JP2007174158A - Ceiling embedded antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna which radiates vertical polarized wave without having orientation in a circumferential direction and is thin (a low posture) so as to be inconspicuous in an arrangement environment. <P>SOLUTION: The ceiling embedded antenna includes a coaxial connector 1; a ground board 2; a radiation element 3; and a cover 4. The ground board 2 includes a recession 6 at the center part. The radiation element 3 is arranged in the recession 6 in a state where the distal end side is projected from the ground board 2. The radiation element 3 includes a central conductor 12 constituting an element body; a stub 11 arranged by contact with the central conductor 12; and a disk 13 which is arranged at the distal end side of the central conductor 12 and is a capacity load. A part of the stub 11 is connected to the ground board 2. The projecting amount of the radiation element 3 from the ground board 2 is set to be 0.1 wavelength of a usage frequency or within its permissible error range. The stub 11 is constituted by bending at least one part of a metallic board. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ceiling-embedded antenna, and more particularly to an antenna structure used as a base station antenna of a mobile phone system.

  As a conventional indoor cellular phone base station antenna, a monopole antenna, a microstrip antenna, and the like are known.

  11A and 11B show a conventional monopole antenna. The configuration will be described below. The monopole antenna includes a connector 101, a ground plate 102, a radiating element 103, and a cover 104. The connector 101 is disposed in the center of the ground plate 102 and is electrically connected to the radiating element 103 on the opposite side of the ground plate 102 through a central hole provided in the ground plate 102. The radiating element 103 is arranged perpendicularly to the center of the ground plate 102 and has a length of a quarter wavelength of the used frequency. The cover 104 is fixed to the ground plate 102 so as to cover the whole.

  Since the radiation pattern in the peripheral direction of the monopole antenna is omnidirectional with vertical polarization, it has an ideal radiation pattern as a mobile phone base station antenna for indoor use. However, since the radiating element 103 requires a length of a quarter wavelength, there is a disadvantage that the antenna cannot be lowered.

  FIGS. 12A and 12B show a conventional microstrip antenna. The configuration will be described below. The microstrip antenna includes a connector 111, a ground plate 112, a printed circuit board 114 on which a radiating element 113 is formed, a support 115, a parasitic element 116, and a cover 117. A connector 111 is disposed on the back surface of the ground plate 112. A printed circuit board 114 is provided on the surface of the ground plate 112. On the surface of the printed circuit board 114, a rectangular radiating element 113 is formed of a conductor. The radiating element 113 is manufactured by an etching technique. A parasitic element 116 is disposed on the printed board 114 via a support 115. The parasitic element 116 has a rectangular shape.

  Since the microstrip antenna having such a parasitic element 116 is generally a broadband having a specific band of 10% or more, it can cover the band of a mobile phone system such as a third generation. Further, the antenna thickness can be lowered to about 0.1 wavelength of the specified frequency. However, the directivity of the microstrip antenna is in the front direction of the antenna surface (directly downward when installed on the ceiling) and has a disadvantage that the gain in the peripheral direction is low. Furthermore, since the polarization plane in the peripheral direction is mixed with vertical and horizontal polarization, it has a disadvantage that it is not suitable for a base station antenna.

As prior art documents related to the monopole antenna, for example, there are the following.
JP 2002-084124 A

  However, the conventional monopole antenna requires a quarter of the wavelength used and must be installed vertically, so that the monopole protrudes from the ceiling surface and becomes conspicuous in the indoor environment. was there. Further, as a means for reducing the attitude of the monopole antenna, for example, as described in Patent Document 1, a disk-like capacitive load is attached to the tip of the monopole so that the wavelength is shorter than a quarter wavelength. Although the antenna can resonate with the length, this has a drawback of a narrow band, and a desired band cannot be obtained in a mobile phone system such as the third generation.

  As for the conventional microstrip antenna, the antenna can be configured with a thickness of about 0.1 wavelength with respect to the ceiling surface. There was a disadvantage that would be mixed. Further, the microstrip antenna has a drawback that the directivity of the antenna is downward, the radio wave is too strong in the downward direction, and is too weak in the peripheral direction.

