JP2019050641A - Planar antenna and reduction method of coupling between antenna elements - Google Patents

Abstract

To provide a planar antenna capable of reducing coupling between antennas in the same frequency band without increasing an area of a planar antenna.SOLUTION: A planar antenna includes: a plurality of antenna elements connected with a ground in a DC manner and radiating an electromagnetic wave in the same frequency band; a general-purpose bus antenna element provided between the respective antenna elements.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for reducing coupling between a planar antenna and an antenna element.

In recent years, Multiple Input Multiple Output (MIMO) has been used to improve frequency utilization efficiency. A terminal that communicates according to this MIMO scheme is equipped with a plurality of antennas, and can communicate simultaneously using a plurality of channels between the terminal and the base station.
However, if the terminal has a plurality of antennas, there is a problem that the coupling between the antennas degrades the reception performance. For example, in the case of a terminal provided with two antennas, when the other antenna receives a signal transmitted from one antenna, the reception performance of the other antenna may be degraded. That is, the coupling between the antennas causes the correlation between the antennas to be high, which may lower the throughput of communication in the MIMO system.

For the reasons described above, it is preferable that the lower the coupling between the multiple antennas in the MIMO scheme, that is, the closer the correlation between the antennas is to "0".
In addition, it is possible to secure high antenna gain while the ground excitation type antenna has a low attitude. On the other hand, this ground excitation type antenna has a disadvantage that coupling between the antennas is likely to occur through the ground.

For this reason, there is a configuration in which coupling between the antennas is suppressed by providing a split-ring resonator (SRR; Split-ring resonator), which is a type of metamaterial structure, between the antennas (see, for example, Non-Patent Document 1).
Further, as a metamaterial structure, there is a configuration in which an electromagnetic band gap structure using a mushroom structure is provided between the antennas to suppress coupling between the antennas (for example, see Non-Patent Document 2).
That is, by absorbing the energy of the electromagnetic wave by the metamaterial structure, the propagation of the electromagnetic wave from one to the other can be suppressed between the antennas, and coupling between the antennas can be reduced.

Dimitra A. Ketzaki, Traianos V. Yioultsis; Metamaterial-Based Design of Planer Compact MIMO Monopoles, IEEE Trans. Antennas Propagation, Vol. 61, No. 5, pp. 2758-2766, May 2013. Ito Atsushi, Michishita Naofumi, Morishita Hisashi; Mutual coupling suppression method between inverted F antennas using mushroom structure, Transactions of IEICE. B, Communication J92-B, No. 6, pp. 930-937, 2009

However, when using a metamaterial structure such as the electromagnetic band gap structure described above, it is necessary to periodically arrange a plurality of cells of the metamaterial structure between antennas. For this reason, the area of an antenna substrate will increase by the increase in the arrangement area of a metamaterial structure. Therefore, it is impossible to achieve the original purpose of forming a plurality of antennas on one dielectric substrate and reducing the size of the antenna.
In addition, the design of the metamaterial structure requires complicated operations such as adjustment of the resonance frequency, and the design using a tool such as an electromagnetic field simulator is required, which requires a long processing time.

  The present invention has been made in view of these circumstances, and provides a planar antenna and a method of reducing coupling between antenna elements that can reduce coupling between antennas of the same frequency band without increasing the area of the planar antenna.

  In order to solve the problems described above, the planar antenna of the present invention is provided between a plurality of antenna elements connected in a direct current manner to the ground and emitting electromagnetic waves in the same frequency band, and each of the antenna elements. And a parasitic antenna element.

  The planar antenna of the present invention is a length of the parasitic antenna element having an inductive reactance with respect to the frequency band, and a capacitance of a gap capacitance formed by the reactance value and a gap between the antenna element. It is characterized in that a resonant frequency based on the value is the frequency band.

  In the planar antenna according to the present invention, the energy of the electromagnetic wave propagating through the ground between each of the antenna elements is reduced by the resonance of the parasitic antenna element in the frequency band of the radio wave emitted by the antenna element. It is characterized by

  In the planar antenna according to the present invention, a resonator corresponding to the frequency band of the antenna element is formed by forming the parasitic antenna element with a length that is an inductive reactance with respect to the frequency band of the antenna element. It is characterized by

  The planar antenna of the present invention is characterized in that the parasitic antenna element is formed in an L shape.

  In the planar antenna according to the present invention, in the L-shaped parasitic antenna element, another pattern is formed at a right angle to the one pattern than the width of the one pattern portion disposed between each of the antenna elements. It is characterized in that the width of the part is narrow.

  The planar antenna according to the present invention is characterized in that the length of the parasitic antenna element is λ / 4 to λ / 2 with respect to the wavelength λ of the frequency band.

  The planar antenna of the present invention is characterized in that the parasitic antenna element is formed along the outer peripheral portion of the antenna element.

  The planar antenna according to the present invention is characterized in that the parasitic antenna elements are provided separately to a plurality of sub parasitic antenna elements, and each of the sub parasitic antenna elements is coupled by a gap capacitance.

  The method for reducing coupling between antenna elements of the present invention is a method for reducing coupling between each of the antenna elements that radiates an electromagnetic wave in the same frequency band in a planar antenna consisting of a plurality of antenna elements connected DC to ground. A parasitic antenna element is disposed between each of the antenna elements, and the parasitic antenna element reduces coupling between each of the antenna elements.

