the combined electric field strength directivity of three or more radiating elements arranged adjacent to each other in the horizontal direction with a predetermined opening angle (even when the mounting radius r shown in Figure 8B is large), and intends to improve the directivity deviation of the reflector-equipped antenna as a whole.

However, the reflector-equipped antenna described in Patent Document 1 has three radiating elements arranged adjacent to each other in the horizontal direction, which results in a large size and weight for each reflector-equipped antenna 110 in Figures 8A and 8B. Therefore, if the reflector-equipped antenna described in Patent Document 1 is installed on a steel tower, the wind-receiving area will be large, which will increase the load on the steel tower.

Patent No. 4823982

Thus, in conventional antennas with reflectors, the larger the mounting radius r, the larger the directional deviation becomes. In order to reduce such directional deviation, for example as described in Patent Document 1, if an attempt is made to increase the number of dipole antennas installed on each surface to improve the electric field strength directivity of each antenna and improve the directional deviation when arranged on four surfaces, the increase in the number of dipole antennas increases the width of the reflector and the wind receiving area, which increases the load on the steel tower on which the antenna is installed. In that case, the mounting radius r also becomes relatively large due to the increase in the number of radiating elements installed in the horizontal plane on each surface.

According to the present invention, there is provided an antenna with a reflector that exhibits good directivity deviation even when the mounting radius r is large.
Specifically, the present invention relates to
A reflector and
a first radiating element disposed at a distance from the reflector and having a feed point;
a balanced line having one end connected to the feed point and the other end extending in a direction approaching the reflector;
and a second radiating element connected to the other end of the balanced line, wherein a straight line connecting the reflector and the first radiating element defines a main axis direction.
Here, it is preferable that the first radiating element and the second radiating element include at least one dipole element or loop element, or are a twin loop element. Also, the reflector may have a planar shape or a grid shape.
Furthermore, there is provided an assembly of antennas with reflectors, in which any of the above-mentioned antennas with reflectors are arranged in N planes (N is an integer of 3 or more), and the radiating elements are installed adjacent to the reflectors so as to be positioned on the outside. Here, it is preferable that the assembly of antennas with reflectors is 3, 4, 5 or 6.

According to the present invention, it is possible to improve the directivity deviation in an assembly in which antennas with reflectors are arranged on N faces. Furthermore, according to the present invention, it is possible to provide an antenna with a reflector of the same size as a conventional product, so that it is possible to reduce the load on the steel tower on which the antenna is attached without increasing the mounting radius r.

1 is a schematic diagram showing the directivity of a reflector-equipped antenna according to an embodiment of the present invention; 1A is a schematic diagram of a radiating element including a dipole or loop element connected together via a balanced line, FIG. 1B is a schematic diagram of a one-wavelength loop element connected together via a balanced line, and FIG. 1C is a schematic diagram of a twin loop element connected together via a balanced line. 1A is a schematic diagram of an antenna with a reflector using, as a radiating element, two dipole elements connected to each other via a balanced line extending from a feed point toward the reflector. 1B is a schematic diagram of an antenna with a reflector using, as a radiating element, one-wavelength loop elements connected to each other via a balanced line extending from a feed point toward the reflector. FIG. 2D is a schematic diagram of a reflector-equipped antenna employing the twin loop element shown in FIG. 2C. 11 is a graph showing calculation results of the angle dependence (horizontal plane directivity) of the phase and the relative electric field intensity for the antenna with a reflector shown in FIG. 4 and the conventional antenna with a reflector shown in FIG. 10 . 5 is a graph showing horizontal plane directivity when the attachment radius r is changed in an assembly in which the reflector-equipped antennas shown in FIG. 4 are arranged on four surfaces. 11 is a graph showing calculations of the directivity deviation when the mounting radius r is changed for an assembly in which the reflector-equipped antennas shown in FIG. 4 are arranged on four surfaces and an assembly in which conventional reflector-equipped antennas shown in FIG. 10 are arranged on four surfaces. 1A is a side view of an assembly in which conventional antennas with reflectors are arranged on four sides at 90° intervals, and FIG. 1B is a top view of the assembly of conventional antennas with reflectors shown in A. FIG. 1 is a schematic diagram showing the directivity of a conventional antenna with a reflector. 1 is a perspective view showing an example of an antenna with a reflector that uses a twin loop element as a radiating element. 11 is a graph showing calculation results of horizontal plane directivity when the attachment radius r is changed in the calculation implementation model of the conventional reflector-equipped antenna shown in FIG. 10. 11 is a graph showing calculations of the directivity deviation when the attachment radius r is changed from 250 mm to 500 mm in a calculation implementation model of a conventional antenna with a reflector using the radiating element shown in FIG. 10.

