JP4515660B2 - Directional antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a directional antenna, for example, a directional antenna for a wireless LAN installed outdoors.
[0002]
[Prior art]
In recent years, wireless LAN has been actively used. In a wireless LAN, radio waves may be transmitted and received from a base station antenna placed outside a building with respect to an antenna of a terminal station provided in each room of a building such as a building or a condominium. Conventionally, a collinear antenna, a cardioid characteristic antenna, a patch antenna, or the like has been used as the base station antenna.
[0003]
[Problems to be solved by the invention]
However, a collinear antenna is an omnidirectional antenna, and cannot transmit and receive radio waves only in the direction of a building, for example, a housing complex. Is bad. In addition, when transmitting and receiving radio waves to and from each antenna of a plurality of terminal stations installed at intervals in the building, both the antenna provided at the end of the building and the antenna provided at the center of the building are under the same conditions. It is desirable that the station antenna can transmit and receive radio waves. For this purpose, it is necessary to make the electric field strengths of the antennas provided at the edges and center of the building substantially equal. However, when a cardioid antenna or patch antenna is installed at a position corresponding to the vicinity of the center of the building, the electric field strength is highest near the center of the building, and the electric field strength near both sides of the building is low. Therefore, the antennas described above are unsuitable as base station antennas that transmit and receive with the antennas of the terminal stations of the building.
[0004]
An object of the present invention is to provide a directional antenna capable of transmitting and receiving under almost the same conditions as an antenna provided at any position of a building such as a building or an apartment building by increasing electric field strength on both sides in the front direction. To do.
[0005]
[Means for Solving the Problems]
One aspect of the directional antenna according to the present invention has a dielectric cylindrical body. This cylindrical body can be a cylindrical body having various cross-sectional shapes such as a columnar shape or a prismatic shape. An antenna element is disposed in the cylindrical body along the length direction thereof. This antenna element has a portion whose directivity is at least approximately semicircular. As such an antenna element, for example, an omnidirectional antenna element such as a monopole antenna or a collinear antenna having a circular directivity characteristic, or an antenna element having a cardioid characteristic having a heart-shaped directivity characteristic may be used. it can. In this antenna element, a portion where the directivity is at least approximately semicircular and a portion where the electric field strength is high, for example, a portion where the electric field strength is maximum, is arranged close to the cylindrical body.
[0006]
In the antenna configured as described above, since the antenna element is disposed close to the cylindrical body, reflection is generated by the cylindrical body, and the electric field strength on the side away from the cylindrical body is reduced. Accordingly, an omnidirectional or cardioid antenna can be used as a directional antenna. In particular, since the electric field strength in the direction opposite to the front direction can be reduced, unnecessary radiation does not occur and the antenna efficiency can be increased. When an antenna element having a cardioid characteristic is used, the cylindrical body approaching the antenna element also acts as a suppression element, and the electric field strength at the approaching portion is slightly reduced. As a result, even as a base station antenna for a building such as a condominium or a building, the electric field strength near the center and near the edge of the building can be made almost equal even if it is installed near the center of the building. it can.
[0009]
In each aspect as described above, the antenna element may have a discone antenna provided on a conductive column. This discone antenna has a ground element and a hot element, and the ground element has a length that is an odd multiple of about 1 / 4λ (λ is a reception wavelength), and is a super-top structure attached to the column. belongs to. The hot element has an open stub structure having an odd multiple of about 1 / 4λ and is attached to the support column. A plurality of such discone antennas can be arranged in a straight line to form a collinear antenna.
[0010]
In such a configuration, the hot-side element is separated from the support in terms of high frequency, but is connected to the support in terms of direct current, and thus has high lightning resistance.
[0011]
A resonant ring element may be disposed around the discone antenna. When configured in this way, it is possible to correct a change in impedance of the antenna element due to the influence of reflection. In addition, it can be set as the antenna with a cardioid characteristic by providing a reflective element in the outward of such a discone antenna.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 show a directional antenna according to a first embodiment of the present invention. This directional antenna is used as an antenna for a base station as described above, and has an antenna element as shown in FIG. As this antenna element, an omnidirectional antenna such as a whip antenna 2 is used. This whip antenna 2 is a linear antenna whose length is selected to be about 0.8λ (about 122 mm) so that, for example, 2 GHz band radio waves can be transmitted and received, and whose diameter is about 12 mm, A square earth plate 3 having a side length of about 30 mm is attached.
