JP2012028830A - Antenna device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a difference of frequencies in an antenna device capable of coping with a plurality of frequency bands.SOLUTION: By forming a radiation electrode 102 on an upper surface of a dielectric roughly in a rectangular parallelepiped shape and forming a ground electrode 114 on a bottom surface, an antenna element 100 is formed. The antenna element 100 is installed in the mounting area 112 of a printed circuit board 110. A ground pattern area at the peripheral edge of the mounting area 112 is connected with the ground electrode 114. One of the radiation electrode 102 is an open end and the other end is connected with the ground electrode 114 as a short circuit end. An area where the ground electrode 114 can be formed in the short circuit end side is limited to a higher harmonic dominant area where the amplitude of three-times higher harmonic standing waves is larger than the amplitude of fundamental standing waves generated in the radiation electrode 102.

Description

  The present invention relates to an antenna device, and more particularly to frequency adjustment thereof.

  A chip-type antenna element built in a small wireless terminal such as a cellular phone is formed by printing a radiation electrode and a feeding electrode on the surface of a block-type dielectric. When an electric field is generated by supplying an alternating current to the feeding electrode, an alternating current also flows through the radiation electrode, and radio waves are generated from the radiation electrode.

  Many portable terminals need to support a plurality of frequency bands such as GPS (Global Positioning System) and Bluetooth (registered trademark). In order to support a plurality of frequency bands while responding to the demand for miniaturization of portable terminals, it is desirable to generate radio waves in a plurality of frequency bands with a single antenna element.

JP 2004-72699 A JP 2002-164729 A

  In Patent Document 1, it is possible to cope with two frequency bands of a main resonance point and a spurious resonance point by devising a radiation conductor pattern printed on an antenna element. In the case of Patent Document 1, the frequency ratio between the main resonance point and the spurious resonance point is about 1: 2. Since the frequency of GPS is about 1.5 GHz and the frequency of Bluetooth (registered trademark) is about 2.4 GHz, the frequency ratio of GPS and Bluetooth (registered trademark) is 1: 1.5. Therefore, the technique of Patent Document 1 cannot cope with these frequency bands. Also in the dual-band antenna shown in Patent Document 2, the frequency ratio is about 1: 2.

  The present invention has been completed in view of the above problems, and a main object thereof is to reduce the difference in frequency in an antenna device that can handle a plurality of frequency bands.

  An antenna device according to the present invention includes an antenna element in which a radiation electrode is formed on the top surface of a substantially rectangular parallelepiped dielectric and a ground electrode is formed on the bottom surface, a mounting region to which the antenna element is attached, and a ground provided on the periphery of the mounting region. A printed circuit board including a pattern region is provided. One end of the radiation electrode is an open end, and the other end is a short-circuited end connected to the ground electrode. The region where the ground electrode is formed on the short-circuit end side is limited to a harmonic dominant region where the amplitude of the predetermined harmonic standing wave is larger than the amplitude of the fundamental standing wave generated in the radiation electrode.

  The harmonic standing wave here may be a standing wave having a frequency three times that of the basic standing wave.

  The antenna element may be formed so that the relative dielectric constant on the short-circuit end side of the dielectric is larger than the relative dielectric constant on the open end side. The dielectric may be formed of a material having a first relative dielectric constant only in the harmonic dominant region, and the dielectric may be formed of a material having a relative dielectric constant lower than the first relative dielectric constant in other regions. .

  By projecting a part of the ground electrode toward the radiation electrode, the facing distance between the radiation electrode and the ground electrode may be shortened. Further, the facing distance between the radiation electrode and the ground electrode may be shortened by projecting a part of the radiation electrode included in the harmonic dominant region toward the ground electrode.

  The radiation electrode may be formed on the entire upper surface of the dielectric. Alternatively, the radiation electrode may be formed to have a first electrode width in the harmonic dominant region and a second electrode width narrower than the first electrode width only in other regions. The radiation electrode has a first electrode width in the region on the short-circuit end side, and a second electrode narrower than the first electrode width only in a region from the position where the first node of the harmonic standing wave appears to the open end. It may be formed to have an electrode width.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes easy to reduce the difference of the frequency in the antenna device which can respond to a some frequency band.

