JP4329971B2 - Planar antenna device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a planar antenna device suitable for relaying terrestrial digital broadcasting by an SNF (Single Frequency Network) system.
[0002]
[Related background]
In the relay of digital terrestrial broadcasting, for example, as schematically shown in FIG. 7, a broadcast wave transmitted from the base station 1 is received by the receiving antenna 3 of the relay station 2 and is transmitted from the transmitting antenna 4 of the relay station 2. This is realized by retransmitting to the broadcast service area. In particular, recently, in order to effectively use the broadcast frequency, SFN (Single Frequency Network) relay that retransmits (broadcasts) the broadcast wave transmitted from the base station 1 from the relay station 2 at the same frequency as the broadcast wave. Attention has been paid.
[0003]
In this case, a wraparound of the broadcast wave transmitted from the transmission antenna 4 to the reception antenna 3 becomes a problem. Incidentally, when a broadcast wave transmitted (radiated) from the transmission antenna 4 wraps around the reception antenna 3 with a certain electric field strength or more, oscillation occurs in the relay station 2 and, for example, a protection circuit is activated to cause a broadcast stoppage. Therefore, a parabolic antenna having sharp directivity is generally used as the receiving antenna 3, but there are problems such as a large antenna shape and a three-dimensional and large structure.
[0004]
[Problems to be solved by the invention]
Therefore, the present inventors considered using a planar antenna device having a microstrip antenna as a radiating element as the receiving antenna 3. This type of planar antenna device has a structure in which a plurality of microstrip antenna elements are arranged on a ground conductor plate made of a flat plate via a dielectric layer. The structure is simple and compact. Have advantages.
[0005]
However, this type of planar antenna device (receiving antenna 3) generally has an antenna surface direction, that is, when the direction perpendicular to the antenna surface is the directivity direction of the antenna, it is ± 90 ° relative to this directivity direction. The direction null characteristic is bad. For this reason, when the planar antenna device is mounted on the same broadcast tower 5 as the transmission antenna 4 in the vertical direction, there is an essential problem that the wraparound of the radio wave from the transmission antenna 4 cannot be ignored.
[0006]
By the way, in a planar antenna device, the size of the ground conductor plate is regarded as an infinite plane, and its theoretical design is performed, so that a predetermined directivity can be obtained, for example, the number of microstrip antenna elements or An array structure including the arrangement interval is determined. Therefore, in theoretical calculation, for example, as shown in FIG. 8, it is possible to obtain antenna characteristics in which a null point is formed in the ± 90 ° direction. However, since the ground conductor plate in the actually manufactured planar antenna device is realized with a size suitable for the arrangement region of the plurality of microstrip antenna elements determined by theoretical calculation, for example, FIG. As shown, there is a problem that the null level in the ± 90 ° direction cannot be made sufficiently low.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is a compact planar antenna device in which a plurality of microstrip antenna elements are arranged on a ground conductor plate, in a ± 90 ° direction. An object of the present invention is to provide a planar antenna device that can make the null level sufficiently low and is suitable as a receiving antenna for relaying terrestrial digital broadcasts via SNF, for example.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a planar antenna device according to the present invention is a planar antenna device in which a plurality of microstrip antenna elements are arranged in a matrix on a ground conductor plate made of a flat plate via a dielectric layer,
In particular, the margin width W between the edge of the ground conductor plate and the edge positioned on the outermost periphery of the microstrip antenna elements arranged on the ground conductor plate is set to the free space wavelength λ of the microstrip antenna element. It is characterized in that the null level in the antenna surface direction (direction of ± 90 ° with respect to the main beam direction) is suppressed by setting it to 0.35 to 0.7 times.
[0009]
Preferably, the margin width W is set to 0.4λ as described in claim 2, and the null level in the antenna plane direction is set to realize SNF relay while minimizing the size of the ground conductor plate. It is characterized by the minimum required -40 dB or less.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a planar antenna device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a planar configuration of the planar antenna device according to the first embodiment, and FIG. 2 is a diagram illustrating a partial cross-sectional structure thereof. This planar antenna device is configured by arranging a plurality of microstrip antenna elements 13 on a ground conductor plate 11 made of a flat plate via a dielectric layer 12. Specifically, in this planar antenna device, for example, nine microstrip antenna elements 13 having a size of 162 mm × 139 mm and a frequency of 485 MHz are placed on the ground conductor plate 11 having a side of 1360 mm and 5 of tan δ is 0.002. A matrix is arranged in 3 rows and 3 columns (3 × 3) with an arrangement pitch P of 310 mm (0.5λ) through a dielectric layer 12 having a thickness of 0.0 mm.
