WO2008038354A1

WO2008038354A1 - Small antenna unit

Info

Publication number: WO2008038354A1
Application number: PCT/JP2006/319197
Authority: WO
Inventors: Toshiteru Hayashi; Yoshio Koyanagi; Nobuaki Tanaka; Yutaka Saito
Original assignee: Panasonic Corporation
Priority date: 2006-09-27
Filing date: 2006-09-27
Publication date: 2008-04-03

Abstract

A small antenna unit in which directivity gain does not deteriorate even if an antenna element and a mounting component are arranged in close proximity to a metal surface. When an antenna element (101) is arranged in close proximity to a metal housing (102) substantially in parallel therewith, a high resistance film (104) is formed, by vapor deposition, on the surface of the metal housing (102) opposing the antenna element (101) in order to increase the surface resistance of the metal housing (102). When an antenna current i101 flows through the antenna element (101), a negative-phase current i102 flows through the high resistance film (104) on the surface of the opposing metal housing (102), but the negative-phase current i102 is dependent on the resistance of the high resistance film (104) and thereby the current component is suppressed to have a relatively small value. Since the apparent antenna current i101 has a large value, directivity gain G101 of the antenna element (101) is increased, thereby enhancing antenna performance.

Description

Specification

Small antenna device

Technical field

TECHNICAL FIELD [0001] The present invention relates to a small antenna device used for a terminal device such as a cellular phone, and more particularly to a small antenna device that improves directivity gain in electromagnetic waves.

Background art

[0002] In recent years, terminal devices such as mobile phones have been improved to be further miniaturized by using small parts or devising a storage space for each part. Therefore, the antenna has been devised in terms of miniaturization and arrangement method while not reducing the directivity gain. For example, a mobile phone is disclosed in which an antenna is mounted on a metal casing, a dipole antenna of λ / 2 (λ is a wavelength) is formed by the antenna and the metal casing, and an antenna device provided with a reflector is mounted. (See Patent Document 1). By configuring the antenna device in such a manner, the antenna housing can be miniaturized because the metal casing acts as an auxiliary antenna, and the radiation efficiency of electromagnetic waves is improved by providing a reflector. Thus, the directivity gain in a predetermined direction can be improved.

Patent Document 1: JP 2000-323921 A

Disclosure of the invention

Problems to be solved by the invention

[0003] However, if a small antenna is placed close to an electronic component mounted on a terminal device such as a metal component surface (hereinafter referred to as a metal surface) or an electronic component, the antenna element and the adjacent component are mutually connected. Since the current components that flow through the channel act to cancel each other, the antenna performance is degraded. The reason will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing an example of an arrangement configuration of an antenna element and a metal casing mounted on a terminal device or the like. As shown in FIG. 1, the antenna element 1 is arranged in parallel and close to the surface of the metal casing 2, and the connection point between the antenna element 1 and the metal casing 2 is a feeding point 3. In the example of the figure, the upper surface (upward direction of the figure) of the antenna element 1 is the main direction of the antenna directivity. In place of the inverted L antenna of antenna element 1, a part or all of the antenna element is almost parallel to adjacent components. Any other antenna may be used as long as it is configured as described above.

FIG. 2 is a conceptual diagram showing the operation of the antenna in the arrangement configuration of the antenna element and the metal housing shown in FIG. As shown in FIG. 2, the antenna current i flowing on the antenna element 1 by the feeding point 3 and the negative phase current i are excited in the metal housing 2 arranged close to the antenna element 1.

1 2 Wake up. Since antenna current i and reverse-phase current i act in different directions, they cancel each other.

1 2

On the other hand, the antenna performance is lowered to suppress the directivity gain G of the antenna element 1. As the distance between the antenna element 1 and the metal housing 2 becomes shorter, the reverse phase current i increases more and more.

2

Therefore, the directivity gain G of the antenna element 1 further decreases.