  As described above, according to the present invention, by using a simple configuration in which a parasitic antenna element is inserted between antennas, a pattern connected to the ground is excited without increasing the area of the planar antenna. The energy of electromagnetic waves propagating from the antenna to the adjacent antenna via the ground can be reduced. Therefore, it is possible to reduce the coupling between the adjacent antennas more easily than suppressing the propagation of the electromagnetic wave using the metamaterial structure.

It is a top view showing an example of composition of a plane antenna formed as a MIMO antenna on a dielectric substrate by this embodiment of the present invention. It is a figure which shows the cross-section of the dielectric substrate 3 in FIG. It is a figure which shows the structural example of the parasitic monopole antenna 15 provided with respect to the antenna element 14 and the antenna element 14 in FIG. It is a figure which shows the structural example of the parasitic monopole antenna 21 provided with respect to the antenna element 11 and the antenna element 11 in FIG. It is a figure showing the result of electromagnetic field simulation which shows the effect at the time of providing a parasitic monopole antenna. It is a figure showing the result of electromagnetic field simulation which shows the effect at the time of providing a parasitic monopole antenna. Fig. 6 shows the level of coupling of each of the antenna elements 12, 14 and 16 corresponding to the 2.4 GHz frequency band. It is a figure which shows the level of each coupling | bonding of antenna element 11, 13 and 15 corresponding to the 5 GHz frequency band. It is a figure which shows the magnitude | size of the correlation between each antenna element in a MIMO antenna. It is a figure which shows the radiation characteristic of the antenna element whose frequency band in this embodiment is 2.4 GHz. It is a figure which shows the radiation characteristic of the antenna element whose frequency band in this embodiment is 5 GHz. It is a figure which shows the concept of coupling reduction between antenna elements by a parasitic antenna in a plane antenna of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing an example of the configuration of a planar antenna formed as a MIMO antenna on a dielectric substrate according to the present embodiment of the present invention. This FIG. 1 is a more specific example of the configuration of FIG. 12, which is a conceptual diagram of the basic configuration of a planar antenna (MIMO antenna) in the present invention described later, corresponding to the embodiment shown below.
The planar antenna 1 includes six antenna elements: an antenna element 11 formed on a dielectric substrate 3, an antenna element 12, an antenna element 13, an antenna element 14, an antenna element 15, and an antenna element 16. .
Each of antenna element 11, antenna element 13 and antenna element 15 is a 5 GHz band MIMO antenna. Each of the antenna element 12, the antenna element 14 and the antenna element 16 is a 2.4 GHz band MIMO antenna.

In the present embodiment, as described later, antenna elements of the same frequency band (the antenna element 11, the antenna element 13, the antenna element of the 5 GHz band of the antenna element 15, or an antenna for suppressing propagation of electromagnetic waves between the antenna elements A parasitic antenna element is provided between adjacent antenna elements which are the antenna elements of the element 12, the antenna element 14 and the 2.4 GHz band of the antenna element 16.
The parasitic antenna element may be any of a monopole antenna, a dipole antenna, and the like. That is, if the resonant frequency by the capacitance value of the gap capacitance in capacitive coupling between the antenna element and the parasitic antenna element and the inductive reactance of the parasitic antenna is configured to be the frequency band of the antenna element, A parasitic antenna element of any type or shape may be used. In the present embodiment, a monopole antenna (parasitic monopole antenna) is used as an example of the parasitic antenna element as described below.

A parasitic monopole antenna 21 is provided between the antenna element 11 and the antenna element 13. The parasitic monopole antenna 21 suppresses the propagation of electromagnetic waves between the antenna element 11 and the antenna element 13, and reduces the coupling between the antenna element 11 and the antenna element 13.
A parasitic monopole antenna 23 is provided between the antenna element 13 and the antenna element 15. The parasitic monopole antenna 23 suppresses the propagation of an electromagnetic wave from the antenna element 13 to the antenna element 15 and reduces the coupling between the antenna element 13 and the antenna element 15.
A parasitic monopole antenna 25 is provided between the antenna element 13 and the antenna element 15. The parasitic monopole antenna 25 suppresses the propagation of an electromagnetic wave from the antenna element 15 to the antenna element 13 and reduces the coupling between the antenna element 13 and the antenna element 15. Here, the case where the parasitic monopole antenna 23 and the parasitic monopole antenna 25 are provided between the antenna element 13 and the antenna element 15 is illustrated. The distance between the antenna element 13 and the parasitic monopole antenna 23 is shorter than the distance between the antenna element 13 and the parasitic monopole antenna 25. Further, the distance between the antenna element 15 and the parasitic monopole antenna 25 is shorter than the distance between the antenna element 15 and the parasitic monopole antenna 23.

In addition, a parasitic monopole antenna 22 is provided between the antenna element 12 and the antenna element 14. The parasitic monopole antenna 22 suppresses the propagation of electromagnetic waves from the antenna element 12 to the antenna element 14 and reduces the coupling between the antenna element 12 and the antenna element 14.
In addition, a parasitic monopole antenna 24 is provided between the antenna element 12 and the antenna element 14. The parasitic monopole antenna 24 suppresses the propagation of electromagnetic waves from the antenna element 14 to the antenna element 12 and reduces the coupling between the antenna element 12 and the antenna element 14.
A parasitic monopole antenna 26 is provided between the antenna element 12 and the antenna element 16. The parasitic monopole antenna 26 suppresses the propagation of electromagnetic waves between the antenna element 12 and the antenna element 16 and reduces the coupling between the antenna element 12 and the antenna element 16. Here, the case where the parasitic monopole antenna 24 and the parasitic monopole antenna 22 are provided between the antenna element 14 and the antenna element 12 is illustrated. The distance between the antenna element 14 and the parasitic monopole antenna 24 is shorter than the distance between the antenna element 14 and the parasitic monopole antenna 22. Further, the distance between the antenna element 12 and the parasitic monopole antenna 22 is shorter than the distance between the antenna element 12 and the parasitic monopole antenna 24.

