JP4705876B2 - Antenna device - Google Patents

Description

  The present invention relates to an antenna device suitable for use in a multi-plane synthetic antenna system used for TV broadcast transmission or the like.

  The polyhedral antenna system is used for transmission of TV broadcasts. For example, as shown in FIG. 8, this multi-plane synthetic antenna system has a configuration in which an antenna device 10 is disposed on each side of a square tower T. Each antenna device 10 is arranged on a concentric circle at intervals of 90 degrees to constitute a four-plane synthetic antenna.

  As shown in FIG. 9, each antenna device 10 includes an antenna element 20 and a main reflector 30 that is a flat plate provided on the back of the antenna element 20. In the antenna device 10, the sub-reflector 40 is provided on one side and the other side of the main reflector 30 and the radome 50 is covered as necessary. The sub-reflecting plate 40 is formed by bending both ends of the main reflecting plate 30 to the antenna element 20 side.

A plurality of antenna elements 20 (two in this example) are arranged at a predetermined interval in the longitudinal direction of the main reflector 30. As each antenna element 20, a double loop antenna element as shown in FIG. 10 is used, for example. Each antenna element 20 is supported on the main reflector 30 by a support member 60.
The antenna device 10 having the above configuration is mounted on the steel tower T shown in FIG. 8 so that the longitudinal axis of the main reflector 30 is directed vertically, and radiates horizontally polarized waves from the antenna element 20.

  By the way, in the multi-plane synthetic antenna system having two or more planes, the protruding distance from the center of the tower (see FIG. 8) may have to be increased depending on the situation of the installation location (strength of the tower and the state of the building). is there. However, when the protrusion distance is increased, a drop amount in the composite directivity described later increases, and there is a problem that a dead zone occurs in the service area.

Here, amplitude directivity and composite directivity when a four-plane synthetic antenna system as illustrated in FIG. 8 is configured will be described. In the four-plane synthetic antenna system, there is a difference between the directivity level on the plane in the installation direction of each antenna device 10 and the directivity level on the composite plane in a direction approximately 45 degrees different from the installation direction. In addition, a drop in the combined directivity occurs in a direction shifted by about 22.5 degrees from the installation direction of each antenna device 10.
The difference in directivity level can be reduced by adjusting the size of the sub-reflection plate 40 (adjustment of 3 dB half-value width or the like by amplitude directivity) or the like.
However, since the amount of drop in the combined directivity greatly depends on the protruding distance of the antenna device 10, it is difficult to improve it by adjusting only the amplitude directivity.

11 and 12 illustrate the relative electric field strength characteristics and phase characteristics of the antenna device 10 alone, respectively. In each figure, the characteristic when the protrusion distance is 0 mm is indicated by a solid line, and the characteristic when the protrusion distance is 330 mm is indicated by a dotted line.
As is clear from FIG. 11, the amplitude directivity does not depend on the protruding distance. However, the phase characteristic greatly depends on the protruding distance, and this causes a drop in the synthetic directivity.

  When constructing a multi-plane synthetic antenna system, in reality, in many cases, it is necessary to increase the protruding distance according to the above-described conditions. Therefore, in the improved conventional antenna apparatus 10 ′ shown in FIGS. 13 and 14, a directivity control plate 70 is provided on the main reflector 30 to suppress the amount of drop in the combined directivity. .

The directivity control plate 70 has a configuration in which both end portions of a rectangular metal plate are bent so as to have a U-shaped cross section. The directivity control plate 70 is disposed so that each of the bent portions facing each other is along a plane perpendicular to the polarization axis of the loop antenna element 20 (the horizontal axis in FIG. 13), and the tip of each bent portion. Are coupled to the main reflector 30.
In this conventional example, the directivity control plate 70 is provided so as to oppose one loop portion 20a of each twin-loop antenna element 20 (see, for example, Patent Document 1).