The radiation directivity of the reflector-attached radiating element 1 will be described with reference to the schematic diagram of the radiation directivity of the reflector-attached antenna 1 according to the embodiment of the present invention shown in FIG. 1. Here, the radiation directivities _3a1 and _3a2 of the radiating element 3 without the reflector 2 (i.e., the radiation directivity of the radiating element 3 alone) are shown by dashed lines. As shown in FIG. 1, the radiation directivities _3a1 and _3a2 shown by dashed lines are asymmetric with respect to the feed point 31 of the radiating element 3 by the following means. The radiation directivity _3a2 toward the rear, i.e., the reflector 2, shown by "Rr" in FIG. 1, is set to be stronger than the radiation directivity _3a1 toward the front, shown by "Fr" in FIG. 1. Next, the radiation directivity caused by the electric image element 3' for the radiating element 3 due to the reflector 2 will be considered. The radiation directivities _3'a1 and _3'a2 by the electric image element 3' in this case are shown by dashed lines. Considering that radiation directivity _3a2 is higher than radiation directivity _3a1 and that the radiation directivity is symmetrical with respect to the reflector ₂ , radiation directivity 3'a2 toward the reflector 2 (forward as indicated by "Fr" in FIG. 1) is higher than radiation directivity _3'a1 . Here, the straight line connecting the reflector 2 and the feed point 31 is the main axis of this reflector-equipped antenna 1. This main axis is perpendicular to the reflector 2 and the radiating element 3. In other words, the reflector 2 and the radiating element 3 are disposed approximately parallel to each other. Also, although the reflector 2 is shown as a flat plate, it may take various forms such as a flat plate, a lattice shape, or a grid shape.

Next, in FIG. 1, the radiation directivities 3S ₁ and 3S ₂ of the whole antenna 1 with a reflector, which are a combination of the above two radiation directivities (i.e., taking into account the influence of the reflector 2), are shown by thick dotted lines. Here, the radiation directivities 3S ₁ and 3S ₂ shown by the thick dotted lines are a combination of the radiation directivities 3a ₁ and 3a ₂ shown by the dashed lines and the radiation directivities 3'a ₁ and 3'a ₂ shown by the dashed lines. In this way, the radiation directivities 3S ₁ and 3S ₂ shown by the thick dotted lines are dominated by the radiation directivity from the radiating element 3 to the rear (the direction of the reflector 2). Here, the radiation reference point 3S ₀ of the whole antenna 1 with a reflector is shown by a black dot. The radiation reference point 3S ₀ shown by this black dot is located near the intersection of the radiation directivities 3S ₁ and 3S ₂ shown by the thick dotted lines. In this case, the radiation reference point 3S ₀ is located near the electric imaging element 3' (not near the radiating element 3). In other words, according to the antenna 1 with a reflector, the radiation reference point 3S ₀ can be located behind the reflector 2.

Next, referring to FIG. 2A, the specific configuration of the radiating element 3 shown simply as a straight line in FIG. 1 for the sake of explanation will be described. Here, the radiating element 3 includes a first dipole element 32 having a feed point 31, a balanced line 33 having one end connected to the first dipole element 32 and extending along the main axis toward the reflector 2 (rearward indicated by "Rr" in FIG. 1), and a second dipole element 34 connected to the other end of the balanced line 33. Here, the first dipole element 32 and the second dipole element 34 are arranged parallel to each other. That is, the radiating element 3 differs in configuration from the conventional radiating element 300 shown in FIG. 10 in that, in addition to the first dipole element 32 having the feed point 31, the radiating element 3 includes a balanced line 33 having one end connected to the first dipole element 32 and extending toward the reflector 2, and a second dipole element 34 connected to the other end of the balanced line 33.

Next, referring to FIG. 2B, a radiating element 3a using a one-wavelength loop element (loop element) will be described instead of the radiating element 3 using a dipole element. Here, the radiating element 3a includes a loop element 32a with a feed point 31a, a balanced line 33a having one end connected to the loop element 32a and extending toward the reflector 2 (rearward indicated by "Rr" in FIG. 1), and another loop element 34a connected to the other end of the balanced line 33a. That is, the radiating element 3a differs in configuration from the radiating element 3 in that it includes two loop elements 32a and 34a (connected to each other via the balanced line 33a).