It is a schematic diagram of the standing wave which generate | occur | produces in an antenna element. 1 is an external view of an antenna device according to a first embodiment. It is an expanded view of the antenna element in 1st Embodiment. Fig.4 (a) is a figure which shows the 1st installation place of the antenna element in a printed circuit board. FIG. 4B is a diagram illustrating a second installation location of the antenna element on the printed circuit board. FIG. 4C is a diagram illustrating a third installation location of the antenna element on the printed circuit board. It is a graph which shows the frequency characteristic for every installation place of an antenna element. It is an external view of the antenna apparatus in 2nd Embodiment. It is an external view of the antenna apparatus in 3rd Embodiment. It is an external view of the antenna apparatus in 4th Embodiment. It is a sectional side view at the time of cut | disconnecting an antenna element along the AA line of FIG. It is an external view of the antenna apparatus in 5th Embodiment. It is a sectional side view at the time of cut | disconnecting an antenna element along the AA line of FIG. It is an external view of the antenna apparatus in 6th Embodiment. It is an external view of the antenna apparatus in 7th Embodiment. It is a graph which shows the frequency characteristic of the antenna apparatus in 1st, 4th-7th embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In each embodiment, an antenna element built in a mobile phone will be described as a theme. An antenna device is formed as a mobile phone incorporating an antenna element.

  FIG. 1 is a schematic diagram of a standing wave generated in an antenna element. In FIG. 1, the y-axis is set to the right in the figure. One end (y = y0) of the radiation electrode 102 is a short-circuited end, and the other end (y = y1) is an open end. When AC power is supplied to the radiation electrode 102, a plurality of standing waves are generated in the radiation electrode 102 with a short-circuited end and an open end as an antinode.

  The fundamental wave 104 is a standing wave corresponding to the length (y1-y0) and the (1/4) wavelength of the radiation electrode 102. The harmonic wave 106 is a standing wave corresponding to the length of the radiation electrode 102 and the (3/4) wavelength. That is, the frequency of the harmonic wave 106 is three times the frequency of the fundamental wave 104. The harmonic wave 106 makes a node at the positions of the short-circuit ends y0 and y = y5. The harmonic 106 shown in FIG. 1 is a third harmonic, but in addition to this, a fifth harmonic, a seventh harmonic, and the like are also generated. In the following description, the harmonic 106 as the third harmonic will be described.

  As described above, the frequency ratio between the fundamental wave 104 and the harmonic wave 106 is 1: 3. The purpose of the antenna device 108 in this embodiment is to reduce the frequency difference between the fundamental wave 104 and the harmonics 106. More specifically, the goal is to approach a frequency ratio of 1: 1.5.

  Referring to FIG. 1, the amplitude of the harmonic 106 is larger than the amplitude of the fundamental wave 104 in the region of y0 ≦ y <y2. Hereinafter, such a region is referred to as a “harmonic dominant region”. In y2 ≦ y ≦ y1, the amplitude of the fundamental wave 104 is larger than the amplitude of the harmonic wave 106. Hereinafter, such a region is referred to as a “basic wave dominant region”. Y2 which is the boundary between the harmonic dominant region and the fundamental wave dominant region is a midpoint between y0 (short-circuited end) and y1 (opened end).

  It is known that the frequency of the standing wave decreases as the impedance of the antenna element 100 decreases. The inventors pay attention to the fact that the antenna element 100 can be divided into a harmonic dominant region and a fundamental dominant region, and if the impedance of the harmonic dominant region is selectively reduced, the fundamental wave 104 and the harmonic 106 are reduced. I thought that the frequency difference could be shortened. That is, if the impedance of the harmonic dominant region is selectively reduced, not only the frequency of the harmonic 106 but also the frequency of the fundamental wave 104 is reduced. However, the harmonic 106 greatly reduces the impedance. The frequency difference will be reduced.

[First Embodiment]
FIG. 2 is an external view of the antenna device 108 according to the first embodiment. The antenna device 108 is formed by installing the antenna element 100 in the mounting area 112 of the printed board 110. In FIG. 2, the y-axis is set in the long side direction of the antenna element 100, the x-axis is set in the short side direction, and the z-axis is set in the height direction. The same applies to the subsequent drawings.

  In the printed circuit board 110, the mounting region 112 is surrounded by a ground pattern. The antenna element 100 is formed by printing a radiation electrode 102 and a ground electrode 114 on the surface of a substantially rectangular parallelepiped dielectric. FIG. 3 is a development view of the antenna element 100. The structure of the antenna element 100 will be described with reference to FIGS. 2 and 3.