The radio wave radiated from the antenna device 10 shown in FIG. 9 is a combination of the radio wave directly radiated from the antenna element 20 and the radio wave radiated after being reflected by the main reflector 30 and the sub-reflector 40. become. Since the phase of the radio wave radiated after being reflected by the reflectors 30 and 40 depends on the shape of the reflectors 30 and 40, the phase characteristics of the antenna device 10 as a whole are adjusted by changing the shape of the wave. can do.
On the other hand, in the antenna device 10 ′, the directivity control plate 70 partially changes the shape of the main reflector 30, so that the phase characteristics can be adjusted by the directivity control plate 70. is there.

  FIG. 15 shows an example of the relative electric field strength characteristic of the antenna device 10 ′ alone by a solid line, and shows an example of the same characteristic of the antenna device 10 shown in FIG. 9 by a dotted line. FIG. 16 shows an example of the phase characteristic of the antenna device 10 ′ alone with a solid line, and shows an example of the same characteristic of the antenna device 10 shown in FIG. 9 with a dotted line.

The characteristics shown in FIGS. 15 and 16 are obtained when the protruding distance is 0 mm. Therefore, the phase characteristic indicated by the dotted line in FIG. 16 matches the phase characteristic indicated by the solid line in FIG.
As is clear from the comparison of the characteristic curves in FIG. 15, the directivity control plate 70 hardly affects the amplitude directivity. However, as is apparent from the comparison of the characteristic curves in FIG. 16, the directivity control plate 70 has a function of changing the phase characteristic from an upwardly convex state to a downwardly convex state.

  As described above, if the directivity control plate 70 is provided, the directivity can be changed with little influence on the amplitude directivity. Therefore, in the antenna device 10 ′, the phase characteristic is adjusted in advance by the directivity control plate 70 so as to reduce the phase change when the protrusion distance is increased. As described above, adjusting the phase characteristic by the directivity control plate 70 means that the protruding distance is equivalently shortened. As a result, if the multi-plane synthetic antenna system is configured by the antenna device 10 ′ including the directivity control plate 70, the drop in the synthetic directivity is suppressed.

Japanese Patent Laid-Open No. 2004-104638

In order to enhance the phase adjustment effect by the directivity control plate 70, it is necessary to bring the directivity control plate 70 close to the antenna element 20. However, when the directivity control plate 70 is brought close to the antenna element 20, the directivity control plate 70 affects the characteristic impedance of the antenna element 20.
On the other hand, the phase adjustment effect by the directivity control plate 70 is obtained by enlarging the surface of the directivity control plate 70 facing the antenna element 20 in the direction of the horizontal polarization axis of the antenna element 20 (the left-right direction in FIG. 13). Can also be enhanced. However, enlarging the facing surface also affects the characteristic impedance of the antenna element 20.
The influence on the characteristic impedance is the V.V. S. W. R. This is a factor that degrades the characteristics and lowers the amplitude directivity of the antenna device 10.

  In view of such a situation, the present invention provides a V.V. S. W. R. An object of the present invention is to provide an antenna device capable of realizing a wide range of phase characteristic adjustments while reducing the influence on the characteristics and amplitude directivity.

The present invention includes a bi-loop antenna element, and the main reflector provided on the back of the twin loop antenna element in the form of parallel to the twin loop antenna element, wherein the loop portion of the twin loop antenna element and said main reflector A directivity adjusting body provided as a phase characteristic adjusting means between the antenna device and the antenna device. The directivity adjusting body is a sub-reflecting plate parallel to the main reflecting plate, and a short-circuit plate positioned between the sub-reflecting plate and the main reflecting plate to short-circuit the sub-reflecting plate to the main reflecting plate. And comprising. The short-circuit plate is disposed along a plane orthogonal to the horizontal polarization axis of the twin-loop antenna element, and is coupled to the main reflector in the projection area of the sub-reflector in the main reflector.

The directivity adjusting body includes, for example, a polarization axis of the twin-loop antenna element, and a cross section of a plane perpendicular to the main reflector has a π shape or a T shape. .

The sub-reflector may have a polygonal shape, a circular shape, or an elliptical shape. For example, the sub-reflecting plate is formed in a rectangular shape, and in this case, the long side is arranged in a form along the polarization axis of the twin loop antenna element. Further, when the sub-reflecting plate is formed in an elliptical shape, the major axis is arranged in a form along the polarization axis of the twin loop antenna element.

