JP2002353719A - Sar reduction device and wireless communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless communication device that attains ease of arrangement of a conductive member and reduces a local average SAR(Specific Absorption Rate). SOLUTION: Resonance is caused to the conductive member 20 in the case of communication. Since a lower end 20a of the conductive member 20 is open and an upper end 20b is connected to ground, that is, earthed, the impedance of the lower end 20a is close to ∞(infinitive impedance) and the impedance of the upper end 20b approaches zero. Since the upper end 20b of the conductive member 20 is connected to a part near an antenna feeding section 18, a current supplied form the antenna feeding section 18 flows through the conductive member 20. Then the current supplied from the conductive member 20 less flows to a part around a speaker 12 to reduce radiation of an electromagnetic wave around the speaker 12. Since the conductive member 20 is fitted to a rear side 14b of a shield case 14, the space to locate the conductive member 20 is easily ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable radio, and more particularly to a SAR (Specific Absorption Rat) for a small portable radio.
e: specific absorption rate).

[0002]

2. Description of the Related Art In recent years, the amount of electromagnetic waves emitted from a portable wireless device that is absorbed by the human body is determined by local average SAR (Specific A
There is a need for a technique that defines the maximum local average SAR value, which is defined by a bsorption rate (specific absorption rate), below a specified value.

[0003] The local average SAR of a portable radio is assumed to be during a call. FIG. 11 shows a state in which a call is being made using the portable wireless device. The mobile phone 100 is a speaker 102
Is provided. The speaker 102 is in contact with the user's ear 302. At this time, the local average SAR becomes the maximum
Usually, it has been confirmed that it is near the ear 304. The reason is considered to be as follows. That is, since the ground conductor or the shield case 104 of the circuit board 101 on the back of the speaker 102 operates as an antenna, electromagnetic waves are radiated. The speaker 102 is in contact with the ear 302 during a call. Therefore, since the ear 302 is close to the part from which the electromagnetic wave is radiated, the local average SAR near the ear 304 is maximized.

Here, the local average SAR near the ear 304
Is known. FIG. 12 is a perspective view of the mobile phone 100 (FIG. 12).
(A)), It is a side view (FIG.12 (b)). As shown in FIG. 12, the conductive member 12 is
0 is provided. The conductive member 120 is a speaker 1
02 and the shield case 104
And a short-circuit portion 124 for short-circuiting. The facing part 122
Is a length L = λ / 4 in the vertical direction. Here, λ is a wavelength corresponding to a radio frequency used by the mobile phone 100 for communication. If there is no conductive member 120, the antenna 106
From the antenna feeder 108 for feeding power to the speaker 102.
Since the high-frequency current flows through the ground conductor of the circuit board or the shield case 104 on the back of the speaker 102, electromagnetic waves are also emitted from the vicinity of the speaker 102. However, the conductive member 12
With 0, such a phenomenon can be avoided. Figure 1 illustrates this principle.
This will be described with reference to FIG.

[0005] From the antenna feeder 108 to the speaker 102
If no high-frequency current flows in the vicinity, the radiation of electromagnetic waves from the vicinity of the speaker 102 can be prevented. Then, speaker 1
If the impedance near 02 is increased, no high-frequency current flows near the speaker 102. Here, the conductive member 120
Satisfies the resonance condition at the radio frequency used for communication, the impedance of the connecting portion 122a where the opposing portion 122 connects to the short-circuit portion 124 approaches zero, and the opposing portion 12
The impedance of the upper end 122b of 2 approaches 近 (infinity). Therefore, the impedance near the speaker 102 also approaches ∞ (infinity), similarly to the impedance of the upper end 122b of the facing portion 122. As a result, no high-frequency current flows from the antenna feed unit 108 to the vicinity of the speaker 102. Note that the mark x in FIG. 12B means that no current flows. Therefore, since the radiation of the electromagnetic wave from the vicinity of the speaker 102 can be prevented, the local average SAR near the ear 304 decreases.