  None of the antennas of any type has radiated vertically polarized waves with no directivity in the surrounding direction like a monopole antenna, and has not realized an antenna with a low profile and wideband characteristics like a microstrip antenna. .

  The present invention relates to a ceiling-embedded antenna used as a base station antenna of a mobile phone system, which radiates vertically polarized waves having no directivity in the surrounding direction, and is thin (low profile) and inconspicuous in an installation environment. The purpose is to provide.

  In order to achieve the above object, a ceiling-embedded antenna according to the present invention is an antenna embedded in a ceiling, and includes a ground plate and a radiating element that radiates radio waves of a predetermined frequency into the space. Is characterized in that a concave portion is formed in the central portion thereof, and the radiating element is disposed in the concave portion in a state in which a tip end side thereof protrudes from the ground plate.

  As a preferred aspect, the radiating element may include a central conductor forming an element body and a stub disposed in contact with the central conductor, and a part of the stub may be connected to the ground plate. The radiating element may further include a plate-like member that forms a capacitive load and is disposed on the distal end side of the central conductor. The amount of protrusion of the radiating element from the ground plate may be 0.1 wavelength of the use frequency of the radio wave or an allowable error range thereof.

  The stub may be bent at least at one place. The stub may be formed in a line-symmetric shape with respect to a center line connecting one end on the center conductor side and the other end on the ground plate side. The plate member may be made of a metal disk, and the stub may be made of a metal plate.

  Furthermore, you may have further the cover which covers the said radiation | emission element and the said ground board. It may further include a coaxial cable connector to which the radiating element is connected, and the connector may be attached to the bottom side of the recess. The concave portion may be constituted by a cap that covers an opening provided in the ground plate, and the connector may be attached to a bottom side of the cap. The ground plate may be fixed to a ceiling surface side of the ceiling, and the cap may be disposed in a state of projecting to the back surface side through an opening provided in the ceiling.

  According to the present embodiment, a ceiling-embedded antenna used as a base station antenna of a mobile phone system radiates vertically polarized waves having no directivity in the surrounding direction, and is thin (low profile) in an installation environment. An inconspicuous antenna can be provided.

  Next, various embodiments of a ceiling-embedded antenna according to the present invention will be described in detail with reference to the drawings.

  First, a first embodiment of the present invention will be described with reference to FIGS.

  The ceiling-embedded antenna (hereinafter simply referred to as “antenna”) according to the present embodiment is used for a base station antenna of a mobile phone system. As shown in FIGS. 1 to 3, the antenna of the present embodiment includes a coaxial connector 1, a ground (ground) plate 2 to which the coaxial connector 1 is fixed, and a microwave that is electrically connected to the coaxial connector 1. The radiating element 3 is radiated, and the cover 4 covers the entire antenna.

  The coaxial connector 1 is connected to a coaxial cable (not shown). The coaxial cable supplies a microwave signal from the transmitter to the radiating element 3 while supplying a microwave signal received by the radiating element 3 to the receiver. The coaxial cable, the transmitter, and the receiver are not directly related to the present invention, and thus detailed description thereof is omitted.

  The ground plate 2 is formed in a disc shape, and a plurality of mounting holes 2a, 2b, and 2c are formed concentrically at predetermined intervals along the circumferential direction at three different positions in the radial direction. Yes. The ground plate 2 has a circular opening at the center thereof, and a circular recess 6 having a predetermined depth is disposed in the opening. In this embodiment, the recess 6 is realized by the inner shape of the cylindrical cap 5 as shown in FIG.

  The cap 5 is fixed in a state of covering the circular opening on the back side of the center portion of the ground plate 2. This fixing is performed by fastening with a mounting bolt 7 via a mounting hole 5b provided on the opening edge side (the flange) of the cap 5 and a mounting hole 2c around the opening of the ground plate 2. The coaxial connector 1 is fixed to the cap 5. This fixing is performed by fastening with an attaching screw 1a. As a result, the coaxial connector 1 is connected to the radiating element 3 located in the recess 6 via the cap 5.