[0005] The present invention has been made in view of the above-described problems, and directivity is achieved even when the antenna element and a mounting part or a metal surface in the terminal such as a metal part or an electronic part are arranged close to each other. It is an object of the present invention to provide such a small antenna device without reducing the gain.

Means for solving the problem

[0006] The small antenna device of the present invention is a small antenna device used in the electronic device in which at least a part of the antenna element is arranged substantially parallel to a mounting part or a metal surface of the electronic device, A configuration is adopted in which a high resistance film having a resistance value higher than that of at least the mounting component or the metal surface is formed on the surface of the mounting component or the metal surface from the antenna element.

[0007] According to such a configuration, the anti-phase current is excited on the surface of the mounting component and the metal surface on the side facing the antenna element by the antenna current flowing on the antenna element. Suppressed by the high resistance film formed on the surface of the mounted component or metal surface. Therefore, the apparent antenna current increases as the negative-phase current that cancels the antenna current decreases, and as a result, the directivity gain of the antenna element improves. Furthermore, when the mounted component in the vicinity is an electronic component, the malfunction of the electronic component can be suppressed by reducing the reverse-phase current flowing on the surface of the electronic component.

In a preferred embodiment of the small antenna device of the present invention, the directivity gain is further improved if the length of the high resistance film is substantially the same as the length of the antenna element in the region facing the antenna element. If the width of the housing is wider than the width of the antenna element, If the width is wider than the width of the antenna element in the region facing the antenna element, the directivity gain is further improved. The most preferred form is that the width of the high resistance film is the same as the width of the housing.

The invention's effect

[0009] According to the small antenna device of the present invention, when the mounting component and the metal surface close to the antenna element are arranged substantially in parallel, the surface of the mounting component and the metal surface facing the antenna element is high. By forming the resistance film, the negative phase current excited by the antenna current can be reduced, so that the directivity gain of the antenna element can be improved. Furthermore, since the reverse-phase current flowing on the surface of the electronic component can be reduced, malfunction of the electronic component can be suppressed. In addition, the high resistance film can be easily formed by mixing or vapor-depositing or applying graphite particles with a volatile solvent, so that the directivity gain of the antenna element can be improved inexpensively and easily. .

Brief Description of Drawings

[0010] [FIG. 1] A conceptual diagram showing an example of an arrangement configuration of an antenna element and a metal casing mounted on a terminal device or the like.

[Fig. 2] Conceptual diagram showing antenna operation in the arrangement configuration of the antenna element and metal casing shown in FIG.

FIG. 3 is a conceptual diagram showing an arrangement configuration of an antenna element and a metal casing in the small antenna device of the present invention.

FIG. 4 is a conceptual diagram showing the operation of the antenna in the small antenna device shown in FIG.

FIG. 5 is a conceptual diagram showing the arrangement configuration of the small antenna device and the operation of the antenna in the first embodiment of the present invention.

FIG. 6 is a performance evaluation diagram showing an improvement in directivity gain realized by the arrangement configuration of the small antenna device shown in FIG.

[Fig. 7] Schematic diagram showing current distribution when a metal housing is made longer than the length of a conventional antenna element and no high resistance film is used.

[Fig. 8] Fig. 8 is a conceptual diagram showing the current distribution when a high resistance film is formed over the entire surface of the metal housing in Fig. 7. FIG. 9 is a conceptual diagram showing the current distribution in FIG. 7 when a high resistance film is formed on the surface of the metal casing by the same length as the antenna element.

[Figure 10] Performance evaluation diagram comparing the magnitude of the effect of improving the directivity gain due to the difference in the length of the high-resistance film formed on the surface of the metal housing

FIG. 11 is a conceptual diagram showing the current distribution when a high resistance film having the same length and width as the antenna element is formed on the metal substrate in FIG.

[FIG. 12] In FIG. 7, a conceptual diagram showing the current distribution when a high-resistance film is formed to be the same length as the antenna element and wider than the antenna element.

