WO2003009417A1

WO2003009417A1 - Battery antenna for portable wireless communication terminal

Info

Publication number: WO2003009417A1
Application number: PCT/KR2002/000302
Authority: WO
Inventors: Hun-Joong Park
Original assignee: Actipass Co., Ltd.
Priority date: 2001-07-20
Filing date: 2002-02-25
Publication date: 2003-01-30
Also published as: KR20010088474A; KR100420546B1

Abstract

A battery antenna (6) for a portable wireless communication terminal matches locations of a feeder (5) provided on a location of said communication terminal, a ground plate (2) of a groove for inserting a battery for said communication terminal, and a short plate (4) such a way to arrive at an improved planar inverted F-antenna (PIFA). The improved PIFA symmetrically adds an inverted L-radiation structure extended from a short plate to the short plate of the conventional PIFA to provide a double resonance structure, therey increasing the available bandwidth. Hence, the present invention prevents efficiency reduction of greater than 25% in the frequency band caused by a small structure of a conventional built-in antenna, and also eliminates the required space for inserting a conventional antenna and greatly reduces electromagnetic waves to the human brain, as well as SAR.

Description

Battery Antenna for Portable Wireless Communication Terminal

BACKGROUND OF THE INVENTION (a) Field of the Invention

The present invention relates to a wireless communication terminal's

antenna used for a portable wireless telephone or a portable terminal. More specifically, the present invention relates to a battery antenna for a wireless communication terminal for minimizing the size of a portable wireless communication terminal, maintaining radiation efficiency, and reducing electromagnetic waves toward human bodies. This is done by using a portable wireless communication terminal's battery as an antenna when manufacturing a very small planar antenna for minimization of the size of the portable wireless terminal and for greatly reducing radiation efficiency, by installing the planar antenna in the rear portion of the portable wireless terminal using a conventional method for reducing the specific absorption rate (SAR) that controls the influences of the electromagnetic waves to the human body when the wireless terminal is used.

(b) Description of the Related Art FIG. 1 shows a conventional monopole antenna, that is, an isotropic antenna for a wireless communication terminal. The monopole antenna radiates electromagnetic waves to the human body in the communication direction so as to cause a high SAR. To solve the problem, a small built-in antenna used for the conventional portable wireless communication terminal, such as a small loop antenna disclosed in the Korean laid-open Patent no. 1997-0068163, has an available frequency band of less than 3%, and a planar inverted F antenna (PIFA) disclosed in the Korean laid-open Patent no. 2000-0045787 reduces 75% of the radiation efficiency (that is, -6dB) to the maximum in the available frequency band. In the above, an electromagnetic wave shield is provided between a radiation surface and a ground plate to cut the electromagnetic waves that flow on the ground plate so that a voltage standing wave ratio (VSWR) that represents the efficiency of the antenna may be less than 2:1. In the actual field, when the gap between the ground plate 2 and the radiation surface 3 of the PIFA of FIG. 2 is set to be from 0.01 to 0.03 times the wavelength, the maximum available frequency band ranges from 1 to 4%, and when a high dielectric material having a permittivity of greater than 10 is used for the minimization of the antenna, the available frequency band ranges from 0.5 to 2%. In this state, in the case of the electromagnetic wave shield as described in the above patent, the electromagnetic waves that reach the voltage standing waves are only cut and are not radiated, thereby representing the same radiation efficiency. FIG. 2 shows a conventional PIFA.

FIG. 3 shows a maximum available frequency band ratio that satisfies the VSWR of 2:1 according to the height from the ground plate to the radiation surface of the PIFA, from "Analysis of Planar Inverted F

Antenna Using Spatial Network Method," by K. Tsunoda, et al from IEEE

1990. The parameter L1 represents a length of the radiation surface (patch), L2 indicates a width of the radiation surface, and H shows the height from the ground surface to the radiation surface of the PIFA. The reference numeral L1 represents a length L of an antenna, L2 indicates a width W of the radiation surface (or a patch), H shows a height, and the numbers provided to the respective top portions of curves represent a ratio of the width of the radiation surface to the width of a short plate.

An equation for finding efficiency with the VSWR from the frequency band ratio of the VSWR of 2:1 is as follows.

An equation for calculating the available frequency band ratio with respect to a predetermined VSWR of the antenna is expressed in Equation 1.

