JP2014042142A - Antenna unit - Google Patents

Abstract

Provided is an antenna unit capable of controlling directivity even with a rough design.
A planar antenna and a substantially rectangular parallelepiped metal casing that accommodates the surface of the planar antenna toward the front surface. The casing has an open front surface and one of the top, bottom, left, and right side surfaces. The distances a between the two side surfaces sandwiching the open side surface of the planar antenna and the casing and the back surface are λ / 6 ≦ a ≦ λ / 2.2, where λ is the wavelength of the target frequency. Further, the processing b between the planar antenna and the side surface facing the opened side surface of the casing may be λ / 20 ≦ b ≦ λ / 4.
[Selection] Figure 1

Description

  The present invention relates to an antenna unit including a reflector and a planar antenna.

  Various communication systems using the 2450 MHz band, such as Wi-Fi and Bluetooth (registered trademark), have been put into practical use and are widely spread. For this reason, devices using the same 2450 MHz band may be installed nearby, and the antennas of both devices may have directivity in the direction of the other party. In such a case, there has been a problem that radio waves radiated from one antenna become unnecessary electromagnetic waves for the other antenna, leading to deterioration in communication quality.

  Therefore, a proposal has been made to provide a metal member in addition to the antenna element to control the directivity of the antenna (for example, Patent Document 1).

JP 2010-161612 A

  The antenna of Patent Document 1 has the following configuration. As a metal casing, there are a waveguide connection portion in which an antenna substrate is accommodated, and two waveguides drawn from the waveguide connection portion and having different opening widths. By switching which one of the two waveguides allows the electromagnetic wave to pass through, the antenna can have directivity and the directivity can be switched.

  However, the antenna of Patent Document 1 needs to have a critical dimension in accordance with the wavelength of the target frequency in order to make the metal casing function as a waveguide, and requires a critical design. Since the antenna is installed in a state of being substantially surrounded by a metal casing, the influence of the metal casing received by the antenna is large and adjustment is necessary, and there is a problem that the characteristics cannot be sufficiently guaranteed by the design of the antenna alone.

  An object of the present invention is to provide an antenna unit that can control directivity even with a rough design.

  An antenna unit according to the present invention includes a planar antenna and a substantially rectangular parallelepiped metal casing that accommodates the planar antenna with its surface facing the front surface. One of the left and right side surfaces is open, and the distance a between the planar antenna and the two side surfaces sandwiching the opened side surface of the casing and the back surface is λ / 6 ≦ a ≦ λ / 2.2.

  The distance a may be in a range of λ / 6 ≦ a ≦ λ / 4.

  Further, the treatment b between the planar antenna and the side surface of the casing facing the opened side surface may be set to λ / 20 ≦ b ≦ λ / 4.

  Further, the planar antenna has an upper side which is a side on which the element is formed, a ground pattern having a left side and a right side sandwiching the upper side, and a vertical element which is formed in a vertical direction from the upper side and has left and right branches at the top. A left horizontal element formed on the left side of the vertical element and connected to the left branch of the vertical element; a right horizontal element formed on the right side of the vertical element and connected to the right branch of the vertical element; and one end A left short stub whose one end is connected to the left lateral element and the other end is connected to the ground pattern, and a right short stub whose one end is connected to the right lateral element and the other end is connected to the ground pattern. The left and right lateral elements are in the form of a flat plate whose aspect ratio is less than twice, and the left shorts Is connected to the left end of the upper side of the ground pattern, and the right short stub rotates the antenna connected to the right end of the upper side of the ground pattern by 90 degrees so that the left and right lateral elements move up and down. It may be installed so as to be vertically connected.

  The left and right short stubs of the planar antenna may be formed to meander between the left and right lateral elements and the left and right ends of the upper side.

  According to the present invention, the planar antenna is accommodated in the casing having the opening on the front surface and one side surface, and the distance between the antenna and the casing is set to the predetermined length with respect to the signal wavelength λ. It becomes possible to control directivity.

The perspective view of the antenna unit which is embodiment of this invention Configuration diagram of the planar antenna built in the antenna unit Diagram showing radiation efficiency of planar antenna The figure which shows the directivity characteristic to the front and rear direction of the plane antenna The figure which shows the directivity characteristic to the up-down direction of a plane antenna The figure which shows arrangement | positioning of the planar antenna in the casing of an antenna unit The figure which shows the input impedance of the antenna unit according to the distance of a planar antenna and a casing Diagram showing the directional characteristics of the antenna unit in the front-rear direction Diagram showing the directional characteristics of the antenna unit in the vertical direction The figure which shows the installation form of the sound bar where the antenna unit is built The figure which shows other embodiment of a casing

  An antenna unit 10 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the antenna unit 10. FIG. 2 is a diagram showing a pattern of the planar antenna 20 built in the antenna unit 10.

