JP2003198236A - Broadband antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadband and low-height antenna capable of covering a plurality of frequency bands used in the working portable telephone system. <P>SOLUTION: A capacitance-loaded monopole antenna has a vertical element 3 inserted between a grounding plate 1 and a capacitance-loaded board 2 facing each other. The vertical element 3 has a shape, approximately bilaterally symmetric with respect to a vertical axis and is formed by a metal plate shaped so that the right and left side edges located at the grounding plate 1 depart more from this plate 1, as spreading to the periphery of the plate 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-profile wide-band antenna suitable as an indoor repeater for mobile communication, which is installed on a ceiling or the like.

[0002]

2. Description of the Related Art FIG. 6 shows a quarter-wave monopole antenna which is a typical antenna in which the directivity in the horizontal plane is omnidirectional. This 1/4 wavelength monopole antenna
A circular grounding plate 100 and a linear vertical element (antenna element) 101 vertically provided at the center of the grounding plate 100 are provided, and power is supplied from the base of the vertical element 101. In addition,
The length of the vertical element 101 is set to ¼ wavelength of the used frequency. The vertical in-plane directivity of the quarter-wave monopole antenna changes depending on the area of the ground plate 100. That is, the larger the area of the ground plate 100 is, the less the electromagnetic waves go around to the rear side of the ground plate 100, and the directivity in the vertical plane is improved.

An antenna having a structure such as the ¼ wavelength monopole antenna is particularly effective as a base station antenna for land mobile communication or the like which is installed and used on the ceiling of a room or the like. This is because this type of antenna can maintain omnidirectionality by being almost unaffected by the ceiling by installing the ground plate so as to be flush with the ceiling surface.

However, it is important for the antenna installed on the ceiling to be as inconspicuous as possible so as not to spoil the aesthetics of the room. Therefore, a so-called capacitively loaded monopole antenna, which can be constructed in a lower posture than the quarter-wave monopole antenna, has been widely used.

As shown in FIG. 7, in this capacitance loaded monopole antenna, the upper part of the vertical element 101 of the quarter-wave monopole antenna shown in FIG.
It has a structure in which a capacity loading disk 102 facing the above is formed. According to this configuration, it is possible to reduce the posture by loading the capacity with the capacity loading disk 102. That is, this capacitance loaded monopole antenna is composed of the vertical element 10
The height of 1'can be reduced to about 1/4 of the vertical element 101 of the 1/4 wavelength monopole antenna to achieve a low profile.

[0006]

With the spread of mobile communication in recent years, the frequency bands to be used for this mobile communication have been studied, and as a result, various frequency bands have been proposed.
Also, due to difficulty in securing frequency resources, it is necessary to use many different frequency bands in one system. For example, in the mobile phone system currently used in Japan, 800MHz band, 1.5GHz
Bands and three frequency bands of 2 GHz band are used.

The antenna is basically required to have a size corresponding to the frequency used. Then, when a plurality of frequency bands are used, an antenna corresponding to each frequency band is required. Therefore, in the base station of the mobile phone system that uses a plurality of frequency bands as described above, in order to cover all the frequency bands to be used, it is necessary to prepare an antenna corresponding to each frequency band. However, as the number of frequency bands used increases, the number of antennas increases and the installation area of the antennas also increases, resulting in an increase in installation work costs and poor aesthetics of the antenna.

The present invention has been made in view of the above circumstances, and provides a wide-band low-profile antenna capable of covering a plurality of frequency bands used in the current mobile phone system. The purpose is to do.

[0009]

The present invention is a capacitive loading type monopole antenna in which a vertical element is interposed between a grounding plate and a capacitive loading panel which face each other, wherein the vertical element has a vertical axis. Formed by a metal plate having a substantially symmetrical shape as a center, and left and right lower edge portions located on the ground plate side are further away from the ground plate toward the outer peripheral side of the ground plate It is characterized by being. According to the present invention, a wide-band property capable of covering a plurality of frequency bands used in a current mobile phone system is realized by a low-profile configuration.

The above vertical element has a corner number of 2n + 1 (n =
1, 2, ...) can be formed to have a polygonal shape. In that case, it is preferable that the angle formed by each side corresponding to the lower left and right edges is set to 90 ° to 150 °. Further, the metal plate may be a metal foil printed on a dielectric substrate. Further, in order to match the characteristic impedance of the power supply line, a short pin can be interposed between the ground plate and the capacitive loading board. This shorting pin may be formed integrally with the above capacity loading board in order to reduce the number of parts.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a wideband antenna according to the present invention. This antenna has a configuration in which a vertical element 3 is interposed between a circular grounding plate 1 and a capacitive loading disc 2 which face each other, that is, a so-called capacitive loading type monopole antenna.