In implementation form, extending the main reflector polarization axis direction of the twin loop antenna elements and be provided with a separate sub-reflector by its extension.

  According to the present invention, the directivity adjuster can be lowered, so S. W. R. Adjustment of a wide range of phase characteristics can be realized in a state where influence on characteristics and amplitude directivity is reduced. Therefore, it is possible to improve the combined directivity by applying to the multi-plane combined antenna system.

Hereinafter, the most preferred embodiment of the present invention will be described in detail with reference to the drawings.
1 and 2 are an elevation view and a perspective view, respectively, showing an embodiment of an antenna device according to the present invention. The antenna device 1 includes a plurality of (in this example, two) antenna elements 2, a main reflection plate 3 formed of a flat plate provided on the back thereof, and a directivity adjusting body 7 disposed on the main reflection plate 3. And a sub-reflection plate 4 provided on one side and the other side of the main reflection plate 30, and a radome 5 covered on the main reflection plate 3.
The sub-reflecting plate 4 is formed by extending the main reflecting plate 3 in the direction of the polarization axis of the antenna element 2 (the left-right direction in FIG. 1) and bending the extended portion to the antenna element 2 side by an appropriate angle. .

  In the present embodiment, a double loop antenna element as shown in the figure is applied as each antenna element 2. Each double-loop antenna element 2 is arranged at a predetermined interval in the longitudinal direction of the main reflector 3 in a form in which the loop portion 2a is parallel to the main reflector 3 to form a 2L double-loop antenna. Each twin loop antenna element 2 is supported by the main reflector 3 by a support member 6.

The directivity adjuster 7 is positioned between the sub-reflector 7 a parallel to the main reflector 3 and the sub-reflector 7 a and the main reflector 3. The sub-reflector 7 a is short-circuited to the main reflector 3. And a pair of short-circuit plates 7b.
The sub-reflecting plate 7 a is made of a rectangular metal plate, and has a long side that is arranged along the direction of the horizontal polarization axis of the antenna element 2. The length of the long side of the sub-reflecting plate 7a is set to be significantly larger than the length of the corresponding side of the directivity control plate 70 shown in FIG. 9 (almost the loop portion 2a of the antenna element 2). Is set equal to the diameter). Therefore, according to the sub-reflection plate 7a, the radio wave from the antenna element 2 can be reflected on a wide surface extending in the direction of the horizontal polarization axis of the antenna element 2.

  Each short-circuit plate 7b is made of a rectangular metal plate having the same width as or substantially the same width as the short side of the sub-reflecting plate 7a, and is disposed so as to face each other in a form along a plane perpendicular to the horizontal polarization axis. ing. The height of the short-circuit plate 7b is set so that the directivity adjusting body 7 is lowered, that is, the height H1 of the directivity adjusting body 7 is the height H2 of the directivity control plate 70 shown in FIG. Is set to be significantly lower.

One short-circuit plate 7b is coupled to the sub-reflecting plate 7a at a portion that is shifted by a distance L from one short side of the sub-reflecting plate 7a to the other short side. The same applies to the other short-circuit plate 7b. Accordingly, both the short-circuit plates 7b are coupled to the main reflector 3 within the projection area of the sub-reflector 7a onto the main reflector 3.
In the directivity adjusting body 7 having such a configuration, the center point of the sub-reflecting plate 7a is positioned on a line that intersects the main reflecting plate 3 vertically through the center point of the loop portion 2a of the antenna element 2. Yes. The cross section of the antenna element 2 along the horizontal polarization axis and perpendicular to the main reflector 3 has a π shape.

A short-circuit current flows through the directivity adjuster 7 through a path 8 indicated by a dotted line in FIG. That is, the short-circuit current passes from the central point of the sub-reflector 7a through the surface thereof to the end thereof, and from the short side to the main reflector 3 through the back surface of the sub-reflector 7a and the short-circuit plate 7b. Reach.
In FIG. 1, a short-circuit current path in the directivity control plate 70 of the antenna device 10 ′ shown in FIG.
The height of the short-circuit plate 7b and the distance L in the directivity adjusting body 7 are set such that the length of the current path 8 is substantially equal to the length of the current path 80, for example. In this case, although the directivity adjusting body 7 is lowered in its posture as compared with the directivity control plate 70, the directivity adjusting body 7 performs a phase adjusting action equivalent to that of the directivity control plate 70.