Further, referring to Fig. 2C, a radiating element 3b, which is an embodiment of a twin loop element, will be described. Fig. 2C is a schematic diagram of a twin loop element 3b in which a feed point 31b is provided at a location different from the feed point 31a of Fig. 2B (instead of feeding at the feed point 31a of Fig. 2B using a one-wavelength loop element (loop element)), and two one-wavelength loop elements of Fig. 2B are provided at intervals symmetrically above and below the feed point 31b, and are connected by a balanced line via the feed point 31b. Here, the radiating element 3b includes a balanced line connected to the feed point 31b and extending so as to be vertically symmetrical with respect to the feed point 31b, first loop elements _32b1 and _32b2 each connected to an end of the balanced line, balanced lines _33b1 and _33b2 each connected at one end to the first loop elements _32b1 and _32b2 and extending toward the reflector 2 ("rear" in FIG. 1), and second loop elements _34b1 and _34b2 each connected to the other end of the balanced lines _33b1 and _33b2 . That is, the radiating element 3b differs from the radiating element ₃ in that it includes a configuration in which the first loop element _32b1 is connected to the second loop element _34b1 via the balanced line _33b1 , and the first loop element _32b2 is connected to the second loop element _34b2 via the balanced line 33b2.

FIG. 3A shows a schematic diagram of a reflector-equipped antenna 1 in which the radiating element 3 shown in FIG. 2A is installed on the reflector 2 at a distance. FIG. 3B shows a schematic diagram of a reflector-equipped antenna 1a in which the radiating element 3a shown in FIG. 2B is installed on the reflector 2 at a distance. Here, the reflector 2 may be a metallic flat plate, or may contain a metal material in a lattice shape (grid shape) in order to reduce the load on the steel tower on which it is installed. Here, when the reflector 2 contains a metal material in a lattice shape (grid shape), it is preferable that such a metal material extends along the longitudinal direction of the radiating elements 3, 3a. The direction parallel to the main axis of the reflector-equipped antenna 1a is shown as the x-axis, and the reflector 2 is perpendicular to the main axis, and its plane extends parallel to the y-axis and z-axis.
In the antenna with a reflector according to the embodiment of the present invention, one radiating element may be arranged on each surface. The first dipole element 32 and the second dipole element 34 shown in Fig. 2A and Fig. 3A, the loop element 32a and the second loop element 34a shown in Fig. 2B and Fig. 3B, and the first loop elements _32b1 and _32b2 and the second loop elements _34b1 and _34b2 shown in Fig. 2C are all examples of phase difference feed elements. In such radiating elements, there are relatively few restrictions on the shape of the radiating element and the shape of the reflector (e.g., a metallic flat plate shape or a grid shape), so that the width of the directivity of the radiating element is wide.

Figure 4 shows a calculation model in which a reflector-equipped antenna 1b is arranged on four sides, including a reflector 2 and a radiating element 3b shown in Figure 2C, which is arranged at a predetermined distance (approximately a quarter wavelength) from the reflector 2.

Figure 5 shows the results of calculating the angle dependence (horizontal plane directivity) of the phase and relative electric field strength for the reflector antenna 1b in Figure 4 alone and the conventional reflector antenna 110 in Figure 10 alone. First, refer to the graph of phase change with respect to angle in Figure 5. Here, comparing the phase change around angles of ±60°, the reflector antenna 1b has a nearly constant phase amount, while the conventional reflector antenna has an upward convex shape. Therefore, the reflector antenna 1b can obtain good horizontal plane directivity (with small directivity deviation) in a four-plane assembly compared to the conventional reflector antenna. Next, refer to the graph of the change in relative electric field strength with respect to angle in Figure 5. Comparing the change in relative electric field strength around angles of ±60°, the reflector antenna 1b has a slight difference in electric field strength compared to the conventional reflector antenna 110, but the impact on the horizontal plane directivity when four planes are combined is minor.

Referring to Figure 6, we will explain the calculation results of the horizontal plane directivity when the mounting radius r is changed to 300 mm, 350 mm, 400 mm, and 450 mm in an assembly in which the reflector-equipped antennas 1b shown in Figure 4 are arranged on four sides. As shown in Figure 6, when the reflector-equipped antennas 1b are arranged on four sides, it can be seen that the directivity deviation in the ±25° direction is about -4 dB when the mounting radius r is 450 mm. It can be seen that this directivity deviation is smaller than the directivity deviation of about -6 dB for the conventional reflector-equipped antenna shown in Figure 11.

Figure 7 shows the results of calculating the directivity deviation versus mounting radius r for an assembly with four reflector-equipped antennas 1b as shown in Figure 4 and an assembly with four conventional reflector-equipped antennas as shown in Figure 10. It can be seen that the directivity deviation of the assembly with four reflector-equipped antennas 1b as shown in Figure 4 (shown by the solid line as "Example" in Figure 7) is smaller than the directivity deviation of the assembly with four conventional reflector-equipped antennas (shown by the dashed line as "Standard twin loop" in Figure 7) within the mounting radius r range of 250 mm to 500 mm. In addition, the directivity deviation of the assembly with four reflector-equipped antennas 1b as shown in Figure 4 is favorable at about -3 dB up to a mounting radius r of approximately 400 mm.