  As shown in FIG. 1, the antenna unit 10 has a metal casing 30 and a planar antenna 20 housed therein. These are mounted on a parent substrate 31 which is a printed circuit board that supports them. The casing 30 is a substantially rectangular parallelepiped and includes an upper side plate 30U, a back plate 30B, a left side plate 30L, and a right side plate 30R, and the front and lower sides are open. The planar antenna is a T-type antenna formed on a printed board as shown in FIG. The antenna unit 10 is built in, for example, the sound bar 1 shown in FIG. The sound bar 1 is an external speaker system installed below the front surface of the television receiver 2. The sound bar 1 receives a control signal and an audio signal using a 2450 MHz band radio wave. Further, the recent television receiver 2 has a Wi-Fi communication function, and radiates a 2450 MHz band electromagnetic wave in the forward direction of the television receiver 2. Note that the antenna unit 10 may have an opening of the casing 30 covered with a non-conductive plastic member or the like, or may be housed in a resin casing such as the sound bar 10.

  FIG. 2 is a diagram showing a line pattern of the planar antenna 20 built in the antenna unit 10. The planar antenna 20 is a planar pattern antenna created by patterning a copper foil affixed on a dielectric circuit board 100 by etching or the like. As the circuit board 100, for example, glass epoxy FR4 (εr = 4) having a thickness of 1 mm may be used.

  The ground pattern 101 is generated in a substantially rectangular shape over the entire right side width of the surface of the dielectric substrate 100. A feeding point 110 is provided at the center of the left side of the ground pattern 101, and the vertical element 111 is taken out from the feeding point 10 to the left. The vertical element 111 goes straight to the left from the feeding point 110, branches up and down at the tip, and is connected to the upper and lower antenna elements 112U and 112D. As a result, the planar antenna 20 has the shape of a vertical T-type antenna. Since the upper and lower antenna elements 112U and 112D are symmetrical about the vertical element 111, the upper antenna element 112U will be described below.

  The upper antenna element 112U has a main element 113U and a short stub 114U. The main element 113U is formed in a substantially rectangular shape. The short stub 114U moves up and left while meandering left and right, and is connected to the ground pattern 101 at the upper left end of the ground pattern 101. By making the main element 113U wide, a relatively large capacitance can be provided between the main element 113U and the ground pattern 101, and the planar antenna 20 is a capacitively loaded antenna. Also, the short stub 114U at the end contributes to radio wave radiation in the vertical direction. The left short stub 114U is formed so that the pattern width gradually becomes narrow, but the pattern width is also arbitrary. What is necessary is just to adjust to the electrical length and width | variety matched with the resonance frequency (wavelength) which the planar antenna 20 makes into the objective. It has been experimentally found that the characteristics of the short stub 114U are made less critical with respect to the size change of the ground pattern 101 by causing the main element 113U to reach the ground pattern 101 while gradually reducing the width. .

  Although the upper antenna element 112U has been described above, the lower antenna element 112D has the same shape as the upper antenna element 112U, only being inverted up and down, and the description thereof will be omitted.

  When the antenna 1 having the above shape is formed with an appropriate size and the resonance frequency is set in the vicinity of the target frequency of 2.45 GHz, the following characteristics are obtained.

  FIG. 3 is a diagram showing the radiation efficiency of the antenna 1 resonated at a frequency near 2.45 GHz. According to this figure, the radiation efficiency is 74% or more in the band of 2.4 to 2.5 GHz, and a gain equivalent to that of the λ / 2 dipole antenna can be obtained. Thus, it can be seen that the electromagnetic field is efficiently radiated from the antenna 1 in a wide frequency band including the target 2.45 GHz band.

  In addition, the planar antenna 20 has directivity characteristics shown in FIGS. 4 and 5 independently. These figures show the horizontal polarization characteristics of 2.45 GHz, and the gain value is shown as a value (dBi) with reference to the isotropic antenna. FIG. 4 is a diagram illustrating the directivity characteristics of the planar antenna 20 in the front-rear direction. The planar antenna 20 alone has a bi-directional characteristic having a figure-eight characteristic in the front-rear direction. The maximum gain is 1.8 dBi, and a gain almost equal to that of the dipole antenna is obtained. FIG. 5 is a diagram showing the directivity characteristics of the planar antenna 20 in the vertical direction. In the XY plane, a high gain is shown in all directions.