In FIG. 1, three antenna elements are provided corresponding to 3 × 3 MIMO for a frequency band of 2.4 GHz. Similarly, for the 5 GHz frequency band, three antenna elements are provided corresponding to 3 × 3 MIMO. However, two antenna elements may be provided corresponding to 2 × 2 MIMO in each of the frequency band 2.4 GHz and the frequency band 2.4 GHz.
Furthermore, in the case of 1 × 1 where one antenna element with a frequency band of 2.4 GHz and one antenna element with a frequency band of 5 GHz are present, decoupling between two antenna elements of the same frequency due to the parasitic monopole antenna described above There is no need to do. In this case, in the case of 1 × 1, the parasitic monopole antenna functions to suppress the spread of the high frequency current due to the propagation of the electromagnetic wave at the ground (layer 33 in FIG. 2) in the dielectric substrate 3.

  FIG. 2 is a view showing a cross-sectional structure of dielectric substrate 3 in FIG. The dielectric substrate 3 in the present embodiment includes a layer 31, a layer 32, a layer 33, a reinforcing dielectric layer 34, and a core substrate 35. That is, on the surface of the core substrate 35, for example, a layer 32 made of copper foil and having a thickness of 35 μm is formed. On the back surface of the core substrate 35, for example, a layer 33 made of copper foil and having a thickness of 35 μm is formed. On the surface of the layer 32, a reinforced dielectric layer 34 as a prepreg is formed. On the surface of the reinforcing dielectric layer 34, for example, a layer 31 made of copper foil and having a thickness of 35 μm is formed. The reinforcing dielectric layer 34 has, for example, a relative dielectric constant of 4.3 and a thickness of 0.2 mm. The core substrate 35 has, for example, a relative dielectric constant of 4.3 and a thickness of 0.4 mm.

  Another layer may be further added to the back surface of the layer 33. In the present embodiment, each of the antenna elements 11 to 16 is formed by patterning the copper foil of the layer 31 with the layer 33 as a reference plane, that is, a ground plane. From the antenna element 11 to each of the antenna elements 16, feeding for radiating electromagnetic waves is performed from the layer 31. In addition, the copper foil of the layer 32 is removed on the entire surface.

FIG. 3 is a view showing a configuration example of the antenna element 14 and the parasitic monopole antenna 24 provided for the antenna element 14 in FIG. In FIG. 3, the three elements of antenna element 12, antenna element 14 and antenna element 16 shown in FIG. 1 have substantially the same configuration. Therefore, the configuration of the antenna element 14 will be described from FIG.
The antenna element 14 has an outer dimension of 34.5 mm (Y-axis direction in FIG. 1) × 11 mm (X-axis direction in FIG. 1) of the main element (area A part) that emits an electromagnetic field.
The antenna element 14 is connected to the element pattern 142R and the element pattern 142L from the feeding point 141 via the feeding pattern 143. Further, one end of the element pattern 142R is connected to the feed pattern 143, and the other end is connected to one end of the element pattern 142RC.

  One end of the element pattern 142L is connected to the feed pattern 143, and the other end is connected to one end of the element pattern 142LC. Each of the element pattern 142RC and the element pattern 142LC is connected to the layer 33 in FIG. A plurality of via holes 144 are provided at substantially equal intervals from one end to the other end of the element pattern 142RC. Similarly, a plurality of via holes 144 are provided at substantially equal intervals from one end of the element pattern 142LC to the other end. The ground pad 140 is connected to the layer 33 by a via hole 145. The ground pad 140 is provided in the vicinity of the feeding point 141.

The parasitic monopole antenna 24 is a resonator having a resonance frequency of 2.4 GHz which is a frequency band of the antenna element 14.
For this reason, the parasitic monopole antenna 24 needs to be formed to a length such that the characteristic becomes inductive reactance. Therefore, when the wavelength of the antenna element 14 is λ _L , the length of the parasitic monopole antenna 24 needs to be longer than λ _L / 4 and shorter than λ _L / 2. In this embodiment, the length is 1.3 times to 1.5 times λ _L / 4, and is approximately λ _L / 3. The parasitic monopole antenna 24 may have a bent shape as long as the characteristic is an inductive reactance as described above.

In FIG. 3, the antenna element 24 is configured to include an antenna element 241 and an antenna element 242 on the basis of the bent position. Assuming that the frequency band of the antenna element 14 is 2.4 GHz and the wavelength reduction ratio is 70%, λ _L is 85.4 mm. Therefore, the length of the parasitic monopole antenna 24 is 29.5 mm, which is the sum of the length 16 mm of the antenna pattern 241 and the length 13.5 mm of the antenna pattern 242. The length 29.5 mm obtained by adding the antenna pattern 241 and the antenna pattern 242 corresponds to about λ _L /2.9.

Further, the parasitic monopole antenna 24 is provided in the vicinity of the antenna element 14 between other antenna elements (the antenna element 12 in FIG. 1) of the same frequency band. The parasitic monopole antenna 24 is L-shaped, and the antenna pattern 241 is connected to the antenna pattern 242 at a right angle. The antenna pattern 241 has a width of 0.5 mm, and the antenna pattern 242 has a width of 1 mm.
The antenna pattern 241 in the parasitic monopole antenna 24 is provided such that the long side is parallel to the long side of the antenna element 142LC. The distance of the gap between the antenna pattern 241 and the antenna element 142LC is set by a numerical value of λ _L / 40 or less.