This antenna is a conventional capacitive loading type monopole antenna designed for the 800 MHz band (see FIG. 7).
Instead of the linear vertical element of (see reference), the vertical element 3 made of a bilaterally symmetrical polygonal metal plate is used. That is, in this embodiment, the vertical element 3 is formed by a pentagonal metal plate obtained by cutting the right and left corners (see the chain double-dashed line) of the isosceles triangle with the apex angle θ1 along the line 4. Has been formed.

The vertical element 3 is arranged vertically to the ground plate 1 so that the top of the isosceles triangle is located at the center of the ground plate 1. The side of the vertical element 3 orthogonal to the axis of symmetry 5 is in contact with the radial line of the capacity loading disk 2 and is joined to the surface of the capacity loading disk 2 by means of solder or the like. Also, the rising part of the vertical element 3 is
It is connected to the input / output connector 6.

The opening angle of the rising portion of the vertical element 3, that is, the apex angle θ1 of the above-mentioned isosceles triangle is 90 ° to 150 °.
It is desirable to set within the range. In this embodiment,
The opening angle θ1 is set to about 120 °. When the opening angle θ1 is set to about 120 ° in this way, the angle formed by the right and left sides of the vertical element 3 facing the ground plate and the ground plate 1 (the rising angle of the vertical element 3) is About (180 ° -12
0 °) / 2.

Four short pins 7 are interposed between the edge of the ground plate 1 and the edge of the capacity loading disc 2. These short pins 7 are used for the input / output connector 6 described above.
It is provided for matching with the characteristic impedance (for example, 50Ω) of a power supply line (not shown) connected via. As shown in FIG. 2, these short pins 7 are provided so as to form a predetermined angle θ3 (in this example, about 30 °) with respect to the surface orthogonal to the surface of the vertical element 3.

In this embodiment, the short pins 7 are formed by extending the peripheral end of the capacity loading disc 2 in the direction along the radial line. In this case, each short pin 7 is bent toward the ground plate 1, and the tips thereof are joined to the edge surface of the ground plate 1 by means of solder or the like. In this way, if the short pin 7 is formed integrally with the capacity loading disc 2, the number of parts can be reduced. Of course, short pin 7
May be formed separately from the capacity loaded disc 2. In this case, the end of the short pin 7 on the capacity loading disk 2 side is joined to the capacity loading disk 2 by means of soldering or the like. In addition,
The short pin 7 can also be formed of a metal wire or the like.

The wideband antenna according to this embodiment is
The ground plate 1 is installed so as to be flush with the ceiling surface. When electric power in the frequency band used is supplied to the antenna via the connector 6, the current flowing in the capacitive loading disc 2 is canceled by the so-called image current. Therefore, in this antenna, only the vertical element 3 will contribute to the radiation.

Since this antenna has a structure as a capacitive loading type monopole antenna, it can be lowered in posture like the antenna shown in FIG. 7, and the vertical element 3 has the shape as described above. Since it is formed of a metal plate, a wider band characteristic than that of the antenna shown in FIG. 7 can be obtained.

That is, as shown in FIG. 3 as an example of the return loss characteristic, this antenna has a wide frequency band (ratio band 106 of approximately 800 MHz to 2.6 GHz).
%), The standing wave ratio (VSWR) shows a value of 2.0 or less. In FIG. 3, the standing wave ratios and frequencies of the points of the upward triangle marks are 1.9973 and 803 MHz, and the standing wave ratios and frequencies of the points of the downward triangle mark are 2.0001 and 2.30, respectively. 6395 GHz.

4 and 5 show the directivity in the horizontal plane and the vertical plane of the antenna according to this embodiment, respectively. As shown in FIG. 4, according to this antenna, good omnidirectionality in the horizontal plane can be obtained in any of the 800 MHz band, the 1.5 GHz band, and the 2 GHz band. Further, as shown in FIG. 5, according to this antenna, good vertical in-plane directivity without disturbance can be obtained in any of the above frequency bands.