[0011]
Incidentally, the number of microstrip antenna elements 13, the arrangement pitch P thereof, and the power distribution to these antenna elements 13 are determined according to the antenna specifications required for the planar antenna device. In particular, a radiation pattern having a predetermined beam width is obtained with a predetermined antenna gain in the direction of the main beam (main lobe) perpendicular to the antenna surface, and a predetermined front-back ratio (front-back characteristic) is obtained. As described above, it is further determined by theoretical calculation that nulls are formed in the direction of ± 90 ° (direction of the antenna surface).
[0012]
In addition, in this planar antenna device, in particular, the margin width W between the edge portion of the ground conductor plate 11 and the edge portion positioned on the outermost periphery of the microstrip antenna elements 13 arranged on the ground conductor plate 11 is: The antenna element 13 is set to be 0.5 times (0.5λ) the free space wavelength λ, thereby obtaining the antenna characteristics as shown in FIG. That is, in the planar antenna device according to this embodiment, the radiation level in the direction of ± 90 ° with respect to the main beam direction perpendicular to the antenna surface of the planar antenna device is −40 dB or less (−43 dB in actual measurement). An antenna characteristic is realized in which a substantial null point is set in the direction of ± 90 °.
[0013]
Note that the free space wavelength λ of the planar antenna device is λ = c / f where c is the speed of light when the frequency of the radio wave transmitted and received by the antenna element 13 is f.
Is defined as Incidentally, by using the free space wavelength λ, the blank width W in the ground conductor plate 11 described above is converted into a wavelength (less dimensioned), and various ground conductor plates 11 having different blank widths W are prepared and the blank space is prepared. When the relationship between the width W and the null level (attenuation amount) in the direction of ± 90 ° was examined, it was found that there was a relationship as shown in FIG.
[0014]
That is, the number of the microstrip antenna elements 13 arranged on the ground conductor plate 11 and the arrangement pitch P of the microstrip antenna elements 13 and the power distribution to these antenna elements 13 are determined in accordance with the antenna specifications. The array structure was designed so that nulls were formed in the ± 90 ° direction (antenna surface direction). Then, the relationship between the edge level of the antenna element 13 positioned on the outermost periphery, the edge portion of the ground conductor plate 11 and the margin width W and the null level (attenuation amount) in the direction of ± 90 ° was examined. As shown in FIG. 4, it was confirmed that the null level in the direction of ± 90 ° can be suppressed as the margin width W increases. Especially between the null level and the margin width W,
[± 90 ° null attenuation (dB)] = − 30 × [margin width (wavelength conversion)] − 28
It has been found that there is an approximate relationship. It has been clarified that the null attenuation in the ± 90 ° direction can be suppressed to −40 dB or less by setting the margin width W formed on the ground conductor plate 11 to 0.4λ or more in terms of wavelength. The increase in the null attenuation amount in the ± 90 ° direction is caused by electromagnetic contact between the edge of the ground conductor plate 11 and the antenna element 13 positioned on the outermost periphery of the antenna elements 13 arranged in an array structure. This is thought to be because the amount of binding changes.
[0015]
Thus, according to the planar antenna device in which the size of the ground conductor plate 11 is determined by paying attention to the margin width W with the antenna element 13 as described above, while taking advantage of the compactness as a planar antenna, the antenna The null attenuation amount in the plane direction (± 90 ° direction) can be increased and suppressed to, for example, −40 dB. Therefore, even when this planar antenna device is used as the receiving antenna 3 for relaying the terrestrial digital broadcast wave to the FNS and installed side by side with the transmitting antenna 4, the radio wave (broadcast wave) from the transmitting antenna 4 is provided. It is possible to prevent the interference and effectively prevent the interference. Therefore, the antenna system that realizes the FNS relay can be easily and compactly constructed by effectively using the limited antenna facility space of the broadcasting tower 5.
[0016]
Further, the margin width W between the edge portion of the ground conductor plate 11 and the antenna element 13 determined as described above is a large guideline in determining the size of the ground conductor plate 11. That is, the above experimental results shown in FIG. 4 show that the theoretical calculation shows that when the array structure is designed so that nulls are formed in the ± 90 ° direction (direction of the antenna surface), the ± 90 ° direction. This is a guideline for setting a null point. Therefore, if the size of the ground conductor plate 11 is determined according to this guideline, the ground conductor plate 11 can be compactly designed to the minimum necessary size while satisfying the null characteristic in the ± 90 ° direction, and the receiving antenna As a result, it is possible to realize a plane antenna device suitable for 3.
[0017]
By the way, according to such a planar antenna device, it is possible to simplify the configuration and greatly reduce the size as compared with the conventional parabolic antenna, and when it is installed in the broadcasting tower 5, it has a structure resistant to rain and wind. Moreover, since it is lightweight, the effect that the load given to the broadcast tower 5 can be reduced is exhibited.