For example, the distance between the antenna pattern 241 and the antenna element 142LC in FIG. 3 is 1.5 mm, which is about λ _L / 60 (actually λ _L / 57). The distance of this gap is set between the antenna pattern 241 and the antenna pattern 142LC such that sufficient capacitive coupling can be obtained. That is, the antenna pattern 241 and the antenna pattern 142LC are AC-connected by capacitive coupling. Then, the resonant frequency by the capacitance value of the gap capacitance in the capacitive coupling of the gap and the inductive reactance of the parasitic monopole antenna 24 is set to a numerical value that is the frequency band of the antenna element 14.

  The antenna pattern 241 is disposed in parallel to the side facing the element pattern 142L. Further, each of the antenna pattern 241 and the antenna pattern 242 is set to a predetermined width, but the width is set to be narrow in order to reduce, for example, the capacitive coupling to the layer 33 in FIG. On the other hand, the antenna pattern 241 has a width of 1.0 mm, and the antenna pattern 242 has a width of 0.5 mm.

FIG. 4 is a view showing a configuration example of the antenna element 11 and the parasitic monopole antenna 21 provided for the antenna element 11 in FIG. In FIG. 4, the three elements of antenna element 11, antenna element 13 and antenna element 15 shown in FIG. 1 have substantially the same configuration. For this reason, the configuration of the antenna element 11 will be described as a representative of the MIMO antenna configured from these.
The antenna element 11 has an outer dimension of 16 mm (Y-axis direction in FIG. 1) × 11 mm (X-axis direction in FIG. 1) of the main element (area B part) that emits an electromagnetic field.

  The antenna element 11 is connected to the element pattern 112R and the element pattern 112L from the feeding point 111 via the feeding pattern 113. Further, one end of the element pattern 112R is connected to the feed pattern 113, and the other end is connected to one end of the element pattern 112RP. The other end of the element pattern 112RP is connected to one end of the element pattern 112RC. The element pattern 112RC is connected to the element pattern 112RP at a right angle.

  Further, one end of the element pattern 112L is connected to the feed pattern 113, and the other end is connected to one end of the element pattern 112LP. The other end of the element pattern 112LP is connected to the element pattern 112LC. The element pattern 112LC is connected at a right angle to the element pattern 112LP. Further, each of the element pattern 112 RC and the element pattern 112 LC is connected to the layer 33 in FIG. 2 by the via hole 114. The plurality of via holes 114 are provided at substantially equal intervals from one end to the other end of the element pattern 112 RC. Similarly, a plurality of via holes 144 are provided at substantially equal intervals from one end of the element pattern 112LC to the other end. The ground pad 110 is connected to the layer 33 by a via hole 115. The ground pad 110 is provided in the vicinity of the feeding point 111.

The parasitic monopole antenna 21 is a resonator having a resonance frequency of 5 GHz which is a frequency band of the antenna element 11.
For this reason, the parasitic monopole antenna 21 needs to be formed to a length such that the characteristic becomes inductive reactance. Therefore, assuming that the wavelength of the antenna element 11 is λ _H , the length of the parasitic monopole antenna 21 needs to be longer than λ _H / 4 and shorter than λ _H / 2. In this embodiment, the length is 1.3 times to 1.5 times λ _H / 4, and is approximately λ _H /2.8. The parasitic monopole antenna 21 may have a bent shape as long as the characteristic is an inductive reactance as described above.

In FIG. 4, the antenna element 24 is configured to include an antenna element 241 and an antenna element 242 on the basis of the bent position. Assuming that the frequency band of the antenna element 11 is 5 GHz and the wavelength reduction rate is 70%, λ _H = 38.5 mm. Therefore, the length of the parasitic monopole antenna 21 is 14 mm, which is the sum of the length 7 mm of the antenna pattern 211 and the length 7 mm of the antenna pattern 212. A length of 14 mm obtained by adding the antenna pattern 211 and the antenna pattern 212 corresponds to about λ _H /2.8.

  Further, the parasitic monopole antenna 21 is provided in the vicinity of the antenna element 11 between other antenna elements (the antenna element 13 in FIG. 1) of the same frequency band. The parasitic monopole antenna 21 is L-shaped, and the antenna pattern 212 is connected to the antenna pattern 211 at a right angle. For example, the antenna pattern 211 has a width of 0.5 mm, and the antenna pattern 212 has a width of 1 mm.

The antenna pattern 212 in the parasitic monopole antenna 21 is provided such that the long side is parallel to the long side of the element pattern 112LP. The antenna pattern 211 in the parasitic monopole antenna 21 is provided such that the long side is parallel to the long side of the element pattern 112LC. The distance of the gap between the antenna pattern 211 and the element pattern 112 LC is set to λ _L / 40 or less.

For example, the distance between the antenna pattern 211 and the element pattern 112LC in FIG. 4 is 0.5 mm, which is about λ _H / 60 (λ _H / 77 in FIG. 4). The distance of this gap is set between the antenna pattern 211 and the element pattern 112 LC so that sufficient capacitive coupling can be obtained. The antenna pattern 211 and the element pattern 112 LC are AC-connected by capacitive coupling. Then, the resonant frequency by the capacitance value of the gap capacitance in the capacitive coupling of the gap and the inductive reactance of the parasitic monopole antenna 21 is set to a numerical value that is the frequency band of the antenna element 11.
Further, each of the antenna pattern 211 and the antenna pattern 212 is set to have a predetermined width, but the width is set to be narrow in order to reduce, for example, the capacitive coupling to the layer 33 in FIG. On the other hand, the antenna pattern 212 has a width of 1.0 mm, and the antenna pattern 211 has a width of 0.5 mm.

