JP2008252201A - Antenna system and portable terminal using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve radiation efficiency of an antenna system during resonance of N-th (N: an odd number of ≥3) order. <P>SOLUTION: An antenna element 13 has a first conductor part 14 and a second conductor part 16 connected to the first conductor part 14 through a fold-back part 15, where at least a portion of the first conductor part 14 and at least a portion of the second conductor part 16 are disposed almost in parallel and the fold-back part 15 is disposed at a node of a potential in resonance of N-th (N: an odd number of ≥3) resonance of the antenna element 13. Resonance currents of N-th order intensify each other at at least the portion of the first conductor 14 and at least the portion of the second conductor part 16, the both being disposed almost in parallel. Consequently, the radiation efficiency of the antenna system 10 during resonance of N-th order can be improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an antenna device for wirelessly transmitting a signal and a portable terminal equipped with the antenna device.

  In recent years, there has been a tendency for mobile terminals to be miniaturized and built-in antenna devices. In addition, since a plurality of systems are used in one mobile terminal, the antenna device needs to support a plurality of frequency bands.

  Some conventional portable terminal antenna devices can handle a plurality of frequency bands with a single antenna element. Such a conventional antenna device is shown in FIG.

  In FIG. 6, a conventional antenna device 1 includes a ground plate 2, a power feeding unit 3 connected to the ground plate 2, and an antenna element 4 connected to the power feeding unit 3. It has the 1st conductor part 5 connected to the electric power feeding part 3, and the 2nd conductor part 7 connected to this 1st conductor part 5 via the folding | turning part 6. FIG. Further, at least a part of the first conductor part 5 and at least a part of the second conductor part 7 are arranged substantially in parallel. In addition, the front-end | tip 8 of the 2nd conductor part 7 is an open end. Thus, the conventional antenna device 1 has been reduced in size by being folded by the folding unit 6.

  In the above configuration, at the frequency at the time of primary resonance where the electrical length of the antenna element 4 is approximately ¼ wavelength, and at the frequency at the time of tertiary resonance where the electrical length of the antenna element 4 is approximately ¾ wavelength, A resonance current flows through the antenna element 4, and the antenna device 1 operates as an antenna. Thus, the antenna device 1 corresponds to two frequency bands with one antenna element 4.

As a prior art document related to the invention of this application, for example, Patent Document 1 is known.
JP 2001-223519 A

  When the conventional antenna device 1 performs third-order resonance, for example, as shown in FIG. 7, the current flowing through the first conductor portion 5 and the current flowing through the second conductor portion 7 in the vicinity 9 of the folded portion 6 are mutually Flow in opposite directions and cancel each other. As a result, there is a problem that the radiation efficiency of the antenna device 1 deteriorates.

  Therefore, an object of the present invention is to improve the radiation efficiency of the antenna device at the time of N (N is an odd number of 3 or more) order resonance.

  In order to achieve this object, an antenna device of the present invention includes a ground plate, a power feeding unit formed on the ground plate, and an antenna element connected to the power feeding unit, and the antenna element includes a power feeding unit. A first conductor portion connected to the first conductor portion and a second conductor portion connected to the first conductor portion via a folded portion, and at least a portion of the first conductor portion and at least a portion of the second conductor portion. Are arranged substantially in parallel, and the folded portion is located at the node of the potential at the N-th resonance (N is an odd number of 3 or more) of the antenna element.

  With the above-described configuration, the Nth order resonance current is strengthened in at least a part of the first conductor part and at least a part of the second conductor part that are arranged substantially parallel to each other. As a result, the radiation efficiency of the antenna device at the Nth order resonance can be improved.

(Embodiment 1)
The first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic diagram of an antenna device according to Embodiment 1 of the present invention.

  In FIG. 1, the antenna device 10 includes a ground plate 11, a power feeding unit 12 connected to the ground plate 11, and an antenna element 13 connected to the power feeding unit 12.

  A portable terminal (not shown) on which the antenna device 10 is mounted includes a signal processing unit (not shown) connected to the power feeding unit 12 and a signal reproduction unit (not shown) connected to the signal processing unit. Z).