[0013]
The whip antenna 2 is surrounded by a cylindrical body 4. The cylindrical body 4 is made of a dielectric material such as a synthetic resin, specifically FRP. The cylindrical body 4 has a cylindrical shape having an inner diameter of about 70 mm and a thickness of about 9 mm, for example. This thickness can be changed, for example, in the range of about 6 mm to 10 mm. In this cylindrical body 4, it arrange | positions in the state which approached the inner surface of the cylindrical body 4 so that the distance of the whip antenna 2 and the inner surface of the cylindrical body 4 may be 5 to 10 mm. That is, the whip antenna 2 is arranged in an eccentric state in the cylindrical body 4.
[0014]
FIG. 2 shows a directivity characteristic diagram of this antenna at 2.4 to 2.5 GHz. Since the whip antenna 2 is originally an omnidirectional antenna, the directional characteristic diagram should be circular. However, in this antenna, the whip antenna 2 is arranged in the cylindrical body 4. For this reason, reflection occurs, and the directivity characteristics as shown in FIG. 2 are obtained. The whip antenna 2 is closest to the inner surface of the cylindrical body 4 in the direction of 0 degrees in FIG. As is apparent from this directional characteristic diagram, the electric field strength greatly decreases in the range from about 120 degrees in the clockwise direction to about 120 degrees in the counterclockwise direction, and clearly has directivity. The half-value width is a wide range of about 140 degrees from about 60 degrees in the clockwise direction to 80 degrees in the counterclockwise direction. Therefore, by arranging the cylindrical body 4 in an eccentric state on the outer periphery of the omnidirectional whip antenna, the antenna has directivity, and can be used at an antenna installation location that requires directivity. In particular, in this embodiment, a directional antenna can be created only by a simple operation of covering the cylindrical body 4 on the whip antenna 2 having a simple configuration.
[0015]
3 to 5 show a directional antenna according to the second embodiment. Similar to the directional antenna of the first embodiment, this directional antenna is also used as a base station antenna, and is used for transmitting and receiving radio waves of about 2.4 to 2.5 GHz band. As shown in FIGS. 3A and 3B and FIGS. 4A and 4B, the directional antenna has an outer cylindrical body 12. The outer cylindrical body 12 has, for example, a cylindrical shape having an outer shape of 88.6 mm (about 0.72λ), an inner diameter of about 70 mm (about 0.58λ), and a thickness of about 9.3 mm (about 0.076λ). It is made of a dielectric material such as synthetic resin, specifically FRP. A base 14 is provided in the outer cylindrical body 12. The base 14 is formed in a disk shape. An inner cylindrical body 16 is attached to the base 14. The inner cylindrical body 16 is formed in, for example, a cylindrical shape having a diameter of about 38 mm (about 0.3λ), and a huge portion 16 a is formed in the lower portion thereof, and this is attached to the base 14. The wall thickness of the inner cylindrical body 16 is about 1.5 mm (about 0.01λ). A disk-shaped cap 18 is attached to the upper part of the inner cylindrical body 16. The base 14 is made of, for example, brass, the inner cylindrical body 16 is made of a dielectric, for example, synthetic resin, specifically, FRP, and the cap 18 is made of a suitable resin material.
[0016]
An antenna element such as a discone antenna 20 is disposed in the inner cylindrical body 16 as shown in FIG. In the discone antenna 20, a conductive pillar 22 provided perpendicular to the base 14 is mounted on the base 14. A center conductor 24 of the feed line is inserted into the center of the support 22, and a feed line insulator 26 is disposed between the center conductor 24 and the inner surface of the support 22. For example, a coaxial line having a characteristic impedance of 50Ω is formed by the central conductor 24, the feeder insulator 26 and the support 22. This coaxial line is coupled to a connector 27 provided on the side of the base 14 opposite to the support 22.