  FIG. 5 is a diagram showing the result of electromagnetic field simulation showing the effect in the case of providing a parasitic monopole antenna. FIG. 5 shows the influence of the antenna element 12 on the antenna element 14 when the antenna element 12 in the 2.4 GHz frequency band is excited to emit an electromagnetic wave. FIG. 5 shows the intensity of the current density distribution when the brightness of the region is excited, and the current density distribution is increased and the brightness is increased also when resonated by the electromagnetic waves of other antenna elements. Therefore, the brighter the area of the unexcited antenna element, the greater the extent to which the other excited antenna elements radiate and resonate with the electromagnetic waves propagating on the ground (layer 33 in FIG. 2).

FIG. 5A shows the result of electromagnetic field simulation in the case where the parasitic monopole antenna 22 is not provided between the antenna element 12 and the antenna element 14.
In FIG. 5A, the area near the antenna element 14 is brighter than the area near the antenna element 16 of the other same frequency band. Thereby, it can be seen that the electromagnetic wave of the antenna element 12 propagates to the antenna element 14 via the layer 33, and the antenna element 14 resonates with the electromagnetic wave emitted by the antenna element 12.

On the other hand, FIG. 5B shows the result of electromagnetic field simulation in the case where the parasitic monopole antenna 22 is provided between the antenna element 12 and the antenna element 14.
In FIG. 5B, the area near the antenna element 14 is less bright than the area near the antenna element 14 of FIG. 5A. Thus, it can be seen that the parasitic monopole antenna 22 suppresses the propagation of the electromagnetic wave emitted by the antenna element 12 to the antenna element 14 via the ground (layer 33 in FIG. 2). That is, it can be seen that the antenna element 14 does not resonate with the electromagnetic wave emitted by the antenna element 12.
Further, in FIG. 5B, the region near the parasitic monopole antenna 22 is in a very bright state, resonates with the electromagnetic wave emitted by the antenna element 12, and the ground efficiently (layer of FIG. 2). It can be seen that the energy of the electromagnetic wave propagating in 33) is absorbed.

  FIG. 6 is a diagram showing the result of electromagnetic field simulation showing the effect when a parasitic monopole antenna is provided. FIG. 6 shows the influence of the antenna element 13 on the antenna element 15 when the antenna element 13 in the 5 GHz frequency band is excited to emit an electromagnetic wave. Also in FIG. 6, similarly to FIG. 5, the intensity of the current density distribution when the brightness of the region is excited is shown, and the current density distribution becomes high even when resonated by the electromagnetic waves of other antenna elements, and the brightness is Increase. Therefore, the brighter the area of the unexcited antenna element, the greater the extent to which the other excited antenna elements radiate and resonate with the electromagnetic waves propagating through the ground (layer 33 in FIG. 2).

FIG. 6A shows the result of electromagnetic field simulation in the case where the parasitic monopole antenna 23 is not provided between the antenna element 13 and the antenna element 15.
In FIG. 6A, the area near the antenna element 15 is brighter than the area near the antenna element 11 of the other same frequency band. Thereby, it can be seen that the electromagnetic wave of the antenna element 13 propagates to the antenna element 15 through the layer 33, and the antenna element 15 resonates with the electromagnetic wave emitted by the antenna element 13.

On the other hand, FIG. 6B shows the result of the electromagnetic field simulation in the case of providing the parasitic monopole antenna 23 between the antenna element 13 and the antenna element 15.
In FIG. 6B, the area near the antenna element 15 is less bright than the area near the antenna element 15 of FIG. Thus, it can be seen that the parasitic monopole antenna 23 suppresses the propagation of the electromagnetic wave emitted by the antenna element 13 to the antenna element 15 through the layer 33. That is, it can be seen that the antenna element 15 does not resonate with the electromagnetic wave emitted by the antenna element 13.
Further, in FIG. 6B, the region in the vicinity of the parasitic monopole antenna 23 is in a very bright state, and as in the case of FIG. 5B, resonance occurs with the electromagnetic wave emitted by the antenna element 13. It can be seen that the energy of electromagnetic breakdown propagating efficiently through the ground (layer 33 in FIG. 2) is absorbed.

FIG. 7 illustrates the level of coupling of each of the antenna elements 12, 14 and 16 corresponding to the 2.4 GHz frequency band. In FIG. 7, | S ₄₂ | indicates a level indicating the degree of coupling between the antenna element 12 and the antenna element 14 (hereinafter referred to as “coupling level”). In addition, | S ₆₂ | indicates the coupling level of the antenna element 12 and the antenna element 16. | S ₆₄ | indicates the coupling level of the antenna element 14 and the antenna element 16.
FIG. 7A shows the level of coupling of each of the antenna elements 12, 14 and 16 when no parasitic monopole antenna is disposed between each of the antenna elements 12, 14 and 16. FIG. In FIG. 7A, the horizontal axis represents frequency, and the vertical axis represents coupling level (dB). | _{S 42} | is shown in solid lines, _{| S 62} | is shown in broken lines, _{| S 64} | is indicated by a dotted line.
It can be seen that the coupling level of each of | S ₄₂ |, | S ₆₂ | and | S ₆₄ | is greater than −20 dB near a frequency of 2.4 GHz. In particular, the coupling level of | S42 | is as high as -14 dB. This is because the distance between the antenna elements 12 and 14 is closer than the distance between the antenna elements 12 and 16 and the distance between the antenna elements 14 and 16, so the energy of the propagating electromagnetic wave is strong.

