JP3793456B2 - Broadband antenna - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In particular, the present invention relates to a low-profile wideband antenna suitable as an indoor relay device for mobile communication that is installed on a ceiling or the like.
[0002]
[Prior art]
FIG. 6 shows a quarter-wave monopole antenna, which is a representative antenna that has non-directional directivity in the horizontal plane. The quarter-wave monopole antenna includes a circular ground plate 100 and a linear vertical element (antenna element) 101 suspended from the center of the ground plate 100. Power is supplied. The length of the vertical element 101 is set to ¼ wavelength of the operating frequency.
The directivity within the vertical plane of the quarter-wave monopole antenna varies depending on the area of the ground plate 100. That is, the larger the area of the ground plate 100, the less electromagnetic waves wrap around the ground plate 100, and the directivity in the vertical plane is improved.
[0003]
An antenna having a structure such as the above-described quarter-wave monopole antenna is particularly effective as a base station antenna for land mobile communication that is installed on a ceiling such as a room. This is because this type of antenna can maintain omnidirectionality with almost no influence from the ceiling by installing the ground plate so that it is flush with the surface of the ceiling.
[0004]
However, it is important that antennas installed on the ceiling be as inconspicuous as possible so as not to impair the aesthetics of the room. Therefore, a so-called capacitively loaded monopole antenna that can be configured in a lower position than the quarter-wave monopole antenna has been widely used.
[0005]
As shown in FIG. 7, this capacitively loaded monopole antenna deforms the upper part of the vertical element 101 of the ¼ wavelength monopole antenna shown in FIG. 6 to form a capacitively loaded disk 102 that faces the ground plate 100. The configuration is as follows. According to this configuration, the posture can be lowered by loading the capacity by the capacity loading disk 102. That is, this capacitively loaded monopole antenna can be reduced in height by reducing the height of the vertical element 101 ′ to about ¼ of the vertical element 101 of the ¼ wavelength monopole antenna.
[0006]
[Problems to be solved by the invention]
With the spread of mobile communication in recent years, frequency bands to be used for mobile communication have been studied, and as a result, various frequency bands have been proposed. In addition, due to the difficulty in securing frequency resources, it is necessary to use many different frequency bands in one system. For example, in mobile phone systems currently used in Japan, three frequency bands of 800 MHz band, 1.5 GHz band and 2 GHz band are used.
[0007]
The antenna basically needs to be sized according to the frequency used. When a plurality of frequency bands are used, antennas corresponding to the individual frequency bands are required. Therefore, as described above, in a base station of a mobile phone system using a plurality of frequency bands, in order to cover all of the frequency bands to be used, an antenna corresponding to each frequency band must be prepared.
However, as the frequency band to be used increases, the number of antennas increases and the installation area of the antenna also increases, which causes problems such as an increase in installation work costs and poor antenna aesthetics.
[0008]
The present invention has been made in view of such a situation, and provides a wide-band and low-profile antenna capable of covering a plurality of frequency bands used in current mobile phone systems. It is aimed.
[0009]
[Means for Solving the Problems]
The present invention is a capacitively loaded monopole antenna in which a vertical element is interposed between a grounding plate and a capacitive loading board facing each other, and the vertical element has a substantially bilaterally symmetric shape about a vertical axis. In addition, the lower left and right edge portions located on the ground plate side are formed by a metal plate having a shape that is separated from the ground plate toward the outer peripheral side of the ground plate.
According to the present invention, the broadband property capable of covering a plurality of frequency bands used in the current mobile phone system is realized by a low-profile configuration.
[0010]
The vertical element can be formed to have a polygonal shape with 2n + 1 (n = 1, 2,...) Corners. In that case, it is preferable to set the angle formed by each side corresponding to the left and right lower edge portions to 90 ° to 150 °. The metal plate may be a metal foil printed on a dielectric substrate.
Furthermore, a short pin can be interposed between the grounding plate and the capacity loading board in order to match the characteristic impedance of the feeder line. This short pin may be formed integrally with the capacity loading board in order to reduce the number of parts.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of a broadband antenna according to the present invention. This antenna has a configuration in which a vertical element 3 is interposed between a circular ground plate 1 and a capacity loading disk 2 that face each other, that is, a configuration as a so-called capacity loaded monopole antenna.
[0012]
This antenna uses a vertical element 3 composed of a symmetrical polygonal metal plate in place of the linear vertical element of a conventional capacitively loaded monopole antenna (see FIG. 7) designed for the 800 MHz band. . 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 two-dot chain line) of the isosceles triangle with the apex angle θ1 along the line 4 respectively. It is formed.
[0013]
The vertical element 3 is arranged perpendicular 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 perpendicular to the symmetry axis 5 of the vertical element 3 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 such as solder. The rising portion of the vertical element 3 is connected to the input / output connector 6.
[0014]
The opening angle of the rising portion of the vertical element 3, that is, the apex angle θ1 of the isosceles triangle is preferably set in the range of 90 ° to 150 °. In this embodiment, the opening angle θ1 is set to about 120 °. Thus, when the opening angle θ1 is set to about 120 °, the angle formed by the left and right sides of the vertical element 3 facing the ground plate side and the ground plate 1 (the rising angle of the vertical element 3) is About (180 ° -120 °) / 2.
[0015]
Four short pins 7 are interposed between the edge of the ground plate 1 and the edge of the capacity loading disk 2. These short pins 7 are provided for matching with a characteristic impedance (for example, 50Ω) of a feeder line (not shown) connected via the input / output connector 6. As shown in FIG. 2, these short pins 7 are provided so as to form a predetermined angle θ <b> 3 (about 30 ° in this example) with respect to a plane orthogonal to the plane of the vertical element 3.