  Further, the antenna element 13 includes a first conductor portion 14 connected to the power feeding portion 12 and a second conductor portion 16 connected to the first conductor portion 14 via a folded portion 15. At least a part of the first conductor part 14 and at least a part of the second conductor part 16 are arranged substantially in parallel. Note that the tip of the second conductor portion 16 is an open end. Further, the folded portion 15 is located at a node of the potential at the time of the third resonance of the antenna device 10.

  Next, the operation of the antenna device 10 in this configuration will be described.

  At the frequency at the time of primary resonance where the electrical length of the antenna element 13 is approximately ¼ wavelength and at the frequency at the time of tertiary resonance where the electrical length of the antenna element 13 is approximately ¾ wavelength, A resonance current flows, and the antenna device 10 operates as an antenna. Thus, the antenna device 10 corresponds to two frequency bands with one antenna element 13.

  Since the folded portion 15 is located at the node of the potential at the time of the tertiary resonance, as shown in FIG. 2, the first conductor portion 14 and the second conductor portion 16 that are arranged substantially parallel to each other have the third order. Resonance currents strengthen each other. As a result, it is possible to improve the radiation efficiency of the antenna device 10 at the time of the third resonance.

  The antenna device 10 may perform communication using primary resonance and N (N is an odd number equal to or greater than 3) order resonance, and the folded portion 15 may be positioned at the node of the potential at the time of the Nth resonance of the antenna element 13. . In this case, the radiation efficiency of the antenna device 10 at the Nth-order resonance can be improved. However, when the antenna device 10 is configured to perform communication using the primary resonance performed at the lowest resonance frequency and the tertiary resonance performed at the second lowest resonance frequency, the antenna device 10 is the smallest.

  Furthermore, it is desirable that the distance between the ground plate 11 and the first conductor portion 14 is smaller than the distance between the ground plate 11 and the second conductor portion 16. Thereby, the antinode of the potential at the third resonance on the first conductor portion 14 is closer to the ground plate 11 than the antinode of the potential at the first resonance on the second conductor portion 16. For this reason, the degree of coupling between the antenna element 13 and the ground plate 11 at the time of the third resonance is greater than the degree of coupling between the antenna element 13 and the ground plate 11 at the time of the primary resonance. That is, by increasing the degree of coupling between the antenna element 13 and the ground plate 11 at the third resonance, the third resonance frequency can be lowered, and as a result, the first resonance frequency and the third resonance frequency are brought closer. Can do. For example, when the primary resonance frequency is approximately 900 MHz, the tertiary resonance frequency does not become approximately 2.7 GHz which is three times as high as the above configuration, but becomes approximately 1.8 GHz. That is, an antenna device corresponding to the frequency bands of 900 MHz and 1.8 GHz can be realized.

(Embodiment 2)
Embodiment 2 of the present invention will be described below with reference to FIGS. 3 (a) and 3 (b). FIG. 3A is a perspective view of an antenna device according to Embodiment 2 of the present invention, and FIG. 3B is an enlarged perspective view of an antenna element. In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different point is described.

  3A and 3B, the difference between the second embodiment and the first embodiment is that the plane including the first conductor portion 14 and the second conductor portion 16 is substantially perpendicular to the ground plate 11. And the antenna element 13 is held by a base 17 made of a dielectric resin.

  With the above configuration, the distance by which the antenna element 13 protrudes from the ground plate 11 can be shortened, and the antenna device 10 can be downsized.

  Furthermore, by adopting a configuration in which the antenna element 13 is held by the base body 17, the antenna device 10 can be further downsized due to the relative dielectric constant of the base body 17. This is because the wavelength of the electromagnetic wave passing through the medium having the relative dielectric constant εr is multiplied by 1 / √εr compared to the wavelength of the electromagnetic wave passing through the medium having the relative dielectric constant 1, so that the antenna element 13 resonates at a lower frequency. Because you can.

(Embodiment 3)
Embodiment 3 of the present invention will be described below with reference to FIG.

  FIG. 4 is a schematic diagram of an antenna device according to Embodiment 3 of the present invention. In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different point is described.

  In FIG. 4, the difference between the third embodiment and the first embodiment is that the antenna device 10 includes a short-circuit portion 18 that connects the ground plate 11 and the first conductor portion 14.