FIG. 7 (b) shows the level of coupling of each of the antenna elements 12, 14 and 16 when a parasitic monopole antenna is disposed between each of the antenna elements 12, 14 and 16. In FIG. 7 (b), the horizontal axis represents frequency, and the vertical axis represents coupling level (dB). | _{S 42} | is shown in solid lines, _{| S 62} | is shown in broken lines, _{| S 64} | is indicated by a dotted line.
It can be seen that the coupling level of each of | S ₄₂ |, | S ₆₂ | and | S ₆₄ | is smaller than −22 dB near a frequency of 2.4 GHz. In particular, it can be seen that the coupling level of | S ₄₂ | is greatly reduced to −25 dB from about −14 dB in FIG. 7A. Also for the other | S ₆₂ | and | S ₆₄ |, it can be seen that the binding level is lowered as compared with the case of FIG. 7 (a). Thus, it can be seen that by arranging parasitic monopole antennas between each of the antenna elements 12, 14 and 16, the coupling level of each of the antenna elements 12, 14 and 16 is reduced.

FIG. 8 is a diagram showing the level of coupling of each of the antenna elements 11, 13 and 15 corresponding to the 5 GHz frequency band. In FIG. 8, | S ₃₁ | indicates a level (hereinafter referred to as a coupling level) indicating the degree of coupling between the antenna element 11 and the antenna element 13. Further, | S ₅₁ | represents the coupling level of the antenna element 11 and the antenna element 15. | S ₅₃ | indicates the coupling level of the antenna element 13 and the antenna element 15. | _{S 31} | is shown in solid lines, _{| S 51} | is shown in broken lines, _{| S 53} | is indicated by a dotted line.
FIG. 8A shows the level of coupling of each of the antenna elements 11, 13 and 15 when no parasitic monopole antenna is disposed between each of the antenna elements 11, 13 and 15. FIG. In FIG. 8A, the horizontal axis represents frequency, and the vertical axis represents coupling level (dB).
It can be seen that the coupling level of | S ₅₃ | is approximately −8.5 dB near a frequency of 5 GHz. This is because the distance between the antenna elements 13 and 15 is closer than the distance between the antenna elements 11 and 13 and the distance between the antenna elements 11 and 15, so the energy of the propagating electromagnetic wave is strong.

FIG. 8 (b) shows the level of coupling of each of the antenna elements 11, 13 and 15 when a parasitic monopole antenna is disposed between each of the antenna elements 11, 13 and 15. In FIG. 8 (b), the horizontal axis represents frequency, and the vertical axis represents coupling level (dB). | _{S 31} | is shown in solid lines, _{| S 51} | is shown in broken lines, _{| S 53} | is indicated by a dotted line.
It can be seen that the coupling level of each of | S ₃₁ | and | S ₅₁ | is almost unchanged from that in the case of FIG. 8A in the vicinity of the frequency of 5 GHz. Also, the coupling level of | S ₅₃ | is reduced from about −10 dB in FIG. 8A to about −22 dB, which is the lowest value, and it can be seen that the coupling level is improved by about 13.5 dB. . Thus, it can be seen that by arranging parasitic monopole antennas between each of the antenna elements 11, 13 and 15, the coupling level of each of the antenna elements 11, 13 and 15 is reduced.

FIG. 9 is a diagram showing the magnitude of the correlation between each antenna element in the MIMO antenna. An envelope correlation coefficient represented by the following equation (1) is known as a method of representing the correlation between antenna elements in a MIMO antenna. The higher the envelope correlation coefficient, the higher the correlation between the antenna elements. In FIG. 9, “without PM” indicates a curve indicating the relationship between the frequency and the envelope correlation coefficient when parasitic monopole antennas are not provided between the antenna elements that are being correlated. Also, “with PM” indicates a curve showing the relationship with the envelope correlation coefficient when the parasitic monopole antenna is provided between the antenna elements that are looking at correlation.
In the following equation (1), | ρ _ij | is an envelope correlation coefficient. S _ii indicates the input impedance of the antenna element i. S _ij indicates the degree of coupling from antenna element j to antenna element i. Also, * means conjugate complex number.

FIG. 9 (a) shows the envelope correlation coefficient | | _ij | between each of the antenna elements 12, 14 and 16 in the 2.4 GHz frequency band. In FIG. 9A, the horizontal axis indicates the frequency, and the vertical axis indicates the envelope correlation coefficient.
| Ρ ₄₂ | represents an envelope correlation coefficient indicating the correlation from the antenna element 12 to the antenna element 14. | Ρ ₆₂ | indicates an envelope correlation coefficient indicating a correlation from the antenna element 12 to the antenna element 16. | Ρ ₆₄ | indicates an envelope correlation coefficient indicating a correlation from the antenna element 14 to the antenna element 16. | [Rho ₄₂ | is shown in solid lines, | ρ ₆₂ | is shown in broken lines, | ρ ₆₄ | is indicated by a dotted line.

