JP2004015733A - Antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna which yields desired directivity by using a colinear antenna housed in a cylindrical body. <P>SOLUTION: A stack coaxial dipole antenna 32 is disposed in a lengthwise direction within a rectangular FRP cylindrical body 30 which has a hollow internal part of a rectangular cross section. The stack coaxial dipole antenna 32 is composed of two coaxial dipole antennas 36a and 36b which are arranged along one diagonal of the cylindrical body 30. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an antenna, and more particularly to an antenna using a plurality of collinear antennas.
[0002]
[Prior art]
The collinear antenna includes, for example, a coaxial dipole antenna. The coaxial dipole antenna is obtained by cutting slots at predetermined intervals in a circumferential direction of an outer conductor of a coaxial line, and attaching cylindrical dipole antennas around each slot. When this coaxial dipole antenna is placed outdoors, for example, a coaxial dipole may be placed inside a tubular body made of synthetic resin along the length direction of the tubular body.
[0003]
[Problems to be solved by the invention]
In such an antenna, since the coaxial dipole antenna is disposed inside the cylindrical body made of synthetic resin, reflection at the cylindrical body, a passage loss when a radio wave passes through the cylindrical body, and the like occur, and a desired directivity is obtained. I couldn't get the sex.
[0004]
An object of the present invention is to provide an antenna capable of obtaining desired directivity in a state where a collinear antenna is housed in a cylindrical body.
[0005]
[Means for Solving the Problems]
In the antenna according to the present invention, a tubular body made of square synthetic resin is provided. This tubular body is hollow inside and has a polygonal cross section, for example, rectangular. As the synthetic resin, for example, FRP can be used. A pair of collinear antennas is arranged inside the cylindrical body along the length direction thereof. The collinear antennas forming a pair have a predetermined interval between them. The number of pairs may be at least one pair, and more pairs can be used. Various types of collinear antennas can be used. For example, a coaxial dipole antenna can be used.
[0006]
In the antenna configured in this manner, since the pair of collinear antennas is disposed inside the cylindrical body, reflection and passage loss due to the cylindrical body made of synthetic resin occur. By utilizing this, it is possible to obtain an antenna having directivity different from the directivity originally possessed by one collinear antenna.
[0007]
For example, when only one collinear antenna having horizontal omnidirectionality is provided inside a rectangular cylindrical body, horizontal omnidirectionality cannot be obtained. However, when the collinear antenna is an even number of horizontal omni-directional antennas and is arranged on the diagonal line of the cylindrical body and close to the corner of the cylindrical body, horizontal omnidirectionality can be obtained.
[0008]
Alternatively, when a plurality of collinear antennas are arranged substantially parallel to one side of the tubular body, the antenna can be a horizontal plane directivity having a main lobe in a direction perpendicular to the one side.
[0009]
Therefore, when the arrangement of the pair of collinear antennas is configured to be changeable inside the cylindrical body, it is possible to change the horizontal directivity of the antenna.
[0010]
The collinear antenna pair may be configured to combine the output signals of the respective collinear antennas on the board on which they are installed. In such a configuration, since synthesis is performed on one substrate, it is not necessary to individually connect a cable to each collinear antenna.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
First, an antenna according to a reference example on which the present invention is based will be described with reference to FIGS. As shown in FIG. 6 (a), the antenna of this reference example has a rectangular synthetic resin, for example, a cylindrical body made of FRP, specifically, an outer cylindrical body 2. As shown in FIG. 1B, the outer cylindrical body 2 has a rectangular cross section, for example, a square shape, and has a hollow interior. The thickness of the outer cylindrical body 2 is, for example, 10 mm. The reason why the outer cylindrical body 2 is of a rectangular shape having a rectangular cross section is that the cost is low and that the antenna is easily attached to a telephone pole or the like.
[0012]
Inside the outer tubular body 2, a collinear antenna, for example, a coaxial dipole antenna 4 as shown in FIG. 7 is accommodated and arranged in an inner tubular body 5 as shown in FIG. The coaxial dipole antenna 4 is for transmitting and receiving radio waves in, for example, a 2.4 GHz (wavelength λ = 125 mm) band, and has a disk-shaped substrate 6 as shown in FIG. A coaxial line 8 is provided vertically from the upper surface of the substrate 6 to the upper surface. The coaxial line 8 has a diameter of, for example, 4 mm.