  The size of the antenna element 100 in this embodiment is x × y × z = 2.5 mm × 10.0 mm × 1.0 mm. The antenna element 100 is fixed to the printed circuit board 110 by bonding a rectangular bottom surface 116 (10.0 mm × 2.5 mm) to the mounting region 112. The four side surfaces of the antenna element 100 are a first side surface 118 (2.5 mm × 1.0 mm), a second side surface 120 (10.0 mm × 1.0 mm), and a third side surface 122 (2.5 mm × 1.0 mm), respectively. The fourth side surface 124 (10.0 mm × 1.0 mm). The mounting region 112 is formed by cutting out a part of the ground pattern with a size of x × y = 4.0 mm × 11.0 mm. Further, the base of the antenna element 100 in the first embodiment is formed of ceramic having a relative dielectric constant of 57.

  The radiation electrode 102 is printed on the entire upper surface 126. The radiation electrode 102 is connected to the ground electrode 114 on the bottom surface 116 via the connection conductor 128 on the third side surface 122. A power supply line 130 is also connected to the connection conductor 128 printed on the third side surface 122. The radiation electrode 102 is supplied with AC power from the power supply line 130 via the connection conductor 128. The short-circuit end of the radiation electrode 102 is on the third side surface 122 side, and the open end is on the first side surface 118 side.

  A ground conductor 132 for stably bonding the antenna element 100 to the printed circuit board 110 is formed on the open end side of the bottom surface 116. The ground conductor 132 is not essential. The area of the ground conductor 132 should be as small as possible.

  In the region where the radiation electrode 102 and the ground electrode 114 face each other, the impedance decreases. For this reason, the ground electrode 114 formed on the bottom surface 116 is formed so as to be within the harmonic dominant region in the y direction. The ground electrode 114 is connected to the ground pattern of the printed circuit board 110.

  As shown in FIG. 2, the ground electrode 114 is formed up to the position of y = y3, and y3 satisfies the relationship 0 <y3 <y2. That is, the region where the ground electrode 114 can be formed is limited to the harmonic dominant region. The formation region of the ground electrode 114 is limited to the harmonic dominant region, and the frequency difference of the fundamental wave 104 and the harmonic wave 106 is shortened by greatly reducing the frequency of the harmonic wave 106 than the frequency of the fundamental wave 104. According to the simulation experiment of the present inventors, the frequency of the fundamental wave 104 was 1.575 (GHz), the frequency of the harmonic 106 was 2.445 (GHz), and the frequency ratio was 1: 1.552.

  FIGS. 4A, 4 </ b> B, and 4 </ b> C all illustrate the installation location of the antenna element 100 on the printed circuit board 110. FIG. 5 is a graph showing frequency characteristics for each place where the antenna element 100 is installed. According to FIG. 5, it can be seen that the return loss changes depending on the installation location of the antenna element 100, but the frequency hardly changes. In each of the following embodiments, description will be made assuming that the antenna element 100 is installed at the position shown in FIG.

[Second Embodiment]
FIG. 6 is an external view of the antenna device 108 according to the second embodiment. The print patterns of the radiation electrode 102 and the ground electrode 114 in the second embodiment are the same as those in the first embodiment. In the antenna element 100 of the second embodiment, a dielectric having a relative dielectric constant of 57 on the short-circuited end side and a dielectric having a relative dielectric constant of 37 on the open end side with the position of y = y4 in the fundamental wave dominant region as a boundary. Two types of dielectrics are used. That is, the relative dielectric constant on the short-circuit end side is larger than the relative dielectric constant on the open end side.

  The length of the antenna element 100 in the y-axis direction is 10 mm, and the boundary (y = y2) between the harmonic dominant region and the fundamental wave dominant region is a position just before 5.0 mm from the short-circuited end (y = y0). It becomes. This is because the wavelength shortening rate is higher in the harmonic dominant region than in the fundamental dominant region. The boundary of the dielectric (y = y4) is in the fundamental wave dominant region. When a dielectric boundary (y = y4) is set at a position 6.35 mm from the short-circuited end (y = y0), the fundamental wave 104 has a frequency of 1.727 (GHz) and the harmonic 106 has a frequency of 2.622. (GHz), the frequency ratio was 1: 1.52. This is a further improvement over the first embodiment. This is because the impedance decreases as the relative dielectric constant of the dielectric increases.