[0006]

However, there is a liquid crystal display device and a keyboard on the side of the portable telephone 100 where the speaker 102 is provided, and it is difficult to secure a sufficient space for disposing the conductive member 120.

Accordingly, an object of the present invention is to provide a wireless communication device in which the conductive members can be easily arranged and in which the local average SAR is reduced.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an SAR reduction device. An SAR reduction device according to the present invention includes a radiation reduction unit, a casing, a current source, a conductive member, and a conductive short-circuit member.

[0009] The radiation reducing section reduces the radiation of electromagnetic waves. The casing has a mounting surface on which the radiation reducing section is mounted and a back surface facing the mounting surface. The current source is mounted on the casing and supplies a current. The conductive member is
It is provided opposite to the back surface, the lower end is open, and causes resonance at the frequency used for communication. The conductive short-circuit member is
The upper end of the conductive member is connected to the ground near the current source on the back surface.

[0010] According to the invention configured as described above, the conductive member resonates during communication. In addition, since the lower end of the conductive member is open and the upper end is connected or grounded, the impedance of the lower end of the conductive member approaches ∞ (infinity) and the impedance of the upper end approaches 0.
Moreover, since the upper end of the conductive member is connected near the current source, the current flowing from the current source flows through the conductive member. Therefore, the current flowing from the current source rarely flows to the radiation reduction unit, and the radiation of the electromagnetic wave from the radiation reduction unit is reduced. Here, “near the current source” means that the current flowing from the current source is close to the current source to such an extent that the current almost flows to the conductive member.

Moreover, since the upper end of the conductive member is mounted on the back surface of the casing, it is not necessary to secure a space for the conductive member on the mounting surface. Therefore, the arrangement of the conductive member is easy.

By setting the electrical length of the conductive member to a length at which resonance occurs at a frequency used for communication,
It is possible for the conductive member to resonate at the frequency used for communication.

When a plurality of types of frequencies used for communication are set, it is preferable to provide a plurality of conductive members having an electrical length that causes resonance for each frequency. Thereby, it is possible to cope with frequencies used for a plurality of types of communication.

Here, it is preferable that the conductive member has a plurality of regions each having an open end corresponding to an electrical length at which resonance occurs at each frequency.

The electrical length in the plurality of regions having open ends is substantially equal to the average of the current paths in each region, but has a certain width. For this reason, there is a certain range in the frequency used for a plurality of types of communication, and it is possible to cope with the frequency band as it were.

Further, the SAR reduction device of the present invention can be used as a portable radio as it is.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a perspective view (FIG. 1A) and a side view (FIG. 1) of a portable telephone (portable radio) 10 according to a first embodiment of the present invention.
(B)).

The mobile phone 10 includes a circuit board 11, a speaker (radiation reducing unit) 12, a shield case 14, and an antenna 1
6, antenna feeding section (current source) 18, conductive member 20,
The conductive short-circuit member 22 is provided.

The circuit board 11 has mounted thereon a transmission / reception circuit for the mobile phone 10 to communicate with the base station and other various circuits. The transmission / reception circuit mounted on the circuit board 11 generates a transmission signal of a predetermined signal format. Further, it receives and demodulates the received signal. Note that a transmission circuit may be mounted on the circuit board 11 instead of the transmission / reception circuit.

The speaker (radiation reducing unit) 12 is for the user to listen to the telephone call of the mobile phone 10, and outputs the communication contents as voice. The speaker 12 comes into contact with the user's ear and has a local average SAR (Specific A).
In order to reduce bsorption rate (specific absorption rate), it is desirable that radiation of electromagnetic waves be reduced.

The shield case 14 is a casing of the mobile phone 10. The shield case 14 is attached to the mounting surface 14.
a, the back surface 14b. The speaker 1 is mounted on the mounting surface 14a.
2 is attached (see FIG. 1B). The back surface 14b is a surface opposite to the mounting surface 14a, that is, opposite to the mounting surface 14a. Note that the shield case 14 is also the ground of the mobile phone 10 and shields the circuit board 11 so that the transmission / reception circuit and other various circuits do not affect each other or the antenna 16 and other devices. . However, the shield case 14 may be a ground conductor mounted on the circuit board 11.