  In this embodiment, as shown in FIG. 2, the radiating element 3 includes a pole-shaped center conductor 12 forming an element body, a metal disk (disk-shaped member) 13 constituting a capacitive load, and a predetermined shape. And a stub 11 formed by bending a metal plate such as brass.

  Among these, as shown in FIG. 3A, the center conductor 12 passes through the opening from the bottom side of the recess 6 in the cap 5 in the vertical or substantially vertical direction (depth direction of the recess 6) from the ground plate 2. It arrange | positions so that a predetermined amount (projection amount H) may protrude. The base end side (the bottom side of the concave portion 6) of the central conductor 12 is electrically connected to the coaxial connector 1, and the distal end side (the opening side of the concave portion 6) is electrically connected to the disk 13.

  The disk 13 is disposed in a state parallel to or substantially parallel to the ground plate 2 at a position on the distal end side of the center conductor 12 protruding from the recess 6. The disk 13 applies a capacitive load to the distal end side of the center conductor 12, whereby the length of the center conductor 12 can be made shorter than a quarter wavelength of the operating frequency. In the present embodiment, the length of the central conductor 12 and the depth of the recess 6 are set so that the protruding amount H of the radiating element 3 from the ground plate 2 is 0.1 wavelength of the operating frequency or within its allowable error range. Has been.

  In this embodiment, as shown in FIGS. 3A and 3B, the stub 11 has a shape obtained by bending a rectangular metal plate at two locations (see the bent portion 11b in FIG. 3B). As shown in FIG. 3A, one end of the stub 11 is in contact with the center conductor 12, and the other end is fixed to the ground plate 2 so as to be conductive to match impedance. Yes. The stub 11 and the ground plate 2 are fixed to each other by fastening them with the screws 8 through the mounting holes 11a (see FIG. 3B) of the stub 11 and the mounting holes 2c of the ground plate 2 (see FIG. 2). Is called.

  The stub 11, the central conductor 12, and the disk 13 are fixed by soldering as shown in FIG. 3A (see the soldering portion 14 in the figure).

  The cover 4 covers the entire antenna and is fixed to the ground plate 2. The cover 4 and the ground plate 2 are fixed by fastening with screws 9 (see FIG. 4A) through the mounting holes of the cover 4 and the mounting holes 2a of the ground plate 2. As the material of the cover 4, for example, ABS or polycarbonate is suitable, and the cover 4 is manufactured by cutting or molding technique.

  Next, with reference to FIGS. 4A and 4B, a method of attaching the antenna having the above structure to the ceiling CE will be described.

  In this mounting, a mounting bracket 16 shown in FIG. 4B is used. As shown in FIG. 4B, the mounting bracket 16 is formed in a disc shape and has a circular opening 16a at the center thereof. The diameter of the opening 16a is set larger than the outer diameter of the antenna cap 5. Mounting holes 16b are formed in the mounting bracket 16 at two locations facing each other in the radial direction across the opening 16a.

  As shown in FIG. 4A, the mounting bracket 16 is arranged on the back side of the ceiling CE where the antenna is installed, with the opening 16a facing the opening provided in the ceiling CE. On the other hand, the antenna is arranged in a state where the cap 5 and the coaxial antenna 1 are inserted into the opening of the ceiling CE and the opening 16a of the mounting bracket 16 as shown in FIG. In this state, the antenna is fixed to the mounting bracket 16 with the ceiling CE interposed therebetween. The antenna and the mounting bracket 16 are fixed to the bolt 17 and the nut 18 along the mounting hole 2b (see FIGS. 1 and 2) of the antenna and the mounting hole 16b of the mounting bracket 16 through the opening of the ceiling CE. It is done by conclusion. In this way, the antenna is installed on the ceiling CE in a state where most of the cap 5 is embedded in the ceiling CE and the bottom portion protrudes to the back side of the ceiling CE.

  Next, the results of examining the radiation pattern and return loss characteristics of the antenna having the above structure will be described. The frequency used for the radio wave was the microwave band used in the base station antenna of the cellular phone system. The protrusion amount H of the radiating element 3 from the ground plate 2 was set to 0.1 wavelength of the use frequency.