[Third Embodiment]
FIG. 7 is an external view of the antenna device 108 according to the third embodiment. The print patterns of the radiation electrode 102 and the ground electrode 114 in the antenna element 100 are the same as those in the first embodiment. In the antenna element 100 of the second embodiment, a dielectric having a relative permittivity of 57 on the short-circuited end side and a dielectric having a relative permittivity of 37 on the open end side with the position of y = y4 in the harmonic dominant region as a boundary. Two types of dielectrics are used.

  When the boundary of the dielectric (y = y4) is set at a position of 4.35 mm from the short-circuited end (y = y0), the frequency of the fundamental wave 104 is 1.752 (GHz) and the frequency of the harmonic wave 106 is 2.647. (GHz), the frequency ratio is 1: 1.51. By using a dielectric having a high relative dielectric constant only in the harmonic dominant region, the frequency ratio can be further improved as compared with the second embodiment.

[Fourth Embodiment]
FIG. 8 is an external view of the antenna device 108 according to the fourth embodiment. FIG. 9 is a side sectional view of the antenna element 100 cut along the line AA shown in FIG. The print patterns of the radiation electrode 102 and the ground electrode 114 in the fourth embodiment are substantially the same as those in the first embodiment. However, in the fourth embodiment, a part of the ground electrode 114 is raised in the direction of the upper surface 126 (z direction). Since the distance at which a part of the ground electrode 114 and the radiation electrode 102 face each other is short, the impedance of the harmonic dominant region can be lowered. When a protrusion having a size of x × y × z = 1.5 mm × 2.5 mm × 0.5 mm is provided in accordance with the position of the antinode of the harmonic 106, the frequency of the fundamental wave 104 is 1.473 (GHz), The frequency of the harmonic wave 106 was 2.188 (GHz), and the frequency ratio was 1: 1.486.

[Fifth Embodiment]
FIG. 10 is an external view of the antenna device 108 according to the fifth embodiment. FIG. 11 is a side sectional view of the antenna element 100 cut along the line AA shown in FIG. The print patterns of the radiation electrode 102 and the ground electrode 114 in the fifth embodiment are substantially the same as those in the first embodiment. In the fifth embodiment, a part of the radiation electrode 102 is depressed on the bottom surface 116 side. This depressed portion is included in the harmonic dominant region. Since a part of the facing distance between the ground electrode 114 and the radiation electrode 102 is short, the impedance of the harmonic dominant region can be lowered. When a depression having a size of x × y × z = 1.5 mm × 2.5 mm × 0.5 mm is provided in accordance with the position of the antinode of the harmonic 106, the frequency of the fundamental wave 104 is 1.485 (GHz), The frequency of the harmonic 106 was 2.190 (GHz), and the frequency ratio was 1: 1.475.

[Sixth Embodiment]
FIG. 12 is an external view of the antenna device 108 according to the sixth embodiment. In the sixth embodiment, the electrode width on the open end side of the radiation electrode 102 is narrowed only partially. Other electrode patterns are the same as those in the first embodiment. Such a region where the electrode width of the radiation electrode 102 is narrowed is referred to as a “narrow discharge region 134”. In the sixth embodiment, the narrow discharge region 134 has a length (y direction) of 3.0 mm and an electrode width (x direction) of 1.0 mm. The narrow discharge region 134 is provided closer to the open end than the node (y5) of the harmonic 106. At least, the narrow discharge region 134 is formed only in the fundamental wave dominant region. In the narrow discharge region 134, the impedance is improved. According to the simulations of the present inventors, the frequency of the fundamental wave 104 was 1.528 (GHz), the frequency of the harmonic 106 was 2.355 (GHz), and the frequency ratio was 1: 1.542.

[Seventh Embodiment]
FIG. 13 is an external view of the antenna device 108 according to the seventh embodiment. Also in the seventh embodiment, the electrode width on the open end side of the radiation electrode 102 is narrowed only partly. In the seventh embodiment, the narrow discharge region 134 has a length (y direction) of 3.0 mm and an electrode width (x direction) of 2.0 mm. The narrow discharge region 134 is provided closer to the open end than the node (y = 5) of the harmonic 106. Since the electrode width of the narrow discharge region 134 is wider than that in the sixth embodiment, the impedance in the narrow discharge region 134 is slightly larger than that in the sixth embodiment. According to the simulations of the present inventors, the frequency of the fundamental wave 104 was 1.558 (GHz), the frequency of the harmonic 106 was 2.410 (GHz), and the frequency ratio was 1: 1.547.