The antenna 16 is an antenna used when the mobile phone 10 performs communication. The antenna 16 shown in FIG. 1 is rod-shaped, but may be helical (spiral).
The shape may be a telescopic type or a combination of a rod shape and a helical shape.

The antenna feeding section 18 performs communication by supplying a high-frequency current to the antenna 16. In addition, the antenna feeding unit 18 is attached to an upper part of the shield case 14. In addition, since the shield case 14 also functions as an antenna, the antenna feed unit 18 also supplies a high-frequency current to the shield case 14. Further, the antenna feed unit 18 is arranged at the root of the antenna 16.

The conductive member 20 faces the back surface 14b. The conductive member 20 has a lower end 20a and an upper end 20b. The conductive member 20 is not connected to the mobile phone 10 at the lower end 20a, and the lower end 20a is an open end. The upper end 20b is located above the lower end 20a when the mobile phone 10 is set up in the posture shown in FIG. The upper end 20b is connected to the shield case 14 by a conductive short-circuit member 22. Here, the length L of the conductive member 20 is set to λ / 4. Here, λ is a wavelength corresponding to a frequency used when the mobile phone 10 performs communication. If L = λ / 4, resonance occurs at the frequency used when the mobile phone 10 performs communication. In addition,
If resonance occurs, a value other than L = λ / 4 (for example, 3λ /
4) It does not matter.

The conductive short-circuit member 22 connects the upper end 20 b of the conductive member 20 to the shield case 14. A connection point 22a where the conductive short-circuit member 22 and the shield case 14 are connected is near the antenna power supply unit 18. In addition,
Here, “near the antenna feed unit 18” means that the current flowing from the antenna feed unit 18 is close to the antenna feed unit 18 to such an extent that the current almost flows to the conductive member 20.

Next, the operation of the first embodiment will be described.

When communication is performed by the mobile phone 10, the antenna feeder 18 supplies current not only to the antenna 16 but also to the shield case 14, so that a high-frequency current may flow near the speaker 12. Speaker 12
Is in contact with the ear, and a large amount of electromagnetic waves radiated from the vicinity of the speaker 12 are absorbed near the ear. Therefore, it is preferable to reduce the amount of electromagnetic waves radiated from the vicinity of the speaker 12.

If a high-frequency current does not flow from the antenna feeding section 18 to the vicinity of the speaker 12, radiation of electromagnetic waves from the vicinity of the speaker 12 can be prevented. Therefore, if an excessive current flows on the opposite side to the vicinity of the speaker 12, that is, on the back surface 14b, regardless of the impedance near the speaker 12,
No high-frequency current flows near the speaker 12. In order to flow an excessive current from the antenna feed unit 18 to the back surface 14b,
What is necessary is just to make the impedance of the part near the antenna feed part 18 in the back surface 14b zero. At this time, speaker 1
The impedance near 2 does not need to approach ∞ (infinity).

Here, since the conductive member 20 satisfies the resonance condition at the radio frequency used for communication, the lower end 20
The impedance of a approaches ∞ (infinity), and the impedance of the connection point 22a of the conductive short-circuit member 22 approaches 0.

As a result, an excessive high-frequency current flows from the antenna feed section 18 to the connection point 22a. Current is at connection point 2
After passing through 2a, it flows to the conductive member 20 and is radiated. Therefore, no high-frequency current flows from the antenna feed section 18 to the vicinity of the speaker 12. Therefore, since the radiation of the electromagnetic wave from the vicinity of the speaker 102 can be prevented, the local average S near the ear is reduced.
AR decreases.

According to the first embodiment, the current flowing from the antenna feeding section 18 flows to the conductive member 20 and rarely flows near the speaker 12, so that the radiation of electromagnetic waves from the vicinity of the speaker 12 is reduced.