  FIG. 5A is a diagram showing a radiation pattern in the elevation angle direction (vertical plane) of the antenna, and FIG. 5B is a diagram showing a radiation pattern in the peripheral direction (horizontal plane) of the antenna. According to this, it was confirmed that the radiation pattern in the elevation angle direction of the antenna became the maximum point in the oblique direction from the horizontal as shown in FIG. 5A, and formed apple-shaped directivity. Moreover, it was confirmed that the radiation pattern in the peripheral direction of the antenna forms omnidirectionality as shown in FIG. As a result, it was found that the antenna according to the present example showed omnidirectionality of vertical polarization, and had an ideal radiation pattern as a mobile phone base station antenna for indoor use.

  FIG. 6 is a diagram illustrating the return loss characteristics of the antenna. According to FIG. 6, the return loss [dB] of the antenna is 10% or less of the specific band (standardized frequency 0.95 to 1.05) across the use frequency of microwave (normalized frequency 1.0 in the figure). Thus, it was confirmed that good return loss characteristics were obtained in a wide band.

  Next, the operation of the present embodiment will be described along the flow of a microwave signal during transmission.

  First, a microwave signal is supplied from the coaxial connector 1 through a coaxial cable from a transmitter or the like. The microwave signal resonates at a desired frequency in the radiating element 3. At this time, the stub 11 is conductively connected to the ground plate 2 to control the current on the radiating element 3 to achieve impedance matching.

  Next, when the radiating element 3 resonates, an electric field is generated between the radiating element 3 and the ground plate 2, and radio waves are radiated into the space with vertically polarized waves. The radiated vertically polarized radio wave forms the radiation pattern described above. That is, this radiation pattern is omnidirectional in the peripheral direction (see FIG. 5B), the elevation angle direction is the maximum point from the horizontal to the diagonal direction, and forms apple-shaped directivity (see FIG. 5A). ).

  The description of the operation of the present embodiment has explained the flow of the microwave signal at the time of transmission. However, at the time of reception, the reversibility can be achieved only by reversing the direction of the flow of the microwave signal. Is omitted.

  As described above, the antenna according to this embodiment has the following characteristics.

1) A concave portion (recess) 6 is provided by a cap 5 at the center of the ground plate 2 where the radiating element 3 is disposed.
2) The stub 11 obtained by bending a metal plate is provided on the radiating element 3. One end of the stub 11 is electrically connected to the ground plate 2.
3) A disk 13 that is a disk-shaped capacitive load is provided on the distal end side of the radiating element 3.
4) The protruding amount of the radiating element 3 from the ground plate 2 is about 0.1 wavelength of the operating frequency.

  Therefore, according to such a feature, the present embodiment has the following effects.

  The first effect is that the antenna can be thinned. In the present embodiment, since the protruding amount of the radiating element 3 from the ground plate 2 can be lowered, the thickness can be reduced to about 0.1 wavelength of the used wavelength except for the cap 5 portion embedded in the ceiling CE. Such a reduction in thickness makes it less noticeable in an installed environment such as a room.

  The second effect is that the directivity of the horizontal plane of the vertically polarized wave radiated from the antenna can be made omnidirectional. In this embodiment, the antenna radiation pattern can realize omnidirectionality of vertically polarized waves in the horizontal direction, as shown in FIG. This is an ideal radiation pattern for an indoor base station antenna of a cellular phone.

  The third effect is that the frequency used by the antenna can be widened. In the present embodiment, as shown in FIG. 6, since it has a characteristic of having a specific bandwidth of 10%, it can be applied to the bandwidth of a mobile phone system such as a third generation.

  The fourth effect is that antenna installation work is facilitated. Since the cap 5 protrudes to the back side of the ceiling CE, there is no interference between the tool and the ceiling plate when the coaxial connector 1 of the coaxial cable is tightened.

  The fifth effect is that the antenna can be easily manufactured. Except for the coaxial connector 1 and the cover 4, all can be manufactured with simple metal parts, and the parts can be manufactured at low cost even in small-scale production.