[Figure 13] Performance evaluation diagram comparing the effects of directivity gain improvement due to differences in the width of the high-resistance film formed on the surface of the metal housing

BEST MODE FOR CARRYING OUT THE INVENTION

In the small antenna device of the present invention, a high resistance film is formed on the surface of a proximity component (that is, a metal housing or an electronic component) arranged in the vicinity of the antenna element so that the surface resistance of the proximity component is increased. It is configured. As a result, the reverse-phase current flowing on the surface of the adjacent component can be suppressed to a small level, so that the ratio of the antenna current and the reverse-phase current canceling each other can be reduced. Since the antenna current increases, the directivity gain of the antenna element can be improved.

FIG. 3 is a conceptual diagram showing an arrangement configuration of an antenna element and a metal casing in the small antenna device of the present invention. In FIG. 3, the small antenna device has a configuration in which the antenna element 101 and the metal casing 102 are arranged substantially parallel to each other in the vicinity of the metal casing 102. Further, the connection point between the antenna element 101 and the metal casing 102 is a feeding point 103 of the antenna element 101. Furthermore, a high resistance film 104 having a resistance value higher than that of the metal casing is formed on the surface of the metal casing 102 facing the antenna element 101 by vapor deposition or coating. In this way, the surface resistance of the metal casing 102 adjacent to the antenna element 101 is increased.

FIG. 4 is a conceptual diagram showing the operation of the antenna in the small antenna device shown in FIG. When the antenna current i flows from the feeding point 103 to the antenna element 101, the antenna element 10 A reverse-phase current i flows through the high resistance film 104 on the surface of the metal casing 102 facing 1. This

102

The negative-phase current i is suppressed by the current component depending on the resistance value of the high-resistance film 104.

102

If the high resistance film 104 is not provided, the negative phase current i is smaller than that in the case. In this way

102

Since the antenna current i 101 becomes smaller than the negative phase current i 102, the apparent antenna current i 101 becomes a large value, and as a result, the antenna performance improves as the directivity gain G increases. Na

101

The negative phase current i is consumed by the product (1) of the resistance component of the high resistance film 104 (1).

102

[0014] Next, some specific embodiments of the small antenna device according to the present invention will be described in detail. In each of the following embodiments, the antenna element and the metal casing are all arranged in the same manner, and the directivity gain of the antenna element depends on the size of the region of the high resistance film formed on the surface of the metal casing. It will be explained how it can be improved. Note that, in the drawings used in each embodiment, the same constituent elements are denoted by the same reference numerals, and redundant description is omitted as much as possible.

FIG. 5 is a conceptual diagram showing the configuration and antenna operation of the small antenna device according to Embodiment 1 of the present invention. As shown in FIG. 5, a high resistance film 104 is deposited or applied over the entire surface of the metal casing 102 arranged in parallel in the vicinity of the antenna element 101. However, the high resistance film 104 is not formed in the vicinity of the feeding point 103 where the metal casing 102 and the antenna element 101 are connected.

[0016] Examples of the high resistance film 104 include an Atchison conductive paint. This Athison conductive coating is formed by mixing a volatile solvent containing acrylic resin as a binder and graphite as conductive particles, and its resistance value is 25 microns. It is about 50 Q Zsq. Therefore, the application of the Atchison conductive paint is used as an antistatic part in a part that is easily touched by humans, and as a shield coating for preventing electromagnetic interference in mobile phones and electronic devices.

As shown in FIG. 5, when the high resistance film 104 is formed with a film thickness of about 25 microns across the entire surface of the metal casing 102 excluding the feeding point 103, the antenna current i becomes high. Resistance

101

The anti-film 104 is excited by the reverse-phase current i. The component of the reverse-phase current i

102 102

Since it is suppressed depending on the resistance value, the antenna current i

101 increased, resulting in antenna The directivity gain G of the element 101 is improved.