Here, if an excessive current flows on the opposite side to the vicinity of the speaker 12, that is, on the back surface 14b, the speaker 1
It is particularly new that attention has been paid to the fact that high-frequency current does not flow near the speaker 12 irrespective of the impedance near the speaker 2. Conventionally, there was an idea to increase the impedance near the speaker 12 to near ∞ (infinity),
This does not suggest the idea of the first embodiment that the impedance near the speaker 12 is not particularly limited.

Moreover, the upper end 20b of the conductive member 20 is
Since it is attached to the back surface 14b of the shield case 14, it is not necessary to secure a space for the conductive member 20 on the attachment surface 14a.

In FIG. 1, the conductive member 20 is shown as being linear. However, as a modification, the conductive member 20 may have a meandering shape (FIG. 2) or a spiral shape (FIG. 3) depending on the space in which the conductive member 20 is arranged. Note that the circuit board 11 is not shown in FIG.

The conductive member 20 may be a rectangular flat plate (FIGS. 4 and 5). FIG. 4 shows the conductive member 20.
Are rectangular, and the conductive short-circuit member 22 is a rod-shaped member similar to FIG. In the example of FIG. 4, the vertical length L1
And the horizontal length L2 are defined as a length at which resonance such as λ / 4 occurs. FIG. 5 shows an example in which the conductive member 20 and the conductive short-circuit member 22 are rectangular, and these rectangles have the same horizontal length. In the example of FIG. 5, the vertical length L3 of the conductive member 20 is set to a length at which resonance such as λ / 4 occurs. When the vertical length L4 of the conductive short-circuit member 22 is increased, the frequency bandwidth used for communication in which the reduction of the local average SAR by the conductive member 20 is effective is increased. For example, when the communication frequency is 900 MHz, L4 is 2−2.
4 mm is preferred.

Further, as shown in FIG.
The dielectric material 24 may be inserted between the back surface 14b and the zero.
In this case, the length L of the conductive member 20 is set to λ ′ / 4.
Here, λ ′ is a wavelength in the dielectric 24 at a frequency used when the mobile phone 10 performs communication. L =
If λ ′ / 4, resonance occurs at the frequency used when the mobile phone 10 performs communication. Note that if resonance occurs, L may not be L = λ ′ / 4 (for example, 3λ ′ / 4).

Second Embodiment The mobile phone 1 according to the second embodiment can reduce the local average SAR even when a plurality of frequencies to be used for communication are set, as compared with the first embodiment. The difference was that

FIG. 7 is a perspective view (FIG. 7A) of a mobile phone (portable wireless device) 10 according to a second embodiment of the present invention.
It is a rear view (FIG.7 (b)). Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The mobile phone 10 includes a circuit board 11, a speaker (radiation reducing unit) 12, a shield case 14, and an antenna 1
6, antenna feeding section (current source) 18, conductive member 20,
The conductive short-circuit member 22 is provided. Circuit board 11, speaker (radiation reducing unit) 12, shield case 14, antenna 1
6. The antenna feed unit (current source) 18 is the same as in the first embodiment. However, the frequency used by the mobile phone 10 for communication is set to two types, f1 and f2. That is, the mobile phone 10 performs so-called dual band communication.

The conductive member 20 includes a first conductive member 202.
And a second conductive member 204. The first conductive member 202 has a lower end 202a and an upper end 202b.

The first conductive member 202 is not connected to the mobile phone 10 at the lower end 202a.
a is an open end. The upper end 202b is the mobile phone 1
0 in the posture shown in FIG.
It is located above a. The upper end 202b is connected to the shield case 14 by a conductive short-circuit member 22.

The lower end 204a of the second conductive member 204 is not connected to the mobile phone 10 at the lower end 204a.
a is an open end. The upper end 204b is the mobile phone 1
0 in the posture shown in FIG.
It is located above a. The upper end 204b is connected to the shield case 14 by a conductive short-circuit member 22.

The length L10 of the first conductive member 202 is
(１ ／) × λ10, and the length L12 of the second conductive member 204 is (１ ／) × λ12. Where λ10
Is a wavelength corresponding to the frequency f1. λ12 is a wavelength corresponding to the frequency f2. L10 = (1/4) × λ
If it is set to 10, resonance occurs at the frequency f1. L1
If 2 = (1/4) × λ12, resonance occurs at the frequency f2. Note that if resonance occurs at the frequency f1, other than L10 = (1/4) × λ10 (for example, (3
/ 4) × λ10). If resonance occurs at the frequency f2, L12 = (1/4) × λ12
(For example, (3/4) × λ12).