FIG. 3 shows a relative electric field strength characteristic of the antenna device 1 according to the present embodiment by a solid line, and shows the same characteristic of the conventional antenna device 10 ′ of FIG. 13 by a dotted line. FIG. 4 shows the phase characteristic of the antenna device 1 alone with a solid line, and shows the same characteristic of the antenna device 10 ′ alone with a dotted line.
As is clear from the comparison of the characteristic curves shown in FIG. 4, according to the antenna device 1 according to the present embodiment, the conventional antenna device 10 is used despite the use of the directivity adjusting body 7 that has been lowered. Phase characteristics equivalent to 'can be obtained.

  According to the antenna device according to the present embodiment including the directivity adjusting body 7, the sub-reflector 7 a of the directivity adjusting body 7 can be largely separated from the antenna element 2, and the radio wave from the antenna element 2 can be obtained. Can be reflected by the wide surface of the sub-reflector 7a. S. W. R. Desired phase characteristics can be realized in a state in which deterioration of characteristics and influence on amplitude directivity are reduced.

  Note that changing the distance L that defines the coupling position of the short-circuit plate 7b to the sub-reflecting plate 7a has an effect equivalent to changing the height of the directivity adjusting body 7. By changing the phase characteristics, the phase characteristics can be changed. This means that a desired phase characteristic can be realized while reducing the orientation of the directivity adjuster 7.

  Since the antenna device 1 according to this embodiment operates as described above, when the antenna device 1 is applied as an antenna device of a multi-plane synthetic antenna system as shown in FIG. S. W. R. It is possible to improve the composite directivity in a state where the deterioration of characteristics and the influence on the amplitude directivity are reduced.

  FIG. 5 is a short dotted line showing the combined directivity in the horizontal plane of the four-plane synthetic antenna system using the conventional antenna device shown in FIG. 9, and the same directivity of the antenna system using the conventional antenna device shown in FIG. In the long dotted line, the same directivity of the antenna system using the antenna device according to the present invention shown in FIG. 1 is illustrated by a solid line. The measurement conditions of the horizontal direction composite directivity are as follows.

(1) The antenna device 10 shown in FIG. 9 is different from the antenna device 10 ′ shown in FIG. 13 only in that the latter includes a directivity control plate 70, and is different from the antenna device 10 ′ shown in FIG. 1 is different from the antenna device 1 shown in FIG. 1 only in the configuration of the former directivity control plate 70 and the latter directivity adjusting body 7.
(2) In the antenna device 10 ′ shown in FIG. 13, the height H2 of the directivity control plate 70 is set to 110 mm, and the width (the width along the polarization axis direction of the antenna element 20) is set to 100 mm. In the antenna device 1 shown in FIG. 1, the height of the directivity adjusting body 7 (height of the short-circuit plate 7b) H1 is set to 70 mm, and the width of the sub-reflection plate 7a (the width along the polarization axis direction of the antenna element 2). ) Is set to 168 mm, and the distance between both short-circuit plates 7 b is set to 100 mm.
(3) Two directivity control plates 70 are arranged in the form shown in FIG. Two directivity adjusting bodies 7 are arranged in the form shown in FIG.
(4) The frequency used is 680 MHz. The protruding distance of each antenna device 10, 10 ′ and 1 is 330 mm.
(5) The four antennas are operated with equal amplitude.

In a four-plane synthetic antenna system, in order to cover an area in a 360-degree direction, omnidirectionality close to a circle is required.
As is apparent from FIG. 5, when the antenna device 1 according to the present embodiment is applied, the amount of sagging in a direction shifted by about 22.5 degrees from the installation direction of the antenna device 1 is remarkably improved. That is, the sagging amount is improved by about 1.4 dB as compared with the case where the conventional antenna device 10 shown in FIG. 9 without a reflector is applied, and the conventional antenna device 10 ′ shown in FIG. 13 is applied. Compared to the case, the sagging amount is improved by about 0.5 dB.