  That is, according to the present embodiment, the ceiling-embedded antenna used as the base station antenna of the mobile phone system is 1) thin about 0.1 wavelength used, and 2) omnidirectional in the surrounding direction. Radiates good vertical polarization, 3) is broadband, 4) is easy to manufacture, and 5) is easy to install. Thereby, it is possible to provide an antenna that is thin (low profile) and inconspicuous in the installation environment.

  Next, a second embodiment of the present invention will be described with reference to FIGS. 7 (a) and 7 (b).

  The shape of the stub 11 of the radiating element 3 described in the first embodiment needs to be appropriately changed according to the band of the antenna and the return loss characteristic. Therefore, in this embodiment, the stub 11 is changed in shape and bending method.

In the antenna according to the present embodiment, as shown in FIG. 7B, the shape of the stub 11 is composed of a rectangular portion including the mounting hole 11a and other substantially trapezoidal portions. The trapezoidal portion is wider than the rectangular portion, is widest at the center side, and narrows toward the end side from there. The stub 11 has a bent portion 11b formed at the boundary between the rectangular portion and the trapezoidal portion, and is a portion in contact with the center conductor 12 in the recess 6 of the cap 5 as shown in FIG. The bent portion 11b is bent. The radiation pattern of the antenna and other operational effects are the same as in the first embodiment.
(Modification)
Next, with reference to FIG.8 and FIG.9, the modification in the case of how the stub 11 is bent is demonstrated.

  In the first embodiment, as shown in FIG. 3, the stub 11 has two bent portions 11b. According to this, the stub 11 is bent diagonally upward in the figure from the ground plate 2 side toward the central conductor 12 side through the first bent portion 11b in the concave portion 6 of the cap 5. . And this stub 11 is the part which touches the center conductor 12, and is bent below the figure along the center conductor 12 via the 2nd bending part 11b.

  On the other hand, in the example shown in FIG. 8A, the bending direction of the first bent portion 11b is changed to an obliquely downward direction in the drawing. In the example shown in FIG. 8B, as in the second embodiment, the first bent portion 11b is not formed between the ground plate 2 and the central conductor 12, and the second bent portion is formed. Only 11b is formed. In the example shown in FIGS. 9A and 9B, a third bent portion 11b is formed between the first bent portion 11b and the second bent portion 11b, and the third Is further bent between the ground plate 2 and the central conductor 12 via the bent portion 11b.

  In the above-described embodiments and modifications, one to three bent portions are formed. However, the present invention is not limited to this, and more bending portions may be formed according to the antenna band and return loss characteristics.

  Next, with reference to FIGS. 10A to 10J, a modification in the case where the shape of the stub 11 is different will be described.

  In the example of FIGS. 10A to 10E, the shape of the stub 11 is composed of a rectangular portion on the side of the mounting hole 11a and a portion having another shape. Other shapes are rectangular (FIG. 10 (a)), circular or oval (FIG. 10 (b)), and a substantially trapezoidal shape opposite to the second embodiment (FIG. 10 (c)). , Substantially hexagonal shape (FIG. 10D) and substantially hourglass shape (FIG. 10E), respectively.

  Moreover, in the example of FIG.10 (f), it is comprised from the substantially inverted triangular part by the side of the attachment hole 11a, and the other rectangular part. In the example of FIG. 10D, it is composed of a substantially triangular portion on the mounting hole 11a side and another rectangular portion. In the example of FIG. 10 (h), it is composed of a substantially inverted triangular portion on the mounting hole 11a side and other rectangular portions. In the example of FIG. 10 (i), the shape of the stub 11 is formed in a substantially cross shape. Furthermore, in the example of FIG. 10J, the shape of the stub 11 is formed in an inverted T shape.

  The shape of the stub 11 is not limited to the above-described embodiments and modifications, and other shapes may be appropriately selected according to the antenna band and return loss characteristics. In this case, the stub 11 is preferably formed in a line-symmetric shape with respect to a center line connecting one end on the center conductor 12 side and the other end on the ground plate 2 side.