The conductive short-circuit member 22 is formed by the first conductive member 2
02 and the upper end 204 b of the second conductive member 204 are connected to the shield case 14. A connection point 22a where the conductive short-circuit member 22 and the shield case 14 are connected is near the antenna power supply unit 18. In addition,
Here, “near the antenna feed unit 18” means that the current flowing from the antenna feed unit 18 is close to the antenna feed unit 18 to such an extent that the current almost flows to the conductive member 20.

The operation of the second embodiment is almost the same as the operation of the first embodiment. However, when the frequency used by the mobile phone 10 for communication is f1, a high-frequency current flows from the antenna feed unit 18 to the first conductive member 202.
When the frequency used by the mobile phone 10 for communication is f2, the antenna feeder 18 is connected to the second conductive member 204.
High-frequency current flows from the

According to the second embodiment, the local average SAR can be reduced even when the mobile phone 10 uses two types of frequencies for communication, that is, when performing dual-band communication. In the second embodiment, the case where there are two types of frequencies used for communication has been described. However, when three or more types of frequencies are set, a conductive member may be provided for each frequency. For example, when three types of frequencies are set, a first conductive member, a second conductive member, and a third conductive member may be provided corresponding to each frequency.

Third Embodiment The mobile phone 1 according to the third embodiment is different from the second embodiment in that the shape of the conductive member 20 is a flat plate with a slit.

FIG. 8 is a perspective view of a mobile phone (portable wireless device) 10 according to the third embodiment of the present invention. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The mobile phone 10 includes a circuit board 11, a speaker (radiation reducing unit) 12, a shield case 14, and an antenna 1
6, antenna feeding section (current source) 18, conductive member 20,
The conductive short-circuit member 22 is provided. Circuit board 11, speaker (radiation reducing unit) 12, shield case 14, antenna 1
6. The antenna feed unit (current source) 18 is the same as in the first embodiment. However, two types of frequencies used by the mobile phone 10 for communication, f1 and f2, are set (f1 <
f2). That is, the mobile phone 10 performs so-called dual band communication.

The conductive member 20 is a planar member having a slit 20c. The conductive member 20 includes the slit 2
0c provides two open ends 20d, 20e. FIG. 9 shows a plan view of the conductive member 20. As shown in FIG.
The conductive member 20 has regions 20f and 20g. The region 20f has an open end 20e. Area 20g is open end 2
0d. The region 20f is a region where a high-frequency current flows from the antenna power supply 18 at the frequency f1. The region 20g is a region where a high-frequency current flows from the antenna power supply 18 at the frequency f2. Here, the average of the paths through which the high-frequency current flows in the region 20f is defined as the electrical length LA of the region 20f. Almost the average of the paths through which the high-frequency current flows in the region 20g is defined as the electrical length LB of the region 20g.

Here, the path through which the high-frequency current flows in the region 20f (20g) is not a single path.
That is, a plurality of routes passing through the region 20f (20g). Normally, since the length differs for each path, the average of the path lengths is taken as the electrical length. Of course, since the length of each path is not equal to the average of the path lengths,
The electrical length of 0f (20 g) is a value within a certain range, rather than a certain value. Also,
Regarding the shape of the region 20f (20g), the open end 20e
What is necessary is to have (20d), and what is shown in FIG. 9 is an approximate shape.

Here, LA is (1/4) × λ10,
LB is (1/4) × λ12. Where λ10 is
This is a wavelength corresponding to the frequency f1. λ12 is the frequency f
2 corresponds to the wavelength. If LA = (1/4) × λ10, resonance occurs at the frequency f1. LB = (1
/ 4) × λ12, resonance occurs at the frequency f2. If resonance occurs at the frequency f1,
LA = other than (1/4) × λ10 (for example, (3/4) × λ
10) It does not matter. If resonance occurs at the frequency f2, LB may be other than (1/4) × λ12 (for example, (3/4) × λ12).