The present invention is not limited to the embodiment described above, and includes various modifications.
That is, the directivity adjusting body 7 is not limited to the π-type cross section, and may be formed, for example, in a cross-sectional T type shown in FIG. In addition, each short-circuit plate 7b in the directivity adjusting body 7 having a π-type cross section may be provided in a cross-sectional shape or a reverse cross-section.
Furthermore, the planar shape of the sub-reflection plate 7a of the directivity adjusting body 7 is not limited to a rectangle, and may be another polygon including a square, a circle, an ellipse, or the like. In the case of an ellipse, it is desirable to provide the major axis along the polarization axis of the antenna element 2.

  In the embodiment, the directivity adjusting body 7 is disposed only on the back portion of one loop portion 2a of the antenna element (double loop antenna element) 2 in order to facilitate layout and the like. Of course, it is also possible to provide the directivity adjusting body 7 on the back of the loop portion 2a. And the antenna element 2 is not limited to a double loop antenna element, For example, other antenna elements, such as a dipole antenna element, may be sufficient.

It is an elevation view showing an embodiment of an antenna device according to the present invention. It is a perspective view of the antenna apparatus shown in FIG. 5 is a graph illustrating the relative electric field strength characteristics of the antenna device according to the present invention and the conventional antenna device. 5 is a graph illustrating the phase characteristics of the antenna device according to the present invention and a conventional antenna device, respectively. 4 is a graph illustrating the in-horizontal combined directivity of a four-plane combined antenna system to which an antenna device according to the present invention is applied and a four-plane combined antenna system to which a conventional antenna device is applied. It is the schematic which shows another structural example of a directivity adjustment body. It is the schematic which shows another structural example of a directivity adjustment body. It is a schematic plan view of a four-plane synthetic antenna system. It is an elevation view showing an example of a conventional antenna device. FIG. 10 is a perspective view of the antenna device shown in FIG. 9. 10 is a graph illustrating the relative electric field strength characteristics of the antenna device shown in FIG. 10 is a graph illustrating the phase characteristics of the antenna device shown in FIG. 9 by projecting distance. It is an elevational view showing another example of a conventional antenna device. It is a perspective view of the antenna apparatus shown in FIG. 14 is a graph illustrating the relative electric field strength characteristics of the antenna device shown in FIG. 9 and the antenna device shown in FIG. 13. 14 is a graph illustrating the phase characteristics of the antenna device shown in FIG. 9 and the antenna device shown in FIG. 13, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 2 Antenna element 2a Loop part 3 Main reflector 4 Sub reflector 5 Radome 7 Directivity adjustment body 7a Sub reflector 7b Short-circuit board 8 Current path

Claims (6)

A double loop antenna element, the phase between the main reflection plate provided on the back of the twin loop antenna element in the form of parallel to the twin loop antenna element, wherein the loop portion of the twin loop antenna element and said main reflector A directivity adjusting body provided as a characteristic adjusting means , and an antenna device comprising:
The directivity adjuster is
A sub-reflector parallel to the main reflector;
A short-circuit plate that is positioned between the sub-reflecting plate and the main reflecting plate and short-circuits the sub-reflecting plate to the main reflecting plate;
The short-circuit plate is disposed along a plane orthogonal to the horizontal polarization axis of the twin-loop antenna element, and is coupled to the main reflection plate inside the projection area of the sub-reflection plate in the main reflection plate. An antenna device comprising: The said directivity adjustment body is comprised so that the cross section by a surface perpendicular | vertical to the said main reflector may include (pi) shape including the polarization axis of the said double loop antenna element. Antenna device. The said directivity adjustment body is comprised so that the cross section by a surface perpendicular | vertical to the said main reflector may include T shape including the polarization axis of the said double loop antenna element. Antenna device.   The antenna device according to claim 1, wherein a shape of the sub-reflecting plate includes a polygon, a circle, and an ellipse. The antenna device according to claim 4, wherein the sub-reflecting plate has a rectangular shape, and a long side is arranged in a form along a polarization axis of the double loop antenna element. 6. The antenna device according to claim 1, wherein the main reflector is extended in a polarization axis direction of the double loop antenna element, and another sub reflector is provided by the extension. .

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