Equation 1

BW = ^{VSWR ~ l}

Q JVSWR

where BW represents the ratio of the available frequency band with respect to a central frequency, VSWR indicates the voltage standing wave ratio, and Q shows a resonance factor of the antenna.

When finding a frequency band, ratio with respect to another VSWR from the frequency band ratio with respect to a predetermined VSWR of the same antenna by offsetting Q from Equation 1 , Equation 2 is obtained as follows. Equation 2

^■ VSWRl VSWR -1 BW = BW\ ^{rj M x}

VSWRl-l JVSWR

where BW1 represents a known frequency band ratio, and VSWR1 indicates a known voltage standing wave ratio as a reference to the previous frequency band ratio.

FIG. 4 shows graphs for calculating an available frequency band VSWR for finding the VSWR of a desired frequency bandwidth BW from a frequency bandwidth BW1 having a VSWR1 of less than 2:1 from Equation 2.

FIG. 5 shows graphs for calculating the standing wave efficiency from the VSWR found from FIG. 4.

As an example for calculating the efficiency of a conventional very small built-in antenna, the PCS frequency band, one mobile communication frequency band, ranges from 1.75 to 1.87GHz thus having the bandwidth of 120MHz, and has a center frequency of 1.81 GHz, and accordingly, the frequency band ratio is 120/1810=0.07.

Table 1 represents the VSWR efficiency of an antenna according to the height of the radiation surface with respect to the ground plate at the frequency band ratio of 0.07 found from the very small antenna.

In Table 1 , the height of the radiation surface represents the gap between the ground plate 2 and a battery antenna 6, and also indicates the height of the short plate 4. Since the wavelength of the electromagnetic wave at 1810MHz is 165.7mm, the height with respect to the height of 1 mm of the radiation surface is 1/165.7=0.006 wavelength.

Referring to FIG. 1 , the VSWR efficiency according to the height of the radiation surface of the very small antenna is 5 to 60%. If considering the current compact trends of up-to-date mobile phones, the mobile phones cannot afford to install an antenna having a length of 10mm on the mobile phone's surface. The antenna's minimum length for adequate operation at 1810MHz is 41mm, that is, the length of 1/4 of the wavelength, and when desiring to reduce the antenna length to 10mm and maintain its electrical length to be 1/4 of the wavelength, it is satisfied that

^permittivity = 41mm /10mm = 4.1 , and the permittivity of the medium becomes 16.8. Referring to FIG. 2, when the permittivity of the medium between the ground plate 2 and the radiation surface 3 is 16.8, it corresponds to high permittivity, and when the antenna is manufactured with a radiation surface height of less than 2mm so as to be installed in a mobile phone, it has the VSWR of 15%, and thereby the efficiency reduces by six times compared to that of 90% in the case of the VSWR of 2:1 of FIG. 5.

Also, since the commonly used monopole antenna of FIG. 1 is isotropic, when a person calls, electromagnetic waves are radiated to the human body, and accordingly, the SAR increases. FIG. 6 shows an electromagnetic wave radiation pattern diagram with respect to the horizontal surface of the monopole antenna in the free space, and FIG. 7 shows an electromagnetic wave radiation pattern diagram with respect to the horizontal surface of the monopole antenna when a wireless communication terminal is adjacent to a user's ear to make a call. Referring to FIG. 7, the electromagnetic waves toward the human body are reduced by 20dB to the maximum reduction, which represents that 99% of the electromagnetic waves are reduced, and the reduced amounts of the electromagnetic waves are reflected on the surface of the human body and absorbed into the human body, particularly into the head. FIG. 8 shows states in which the electromagnetic waves radiated from the monopole antenna are absorbed into the human body, indicating that the electromagnetic waves are greatly reduced in the head step by step, and are deeply penetrated into the head, through the ear in particular. SUMMARY OF THE INVENTION

It is an object of the present invention to reduce the electromagnetic waves to be radiated to the human body from the conventional portable wireless communication terminal's monopole antenna, improve SAR,

improve the decrease of radiation efficiency of a very small built-in antenna installed on the rear portion of a wireless communication terminal, remove the conventional wireless communication terminal's monopole antenna to

improve its appearance, improve portability problems, and eliminate the space of the conventional wireless communication terminal's built-in antenna to thereby slim the size of the wireless communication terminal.