The width and height of the vertical element 3, the opening angle θ1 of the rising portion of the vertical element 3, and the angle θ2 of the left and right corners of the vertical element 3 defined by the cut line 4 shown in FIG. Is an element that affects the input impedance of the antenna. Therefore, each of the above elements is appropriately selected so that the input impedance exhibits a desired magnitude in a specific operating frequency range.

By the way, the vertical element 3 made of the above metal plate
When the above is used, the radiation intensity of radio waves on the wide surface of the vertical element 3 tends to be higher than that on the narrow surface (the surface in the thickness direction of the vertical element 3). Therefore, in the antenna according to this embodiment, the short pin 7 is used to make the radiation intensity of the radio wave on the wide surface of the vertical element 3 uniform with that on the narrow surface.

That is, since the short pin 7 has a function of attenuating the radio wave, the arrangement angle θ3 of the short pin 7 (see the figure) is set so that the intensity of the radio wave radiated from the wide surface of the vertical element 3 is appropriately attenuated. 2) is set to make the radiation intensity of the radio wave on the wide surface and that on the narrow surface uniform. The uniformity of the radiation intensity is realized not only by the position where the short pin 7 is arranged, but also by selecting the width of the pin 7 (the diameter of the wire when a wire is used). be able to.

The number of the short pins 7 provided is not limited to the number (4) in the embodiment. That is,
For example, one or three short pins 7 can be arranged at symmetrical positions with respect to the vertical element 3, for example.

Further, the shape of the vertical element 3 is not limited to the polygonal shape (pentagonal shape) in the embodiment. That is, the vertical element 3 has a shape that is substantially left-right symmetric with respect to the vertical axis, and the left and right side edges located on the ground plate 1 side are closer to the outer peripheral side of the ground plate 2 from the ground plate 1. It only has to have a shape that satisfies the condition of being separated. When the vertical element 3 has a polygonal shape, the number of corners is 2n + 1.
(N = 1, 2, ...) Is set.

Further, the vertical element 3 may be formed of a material other than a general metal plate such as a copper plate. That is, the vertical element 3 can also be formed of, for example, a metal foil (eg, copper foil) printed on a dielectric substrate.

[0027]

As is apparent from the above description, according to the present invention, it is possible to obtain a good V.2 signal over a wide band without providing an individual feeding element or parasitic element for a plurality of frequency bands. S. W. An R characteristic and a radiation characteristic are obtained. Therefore, it is possible to provide a wideband antenna capable of simplifying the configuration, reducing the cost, and improving the productivity.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an antenna according to the present invention.

FIG. 2 is a plan view of the antenna.

FIG. 3 is a graph showing a return loss characteristic of the antenna.

4 (a), (b) and (c) are 800 MHz band, 1.5 GHz band and 2 G of the above antenna, respectively.
It is a figure which shows the directional characteristic in a horizontal plane in a Hz band.

5 (a), (b) and (c) are 800 MHz band, 1.5 GHz band and 2 G of the above antenna, respectively.
It is a figure which shows the vertical in-plane directional characteristic in a Hz band.

FIG. 6 is a perspective view showing a conventional quarter-wave monopole antenna.

FIG. 7 is a perspective view showing a conventional capacitively loaded monopole antenna.

[Explanation of symbols]

1 ground plate 2 capacity loading disk 3 vertical elements 6 connector 7 short pins

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Nakamura             3-3-1 Marunouchi, Chiyoda-ku, Tokyo             Ki Kogyo Co., Ltd. (72) Inventor Takashi Kanemoto             2-11-1, Nagatacho, Chiyoda-ku, Tokyo Stock             Ceremony company NTT Docomo

Claims (5)

[Claims] 1. A capacitive loading type monopole antenna in which a vertical element is interposed between a grounding plate and a capacitive loading panel that face each other, wherein the vertical element has a shape that is substantially left-right symmetric about a vertical axis. A wide band characterized in that it is formed by a metal plate having left and right side edge portions located on the ground plate side and further away from the ground plate toward the outer peripheral side of the ground plate. antenna. 2. The vertical element has a corner number of 2n + 1 (n =
1, 2, ...) and the angle formed by each side corresponding to the left and right side edges is set to 90 ° to 150 °. antenna. 3. The broadband antenna according to claim 1, wherein the metal plate is a metal foil printed on a dielectric substrate. 4. The wide band antenna according to claim 1, wherein a short pin is interposed between the ground plate and the capacitive loading plate. 5. The wideband antenna according to claim 4, wherein the short pin is integrally formed with the capacitive loading board.