101

[0018] When the component close to the antenna element 101 is not the metal casing 102 but an electronic component, the high-resistance film 104 formed on the surface of the electronic component causes a reverse phase to flow on the surface of the electronic component. The malfunction of the electronic component is suppressed by reducing the current i. One

102

In other words, by forming the high resistance film 104 on the surface of the electronic component adjacent to the antenna element 101, the noise margin of the electronic component can be improved.

FIG. 6 is a performance evaluation diagram showing the improvement of the directivity gain realized by the configuration of the small antenna device shown in FIG. 5. The horizontal axis shows the types with and without the high resistance film. The vertical axis shows the directivity gain (dBi). As shown in Fig. 6, the directivity gain without the high resistance film 104 on the surface of the metal housing 102 is 3.015 dBi, whereas the entire surface of the metal housing 102 (however, the feed point 103 The directivity gain when the high-resistance film 104 is formed on (except the portion) is 3.366 dBi. Therefore, the directivity gain is improved by about 0.3 dBi by forming the high resistance film 104 over the entire surface of the metal casing 102. This improvement can be said to be a significant improvement for mobile phones that receive signals with a directivity gain of several dBi.

[0020] It should be noted that there is almost no difference in the effect of improving the directivity gain due to the difference in the film thickness of the high resistance film 104 (that is, Acheson conductive paint) formed on the surface of the metal casing 102. Therefore, since the film thickness of the high resistance film 104 is hardly affected, the high resistance film 104 may be formed by coating that has a relatively thick film thickness rather than vapor deposition. In addition, since the directivity pattern of the antenna element 101 does not change between the case where the high resistance film 104 is formed on the surface of the metal casing 102 and the case where the high resistance film 104 is not formed, the high resistance film 104 is formed on the surface of the metal casing 102. This is considered to have no effect on the antenna characteristics.

In the second embodiment, the difference in the directivity gain improvement effect due to the difference in the length of the high resistance film formed on the surface of the metal casing 102 will be examined, and the optimum length of the high resistance film will be described. Fig. 7 is a conceptual diagram showing the current distribution when a high-resistance film is not used in the proximity portion facing the conventional antenna element. As shown in FIG. 7, when an antenna current i flows from the feed point 103 onto the antenna element 101, the surface of the metal casing 102 facing the antenna element 101 is reversed. Phase current i flows, and the surface area force facing the antenna element 101 in a chained manner is also separated.

102

Common-mode current i and common-mode current i

103 104 Flowing. Such common-mode currents i and i contribute to improving the directivity gain of the antenna element 101.

103 104

Give.

FIG. 8 is a conceptual diagram showing a current distribution when the high resistance film is formed over the entire surface of the metal casing 102 of FIG. That is, as shown in FIG. 7, when the length of the metal casing 102 is made longer than the length of the antenna element 101, the metal casing 102 has a reverse phase current i.

As shown in Fig. 8, there is a region where in-phase currents i and i flow as well as a region where 102 flows.

103 104

When the high resistance film 104 is formed over the entire surface of the metal housing 102, the reverse phase current i i that flows through the high resistance film 104

The force by which 102 is reduced

103 104 will also decrease. This is a factor that decreases the directivity gain of the antenna element 101. That is, when the length of the high resistance film 104 is made longer than the length of the antenna element 101, the directivity gain of the antenna element 101 is lowered.

FIG. 9 is a conceptual diagram showing a current distribution when a high resistance film is formed on the surface of the metal casing 102 by the same length as the antenna element in the metal casing 102 of FIG. In this case, as shown in FIG. 9, the reverse-phase current i flowing through the region of the high-resistance film 104 decreases, but the common-mode current

102

i and i do not decrease because the high resistance film 104 is not formed. That is, the common-mode current i

103 104 103

, I is the current that contributes to the improvement of the directivity gain of the antenna element 101.

104

By making the length of the element and the length of the high-resistance film 104 the same, the directivity gain of the antenna element 101 is improved.