  In the above embodiment, the case where the stub 11 and the disk 13 are not in direct contact with each other is described. However, the present invention is not limited to this, and the stub 11 and the disk 13 may be in direct contact with each other. Good. Also in this case, the same effect as described above can be obtained.

  The present invention can be applied to a use of a ceiling-embedded antenna such as a base station antenna of a mobile phone system.

1 is a perspective view showing an overall configuration of a ceiling-embedded antenna according to a first embodiment of the present invention. FIG. 3 is a development view of a ceiling-embedded antenna in the first embodiment. (A) is principal part sectional drawing which shows the detail of a stub in 1st Example, (b) is the expanded view of the stub. (A) is sectional drawing at the time of ceiling mounting of the ceiling-embedded antenna in a 1st Example, (b) is a figure which shows the attachment metal fitting. (A) is a figure which shows the radiation pattern of an elevation angle direction in a 1st Example, (b) is a figure which shows the radiation pattern of the circumference direction. In a 1st Example, it is a figure which shows a return loss characteristic. (A) is a perspective view which shows the principal part structure of the ceiling-embedded antenna which concerns on the 2nd Example of this invention, (b) is a development view of a stub. (A) And (b) is a figure explaining the modification in case the way of bending a stub differs. (A) And (b) is a figure explaining the other modification when the bending method of a stub differs. (A)-(j) is a figure explaining the modification in case the shape of a stub differs. (A) is sectional drawing which shows the monopole antenna of a prior art example, (b) is the perspective view. (A) is sectional drawing which shows the microstrip antenna of a prior art example, (b) is the perspective view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coaxial connector 2 Ground board 2a, 2b, 2c Mounting hole 3 Radiation element 4 Cover 5 Cap 6 Recessed part (dent)
7 Bolt 8 Screw 9 Screw 11 Stub 12 Central conductor 13 Disk 15 Screw 16 Mounting bracket 16a Circular opening 16b Mounting hole 17 Bolt 18 Nut

Claims (13)

In antennas that are embedded in the ceiling,
A ground plate and a radiating element that radiates radio waves of a predetermined frequency into space;
The ground plate has a recess formed in the center thereof,
The ceiling-embedded antenna according to claim 1, wherein the radiating element is disposed in the concave portion with a tip side projecting from the ground plate.   The radiating element includes a central conductor forming an element main body and a stub disposed in contact with the central conductor, and a part of the stub is connected to the ground plate. The ceiling-embedded antenna described in 1.   3. The ceiling-embedded antenna according to claim 1, wherein the radiating element further includes a plate-like member that forms a capacitive load and is disposed on a front end side of the central conductor.   The ceiling according to any one of claims 1 to 3, wherein an amount of protrusion of the radiating element from the ground plate is 0.1 wavelength of a use frequency of the radio wave or an allowable error range thereof. Embedded antenna.   The ceiling-embedded antenna according to any one of claims 2 to 4, wherein the stub is bent at least at one place.   6. The stub is formed in a line-symmetric shape with respect to a center line connecting one end on the center conductor side and the other end on the ground plate side. The ceiling-embedded antenna according to the item.   The ceiling-embedded antenna according to any one of claims 3 to 6, wherein the plate-like member is made of a metal disk, and the stub is made of a metal plate.   The ceiling-embedded antenna according to claim 1, further comprising a cover that covers the radiating element and the ground plate. A coaxial cable connector to which the radiating element is connected;
The ceiling-embedded antenna according to claim 1, wherein the connector is attached to a bottom side of the recess. The concave portion is constituted by a cap that covers an opening provided in the ground plate,
The ceiling-embedded antenna according to claim 9, wherein the connector is attached to a bottom side of the cap. The ground plate is fixed to a ceiling surface side of the ceiling,
The ceiling-embedded antenna according to claim 10, wherein the cap is arranged in a state of projecting to the back side through an opening provided in the ceiling.   8. The ceiling-embedded antenna according to claim 7, wherein the disk and the stub are not in direct contact with each other.   The ceiling-embedded antenna according to claim 7, wherein the disk and the stub are in direct contact with each other.

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