JP2014003436A - Antenna device using ebg structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a degree of freedom in design of an antenna device by downsizing an EBG unit cell constituting an EBG structure while maintaining a low profile and broadband characteristics thereof.SOLUTION: An antenna device comprises an EBG structure in which a plurality of EBG unit cells (10) are periodically arranged, and an antenna disposed on the EBG structure. Each of the EBG unit cells (10) has a regular polygon shape with a side length W1, the shape allowing the cells to be periodically arranged at an interval of a predetermined gap width δ, and it includes a first metal patch (12) arranged by being spaced by a height hfrom a ground layer (11), and second metal patches (13) each of which has a regular 2n-polygonal (n is 2, 3, 4...) shape with a side length W2(<W1) and that are arranged so that the first metal patches (12) adjacent to each other are symmetrically overlaid therewith.

Description

  The present invention relates to an antenna device using an EBG structure having a high impedance surface as a reflecting surface.

A reflector is used as a means for giving the antenna radiation beam directivity in a single direction. Generally, this reflecting plate is made of a plate-like metal, and the reflected wave thereby has an electric wall characteristic in which the phase is inverted 180 degrees with respect to the incident wave. Thus, ₀ the wavelength of the center frequency f ₀ of the frequency band used _lambda, when the antenna height and h, the radiation efficiency is the best in the case of h ≒ lambda _0/4, as h is decreased, which is 180 degrees out of phase inversion Radiation efficiency decreases due to the influence of reflected waves.

In order to suppress a decrease in radiation efficiency due to the low attitude of the antenna, it has been proposed to employ an EBG (Electromagnetic Band Gap) structure on the reflecting surface (for example, Non-Patent Document 1, Patent). Reference 1).
FIG. 13 is a top view of a unit cell in a conventional EBG structure, and FIG. 14 is a sectional view taken along line BB in FIG. The EBG unit cell 100 is connected to the ground layer 101 by a square-shaped metal patch 102 horizontally arranged at a height portion separated from the ground layer 101 made of metal by h _EBG and having a side W. And a metal pin 103.

The EBG structure is configured by arranging the EBG unit cells 100 vertically and horizontally. In this EBG structure, the metal patches 102 of each EBG unit cell 100 are periodically arranged so as to form a two-dimensional plane, thereby forming the reflection surface. The metal patch 102 adjacent are separated by a gap of width [delta] _G.

Here, the capacitor component generated between the ground layer 101 and the metal patch 102 is C ₁ , the inductor component generated by the metal pin 103 is L ₁ , and the capacitor component generated from the gap δ _G between the adjacent metal patches 102 is C _2. , an inductor component by the edge of the metal patch 200 When L _2, it is possible to draw the LC equivalent circuit shown in FIG. 15. This LC equivalent circuit can be resonated at an arbitrary frequency by appropriately setting the L and C parameters.

Since the reflection surface of the EBG structure configured using such an EBG unit cell 100 has high impedance, a reflected wave having the same phase is generated at the resonance frequency by the LC equivalent circuit. In other words, ideally, when the antenna height h is 0, the magnetic wall characteristic has the best radiation efficiency at the use frequency f ₀ .
Even if the metal pin 103 is omitted for simplification of the structure, the above-described electrical characteristics can be obtained.

Fan Yang, etc., “Reflection Phase Characterizations of the EBG Ground Plane for Low Profile Wire Antenna Applications”. IEEE, Trans. On Antennas and Prop., Vol. 51, No. 10, Oct. 2003. JP 2003-306113 A

FIG. 16 shows the reflection phase characteristics of the EBG unit cell 100. This reflection phase characteristic is obtained when the metal pin 103 is omitted. As shown in the reflection phase characteristic, when h _EBG = 0.028λ ₀ , δ _G = 0.006λ ₀ , and W = 0.307λ ₀ , the reflection phase φ at the frequency f ₀ is about 0 degree. The frequency bandwidth at which the reflection phase φ is −90 to +90 degrees is 0.17f ₀ . The number of structural parameter combinations exhibiting similar characteristics is not limited to this, and there are innumerable numbers.