[0017]
A ground side element 28 is attached to the column 22. The ground element 28 has a super-top structure and is formed of a conductive metal in a cylindrical shape having an open lower end. The length is about 0.15 to 0.25 of the transmission / reception wavelength λ, for example, 25 mm (about 0.2λ), and the upper end portion is arranged concentrically with the column 22. The diameter of this upper end is about 15 mm. Thus, since it has a super top structure, an unnecessary high-frequency current does not flow through the column 22.
[0018]
A hot-side element 30 is attached to the support 22 above the ground-side element 28. The hot-side element 30 is also formed in the same size and shape as the ground-side element 28, and is attached to the column 22 so that the lower end of the hot-side element 30 is positioned about 4 mm above the upper end of the ground-side element 28. ing. A central conductor 24 led out from the column 22 is connected to the hot side element 30. Since it is configured as an open stub in this way, the hot-side element 30 is separated from the support 22 in terms of high frequency, but is connected to the support 22 in terms of DC. Therefore, it is rich in lightning resistance.
[0019]
A resonant ring element 32 is arranged so as to surround the hot side element 30 and the ground side element 28. The resonant ring element 32 is formed of a conductive metal in a cylindrical element having a diameter of about 25 mm and a length of about 27 mm.
[0020]
A plurality of, for example, two, for example, two conductive metal pipes 34 are arranged outside the inner cylindrical body 16 in the back direction. These pipes 34 have a diameter of about 4 mm, for example, and as shown in FIGS. 3 (b) and 4 (b), the distance between them is about 25 mm on both sides in the back direction, and the inner cylindrical shape is also used. It is attached to the body 16 so as to maintain a distance of about 25 mm. These pipes 34 are provided between the base 14 and the cap 18.
[0021]
The discone antenna 20 is originally an omnidirectional antenna, but the antenna 21 has a cardioid characteristic by being an antenna 21 combined with the pipe 34. Further, the front direction (the side opposite to the side where the pipe 34 is provided), which is the portion where the electric field strength of the cardioid characteristic is the largest, approaches the outer cylindrical body 12, that is, decentered, and becomes the outer cylindrical shape. It is arranged in the body 12.
[0022]
FIG. 6 shows a directional characteristic diagram at 2.45 GHz of vertical polarization of the antenna 21 (antenna combined with the discone antenna 20 and the pipe 34) with the outer cylindrical body 12 removed. It exhibits a geoid characteristic, and its maximum gain is in the front direction (0 degree). FIG. 7 shows the directivity characteristics of vertically polarized waves at 2.45 GHz when the outer cylindrical body 12 is attached to the antenna 21. As is apparent from FIG. 7, the front-side gain is reduced by attaching the outer cylindrical body in an eccentric state, and the maximum gain exists in the vicinity of 60 to 70 degrees on the left and right from the front direction. Further, the gain in the back direction is also reduced. FIG. 8 shows the change of the vertical polarization of the antenna 21 with the frequency in the front direction (maximum gain) with the outer cylindrical body 12 removed, and FIG. 9 shows the state where the outer cylindrical body 12 is attached. FIG. 10 shows the change of the gain of the vertical polarization in the front direction with the frequency when the outer cylindrical body 12 is attached. As is clear from these comparisons, the outer cylindrical body is eccentric and attached to the antenna 21, so that the gain in the front direction is reduced, but unnecessary radiation in the rear direction is reduced. The maximum gain is increased by minutes. 7, 9, and 10 are obtained by shifting the antenna 21 having the cardioid characteristic of FIG. 6 by about 5 mm in the front direction (maximum gain direction) and attaching the outer cylindrical body 12, respectively. It is.
[0023]
FIG. 11 shows changes in VSWR due to frequency changes in this directional antenna. The minimum is about 1.05 and the maximum is about 1.2, and there is no significant change in VSWR. If the resonance ring 32 is not provided, the antenna impedance changes greatly due to reflection at the thickness of the outer cylindrical body 12. However, the provision of the resonant ring 32 stabilizes the antenna impedance, resulting in a substantially constant VSWR as described above.