Also, thin lines show cases where parasitic monopole antennas are not provided between antenna elements, and thick lines show cases where parasitic monopole antennas are provided between antenna elements.
In the 2.4 GHz frequency band, it can be seen that each of | ρ ₄₂ |, | ρ ₆₂ | and | ρ ₆₄ | is lowered to near zero by providing a parasitic monopole antenna between the antenna elements.

FIG. 9 (b) shows the envelope correlation coefficient | ρ _ij | between each of the antenna elements 11, 13 and 15 in the 5 GHz frequency band. In FIG. 9B, the horizontal axis indicates the frequency, and the vertical axis indicates the envelope correlation coefficient.
| Ρ ₃₁ | indicates an envelope correlation coefficient indicating the correlation from the antenna element 11 to the antenna element 13. | Ρ ₅₁ | indicates an envelope correlation coefficient indicating a correlation from the antenna element 11 to the antenna element 15. | Ρ _{53 |} indicates an envelope correlation coefficient indicating a correlation from the antenna element 13 to the antenna element 15. | [Rho ₃₁ | is shown in solid lines, | ρ ₅₁ | is shown in broken lines, | ρ ₅₃ | is indicated by a dotted line.

Also, thin lines indicate cases where parasitic monopole antennas are not provided between antenna elements, and thick lines indicate cases where parasitic monopole antennas are provided between antenna elements.
In the 5 GHz frequency band, each of | ρ ₃₁ | and | ρ ₅₁ | does not change so much. However, by providing the parasitic monopole antenna 23 between the antenna element 13 and the antenna element 15, the | ρ ₅₃ | is greatly reduced and a great improvement can be seen.

FIG. 10 is a diagram showing the radiation characteristic of the antenna element whose frequency band is 2.4 GHz in the present embodiment. FIG. 10 shows the radiation directivity characteristic in the XZ plane, where the radius indicates the gain of the antenna element and the angle indicates the radiation direction.
FIG. 10A shows the radiation directivity characteristic of the antenna element 14. FIG. 10 (b) shows the radiation directivity characteristic of the antenna element 12. FIG. 10C shows the radiation directivity characteristic of the antenna element 16.
Although the plane that provides the maximum gain differs depending on the antenna element, the maximum gain of each antenna element is about 2 dBi. For this reason, each of the 2.4 GHz antenna elements 12, 14 and 16 in the present embodiment includes sufficient characteristics for achieving MIMO performance, including the values of the envelope correlation coefficient in FIG. 9 (a). It comprises the antenna element array which it had.

FIG. 11 is a diagram showing the radiation characteristics of the antenna element whose frequency band is 5 GHz in the present embodiment. Similar to FIG. 10, FIG. 11 shows the radiation directivity characteristic in the XZ plane, where the radius of the radius indicates the gain of the antenna element, and the angle indicates the radiation direction.
FIG. 11A shows the radiation directivity characteristic of the antenna element 11. FIG. 11 (b) shows the radiation directivity characteristic of the antenna element 13. FIG. 11 (c) shows the radiation directivity characteristic of the antenna element 15.
As in the case of FIG. 10, although the plane of maximum gain differs depending on the antenna element, the maximum gain of each antenna element is about 2 dBi. For this reason, each of the antenna elements 11, 13 and 15 of 5 GHz in the present embodiment has sufficient characteristics for exerting MIMO performance including the numerical value of the envelope correlation coefficient of FIG. 9 (b). An antenna element array is configured.

  As described above, in the present embodiment, a parasitic monopole antenna is inserted between antenna elements. Thereby, according to the present embodiment, the energy of the electromagnetic wave propagating through the ground from the antenna element exciting the pattern connected to the ground to the other adjacent antenna element is reduced, and the coupling between the antenna elements is performed. A reduction can be made. Moreover, according to the present embodiment, the design is simpler and the adjustment of the wavelength corresponding to the resonance frequency and the decoupling to the antenna element are simpler than the configuration in which the energy of the electromagnetic wave between the antenna elements is reduced using the metamaterial. By using a parasitic monopole antenna whose frequency is easily corrected, it is possible to easily reduce coupling between adjacent antennas. Further, according to the present embodiment, since the area of the parasitic monopole antenna is smaller than that of the metamaterial, the area formed by the MIMO antenna does not increase without taking an extra occupied area.

Also, the parasitic monopole antenna in the present embodiment may be provided separately to a plurality of sub-parasitic monopole antennas. Adjacent sub-parasitic monopole antennas are coupled (capacitively coupled) by the gap capacitance between the sub-parasitic monopole antennas to form an element having an electrical length sufficient for high frequency.
In addition, the antenna element in the present embodiment may be changed to SRR (Split Ring Resonator). That is, the present invention can be applied to a type of antenna that uses ground as a part of high frequency current return and radiation element, that is, to reduce coupling between antennas of the same frequency band having a structure that electromagnetic waves easily propagate to ground. It is.
Moreover, in this embodiment, although the case where a parasitic antenna element (parasitic monopole antenna) was L-shaped was demonstrated, you may form as a linear or curvilinear shape.
In the present embodiment, the parasitic antenna element (parasitic monopole antenna) may be formed along the element pattern in the outer peripheral portion of the antenna element. In addition, when the parasitic antenna element (parasitic monopole antenna) is linear, it may be disposed parallel to the antenna element.