If the EBG unit cells 100 having the structural parameters that realize the reflection phase characteristics as described above are not periodically arranged, the reflection plate made of the EBG structure can obtain the magnetic wall characteristics with the best radiation efficiency. Can not.
The degree of freedom of periodic arrangement of the EBG unit cell 100 is improved by reducing the length W of one side of the metal patch 102, that is, by reducing the area of the EBG unit cell. And if the freedom degree of this periodic arrangement | positioning improves, it will become possible to give a various shape to a ground layer. However, since the conventional EBG structure needs to increase h _EBG as the length W of one side of the metal patch 102 is reduced, there is a problem that the low posture cannot be maintained.

  The present invention has been made in view of such circumstances, and an object of the present invention is to reduce the size of an EBG unit cell constituting an EBG structure while maintaining a low attitude and wideband characteristics, and to provide an antenna having a high degree of freedom in design. To provide an apparatus.

The present invention is an antenna device comprising an EBG structure formed by periodically arranging a plurality of EBG unit cells, and an antenna disposed on the EBG structure, wherein the EBG unit cell has a predetermined gap width. has a [delta] _G a dude periodically arranged so it is possible regular polygon of side length W1, a first metal patches spaced by a height h _EBG from ground layer, the side length W2 (< W1) having a positive 2n (n is 2, 3, 4...) Square shape, and a second metal patch disposed so as to symmetrically straddle the adjacent first metal patch. .

In an embodiment, the second metal patch is disposed at a position higher than the height h _EBG of the first metal patch. However, the second metal patch may be disposed at a position lower than the height h _EBG of the first metal patch.
In the embodiment, the first metal patch and the second metal patch are formed by metal foils adhered to one surface and the other surface of the dielectric substrate, respectively.

The height _{h EBG} of the first metal patches, it is desirable to set, for example, 0.02 [lambda] ₀ or more. Further, side length W1 of the first metal patch, for example, it is desirable to set the 0.2? ₀ or less.
In addition, for example, a dipole antenna is used as the antenna.

  According to the present invention, since the EBG unit cells constituting the EBG structure are reduced in size while maintaining a low profile and wideband characteristics, the degree of freedom of periodic arrangement of the EBG unit cells is improved, thereby allowing freedom of design. An antenna device having a high degree can be provided.

It is a top view which shows one structural example of the EBG unit cell which concerns on this invention. It is sectional drawing by the AA line of FIG. It is a graph which shows the reflection phase characteristic of an EBG unit cell. It is a top view of the EBG structure formed by N-stage periodic arrangement of EBG unit cells in a two-dimensional plane. It is a graph which shows the frequency characteristic of the reflection phase at the time of changing the arrangement | sequence number of an EBG unit cell. It is sectional drawing which shows embodiment of the antenna device which concerns on this invention comprised by arrange | positioning a dipole antenna on an EBG structure. 7 is a graph showing the VSWR characteristics of the antenna device of FIG. It is a top view which shows the periodic arrangement | sequence form of the EBG unit cell in the EBG structure using a square-shaped ground. It is a top view which shows the periodic arrangement | sequence form of the EBG unit cell in the EBG structure which uses a circular-shaped ground. It is a top view which shows the periodic arrangement | sequence form of the EBG unit cell in the EBG structure which uses a rectangular-shaped ground. It is a top view which shows the other structure of an EBG unit cell. It is sectional drawing which shows the structure of the EBG unit cell which has arrange | positioned the upper metal patch and lower metal patch which were shown in FIG. 2 reversely. It is a top view which shows the structure of the conventional EBG unit cell. It is sectional drawing by the BB line of FIG. It is a circuit diagram which shows the equivalent circuit of the conventional EBG unit cell. It is a graph which shows the reflection phase characteristic of the conventional EBG unit cell.

FIG. 1 is a plan view showing a configuration of a unit cell of an EBG structure used in an antenna device according to the present invention. FIG. 2 is a cross-sectional view taken along line AA in FIG.
The EBG unit cell 10 includes a square-shaped metal patch 12 having a side length W1 that is horizontally disposed in a portion separated from the ground layer 11 by a height h _EBG , and sides positioned on the sides of the metal patch 12. A square-shaped metal patch 13 having a length W2 (<W1).