So far, a method for improving directivity deviation has been described using an example of an assembly in which antennas with reflectors according to an embodiment of the present invention are arranged on four surfaces. In the case of an assembly in which antennas with reflectors are arranged on four surfaces, the antennas with reflectors can be designed so that the half-width of the electric field is 90° (=360°÷4). For example, in the case of an assembly in which five surfaces are arranged, the half-width of the electric field can be designed to be 72° (=360°÷5), and in the case of an assembly in which six surfaces are arranged, the half-width of the electric field can be designed to be 60° (=360°÷6). In other words, the half-width of the electric field can be designed to be 360°/N, where N is the number of surfaces arranged.

Therefore, when designing a multi-faceted assembly of reflector-equipped antennas with electric field half-widths of 90°, 72°, or 60° as described above, the electric field half-width of the reflector-equipped antenna can be changed by changing the distance between the first dipole element 32 and the second dipole element 34 shown in FIG. 3A, by changing the distance between the first loop element 32a and the second loop element 34a shown in FIG. 3B, by changing the shape of the second dipole element 34 shown in FIG. 3A (for example, by changing the length of the second dipole element 34 in FIG. 3A), or by changing the shape of the second loop element 34a shown in FIG. 3B (for example, by changing the size of the second loop element 34a in FIG. 3B).

In addition, with the reflector-equipped antenna according to the embodiment of the present invention, it is sufficient to arrange one radiating element in the horizontal direction on each surface, making it possible to realize a cheaper system compared to, for example, a conventional six-surface antenna with two radiating elements adjacent in the horizontal direction. Furthermore, with the reflector-equipped antenna according to the embodiment of the present invention, only one radiating element is required, so it requires less than half the space compared to a conventional six-surface antenna with two radiating elements. Alternatively, it is possible to use the space thus freed up to install another antenna system. The advantages of the reflector-equipped antenna according to the embodiment of the present invention described above are the same when compared to a conventional five-surface antenna.

Although the present invention has been described with reference to a broadcast antenna as an example, those skilled in the art will appreciate that the present invention is not limited to such broadcast antennas and may be applied to any antenna for any purpose.
In order to maintain the disclosure matters as originally filed, the contents of claims 1 to 6 as originally filed are added below.
(Claim 1)
A reflector and
a first radiating element disposed at a distance from the reflector and having a feed point;
a balanced line having one end connected to the feed point and the other end extending in a direction approaching the reflector;
a second radiating element connected to the other end of the balanced line;
wherein a straight line connecting the reflector and the first radiating element defines a main axis direction.
(Claim 2)
The reflector-equipped antenna of claim 1 , wherein the first radiating element and the second radiating element include at least one of a dipole element or a loop element.
(Claim 3)
2. The reflector antenna of claim 1, wherein the first radiating element and the second radiating element are twin loop elements.
(Claim 4)
3. The antenna with a reflector according to claim 1, wherein the reflector has a planar shape or a grid shape.
(Claim 5)
An assembly of reflector-equipped antennas, comprising: antennas with reflectors according to any one of claims 1 to 4 arranged in N planes (N being an integer of 3 or more), each of the radiating elements being installed adjacent to the reflector so as to be positioned on the outside.
(Claim 6)
6. The reflector-antenna assembly of claim 5, wherein N is 3, 4, 5 or 6.

1, 1a, 1b Antenna with reflector 2 Reflector 3, 3a, 3b Radiation element 31, 31a, 31b, 301 Feed point 3', 300' Electrostatic image element 32 First dipole element 32a Loop element 32b ₁ , 32b ₂ First loop element 33, 33a, 33b ₁ , 33b ₂ Balanced line 34 Second dipole element 34a, 34b ₁ , 34b ₂ Second loop element 100 Conventional assembly of antennas with reflector 110, 110b Conventional antenna with reflector 120 Pole section 300 Radiation element 302a ₁ , 302a ₂ Dual loop element

Claims (5)

A reflector and
A first loop element is disposed at a distance from the reflector and has a feeding point;
a balanced line having one end connected to the feed point and the other end extending in a direction approaching the reflector;
a second loop element connected to the other end of the balanced line, wherein a straight line connecting the reflector and the first loop element defines a main axis direction. 2. The reflector-equipped antenna according to claim 1, wherein the first loop element and the second loop element are twin loop elements. The antenna with reflector according to claim 1 or 2, wherein the reflector has a planar shape or a grid shape. An assembly of antennas with reflectors, comprising N-plane arrangements of antennas with reflectors according to any one of claims 1 to 3 (N being an integer of 3 or greater), each of the loop elements being installed adjacent to the reflector so as to be positioned on the outside. 5. The reflector-antenna assembly of claim 4 , wherein N is 3, 4, 5 or 6.

Images