  FIG. 12 is a view showing a concept of coupling reduction between antenna elements by a parasitic antenna in the planar antenna of the present invention. FIG. 12 shows a planar antenna configured of an antenna element 101 and an antenna element 102 (a plurality of antenna elements) formed on the surface 3S (one surface of the dielectric substrate) of the dielectric substrate 3 (dielectric substrate). , In a plan view. Each of an antenna element 101 and an antenna element 102 (a plurality of antenna elements) including an element pattern (element pattern) is formed on the surface 3S (one surface of the dielectric substrate) of the dielectric substrate 3 (dielectric substrate) ing. Each of the antenna element 101 and the antenna element 102 (a plurality of antenna elements) is connected to the ground in a direct-current manner (connection point not shown). In addition, each of the antenna element 101 and the antenna element 102 (a plurality of antenna elements) emits an electromagnetic wave of the same frequency band by excitation.

A parasitic antenna element 103 (a parasitic antenna element) is formed on the surface 3S of the dielectric substrate 3 between each of the antenna element 101 and the antenna element 102 (a plurality of antenna elements). The parasitic antenna element 103 (paramagnetic antenna element) is AC-connected to one or both of the antenna element 101 and the antenna element 102 (a plurality of antenna elements) by capacitive coupling.
Here, the capacitance value of the gap capacitance and the parasitic antenna element in the capacitive coupling between the parasitic antenna element 103 (parasitic antenna element) and either or both of the antenna element 101 and the antenna element 102 (a plurality of antenna elements) It is assumed that the resonant frequency due to the inductive reactance of 103 (a parasitic antenna element) is a frequency band of the electromagnetic wave emitted by each of the antenna element 101 and the antenna element 102 (a plurality of antenna elements). A feeding antenna element is configured.

  As a result, the non-feeding antenna element 103 (non-feeding antenna element) resonates with the electromagnetic wave radiated by either or both of the antenna element 101 and the antenna element 101 (plural antenna elements), whereby the antenna element 101 and the antenna element The antenna element 101 and the antenna element 102 (a plurality of antenna elements) efficiently absorb the energy of an electromagnetic breakdown propagating through a ground layer (not shown) to which each of the plurality 102 (a plurality of antenna elements) is connected in a DC manner. Coupling of electromagnetic waves in the same frequency band).

Hereinafter, other configurations of the present invention will be described.
Another configuration of the present invention is a dielectric substrate and an element pattern provided on one surface of the dielectric substrate and connected to a ground in a direct-current manner, and electromagnetic waves are transmitted in the same frequency band It comprises: a plurality of antenna elements for exciting and radiating an element pattern; and a parasitic antenna element which is a pattern which is provided between the antenna elements and is AC connected to the element pattern in a capacitive coupling manner. It features.
Further, according to another structure of the present invention, in a planar antenna provided on one surface of a dielectric substrate and formed from an element pattern connected in a direct current manner to the ground, the electromagnetic waves are transmitted in the same frequency band. A method for reducing coupling between a plurality of antenna elements that excites and radiates an element pattern, and arranges a parasitic antenna element that is a pattern that is AC connected to the element pattern in a capacitive coupling manner, The antenna elements reduce the coupling between the antenna elements.

  DESCRIPTION OF SYMBOLS 1 ... planar antenna 3 ... dielectric substrate 11, 12, 13, 14, 15, 16 ... antenna element 21, 22, 23, 24, 25, 26 ... parasitic monopole antenna 31, 32, 33 ... layer 34 ... reinforcement dielectric Body layer 35: Core substrate 110, 140: Ground pad 111, 141: Feed point 112R, 112L, 112LC, 112LP, 112RC, 112RP, 142L, 142R, 142LC, 142RC ... Element pattern 113, 143: Feed pattern 211, 212, 241, 242 ... antenna pattern

Claims (10)

A plurality of antenna elements connected in a direct current manner to the ground and emitting electromagnetic waves in the same frequency band;
A planar antenna comprising: parasitic antenna elements provided between each of the antenna elements. The resonant antenna element has a length having an inductive reactance with respect to the frequency band, and a resonant frequency by the reactance value and a capacitance value of a gap capacitance formed by a gap between the antenna elements is It is a frequency band. The flat antenna according to claim 1 characterized by things. The parasitic antenna element resonates in a frequency band of a radio wave emitted by the antenna element to reduce energy of an electromagnetic wave propagating through the ground between each of the antenna elements. The planar antenna according to Item 2. By forming the parasitic antenna element with a length to be an inductive reactance with respect to the frequency band of the antenna element, a resonator corresponding to the frequency band of the antenna element is characterized. The planar antenna according to claim 2 or claim 3. The planar antenna according to any one of claims 1 to 4, wherein the parasitic antenna element is formed in an L shape. In the L-shaped parasitic antenna element, the width of the other pattern portion formed perpendicular to the one pattern is narrower than the width of the one pattern portion disposed between each of the antenna elements. The planar antenna according to claim 5, characterized in that: The plane according to any one of claims 1 to 6, wherein the length of the parasitic antenna element is λ / 4 to λ / 2 with respect to the wavelength λ of the frequency band. antenna. The planar antenna according to any one of claims 1 to 6, wherein the parasitic antenna element is formed along an outer peripheral portion of the antenna element. The parasitic antenna element is
9. The plurality of sub parasitic antenna elements are provided separately, and each of the sub parasitic antenna elements is coupled by a gap capacitance. Flat antenna. A planar antenna comprising a plurality of antenna elements connected in a direct current manner to a ground, wherein the method of reducing coupling between each of the antenna elements that radiates an electromagnetic wave in the same frequency band,
A method of reducing coupling between antenna elements, comprising: arranging parasitic antenna elements between each of the antenna elements; and reducing coupling between each of the antenna elements by the parasitic antenna elements.