FIG. 10 is a performance evaluation diagram comparing the magnitude of the effect of improving the directivity gain due to the difference in the length of the high resistance film 104 formed on the surface of the metal casing 102. 10A shows the difference in the length of the high-resistance film formed on the surface of the metal housing, and length A shows the case where the high-resistance film is formed by half the length of the antenna element. B shows the case where the high resistance film is formed by the same length as the length of the antenna element, and length C shows the case where the high resistance film is formed in the region facing the antenna element and in the entire region in front of it. The length D indicates the case where a high resistance film is formed over the entire surface of the metal housing!

FIG. 10B shows the directivity gain with respect to the length of each high resistance film 104 in FIG. 10A. The horizontal axis represents the length of the high-resistance film A, B, C, and D, and the vertical axis represents the directivity gain. For reference, V indicates that the high resistance film is not formed on the surface of the metal casing 102, and the magnitude of the directivity gain is also shown.

That is, when the high resistance film 104 is formed over the entire surface of the metal casing 102, the directivity gain in (D) is 3.366 dBi, and the high resistance film 104 is formed on the surface of the metal casing 102. Although the directivity gain is larger than the directivity gain (3.015 dBi) in the case of not doing so, the effect of forming the high-resistance film 104 is the lowest. Next, when the high-resistance film 104 is formed by half the length of the antenna element 101, the directivity gain in (A) is 3.498 dBi, and the high-resistance film 104 extends over the entire surface of the metal housing 102. The effect of improving the directivity gain is slightly greater than when (D) is formed. In addition, when the high resistance film 104 is formed in the region facing the antenna element 101 and in the entire region in front of it, the directivity gain in (C) is 3.556 dBi, which is more directional than in (A). The effect of improving the sex gain is great. The effect of improving the directivity gain is greatest when the high resistance film 104 is formed by the same length as the antenna element 101 (B), and the directivity gain is 3.651 dBi. That is, when the high resistance film 104 is formed by the same length as the length of the antenna element 101 (B), the directivity gain is improved to about 0.6 dBi compared to the case where the high resistance film 104 is not provided.

That is, the length of the high resistance film 104 formed on the surface of the metal casing 102 is the same as that of the antenna element 101, which contributes to the improvement of the directivity gain. In other words, the high resistance film 104 is formed on the surface of the metal casing 102 by focusing on the region where the reverse phase current i flows.

102

Thus, the directivity gain is most improved by suppressing only the reverse phase current. This means that when the metal casing 102 is replaced with an electronic component, the high resistance film 104 is formed on the surface of the electronic component that is close to the antenna element 101 by the same length, thereby flowing on the surface of the electronic component. Since only the reverse phase current can be suppressed, it is possible to suppress malfunction of the corresponding electronic component.

In Embodiment 3, the difference in the effect of improving the directional gain due to the difference in the width of the high resistance film formed on the surface of the metal casing 102 will be examined, and the optimum width of the high resistance film will be described. Fig. 1 1 shows a high-resistance film 104 of the same length and the same width as the antenna element in Fig. 7. 2 is a conceptual diagram showing a current distribution when formed in FIG. As shown in FIG. 11, when an antenna current i flows from the feed point 103 to the antenna element 101, the antenna element 101 faces the antenna element 101.

101

The reverse phase current i flows through the region of the high resistance film 104 that

102 102 A small value depending on the resistance value of the film 104.

However, since the width of the high resistance film 104 is the same as the width of the antenna element 101, the reverse phase currents i and i leak out on the surfaces of both side portions protruding from the width of the high resistance film 104.

102a 102b

It flows in. Therefore, the anti-phase current i on the high-resistance film 104 where the antenna current i force is also canceled

101 10

2 is small, but the opposite phase currents i and i on both sides

102a 102b exists, so the antenna current i

As a result, the apparent antenna current i becomes smaller.

1 101

The directivity gain of the N element 101 is reduced. The common-mode current i and the common-mode current i

103 104 flows, and this common-mode current i, i contributes to the improvement of the directivity gain of the antenna element 101.