  With the above configuration, even when the input impedance of the antenna device 10 is reduced by reducing the size of the antenna device 10, the short circuit 18 operates as an impedance matching element, so that the wireless circuit connected to the antenna device 10 and the power feeding unit 12 Impedance matching with (not shown) can be easily taken. In other words, when there is no short-circuit portion 18, the amplitude of the resonance current is maximized in the power feeding unit 12, whereas by providing the short-circuit portion 18, the amplitude of the resonance current is maximized in the short-circuit portion 18. Then, the amplitude of the resonance current in the power feeding unit 12 is reduced, and the input impedance of the antenna device 10 in the power feeding unit 12 is increased. As a result, impedance matching between the antenna device 10 and the wireless circuit connected to the power feeding unit 12 can be easily achieved, and the radiation efficiency of the antenna device 10 can be improved.

(Embodiment 4)
Hereinafter, Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 5A is a schematic diagram of an antenna device according to Embodiment 4 of the present invention. In addition, about the structure similar to Embodiment 1, the same code | symbol is attached | subjected, the description is abbreviate | omitted, and a different point is described.

  5 (a) and 5 (b), the difference between the fourth embodiment and the first embodiment is that the antenna device 10 is connected to the second conductor portion 16 and the wavelength of the antenna element 13 at the time of primary resonance is 8. This is a point provided with a third conductor portion 19 having an electrical length of 1 / min or less.

  The third conductor portion 19 can reduce the resonance frequency of the antenna element 13. Further, since the third conductor portion 19 has an electrical length of 1/8 or less of the wavelength at the time of primary resonance of the antenna element 13 and the distal end side of the third conductor portion 19 is an open end, the third conductor portion 19 Almost no current flows. Thus, for example, as shown in FIG. 5B, even when the third conductor portion 19 is disposed between the first conductor portion 14 and the second conductor portion 16, the current flowing through the third conductor portion 19 The current flowing through the first conductor portion 14 and the second conductor portion 16 is hardly affected, and the radiation efficiency of the antenna device 10 is hardly deteriorated.

  As described above, the antenna device of the present invention can improve the radiation efficiency at the time of N (N is an odd number of 3 or more) order resonance, and can be applied particularly to a small portable terminal having a plurality of systems. .

Schematic diagram of the antenna device according to Embodiment 1 of the present invention. Schematic diagram of current distribution in Embodiment 1 of the present invention (A) (b) is a perspective view of the antenna apparatus in Embodiment 2 of this invention. Schematic diagram of an antenna device according to Embodiment 3 of the present invention (A) (b) is the schematic diagram of the antenna device in Embodiment 4 of this invention. Schematic diagram of a conventional antenna device Schematic diagram of current distribution of conventional antenna device

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Antenna apparatus 11 Ground plate 12 Feed part 13 Antenna element 14 1st conductor part 15 Folding part 16 2nd conductor part 17 Base 18 Short circuit part 19 3rd conductor part

Claims (8)

A ground plate, a power feeding portion formed on the ground plate, and an antenna element connected to the power feeding portion,
The antenna element has a first conductor portion connected to the feeding portion, and a second conductor portion connected to the first conductor portion via a folded portion,
At least a part of the first conductor part and at least a part of the second conductor part are arranged substantially in parallel,
The folded portion is an antenna device positioned at a node of potential at the N-th resonance of the antenna element (N is an odd number of 3 or more). The antenna apparatus according to claim 1, wherein the Nth-order resonance is a third-order resonance. The antenna device according to claim 1, wherein a distance between the ground plate and the first conductor portion is smaller than a distance between the ground plate and the second conductor portion. 2. The antenna device according to claim 1, wherein a plane including the first conductor portion and the second conductor portion is disposed substantially perpendicular to the ground plate. The antenna device according to claim 1, wherein the antenna element is held by a base made of a dielectric resin. The antenna device according to claim 1, further comprising a short-circuit portion that connects the ground plate and the first conductor portion. 2. The antenna device according to claim 1, wherein the antenna element includes a third conductor portion connected to the second conductor portion and having an electrical length equal to or less than one-eighth of a wavelength at the time of primary resonance of the antenna element. . The portable terminal provided with the signal processing part connected to the said electric power feeding part of the antenna apparatus of Claims 1-7, and the signal reproduction | regeneration part connected to this signal processing part.

Images