Referring to FIG. 9, the present invention comprises a feeder 5 for transmitting and receiving signals from the ground plate 2 of a groove for inserting a battery of a portable wireless communication terminal to the battery antenna 6, and a short plate 4 for using the battery antenna 6 as a PIFA. The location of the short plate 4 is set to satisfy a frequency F of

Equation 3 when a width of the short plate 4 is manufactured to be narrower than that of the battery antenna 6.

Equation 3

_-?-i W.._ 4(L-+-H-) ₊ - W.) 4(L +W ^e- + — H -S) -

where F represents a resonance frequency, c indicates the speed of light, S shows a width of the short plate, W represents a width of the battery antenna 6, L shows a distance from the top end point of the battery antenna 6 to the short plate 4, and H indicates a height of the short plate 4.

To maximize the available frequency band of the battery antenna 6, a condition that S=W must be satisfied, and when a state that S/W=1 is substituted, Equation 3 is expressed as Equation 4.

Equation 4

4(1 +H)

The location of the short plate 4 found from Equation 4 is expressed in Equation 5.

Equation 5

L = — -H

4 where λ represents a wavelength to be expressed by C/F.

In the actual manufacturing, the L is close to a value of

0.951, / ^material's permittivity - (thickness fimction of the battery antenna) becaus

e of the size and material of the wireless communication terminal. When the length L between the top portion of the battery antenna 6 and the short plate 4 is determined through the above-described method, a double resonance process is performed on the bottom portion of the short plate 4 so as to function as another antenna for increasing the available frequency band of the antenna. The length from the short plate 4 to the bottom portion of the battery antenna 6 is designed to be shorter than the length L of the top portion by 2 to 3%, so that it may resonate at a predetermined frequency to increase the available frequency bandwidth. The location of the feeder 5 is adjusted to be at a point where the radiation

resistance at the top portion of the short plate 4 is 50 Ω and the available

frequency band is the widest. This antenna will be referred to as an inverted

F antenna having an inverted L short plate and a shared double resonance

structure. The antenna according to the present invention increases

bandwidths according to its thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the

invention, and, together with the description, serve to explain the principles of

the invention:

FIG. 1 shows a configuration of a conventional monopole antenna

for a wireless communication terminal; FIG. 2 shows a configuration of a conventional planar inverted F

antenna;

FIG. 3 shows a graphical diagram of frequency bandwidth of a

conventional planar inverted F antenna;

FIG. 4 shows graphs for calculating frequency band ratios in terms of

the voltage standing wave ratio (VSWR);

FIG. 5 shows graphs for calculating the VSWR in terms of efficiency;

FIG. 6 shows a horizontal radiation pattern diagram of a conventional

wireless communication terminal's monopole antenna in the free space; FIG. 7 shows a horizontal radiation pattern diagram when a conventional wireless communication terminal's monopole antenna is

adjacent to a human body;

FIG. 8 shows a phenomenon in which electromagnetic waves are absorbed into a human body when a person calls;

FIG. 9 shows a configuration of a battery antenna for a wireless communication terminal according to a first preferred embodiment of the present invention;

FIG. 10 shows VSWR characteristics of the battery antenna for a wireless communication terminal according to a first preferred embodiment of the present invention;

FIG. 11 shows a horizontal radiation pattern diagram of a wireless communication terminal's battery antenna in the free space according to a first preferred embodiment of the present invention; FIG. 12 shows a side view of a wireless communication terminal's battery antenna according to a second preferred embodiment of the present invention;

FIG. 13 shows a side view of a wireless communication terminal's

battery antenna according to a second preferred embodiment of the present invention;

FIG. 14 shows a side view of a wireless communication terminal's battery antenna according to a second preferred embodiment of the present invention; FIG. 15 shows a side view of a wireless communication terminal's

battery antenna according to a second preferred embodiment of the present

invention;

FIG. 16 shows a side view of a wireless communication terminal's

battery antenna according to a third preferred embodiment of the present

invention;

FIG. 17 shows a side view of a wireless communication terminal's

battery antenna according to a third preferred embodiment of the present

invention; FIG. 18 shows a side view of a wireless communication terminal's

battery antenna according to a third preferred embodiment of the present

invention; and

FIG. 19 shows a front view of a wireless communication terminal's

battery antenna according to a fourth preferred embodiment of the present

invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiments

of the invention have been shown and described, simply by way of illustration

of the best modes contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in

various obvious respects, all without departing from the invention.

Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.