103 104

This is the same as described in the second embodiment.

FIG. 12 is a conceptual diagram showing a current distribution when the length of the high resistance film 104 is the same as that of the antenna element 101 and the width is wider than the width of the antenna element 101 in FIG. That is, as shown in FIG. 12, when the width of the high-resistance film 104 of the metal casing 102 is wide, the high-resistance film 104 suppresses all of the reverse-phase current i generated by the opposing antenna element 101.

102

And negative phase current i

102 decreases, so the apparent antenna current i

101 gets bigger. As a result, the directivity gain of the antenna element 101 is improved. In other words, when the width of the metal casing 102 wider than the width force antenna element 101 of the high resistance film 104 is increased to the full width, the directivity gain of the antenna element 101 acts in the direction of improvement.

FIG. 13 is a performance evaluation diagram comparing the magnitude of the directivity gain improvement effect due to the difference in the width of the high resistance film 104 formed on the surface of the metal casing. That is, FIG. 13A shows the difference in the width of the high resistance film formed on the surface of the metal casing 102, the width E shows the case where the high resistance film is formed by the same width as the width of the antenna element 101, and the width F is The case where a high resistance film is formed wider than the width of the antenna element is shown!

[0032] FIG. 13B shows the magnitude of the directivity gain with respect to the width of each high resistance film 104 in FIG. 13A. The horizontal axis represents the types of widths E and F of the high resistance film 104, and the vertical axis represents Table of sex gain I am. For reference, the directivity gain when the high resistance film is not formed on the surface of the metal casing 102 is also shown.

That is, when the high resistance film having the same width as the antenna element 101 is formed, the directivity gain of (E) is 3.651 dBi, and the direction when the high resistance film is not formed on the surface of the metal housing 102 The directivity gain is larger than the directivity gain (3.015 dBi). However, when the high resistance film 104 is formed wider than the width of the metal housing 102, the directivity gain in (F) is 4.163 dBi, which is about 1. ldBi compared to the case without the high resistance film. Will improve. That is, when the width of the metal casing 102 is wider than the width of the antenna element 101, the directivity gain is improved to the maximum by increasing the width of the high-resistance film 104.

That is, in the region where the reverse phase current flows, the directivity gain is most improved by forming a high resistance film over the entire width of the metal casing 102 and suppressing only the reverse phase current. This means that when the metal housing 102 is replaced with an electronic component, a high-resistance film is formed on the surface of the electronic component with a width wider than that of the antenna element, so that only the reverse phase current flowing on the surface of the electronic component can be obtained. Since it can be suppressed, it is possible to suppress malfunction of the corresponding electronic component.

Industrial applicability

[0035] According to the small antenna device of the present invention, the directivity gain is greatly improved by forming a high-resistance film with an appropriate length and width on a mounting component close to the antenna element or a surface close to the metal surface. Therefore, it can be used effectively for mopile terminals such as mobile phones and mobile terminals.

Claims

The scope of the claims

[1] A small antenna device used in the electronic device in which at least a part of the antenna element is arranged in parallel with a mounting part of an electronic device or a metal surface, and the antenna element force, the mounting component or A small antenna device in which a high resistance film having a resistance value higher than that of at least the mounting component or the metal surface is formed on a surface of the metal surface.

[2] The small antenna device according to [1], wherein the length of the high-resistance film is substantially the same as the length of the antenna element in a region facing the antenna element.

[3] When the width of the mounting component or the metal surface is wider than the width of the antenna element, the width of the high resistance film is wider than the width of the antenna element in a region facing the antenna element. The small antenna device according to claim 1.

4. The small antenna device according to claim 3, wherein a width of the high resistance film is the same as a width of the mounting component or the metal surface.

5. The small antenna device according to claim 1, wherein the high resistance film is formed on a surface of the mounting component or the metal surface by vapor deposition or coating.