[0016]
In this embodiment, each short pin 7 is formed by extending the peripheral end of the capacity loading disk 2 in the direction along the radial line. In this case, the short pins 7 are bent toward the ground plate 1 and their tips are joined to the edge surface of the ground plate 1 by means such as solder.
Thus, if the short pin 7 is integrally formed with the capacity loading disk 2, the number of parts can be reduced.
Of course, the short pin 7 may be formed separately from the capacity loading disk 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 such as solder. The short pin 7 can be formed of a metal wire or the like.
[0017]
The broadband antenna according to this embodiment is installed in such a manner that the ground plate 1 is flush with the ceiling surface. When electric power in the operating frequency band is supplied to the antenna via the connector 6, the current flowing through the capacity loading disk 2 is canceled by so-called image current. Therefore, in this antenna, only the vertical element 3 contributes to radiation.
[0018]
Since this antenna has a configuration as a capacity loaded monopole antenna, the posture can be lowered similarly to the antenna shown in FIG. 7, and the vertical element 3 is made of a metal plate having the shape as described above. Since it is formed, characteristics with a wider band than that of the antenna shown in FIG. 7 can be obtained.
[0019]
That is, this antenna has a standing wave ratio (VSWR) in a wide frequency band (ratio band 106%) ranging from approximately 800 MHz to 2.6 GHz as shown in an example of the return loss characteristic in FIG. A value of 2.0 or less is shown. In FIG. 3, the standing wave ratio and the frequency of the upward triangle mark point are 1.9973 and 803 MHz, respectively, and the standing wave ratio and the frequency of the downward triangle mark point are 2.0001 and 2. 6395 GHz.
[0020]
4 and 5 show the directivities in the horizontal plane and in 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 frequency band of 800 MHz band, 1.5 GHz band, and 2 GHz band. Moreover, as shown in FIG. 5, according to this antenna, it is possible to obtain a good vertical in-plane directivity without any disturbance in any of the above frequency bands.
[0021]
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. This is an element that affects the input impedance of the antenna. Therefore, the above elements are appropriately selected so that the input impedance exhibits a desired magnitude in a specific use frequency range.
[0022]
By the way, when the vertical element 3 made of the metal plate is used, the radiation intensity of the radio wave on the wide surface of the vertical element 3 tends to be higher than that of the narrow surface (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 equalize the radiation intensity of the radio wave on the wide surface of the vertical element 3 and that on the narrow surface.
[0023]
That is, since the short pin 7 has an action of attenuating the radio wave, the arrangement angle θ3 of the short pin 7 (see FIG. 2) so that the intensity of the radio wave radiated from the wide surface of the vertical element 3 is moderately attenuated. Is set to equalize the radiation intensity of the radio wave on the wide surface and that on the narrow surface.
The uniform radiation intensity is realized not only by the position of the short pin 7 but also by selecting the width of the pin 7 (the diameter of the wire when a wire is used). be able to.
[0024]
The number of the short pins 7 provided is not limited to the number (4) in the embodiment. In other words, for example, one or three short pins 7 may be arranged at symmetrical positions with the vertical element 3 interposed therebetween.
[0025]
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 substantially bilaterally symmetric shape about the vertical axis, and the left and right side edges located on the ground plate 1 side move away from the ground plate 1 toward the outer peripheral side of the ground plate 2. It only needs to have a shape that satisfies the condition of leaving. When the vertical element 3 is polygonal, the number of corners is set to 2n + 1 (n = 1, 2,...).
[0026]
Further, the vertical element 3 may be formed of a material other than a general metal plate made of a copper plate or the like. That is, the vertical element 3 can be formed of, for example, a metal foil (for example, copper foil) printed on a dielectric substrate.
[0027]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to obtain a good V.V. over a wide band without providing individual feeding elements or parasitic elements for a plurality of frequency bands. S. W. R characteristics and radiation characteristics are obtained. Therefore, it is possible to provide a broadband antenna that can be simplified in configuration, reduced in cost, and improved in productivity.
[Brief description of the 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 return loss characteristics of the antenna.
FIGS. 4A, 4B, and 4C are diagrams showing horizontal plane directivity characteristics of the antenna in the 800 MHz band, 1.5 GHz band, and 2 GHz band, respectively.
FIGS. 5A, 5B, and 5C are diagrams showing vertical in-plane directivity characteristics of the antenna in the 800 MHz band, 1.5 GHz band, and 2 GHz band, respectively.
FIG. 6 is a perspective view showing a conventional quarter-wave monopole antenna.
FIG. 7 is a perspective view showing a conventional capacity-loaded monopole antenna.
[Explanation of symbols]
1 Grounding plate 2 Capacity loading disk 3 Vertical element 6 Connector 7 Short pin

Claims (3)

A capacity-loaded monopole antenna in which a vertical element is interposed between an opposing ground plate and a capacity loading board,
The vertical element has a substantially bilaterally symmetric shape about a vertical axis, and the left and right side edges located on the ground plate side are separated from the ground plate toward the outer peripheral side of the ground plate. Formed by a metal plate having
The vertical element has a polygon with 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 °. ,
Furthermore, a short pin is interposed between the ground plate and the capacity loading board, and the short pin makes the intensity of the radio wave radiated from the wide surface of the vertical element uniform with the intensity of the radio wave radiated from the narrow surface. A wideband antenna characterized by being provided at a position to be operated.   The broadband antenna according to claim 1, wherein the metal plate is a metal foil printed on a dielectric substrate. The broadband antenna according to claim 1, wherein the short pin is integrally formed with the capacity loading board.

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