  FIG. 6 is a view showing the arrangement of the planar antenna 20 in the casing 30 (upper side plate 30U, back plate 30B, left side plate 30L, right side plate 30R). FIG. 2A is a plan view, and FIG. 2B is a front view. In the plan view of FIG. 3A, the upper side plate 30U is not shown and the internal structure is shown.

  The distance from the planar antenna 20 to the left and right side plates 30L, 30R and the back plate 30B of the casing 30 is a, the distance from the planar antenna 20 to the upper side plate 30U of the casing 30 is b, and the front opening of the casing 30 is from the planar antenna 20 When the distance to the end is c, it is preferable to arrange the planar antenna 20 so that a, b, c are in the following size range.

a: about λ / 6 to λ / 4 (in the case of 2450 MHz band, about 20 mm to 30 mm)
The left side, right side, and back side a may not be the same.
b: about λ / 20 to λ / 4 (in the case of 2450 MHz band, about 6 mm to 30 mm)
c: about λ / 20 (in the case of 2450 MHz band, about 6 mm)

  Since a and b affect the radiation characteristics and impedance matching of the planar antenna 20, it is desirable to set the dimension to λ / 4. However, when vertical radiation is not necessary, b can be reduced to about λ / 20. Further, by using a broadband antenna as shown in FIGS. 2 to 5 as the planar antenna 20, it is possible to give the above margin to the dimension range of a and b.

  The size of c affects the shielding of unnecessary electromagnetic waves from the oblique direction and the radiation directivity in the forward direction. In order to ensure a wide range of radiation directivity, it is preferable to shorten c, and about λ / 20 is preferable in consideration of the shielding performance of unnecessary electromagnetic waves from obliquely behind. However, if it is desired to reduce the radiation directivity of radio waves and increase the FB ratio, c may be increased.

  Since the casing 30 is sufficiently large with respect to a frequency of 2450 MHz and can be regarded as a ground in terms of high frequency, the impedance Zin of the metal casing viewed from the antenna side can be approximated by the following equation, assuming that the planar antenna 20 is a minimal dipole antenna. .

Zin = j120π · (2π / λ) · a · tan ((2π / λ) · a)
Here, a is the distance (m) from the casing 30 described above, and the change in Zin when a is changed is shown in the graph of FIG.

  When a <λ / 4 (about 30.6 mm), Zin is a positive value, that is, inductive impedance, and the phase of the electromagnetic wave radiated from the planar antenna 20 is delayed by λ / 4 on the casing 30. Acts like a reflector. When a> λ / 4, Zin is a negative value, that is, capacitive impedance, and the phase of the electromagnetic wave radiated from the planar antenna 20 advances by λ / 4 on the casing 30, but the casing 30 has a high frequency. Since it is regarded as ground, there is no director effect.

  As can be seen from the graph of FIG. 7, Zin substantially coincides with the free space impedance (120π≈377Ω) when the value of a is about 16.8 mm (about λ / 7.3). Therefore, in order for the casing 30 to function as a reflector, the value of a may be designed so that the value of Zin has an inductive impedance larger than this. However, it is preferable to design within the range of λ / 6 ≦ a ≦ λ / 4 as described above. However, even if a exceeds λ / 4 and Zin becomes capacitive, the impedance value is sufficiently large (300Ω or more) within the range of λ / 4 ≦ a ≦ λ / 2.2. It is also possible to function as a reflector.

  By designing a to a value within the above-described range, the casing 30 functions as a reflector, and the electromagnetic wave radiated from the planar antenna 20 is reflected by the casing 30 and radiated from the opening surface. Thus, since the casing 30 may be designed within a range where a is 20 mm (λ / 6) ≦ a ≦ 56 mm (λ / 2.2), it is rougher than the cavity resonator or the waveguide. Design is possible.

  8 and 9 show the directivity of the antenna unit 10 when the planar antenna 20 shown in FIGS. 2 to 5 is built in and the dimensions a, b and c are λ / 6, λ / 20 and λ / 20, respectively. It is a figure which shows a characteristic. These figures show the horizontal polarization characteristics of 2.45 GHz, and the gain value is indicated by a value (dBi) based on the isotropic antenna. FIG. 8 is a diagram showing the directional characteristics of the antenna unit 10 in the front-rear direction (horizontal plane), and FIG. 9 is a diagram showing the directional characteristics of the antenna unit 10 in the vertical direction.

  In FIG. 8, radio waves having directivity are radiated in the front direction of the horizontal antenna unit 10, that is, in the opening surface direction of the casing 30, and also have wide directivity in the left-right direction. On the contrary, the gain to the back which is shielded by the casing 30 is small and no radio wave is radiated.