[0013]
The coaxial line 8 is provided with slits (not shown) at positions 135 mm (approximately 1.1λ) from the substrate 6 and at positions 85 mm (approximately 0.7λ) above this position. On both upper and lower sides of these slits, cylindrical, for example, cylindrical antenna elements 10a, 10b, 12a, 12b are provided so as to be connected to the outer conductor of the coaxial line 8. These antenna elements 10a and 10b form a dipole antenna, and the antenna elements 12a and 12b form a dipole antenna.
[0014]
A position 85 mm further from the upper slit is the tip of the coaxial line 8, and a cylindrical antenna element 14 connected to the outer conductor of the coaxial line 8 is provided below the tip. A whip antenna 16 is connected to the end of the center conductor of the coaxial line 8. The whip antenna 16 and the cylindrical antenna element 14 also form a dipole antenna.
[0015]
Each cylindrical antenna element 10a, 10b, 12a, 12b, 14 has a diameter of 15 mm (about 0.12λ) and a length of 23 mm (about 0.2λ). The whip antenna 16 is formed to have a length of 36 mm (about 0.3λ). At the position of each slit, a spacer 18 made of an insulator and having a thickness of, for example, 3 mm is provided.
[0016]
A copper foil film element 20 functioning as a resonance ring is provided outside each of the spacers 18 so as to surround each dipole antenna. The length of these copper foil film elements 20 is selected to be 33 mm (about 0.26λ). These copper foil film elements 20 are provided to adjust the impedance of the antenna and to tilt the directivity.
[0017]
As shown in FIG. 6A, the coaxial dipole antenna 4 is accommodated in the inner cylindrical body 5 so that the length direction of the coaxial line 8 extends along the length direction thereof. A cap 21 is attached to the upper end of the inner cylindrical body 5. The inner tubular body 5 is disposed inside the outer tubular body 2 along the length direction of the outer tubular body 2. In this arrangement state, the coaxial dipole antenna 4 is located at the center of the outer cylindrical body 2 as shown in FIG. The inner tubular member 5 is a cylindrical member made of a synthetic resin, for example, FRP, and has a thickness of, for example, 1 mm to 1.8 mm, which is extremely thin as compared with the outer tubular member 2. Therefore, the directivity of the coaxial dipole antenna 4 is not affected.
[0018]
FIG. 8A shows the horizontal directivity of this antenna, and FIG. 8B shows the vertical directivity of this antenna. The coaxial dipole antenna originally has the property that the horizontal plane directivity becomes omnidirectional. However, by inserting the coaxial dipole antenna 4 into the outer tubular body 2, the gain is reduced in the direction corresponding to each corner of the tubular body 2, and no omnidirectionality is exhibited. This is thought to be mainly due to the following reasons. That is, a radio wave is propagated from the coaxial dipole antenna 4 to the outer cylindrical body 2 as indicated by an arrow in FIG. The radio waves vary from those traveling vertically toward the wall surface of the outer tubular body 2 to those traveling toward the corners. The propagation distance of these radio waves is the shortest when traveling perpendicular to the wall surface of the outer cylindrical body, and gradually increases as it approaches the corner, and the propagation distance gradually increases toward the corner. become longer. Thus, at the corner where the propagation distance is the longest, the loss accompanying propagation is the largest, and the overall horizontal directivity is not omnidirectional.
[0019]
As shown in FIG. 1A, an antenna according to an embodiment of the present invention houses an inner cylindrical body 31b with a cap 31a inside an outer cylindrical body 30 made of a square synthetic resin, for example, FRP. The stack type coaxial dipole 32 is arranged inside the inner cylindrical body 31b. Since the outer tubular body 30 and the inner tubular body 31b are configured in the same manner as the outer tubular body 2 and the inner tubular body 5 shown in the reference example, detailed description will be omitted.
[0020]
The stack type coaxial dipole antenna 32 is for transmitting and receiving radio waves in the 2.4 GHz band, similarly to the coaxial dipole antenna 4 of the reference example. As shown in FIGS. For example, two coaxial dipole antennas 36a and 36b are arranged at an interval of, for example, 35 mm (about 0.28λ).
[0021]
These coaxial dipole antennas 36a and 36b have the same configuration, and have coaxial lines 40a and 40b having a diameter of 4 mm as shown in FIG. Slits (not shown) are provided at positions 190 mm (about 1.5λ) from the lower ends of the coaxial lines 40a and 40b, as shown in FIG. Above and below this slit, cylindrical antenna elements 42a, 42b, 44a, 44b are arranged concentrically with the coaxial lines 40a, 40b and connected to the external conductors of the coaxial lines 40a, 40b. These antenna elements 42a and 44a constitute one dipole antenna, and the antenna elements 42b and 44b constitute one dipole antenna.