Here, as another embodiment of the present invention, nine microstrip antenna elements 13 having a frequency of 509 MHz are arranged in a matrix of 3 rows and 3 columns (3 × 3) and formed on the ground conductor plate 11 having a side of 1200 mm, When a prototype of a planar antenna device having a margin width W of 0.4λ was made, the null attenuation in the ± 90 ° direction was −41 dB. Further, in order to realize a planar antenna device having a frequency of 752 MHz, as shown in FIG. 5, 12 microstrip antenna elements 13 are arranged in a matrix of 4 rows and 3 columns (4 × 3), and a ground conductor plate 11 having a side of 1200 mm is formed. The margin width W was set to 0.6λ. Then, the antenna characteristics in this planar antenna device were obtained as shown in FIG. 6, and it was confirmed that the null attenuation amount in the ± 90 ° direction reached -43.5 dB. Also from these modified examples, by setting the margin width W between the outermost peripheral edge of the microstrip antenna element 13 arranged in matrix and the edge of the ground conductor plate 11 to be equal to or greater than 0.4λ, It was confirmed that the null point could be set reliably in the ± 90 ° direction.
[0018]
The present invention is not limited to the embodiment described above. For example, considering the size of the ground conductor plate 11 and satisfying the compactness as a planar antenna device and setting a null point in the ± 90 ° direction, the margin width W is set to 0.35 to 0.5. 7λ is preferable, and 0.4λ is more preferable. However, when the null attenuation amount in the ± 90 ° direction may be about −35 dB, it is sufficient that the margin width W is set to 0.25λ, and further downsizing can be achieved.
[0019]
As for the array structuring conditions of the plurality of microstrip antenna elements 13, various conventional antenna design techniques may be used. For power distribution, the element spacing is 0.5λ in the three-element array here. [1: 4: 1] is set, however, it is sufficient to set as appropriate using a Chebyshev type weight or the like. In the embodiment, an example in which the null point is obtained in the ± 90 ° direction has been described. However, the present invention can be similarly applied to the case where the null point is reliably obtained in other directions such as the ± 100 ° direction. . In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.
[0020]
【The invention's effect】
As described above, according to the present invention, an array structure composed of a plurality of microstrip antenna elements is designed so that nulls are formed in the ± 90 ° direction (direction of the antenna surface) in theoretical calculation. Since the margin width W between the edge of the antenna element positioned on the outermost periphery and the edge of the ground conductor plate is set to 0.3 to 0.7λ, preferably 0.4λ in terms of wavelength, A planar antenna device in which a null point is set in the ± 90 ° direction while minimizing the size can be realized. In particular, it is possible to realize a compact planar antenna device suitable as a reception antenna for SNF relay, which can secure a null level of −40 dB or more necessary for preventing interference with a transmission antenna in SNF relay.
[Brief description of the drawings]
FIG. 1 is a diagram showing a planar configuration of a planar antenna device according to an embodiment of the present invention.
2 is a diagram showing a partial cross-sectional structure of the planar antenna device shown in FIG. 1;
3 is a diagram showing antenna characteristics of the planar antenna device shown in FIG. 1. FIG.
FIG. 4 is a diagram showing a relationship between a margin width W between an edge portion of a ground conductor plate and an antenna element in a planar antenna device, and a null level (attenuation amount) in the ± 90 ° direction.
FIG. 5 is a diagram showing a planar configuration of a planar antenna device according to another embodiment of the present invention.
6 is a diagram showing antenna characteristics of the planar antenna device shown in FIG. 5. FIG.
FIG. 7 is a diagram schematically showing an aspect of SNF relay of terrestrial digital broadcasting.
FIG. 8 is a diagram showing antenna characteristics obtained by theoretical calculation of a planar antenna device.
FIG. 9 is a diagram showing general antenna characteristics of a conventional planar antenna device.
[Explanation of symbols]
11 Ground conductor plate 12 Dielectric layer 13 Microstrip antenna element W Margin width

Claims (2)

A planar antenna device in which a plurality of microstrip antenna elements are arranged in a matrix on a ground conductor plate made of a flat plate via a dielectric layer,
The margin width W between the edge of the ground conductor plate and the edge positioned on the outermost periphery of the microstrip antenna elements arranged on the ground conductor plate is 0 with respect to the free space wavelength λ of the microstrip antenna element. A planar antenna device characterized in that the null level in the direction of the antenna surface is suppressed by setting it to .35 to 0.7 times. The planar antenna according to claim 1, wherein the margin width W is set to 0.4λ, and the null level in the antenna surface direction is set to -40 dB or less while minimizing the size of the ground conductor plate. apparatus.

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