[0024]
Since this directional antenna has directivity characteristics as shown in FIG. 7, it is for a terminal station provided in each room of a building as shown in FIGS. When used as a base station antenna disposed at a position corresponding to the vicinity of the center of the apartment house 6 for transmission / reception with the antenna 8, the field strength is substantially equal at the terminal station antenna 8 at the end of the apartment house 6 or at the center. It can be. Note that the half width can be changed by adjusting the interval between the pipes 34, the half width can be increased when the pipes 34 are brought closer to each other, and the half width can be reduced when the pipes 34 are separated from each other.
[0025]
As shown in FIG. 13, the directional antenna of the third embodiment is the same as that of the second embodiment except that the collinear antenna having the discone antennas 40 and 42 provided in two stages has an antenna element. It is configured in the same way as a directional antenna. Equivalent parts are denoted by the same reference numerals and description thereof is omitted.
[0026]
The first-stage discone antenna 40 includes, for example, a super top 44 below the support 22. The super top 44 has a diameter of about 15 mm and a length of about 25 mm and is formed of a conductive metal in a short cylindrical shape with an open upper end. The lower end of the super top 44 is coupled to the column 22. . A radiating element including a hot-side element 46 a and a ground element 46 b is provided on the upper part of the super top 44. These hot-side and ground-side elements 46a and 46b are also made of conductive metal in a short cylindrical shape having a diameter of about 15 mm and a length of about 25 mm, with the upper end open, and each lower end is a column. 22. Further, the open end of the upper end of the hot side element 46 a is connected to the central conductor in the support column 22. Note that the distance between the upper end of the super top 44 and the lower end of the hot-side element 46a is about 5 mm. The distance between the upper end of the hot side element 46a and the lower end of the ground side element 46b is also about 5 mm.
[0027]
Similarly to the first-stage discone antenna 40, the second-stage discone antenna 42 also includes a super top 48, a hot-side element 50a, and a ground-side element 50b. The super top 48, the hot side and ground side elements 50a, 50b are formed in the same size and shape as the super top 44, the hot side and ground side elements 46a, 46b. The hot-side element 50a is arranged so that the closed lower end portion is positioned approximately 37 mm above the ground-side element 46b, and the closed lower end of the ground-side element 50b is approximately 5 mm above the opened upper end portion. The part is located. The open lower end portion of the super top 48 is located approximately 5 mm above the open upper end portion of the ground element 50b. Therefore, the super top 48 is attached in the opposite direction to the super top 44. Note that the open upper ends of the hot-side elements 46 a and 50 a are coupled to the center conductor in the support column 22. Each discone antenna is provided with resonant rings 51 and 52 as in the second embodiment.
[0028]
FIG. 14 is a diagram showing the directivity characteristic of vertical polarization of this antenna at 2.45 GHz with the outer cylindrical body 12 removed. This directivity characteristic generally shows a cardioid characteristic, and its maximum gain is in the front direction (0 degree). FIG. 15 is a directional characteristic diagram of vertical polarization at 2.45 GHz with the outer cylindrical body 12 attached. The gain in the front direction decreases, and the maximum gain is in the vicinity of the 65 ° direction on the left and right. As is clear from the comparison between the two, by attaching the outer cylindrical body 12, the gain in the front direction (0 degree) decreases, the maximum gain moves in the direction of about 65 degrees to the left and right, and the half-value width also increases. .
[0029]
FIG. 16 shows the frequency change of the gain in the front direction of this antenna, and FIG. 17 shows the frequency change of the maximum gain of this antenna. As is clear from these figures, the gain in the front direction is reduced by attaching the outer cylindrical body 12, but the unnecessary radiation in the rear direction is reduced, so the maximum gain is increased accordingly. is doing. FIG. 18 shows the frequency change of the VSWR of this antenna, which is a value of 1.2 to 1.3 near the center frequency of 2.45 GHz, which is sufficiently practical.
[0030]
Therefore, this antenna can also be used as a base station antenna as shown in FIG. 15, 16, and 17 were measured by shifting the antenna having the cardioid characteristic shown in FIG. 14 by about 5 mm in the front direction (maximum gain direction) and attaching the outer cylindrical body. is there.