[0022]
A slit (not shown) is provided at a position 85 mm (about 0.7λ) further above the slit. Above and below, cylindrical antenna elements 46a, 46b, 48a, 48b are arranged concentrically with the coaxial lines 40a, 40b and connected to the outer conductors of the coaxial lines 40a, 40b. One dipole antenna is formed by the antenna elements 46a and 48a, and one dipole antenna is formed by the antenna elements 46b and 48b.
[0023]
A position 85 mm further upward from the slit is the tip of the coaxial lines 40a and 40b, and cylindrical antenna elements 50a and 50b are disposed concentrically with the coaxial lines 40a and 40b below the slits and connected to an external conductor. . Whip antennas 52a and 52b are connected to the ends of the center conductors of the coaxial lines 40a and 40b. These whip antennas 52a and 52b are located on the same straight line as the coaxial lines 40a and 40b. One dipole antenna is constituted by the antenna element 50a and the whip antenna 52a, and one dipole antenna is constituted by the antenna element 50b and the whip antenna 52b.
[0024]
Each of the cylindrical antenna elements 42a, 42b, 44a, 44b, 46a, 46b, 48a, 48b, 50a, 50b has a diameter of 15 mm (about 0.12λ) and a length of 23 mm (about 0.18λ). Are also formed. The whip antennas 52a and 52b have a length of 27 mm (about 0.2λ).
[0025]
A spacer 54 made of an insulator is provided between the antenna elements 42a, 44a, 42b, 44b, 46a, 48a, 46b, 48b, 50a, 52a, 50b, 52b. This is because when the stacked coaxial dipole antennas 32 are arranged in the inner cylindrical body 31b, they come into contact with the inner surface of the inner cylindrical body 31b to maintain the postures of the coaxial dipole antennas 36a and 36b. It is for. Further, these spacers 54 have a thickness of, for example, 3 mm, and form a pair between the antenna elements 42a and 44a, between 42b and 44b, between 46a and 48a, between 46b and 48b, and between 50a and 52a. , 50b, and 52b, respectively, so as to maintain a space corresponding to the thickness of the spacer 54.
[0026]
The coaxial lines 40a and 40b are connected to a combiner provided inside the board 34, and the output side of the combiner is connected to a coaxial connector 56 provided on the lower surface of the board 34. Therefore, the coaxial cable for power supply only needs to be connected to the coaxial connector 56, and does not need to be individually connected to the coaxial dipole antennas 36a and 36b.
[0027]
A stacked coaxial dipole antenna 32 housed in the inner tubular body 31b is inserted into the outer tubular body 30. The insertion is performed such that the length direction of the coaxial dipole antennas 36a and 36b is along the length direction of the outer tubular body 30. Moreover, the insertion is performed such that a straight line connecting the coaxial dipole antennas 36a and 36b is located on one diagonal line of the outer cylindrical body 30, as shown in FIG. 1B, for example. Alternatively, as shown in FIG. 1C, the straight line connecting the coaxial dipole antennas 36a and 36b is arranged along the long side of the outer tubular body 30 and at the center of the short side. . Since the inner cylindrical body 31b is formed in a cylindrical shape, it is easy to change from the state shown in FIG. 1B to the state shown in FIG. 1C or from the state shown in FIG. 1C to the state shown in FIG. I can do it.
[0028]
FIG. 4A shows horizontal plane directivity at 2450 MHz when the coaxial dipole antennas 36a and 36b are arranged diagonally as shown in FIG. 1B. FIG. 2B shows the horizontal directivity at 2450 MHz when the coaxial dipole antennas 36a and 36b are arranged in parallel to one side of the outer cylindrical body 30 as shown in FIG. 1C.
[0029]
When arranged as shown in FIG. 1C, the gain in the direction along both diagonal lines of the cylindrical body is reduced. This is because the thickness of each corner on the extension of both diagonals is a value obtained by multiplying the thickness of the other part by the square root of 2 (about 14 mm when the thickness of the other part is 10 mm), As described above, the reflection of radio waves and the loss that occurs when passing through these corners are increased, and as described above, the radio waves that are perpendicular to the wall of the outer cylindrical body 30 and are closer to the corners than this. This is because, when comparing the radio wave going to the wall and the radio wave going to the corner, the propagation distance gradually increases from the radio wave going perpendicular to the wall of the outer tubular body 30 to the radio wave going to the corner. In the horizontal direction, it is considered that the distance between the coaxial dipole antennas 36a and 36b has an influence and cancels each other, thereby reducing the gain. As a result, as shown in FIG. 4B, a horizontal plane directivity indicating a large gain in the front-rear direction is obtained.