  In FIG. 9, since the upper side is shielded by the casing 30, the emission of radio waves is suppressed. On the other hand, the light is radiated efficiently in the downward direction and the left-right direction. Note that the decrease in gain in the right direction is due to the ground pattern 101 of the planar antenna 20. If the upper side surface is opened and the lower side surface is shielded, the characteristics obtained by reversing the top and bottom of FIG. 9 can be obtained.

  FIG. 10 is a diagram showing an installation form of the sound bar 1 incorporating the antenna unit 10. The television receiver 2 is installed on the television stand 4, and the sound bar 1 is installed on the television stand 4 in front of it. An independent subwoofer unit 3 is installed inside the TV stand 4. The sound bar 1 includes left and right channel speakers 11L and 11R on the left and right, and a center speaker 12 in the center. The antenna unit 10 is provided slightly from the center left. The subwoofer unit 3 is provided with a subwoofer speaker 15. Further, a Wi-Fi antenna 2A is provided below the screen of the television receiver 2, and the antenna unit 10 receives electromagnetic waves radiated from the antenna 2A of the television receiver from behind. Since the antenna unit 10 has the above-described configuration, even if it receives an electromagnetic wave from the back, the antenna unit 10 efficiently blocks the electromagnetic wave and does not radiate the electromagnetic wave strongly to the antenna 2A behind.

  Moreover, FIG. 11 is a figure which shows the modification of the casing 30 of the antenna unit 10 of this invention. The casing 30 of the antenna unit 10 is provided with flanges 300L, 300R, and 300U that extend outward at the front opening ends of the left and right side plates 30L and 30R and the upper side plate 30U. By providing these flanges 300L, 300R, and 300U, while ensuring wide directivity in the forward direction, the diffraction of the unnecessary electromagnetic wave from behind by the edge of the casing 30 is cut off to improve the backward directivity. Can do.

  In this embodiment, the planar antenna 20 accommodated in the casing 30 is a pattern antenna formed on the printed circuit board 100, but the planar antenna of the present invention is not limited to the pattern antenna. Further, the material of the casing 30 is not limited to metal. The target frequency of the antenna unit 10 (planar antenna 20) is not limited to the 2450 MHz band. It can be higher or lower. What is necessary is just to design the dimension of each part according to the target frequency.

1 Sound bar (external speaker system)
2 TV receiver 2A Wi-Fi antenna 10 Antenna unit 20 Planar antenna 30 Casing 30L Left side plate 30R Right side plate 30U Upper side plate 30B Rear plate 31 Parent substrate 100 Printed circuit board 101 Ground pattern 110 Feed point 111 Vertical element 113U, D Main element 114U , D Short stub 300L, 300R, 300U Flange

Claims (5)

A planar antenna, and a substantially rectangular parallelepiped metal casing that accommodates the surface of the planar antenna toward the front surface;
Have
The casing has an opening on the front surface and one of the top, bottom, left and right side surfaces,
A distance a between the planar antenna and the two side surfaces sandwiching the opened side surface of the casing and the rear surface is λ / 6 ≦ a ≦ λ / 2.2, where λ is the wavelength of the target frequency.   The antenna unit according to claim 1, wherein the distance a is λ / 6 ≦ a ≦ λ / 4.   3. The antenna unit according to claim 1, wherein a process b between the planar antenna and a side surface of the casing facing the opened side surface satisfies λ / 20 ≦ b ≦ λ / 4. The planar antenna is
A ground pattern having an upper side which is a side on which an element is formed, a left side and a right side sandwiching the upper side, a vertical element which is formed in a vertical direction from the upper side and has left and right branches, and a left side of the vertical element A left horizontal element formed and connected to the left branch of the vertical element, a right horizontal element formed on the right side of the vertical element and connected to the right branch of the vertical element, and one end connected to the left horizontal element A left short stub whose other end is connected to the ground pattern and a right short stub whose one end is connected to the right lateral element and the other end is connected to the ground pattern are formed on a plane,
The left and right lateral elements have a flat plate shape with an aspect ratio smaller than twice, the left short stub is connected to the left end of the upper side of the ground pattern, and the right short stub is the upper side of the ground pattern. Connect the antenna connected to the right end of
The antenna unit according to any one of claims 1 to 3, wherein the antenna unit is installed so as to turn 90 degrees and the left and right lateral elements are vertically connected vertically.   The antenna unit according to claim 4, wherein the left and right short stubs are formed to meander between the left and right lateral elements and the left and right ends of the upper side.

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