(First preferred embodiment)

Table 2 shows approximate design values of a battery antenna used for the frequency bands of between 1.75 and 1.87GHz, and corresponding frequency bandwidth performance that satisfies the VSWR of 2:1.

Table 2

The above-described antenna satisfies the VSWR of 2:1 with respect to the thickness of 6mm as shown in Table 2, in the frequency band of from 1.74 to 1.88GHz as shown in FIG. 10, which thereby satisfies 90% of the

VSWR of FIG. 5, and has efficiency six times that of the PIFA (i.e., 15%) that uses a 2mm-thick dielectric material to be installed in the very small size antenna as shown in Table 2.

Also, FIG. 11 shows a horizontal radiation pattern diagram of the 6mm-thick antenna in the free space in Table 2. Referring to FIG. 1 1 , the

angle 0 indicates the direction to the human body, and when comparing it

with the horizontal radiation pattern diagram of the conventional wireless

communication terminal's monopole antenna in the free space in FIG. 6, it is

found that the intensity of the electromagnetic waves radiated in the direction

of the human body is reduced to below 15dB.

(Second preferred embodiment)

In the first preferred embodiment of the present invention, the size of

the antenna was considered for improving the antenna performance. However, in the case of the battery also used as an antenna according to the

present invention, its size depends on the battery's functions. Also, the size

of the battery is determined according to the size and needs of the wireless communication terminal. Therefore, when the length of the antenna at

operating frequency is less than needed, electrical compensation is required. FIGs. 12 to 14 show side views for illustrating a capacitive reactance added

between the ground plate and the antenna so as to extend the length of the

antenna. FIG. 15 shows a side view of the extended antenna. As described, the structure for extending the length of the antenna implements excellent

performance in that it improves radiation efficiency and reduces

electromagnetic waves to a human body.

(Third preferred embodiment)

When the length of the antenna is longer than needed, the third

preferred embodiment compensates for this so as to not reduce the antenna performance. To solve this problem, as shown in FIGs. 16 to 18, a capacitive

reactance is added between the ground plate and the antenna, close to the

bottom portion of the short plate, thereby obtaining effects of decreasing

electrical length of the antenna and performing double resonance at a

desired frequency, and increasing the available frequency bandwidth so as

to maximize the performance of the antenna. As described, the method for

reducing the length of the antenna by adding a capacitive reactance

implements excellent performance for improving radiation efficiency and

reducing electromagnetic waves to a human body. (Fourth preferred embodiment)

Regarding the inverted F antenna having an inverted L short plate and a shared double resonance structure, and a battery also used as an antenna by applying the inverted F antenna, it is required to split the short

plate into at least two plates because of two targets. The first one is to distribute the VSWR according to frequencies and increase the available

frequency bandwidths. The second one is to sustain the original frequency

bandwidth and provide a short plate between a battery antenna and a ground plate at a wireless communication terminal. In this instance, since the

wireless communication terminal is removable from the battery, the short

plate is divided into at least two short plates that are not continuous, as

shown in FIG. 19, so that they may correspond to the removable structure.

As described, the method for dividing the short plate into at least two

improves radiation efficiency and reduces electromagnetic waves to a human body.

The battery antenna for the portable wireless communication terminal according to the present invention uses the battery provided to a back side of the portable wireless communication terminal, that is, the side opposite to the human body, it reduces the electromagnetic waves provided to the human body by at least 15dB so as to reduce the SAR, and it maximizes the antenna performance that is inevitably decreased because of the restricted size and structure of the conventional very small antenna, compared to the conventional monopole antenna that radiates the electromagnetic waves to the human body in the same intensity that it radiates them for communication and thereby generates a high great SAR.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A battery antenna comprising: an antenna ^' formed on one side of a wireless communication terminal battery; a feeder for transmitting and receiving signals between the antenna and the wireless communication terminal; and a short plate formed between the antenna and a ground plate of a groove for inserting the wireless communication terminal battery.

2. The battery antenna of claim 1 , wherein the antenna is a planar inverted F antenna.

3. The battery antenna of claim 1 , wherein the battery antenna further comprises an inverted L antenna on the bottom portion of the short plate.

4. The battery antenna of claim 1 , wherein the battery antenna further comprises at least one capacitive reactance between the antenna and the ground plate.

5. The battery antenna of claim 1 , wherein the battery antenna further comprises at least one capacitive reactance on one side of the

antenna.

6. The battery antenna of claim 1 , wherein the short plate is at

least one plate.