[0030]
On the other hand, when the antennas are arranged on a diagonal line as shown in FIG. 1B, the coaxial dipole antennas 36a and 36b are arranged close to each other in the angular direction where the gain tends to decrease. it can. By appropriately adjusting the interval between the two coaxial dipole antennas 36a and 36b, it is possible to have horizontal plane directivity close to non-directional as shown in FIG.
[0031]
It is to be noted that the horizontal plane directivity can be changed by changing the positions of the coaxial dipole antennas 36a and 36b as shown in FIG. 1 (b) or (c).
[0032]
FIG. 5A shows the frequency vs. VSWR characteristics when the coaxial dipole antennas 36a and 36b are arranged as shown in FIG. 1B, and FIG. 5B shows the frequency vs. gain characteristics. (C) also shows the horizontal plane directivity at 2450 MHz, and FIG. (D) also shows the vertical plane directivity at 2450 MHz.
[0033]
Since the VSWR is 1.4 at 2400 MHz, 1.2 at 2450 MHz, and 1.4 at 2500 MHz, a sufficiently practical VSWR can be realized in this antenna. Further, since the gain of about 4 dB is realized at 2400 MHz and 2450 MHz, and the gain of about 4.6 dB is realized at 2500 MHz, the antenna is sufficiently practical in terms of gain. Further, since the horizontal plane directivity indicates almost non-directivity, it is suitable for receiving radio waves arriving from various directions satisfactorily, such as a wireless LAN.
[0034]
In the above embodiment, the stacked coaxial dipole antenna 32 is configured by the two coaxial dipole antennas 36a and 36b. However, a stacked coaxial dipole antenna can be configured by using more coaxial dipole antennas. . For example, two coaxial dipole antennas having the same configuration as the coaxial dipole antennas 36a and 36b are arranged on a straight line orthogonal to the coaxial dipole antennas 36a and 36b, and also on the other diagonal line of the outer cylindrical body 30. It is also possible to arrange a pair of coaxial dipole antennas. Further, in the above embodiment, a coaxial dipole antenna is used as a collinear antenna, but the present invention is not limited to this, and another collinear antenna can be used. In the above-described embodiment, the cylindrical body is made of FRP, but may be made of another synthetic resin. In the above-described embodiment, the outer tubular body 30 has a square cross-sectional shape, but may have a rectangular shape or another polygonal shape.
[0035]
【The invention's effect】
As described above, according to the present invention, an antenna having a desired directional characteristic can be realized by inserting a plurality of pairs of collinear antennas into a rectangular cylindrical body and adjusting the arrangement thereof.
[Brief description of the drawings]
FIG. 1 is a perspective view of an antenna according to an embodiment of the present invention, and a plan view of an internal stack type coaxial dipole antenna in a different arrangement.
FIG. 2 is a perspective view of a stacked coaxial dipole antenna used in the antenna of FIG.
FIG. 3 is a longitudinal sectional view showing a state in which the stacked coaxial dipole antenna of FIG. 2 is housed in an inner cylindrical body.
FIG. 4 is a horizontal plane directivity diagram when the internal stack type coaxial dipole antenna is arranged differently in the antenna of FIG. 1;
FIG. 5 is a diagram showing frequency vs. VSWR characteristics, a diagram showing frequency vs. gain characteristics, a water surface directivity diagram, and a vertical surface directivity diagram for the antenna of FIG. 1;
FIG. 6 is a perspective view and a plan view of an antenna according to a reference example of the present invention.
FIG. 7 is a perspective view of a coaxial dipole antenna used in the antenna of FIG. 6;
8 shows a horizontal plane directivity diagram and a vertical plane directivity diagram of the antenna of FIG. 6;
[Explanation of symbols]
30 cylindrical body 32 stack type coaxial dipole antenna (colinear antenna pair)
36a 36b Coaxial dipole antenna

Claims (4)

A tubular body with a hollow inside and a square cross-section made of synthetic resin,
Inside the cylindrical body, disposed along the length direction of the cylindrical body, having a predetermined interval therebetween, and a pair of collinear antennas forming a pair,
Antenna to equip. The antenna according to claim 1, wherein the collinear antenna is an even number of horizontal omnidirectional antennas, and is disposed on a diagonal line of the cylindrical body and close to a corner of the cylindrical body. 2. The antenna according to claim 1, wherein the plurality of collinear antennas are arranged substantially parallel to one side of the tubular body. The antenna according to claim 1, 2 or 3, wherein the pair of collinear antennas are combined with output signals of the respective colinear antennas on a board on which the pair of collinear antennas are installed.

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