The EBG structure is configured by periodically arranging such EBG unit cells 10 vertically and horizontally, that is, by periodically arranging them in a two-dimensional plane. In the EBG structure, so that the metal patch 12 of each unit cell 10 is closely arranged via a gap width [delta] _G.

As shown in FIG. 2, the metal patch 12 and the metal patch 13 are made of a metal foil (attached to the lower and upper surfaces of the dielectric substrate 14 having a relative dielectric constant ε _r (≧ 1) and a dielectric loss tangent tan δ (≧ 0) For example, copper foil). The metal patches 12 and 13 made of such metal foil can be formed by using a printed wiring pattern forming method. Since FIG. 1 is a perspective view assuming that the dielectric substrate 14 is transparent, the metal patch 12 is represented by a solid line.

  Since the metal patch 13 is provided symmetrically across the adjacent metal patch 12, the boundary line (see the alternate long and short dash line) of each EBG unit cell 10 is located on the center line. The metal patch 13 forms a stray capacitance with the metal patch 12. As will be described later, this stray capacitance contributes to a reduction in the area of the metal patch 12 of the EBG unit cell 10.

In this embodiment, referring to the parameter values of the conventional EBG unit cell, h _EBG = 0.028λ ₀ , δ _G = 0.006λ _0, and ε _r = 1, tan δ = 0, W1 = 0 .157λ ₀ and W 2 = 0.067λ ₀ . Here, λ ₀ is the wavelength of the center frequency f ₀ of the used frequency band.
The operation characteristics of the EBG unit cells 10 are analyzed under a periodic boundary condition (PBC) indicated by a one-dot chain line, that is, under a condition that they are arranged in an infinite period in a two-dimensional plane.

FIG. 3 shows the reflection phase characteristics of the EBG unit cell 10 in which the parameter values are set as described above. As shown in this characteristic diagram, the reflection phase φ at the use center frequency f ₀ is approximately 0 degrees, and the frequency bandwidth at which the reflection phase φ is −90 to +90 degrees is approximately 0.17 f ₀ . This reflection phase characteristic is equivalent to the reflection phase characteristic of the conventional EBG unit cell 100 shown in FIG.

The EBG unit cell 10 is the side length W1 of the metal patch 12 is 0.157Ramuda _0, conventional EBG unit cell 100 shown in FIG. 13, the side length W of the metal patch 102 is 0.307Ramuda ₀ . Therefore, according to the EBG unit cell 10 described above, although it has the same height (h _EBG = 0.028λ ₀ ) and reflection phase characteristics as those of the conventional EBG unit cell 100, it is 51% smaller (area ratio). , The size can be reduced by 26%, that is, about 1/4 of the area).
Such miniaturization is realized based on the stray capacitance formed by the metal patch 13. This is because the stray capacitance is decreased inductance component L ₂ in FIG. 15, that is, because that allows a reduction in area of the metal patch 12.

The value of the structural parameter in the EBG unit cell 10 is an example, and there are innumerable combinations of parameter values exhibiting similar characteristics. However, the height h _EBG of the metal patch 12 is set to 0.02λ ₀ ≦ h _EBG ≦ 0.1λ _{0 in} order to reduce the size of the EBG unit cell 10 while realizing both the low profile of the antenna and the broadband characteristics. selected in the range of, it is desirable to set the side length W1 of metal patches 12 in 0.2? ₀ or less. Further, the gap width δ _G needs to increase the inductor component (see L _{2 in} FIG. 15) of the metal patch 12 as the capacitor component (see C _{2 in} FIG. 15) generated by the gap width δ _G decreases. it is necessary to increase the area, is set to 0.012Ramuda ₀ or less, it is desirable to maximize the capacitor components.
Note that the metal patches 13 should not overlap each other. Therefore, in the above embodiment, it is set side lengths W2 of the metal patch 13 in the range of _{W2 <(W1 + δ G)} / 2.

FIG. 4 is a plan view of an EBG structure in which the EBG unit cells 10 are periodically arranged in N dimensions (N = 2 to ∞) in a two-dimensional plane. FIG. 5 shows frequency characteristics of the reflection phase φ when the number N of arrangement stages is changed.
As shown in FIG. 5, when N ≧ 16, substantially the same reflection phase characteristic as that of the infinite periodic structure is obtained. On the other hand, when N <16, the frequency at which the reflection phase φ becomes φ≈0 degrees increases as N decreases. In this case, to match the operating frequency f _0, it is necessary to perform an additional adjustment of the parameters of the unit cell 10.