The conductive short-circuit member 22 connects the upper left of the conductive member 20 to the shield case 14. A connection point 22a where the conductive short-circuit member 22 and the shield case 14 are connected is near the antenna power supply unit 18. Here, “in the vicinity of the antenna power supply unit 18” means that the current flowing from the antenna power supply unit 18 is close to the antenna power supply unit 18 to the extent that the current almost flows to the conductive member 20.

The operation of the third embodiment is almost the same as the operation of the second embodiment. However, when the frequency used by the mobile phone 10 for communication is f1, a high-frequency current flows from the antenna feed unit 18 to the area 20f. When the frequency used by the mobile phone 10 for communication is f2,
A high-frequency current flows from the antenna feed unit 18 to the region 20g.

Here, the electrical length LA (L) of the region 20f (20g) is changed by the change in the shape of the region 20f (20g) and the change in the path of the current flowing through the region 20f (20g).
B) varies. Therefore, it is possible to broaden the communication frequency band in which the local average SAR can be reduced. FIG. 10 shows a comparison of the reflection loss (corresponding to the local average SAR) characteristic.
For example, when the conductive member 20 is linear as in the second embodiment (see FIG. 7), the electrical length is substantially constant, and therefore the communication frequency at which the reflection loss, that is, the local average SAR is equal to or less than a predetermined value. Has a narrow width W1. However, in the case of the conductive member 20 as in the third embodiment, the electrical length LA (L
Since B) fluctuates to some extent, the width W2 of the communication frequency at which the reflection loss, that is, the local average SAR becomes equal to or less than a predetermined value, is increased.

According to the third embodiment, the local average SAR can be reduced even when the mobile phone 10 uses two types of frequencies for communication, that is, when performing dual-band communication. Moreover, the region 20f (20g) of the conductive member 20
Since the electrical length LA (LB) of the first embodiment fluctuates to some extent, the width of the communication frequency at which the local average SAR becomes equal to or less than a predetermined value can be widened.

[0058]

According to the present invention, the conductive member resonates during communication. Moreover, the lower end of the conductive member is opened,
Since the upper end is connected or grounded to the ground, the impedance at the lower end of the conductive member approaches ∞ (infinity) and the impedance at the upper end approaches 0. Moreover, since the upper end of the conductive member is connected near the current source, the current flowing from the current source flows through the conductive member. Therefore, the current flowing from the current source rarely flows to the radiation reduction unit, and the radiation of the electromagnetic wave from the radiation reduction unit is reduced.

Moreover, since the upper end of the conductive member is attached to the back surface of the casing, it is not necessary to secure a space for the conductive member on the mounting surface.

[Brief description of the drawings]

FIG. 1 is a perspective view (FIG. 1A) and a side view (FIG. 1) of a mobile phone (portable wireless device) 10 according to a first embodiment of the present invention.
(B)).

FIG. 2 is a perspective view showing a modification (meandering type) of the mobile phone (portable wireless device) 10 according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a modification (spiral) of the mobile phone (portable wireless device) 10 according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a modification (rectangular flat plate) of the mobile phone (portable wireless device) 10 according to the first embodiment of the present invention.

FIG. 5 is a perspective view showing a modification (rectangular flat plate) of the mobile phone (portable wireless device) 10 according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a modification (dielectric) of the mobile phone (portable wireless device) 10 according to the first embodiment of the present invention.

FIG. 7 is a perspective view (FIG. 7A) and a rear view (FIG. 7) of a mobile phone (portable wireless device) 10 according to a second embodiment of the present invention.
(B)).

FIG. 8 is a perspective view of a mobile phone (portable wireless device) 10 according to a third embodiment of the present invention.

FIG. 9 is a plan view of the conductive member 20.

FIG. 10 is a graph showing a comparison of reflection loss (corresponding to a local average SAR) characteristic.