  FIG. 14 is a graph showing the frequency characteristics of the antenna device 108 in the first and fourth to seventh embodiments. First, as in the fourth and fifth embodiments, it was confirmed that the frequency difference between the fundamental wave 104 and the harmonic wave 106 can be greatly shortened by providing a recess in the dielectric. Considering in more detail, the frequency of the fundamental wave 104 of the fourth embodiment is lower than the frequency of the fundamental wave 104 of the fifth embodiment. It was confirmed that the frequency difference between the fundamental wave 104 and the harmonic wave 106 can be shortened also by providing the narrow discharge region 134 on the open end side as in the sixth and seventh embodiments.

  The antenna device 108 according to the present invention has been described above based on the first to seventh embodiments. In any case, the frequency difference between the fundamental wave 104 and the harmonic wave 106 can be shortened by forming the antenna element 100 so that the impedance in the harmonic dominant region is lower than the impedance in the fundamental wave dominant region. In particular, the ground electrode 114 formed only in the harmonic dominant region has a large frequency difference shortening effect. It should be understood by those skilled in the art that any two or more of the first to seventh embodiments can be combined.

  The present invention has been described based on the embodiments. It will be understood by those skilled in the art that the embodiments are illustrative, and that various modifications and changes are possible within the scope of the claims of the present invention, and that such modifications and changes are also within the scope of the claims of the present invention. By the way. Further, it will be understood by those skilled in the art that if the configuration opposite to that of the embodiment of the present invention is adopted, the frequency ratio between the fundamental wave and the harmonic can be set to be large. Accordingly, the description and drawings herein are to be regarded as illustrative rather than restrictive.

  100 antenna element, 102 radiation electrode, 104 fundamental wave, 106 harmonic, 108 antenna device, 110 printed circuit board, 112 mounting area, 114 ground electrode, 116 bottom surface, 118 first side surface, 120 second side surface, 122 third side surface, 124 4th side surface, 126 upper surface, 128 connection conductor, 130 feeder line, 132 ground conductor, 134 narrow discharge region.

Claims (9)

An antenna element in which a radiation electrode is formed on the top surface of a substantially rectangular parallelepiped dielectric and a ground electrode is formed on the bottom surface;
A printed circuit board including a mounting area to which the antenna element is attached and a ground pattern area provided at the periphery of the mounting area;
One end of the radiation electrode is an open end, the other end is a short-circuited end connected to the ground electrode,
The region where the ground electrode is formed on the short-circuit end side is limited to a harmonic dominant region where the amplitude of the predetermined standing harmonic wave is larger than the amplitude of the fundamental standing wave generated in the radiation electrode. An antenna device characterized by the above.   The antenna device according to claim 1, wherein the predetermined harmonic standing wave has a frequency three times that of the fundamental standing wave.   The antenna device according to claim 1, wherein a relative dielectric constant of the dielectric on the short-circuit end side is larger than a relative dielectric constant on the open end side.   The dielectric is formed of a material having a first relative permittivity only in the harmonic dominant region, and is formed of a material having a relative permittivity lower than the first relative permittivity in other regions. The antenna device according to claim 3.   5. The antenna device according to claim 1, wherein a facing distance between the radiation electrode and the ground electrode is shortened by projecting a part of the ground electrode toward the radiation electrode.   2. The facing distance between the radiation electrode and the ground electrode is shortened by projecting a part of the radiation electrode included in the harmonic dominant region toward the ground electrode. 6. The antenna device according to any one of 5.   The antenna device according to claim 1, wherein the radiation electrode is formed on an entire upper surface of the dielectric.   The radiation electrode has a first electrode width in the harmonic dominant region, and a second electrode width narrower than the first electrode width only in the other region. The antenna device according to any one of 1 to 6.   The radiating electrode has a first electrode width in the region on the short-circuit end side, and only from the first electrode width to a region from the position where the first node of the harmonic standing wave appears to the open end. The antenna device according to claim 1, wherein the antenna device has a narrow second electrode width.

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