FIG. 6 shows an embodiment of an antenna device according to the present invention. This antenna device has a configuration in which a dipole antenna 15 is disposed on an EBG structure configured using the EBG unit cell 10.
The antenna apparatus, for example when the height _{h A} of the dipole antenna 15 from the ground layer 11 is set to 0.043Ramuda _0, showing a VSWR (standing wave ratio) characteristic shown in FIG.
According to this antenna device, the frequency band where VSWR ≦ 2 is calculated as 13%. This indicates that good radiation characteristics can be obtained despite the low-profile configuration.

8 shows a periodic arrangement of unit cells 10 in an EBG structure having a square ground layer 11, FIG. 9 shows that in an EBG structure having a circular ground layer 11, and FIG. Each of them is shown in an EBG structure having a ground layer 11 having a shape.
Since the unit cell 10 configured in a small size has a high degree of freedom in periodic arrangement, even when the ground layer 11 has a complicated shape including a curve or the like, the unit cell 10 corresponds to the shape. Periodic arrangement is possible. Therefore, the antenna device of the present invention has a high degree of design freedom.

The present invention is not limited to the above-described embodiment, and may include various variations as shown below, for example.
(A) In the EBG unit cell 10 shown in FIG. 1, the square-shaped metal patch 12 is used. For example, the regular hexagonal metal patch 22 is used as in the EBG unit cell 20 shown in FIG. It is also possible.
In addition, what has the regular polygon shape which satisfy | fills the metal patch equivalent to the said metal patches 12 and 22 satisfy | filling the said gap width (delta) _G and being periodically arrangeable is applied. For example, those having a regular pentagon shape, when periodically arranged, it means that portion can not be maintained the gap width [delta] _G is present, that is, can not be applied since it can not satisfy the above conditions.
(B) The EBG unit cell 10 shown in FIG. 1 uses a square-shaped capacitor addition metal patch 13. However, this capacity-adding metal patch can be applied as long as it has a regular 2n (n is 2, 3, 4...) Square shape.
(C) In the EBG unit cell 10 shown in FIG. 2, the metal patch 13 is arranged above the metal patch 12. However, as shown in FIG. 12, the metal patch 13 is arranged below the metal patch 12. It is also possible.
(D) In the EBG unit cell 10 shown in FIG. 2, the dielectric substrate 14 is interposed between the metal patches 12 and 13, but air may be interposed between the metal patches 12 and 13. A vacuum may be applied between the patches 12 and 13.
(E) Although the metal pin for connecting the metal patch 12 to the ground layer 11 is omitted in the above embodiment, this metal pin may be provided as necessary.
(F) The antenna arranged on the EBG structure is not limited to the dipole antenna 15 shown as the embodiment, and another antenna such as a loop antenna may be arranged.

10,20 EBG unit cell 10
11 Ground Layer 12, 22 Metal Patch 13, 23 Metal Patch 14 Dielectric Substrate

Claims (5)

An antenna device comprising an EBG structure formed by periodically arranging a plurality of EBG unit cells, and an antenna disposed on the EBG structure, wherein the EBG unit cell comprises:
Has a regular polygonal shape with a predetermined gap width [delta] _G capable of periodically spaced side length W1, a first metal patches spaced by a height h _EBG from the ground layer,
A second metal having a positive 2n (n is 2, 3, 4...) Square shape having a side length W2 (<W1) and symmetrically straddling the adjacent first metal patch. Patches,
An antenna device comprising: The antenna device according to claim 1, wherein the second metal patch is disposed at a position higher than a height h _EBG h _EGB of the first metal patch.   The antenna device according to claim 1, wherein the first metal patch and the second metal patch are formed on one surface and the other surface of the dielectric substrate, respectively. The first metal patch is square, the height h _EBG of the first metal patch is set to 0.02λ ₀ or more, and the side length W1 of the first metal patch is set to 0.2λ ₀ or less. The antenna device according to claim 1.   The antenna apparatus according to claim 1, wherein the antenna is a dipole antenna.

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