FIG. 11 is a diagram showing a state in which a telephone call is being made by a portable wireless device in the related art.

FIG. 12 is a perspective view (FIG. 12 (a)) and a side view (FIG. 12 (b)) of a mobile phone 100 according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Cellular phone 11 Circuit board 12 Speaker (radiation reduction part) 14 Shield case 16 Antenna 18 Antenna feed part (current source) 20 Conductive member 20d Open end 20e Open end 20f Area 20g Area 202 First conductive member 204 Second conductive Conductive member 22 conductive short-circuit member

Claims (18)

[Claims] 1. A radiation reducing portion for reducing radiation of an electromagnetic wave, a casing having a mounting surface on which the radiation reducing portion is mounted, and a back surface facing the mounting surface, and mounted on the casing to supply current. A current source, a conductive member provided opposite to the back surface, having a lower end opened and causing resonance at a frequency used for communication, and an upper end of the conductive member connected to a ground near the current source on the back surface. And a conductive short-circuit member. 2. The SAR reduction device according to claim 1, wherein the electrical length of the conductive member is a length that causes resonance at a frequency used for communication. 3. The SAR reduction device according to claim 2, wherein the shape of the conductive member is any one of a straight line, a meandering shape, and a spiral. 4. The SAR reduction device according to claim 1, wherein the conductive member has a rectangular shape, and a sum of a vertical length and a horizontal length of the conductive member is a frequency used for communication. SAR is the length that causes resonance in
Reduction device. 5. The SAR reduction device according to claim 1, wherein the conductive member and the conductive short-circuit member are rectangles having a common horizontal length, and a vertical length of the conductive member. The SAR reduction device has a length that causes resonance at a frequency used for communication. 6. The SAR reduction device according to claim 1, wherein a plurality of types of frequencies used for communication are set, and the plurality of conductive members having an electrical length causing resonance for each of the frequencies are provided. SAR reduction device provided. 7. The SAR reduction device according to claim 6, wherein the shape of the conductive member is a straight line. 8. The SAR reduction device according to claim 1, wherein a plurality of types of frequencies used for communication are set, and the conductive member corresponds to an electrical length at which resonance occurs for each frequency. And a plurality of regions each having an open end. 9. The SAR reduction device according to claim 2, further comprising a dielectric inserted between the conductive member and the back surface. 10. A radiation reducing portion for reducing radiation of an electromagnetic wave, a casing having a mounting surface on which the radiation reducing portion is mounted, and a back surface facing the mounting surface, and mounted on the casing to supply current. A current source, a conductive member provided opposite to the back surface and having a lower end opened and causing resonance at a frequency used for communication; and an upper end of the conductive member connected to a ground near the current source on the back surface. And a conductive short-circuit member. 11. The portable wireless communication device according to claim 10, wherein an electrical length of said conductive member is a length that causes resonance at a frequency used for communication. 12. The portable wireless communication device according to claim 11, wherein the shape of the conductive member is any one of a straight line, a meandering shape, and a spiral. 13. The portable wireless communication device according to claim 10, wherein the conductive member has a rectangular shape, and a total of a vertical length and a horizontal length of the conductive member is used for communication. A portable wireless communication device that is long enough to resonate at frequencies. 14. The portable wireless communication device according to claim 10, wherein the conductive member and the conductive short-circuit member have a rectangular shape having a common horizontal length, and the conductive member has a vertical shape. A portable wireless communication device whose length is a length that causes resonance at a frequency used for communication. 15. The portable wireless communication device according to claim 10, wherein a plurality of types of frequencies used for communication are set, and a plurality of said conductive members having an electrical length causing resonance for each of said frequencies. A portable wireless communication device comprising: 16. The portable wireless communication device according to claim 15, wherein said conductive member has a straight shape. 17. The portable wireless communication device according to claim 10, wherein a plurality of types of frequencies used for communication are set, and said conductive member has an electrical length that causes resonance for each frequency. A portable wireless communication device having a plurality of regions, each having an open end. 18. The portable wireless communication device according to claim 11, further comprising a dielectric inserted between said conductive member and said back surface.