[0031]
In each of the above embodiments, the entire antenna element is surrounded by the outer cylindrical body. However, it is not always necessary to surround the entire antenna element. For example, a dielectric suppressor having a certain width is used as the antenna. You may approach the element and provide it in the front direction. In the second and third embodiments, the plurality of pipes 34 arranged at intervals are used as the reflective elements. However, a plate-like body having a certain width is used as the reflective elements. You can also. In the third embodiment, a collinear antenna having two stages is used. However, a collinear antenna having a larger number of stages may be used. In the second and third embodiments, the inner cylindrical body 16 is provided, but may be unnecessary depending on circumstances.
[0032]
【The invention's effect】
As described above, in the directional antenna according to the present invention, for example, by providing a cylindrical body with respect to an antenna having omnidirectionality or cardioid characteristics, a directional antenna can be obtained. Since the electric field strength on both sides in the front direction of a geoid antenna can be increased, transmission and reception can be performed under almost the same conditions as the antenna installed at any location in a building such as a building or apartment. Is possible.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a directional antenna according to a first embodiment of the present invention.
2 is a directional characteristic diagram of the directional antenna of FIG. 1. FIG.
FIG. 3 is a front view and a partially cutaway perspective view of a directional antenna according to a second embodiment of the present invention.
FIGS. 4A and 4B are a partially broken side view and a partially broken rear view of a directional antenna according to a second embodiment of the present invention. FIGS.
5 is a partially omitted enlarged view of the directional antenna of FIG. 4;
6 is a directional characteristic diagram in a state where an outer cylindrical body in the antenna of FIG. 4 is removed.
7 is a directional characteristic diagram of the antenna of FIG. 4;
8 is a diagram showing a relationship between front gain and frequency in a state where an outer cylindrical body in the antenna of FIG. 4 is removed. FIG.
9 is a diagram showing the relationship between the maximum gain and the frequency in the antenna of FIG.
10 is a diagram showing a relationship between front gain and frequency in the antenna of FIG. 4;
11 is a diagram showing the relationship between VSWR and frequency in the antenna of FIG. 4; FIG.
12A and 12B are a side view and a plan view showing a usage state of the directional antenna of the second embodiment.
FIG. 13 is a diagram illustrating an antenna element used for a directional antenna according to a third embodiment of the present invention.
14 is a directional characteristic diagram with the outer cylindrical body removed in the antenna of FIG. 13; FIG.
15 is a directivity characteristic diagram of the antenna of FIG. 13;
16 is a diagram showing the relationship between the front gain and frequency of the antenna of FIG.
17 is a diagram showing the relationship between the maximum gain and frequency of the antenna of FIG.
18 is a diagram showing a relationship between VSWR and frequency of the antenna of FIG.
[Explanation of symbols]
2 Whip antenna (antenna element)
4 cylindrical body 12 outer cylindrical body (cylindrical body)
28 44 48 46b 50b Ground side element (antenna element)
30 46a 50a Hot side element (antenna element)
32 51 52 Resonant ring element 34 Pipe (reflective element)

Claims (5)

A dielectric cylinder;
In this cylindrical body, an antenna element that is disposed along the length direction thereof and has a portion whose directivity is at least approximately semicircular,
The antenna element has a portion where the electric field strength on the side showing the at least substantially semicircular directivity is close to the cylindrical body to cause reflection in the cylindrical body, A directional antenna that reduces the electric field strength on the side away from the cylindrical body . The directional antenna according to claim 1, wherein the antenna element has a cardioid characteristic and a direction in which the electric field strength is greatest is made to approach the cylindrical body . 3. The directional antenna according to claim 1 or 2 , wherein the antenna element has a discone antenna provided on a conductive column, and the discone antenna has about 1 / 4λ (λ is a reception wavelength). And a hot element attached to the support with an open stub having an odd multiple of about 1 / 4λ. Directional antenna. 4. The directional antenna according to claim 3, wherein the antenna element has a reflective element on a side opposite to a portion where the antenna element is close to the cylindrical body . 5. The directional antenna according to claim 3, wherein a resonant ring element is disposed around the discone antenna.

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