JPH09153724A - Sheet-shaped loop antenna system for portable telephone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain stable speaking at the place of low electric field intensity by attaining the improvement of sensitivity in reception/transmission by fitting a device to a radio communication unit such as a portable telephone. SOLUTION: This antenna system is formed planar and symmetric on left and right sides and composed of a pair of loop antennas 1A and 1B, which are provided with opening parts 11 to be operated as tuning capacitor parts at respective one-side terminals, and a feeder 3 for connecting counter terminals as the opposite terminals of respective opening parts 11 of a pair of loop antennas 1A and 1B, and a pair of loop antennas 1A and 1B are connected by the same power feeding impedance. Then, both the terminals of feeder 3 are connected through a matching circuit 2 for increasing the power feeding impedance of loop antennas to a pair of loop antennas 1A and 1B as needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-shaped loop antenna device for a mobile phone, and in particular, it is attached to a wireless communication unit such as a mobile phone to increase the sensitivity of reception / transmission.
The present invention relates to a sheet-shaped loop antenna device for a thin mobile phone, which maintains a stable call in a place having a low electric field strength.

[0002]

2. Description of the Related Art As is well known, when a mobile phone is used, it is possible or impossible to make a call even in the talking area in a valley of a building, in a car, in a basement, in a tunnel or the like where the electric field strength is low. However, there was a problem that it was difficult to maintain a stable call.

Therefore, as a solution to this problem, a repeater antenna or an external antenna having a gain higher than that of an antenna attached to a mobile phone is commercially available and used.

[0004]

However, in the case where the user holds the mobile phone as a single body and acts freely, the use of the repeater antenna exhibits its effect only near the mounting location. Therefore, the behavior of the user is limited, it is not possible to use it far away from the antenna installation place, and when using an external antenna,
Since the shape of the antenna becomes large, there is a problem in that it is practically difficult to mount or use it on a mobile phone.

The present invention has been made in order to solve the above problems, and can be easily attached to the body of the mobile telephone without any modification and without any assembly technique, and after attachment, it is mass-weighted. A loop for mobile phones on a seat, which is a miniature type whose presence is almost unnoticeable, which greatly increases the sensitivity of transmission and reception, and can maintain stable call quality in places with low electric field strength. An object is to provide an antenna device.

Another object of the present invention is to provide a high radiation efficiency and an excellent voltage standing wave ratio (VS) in spite of such a micro type.
A mobile phone which has a WR) characteristic and a high gain effect, and is advantageous over a conventional antenna when used in a state of being close to the ground, and is directly attached to the mobile phone body and used integrally with the phone. The purpose is to provide a sheet-shaped loop antenna device.

[0007]

In order to achieve the above object, a sheet-shaped loop antenna device for a mobile phone according to the present invention is formed in a plane and bilaterally symmetrical shape, and acts as a tuning capacitor unit at one end of each. A pair of loop antennas provided with an opening and a feed line connecting opposite ends of the pair of loop antennas, which are opposite ends of the respective openings, are connected to each other with the same feed impedance. Become.

According to a preferred embodiment of the present invention, both ends of the feed line are connected to the pair of loop antennas through matching circuits for raising the feed impedance of the loop antenna, respectively.

Further, according to a preferred embodiment of the present invention, the loop antenna is formed of a good conductor metal material into a flat thin sheet, and one surface of the loop antenna is coated with an adhesive so that the loop antenna can be attached to the main body of the mobile phone. I have to.

According to a preferred embodiment of the present invention, the loop antenna, the matching circuit,
The power supply line is integrally formed of a metal conductor in a thin sheet shape. As the sheet-shaped conductor, a metal foil such as gold, silver, copper, or aluminum, or a hot stamped metal foil on a plastic film, a metal film deposited on a plastic film, or a metal plated metal Composed.

According to the sheet-shaped loop antenna for a mobile phone having such a structure, it can be easily attached to the main body of the mobile phone simply by sticking the same without modifying the main body of the mobile phone or requiring any assembly technique. , It is a miniature type whose presence is almost unnoticeable after mounting, and the sensitivity of transmission and reception can be greatly increased, and stable call quality can be maintained in a place with low electric field strength. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Before explaining the structure of a sheet-shaped loop antenna device of the present invention, first, a conceptual diagram (A) is shown.
The basic theoretical concept on which the present invention is based will be described with reference to (B). The loop antenna used here is a magnetic field detection type small magnetic antenna, and when attached to the human body 10 or used near the human body 10, an equivalent magnetic dipole 20 is applied to the human body from the basic form of the electric field component. Image antennas 30 are formed in parallel. (See FIG. 1A). Further, in terms of the form of the magnetic field component, the loop antenna 20 ′ can also have an image antenna 30 ′ that is parallel to the human body 10.

The features of this antenna are: Since the equivalent circuit of the minute loop is an inductance circuit as shown in FIG. 1, a capacitance that cancels this is inserted to perform tuning. 2. Since the radiation resistance is extremely low, the input impedance is adjusted by using a tap etc. for power feeding. 3. The micro loop is equivalent to a micro magnetic dipole and is a magnetic field detection type. 4. An image loop is created when the device is worn on the human body and is used near the human body, and a current having the same phase as the actual loop flows. Currents of opposite phases flow in the electric detection type dipole antenna.

The minute dipole shown in FIG. 1 (A) can be an electric field detection type image antenna having an opposite phase, and the minute loop shown in FIG. 1 (B) can be an image antenna having the same phase. In this way, in the case of a mobile phone antenna that is attached to the human body or used near the human body, its image (image)
Although it is not possible to escape from the magnetic field detection type of the present invention,
The point is that the features are used effectively by taking advantage of them.

As shown in FIG. 1, the radiation resistance of the small dipole decreases in proportion to the square of the antenna length.
Further, the radiation resistance of the minute loop decreases in proportion to the square of the loop area (not the effective area). For example, one side is λ
With a square minute loop of / 10, the value is as small as 3.12Ω. Of course, the efficiency seems to be close to 100% and there seems to be no problem. However, in reality, the impedance of the micro antenna is composed of this small radiation resistance and the reactance which is opposite to this and becomes large.

In the small loop, the reactance is capacitive and increases in inverse proportion to the antenna length. Therefore, a fairly large value of inductive reactance (coil) is required to cancel this and obtain matching. On the contrary, the minute loop needs a capacitive reactance (coil) that matches the inductive reactance. With a small dipole,
Loss resistance occurs due to conductor loss in the loop element,
Part of the electric wave is consumed. Also, with a small dipole,
Loss resistance due to the conductor loss of the coil also occurs, and when the antenna is made smaller, the radiation resistance becomes smaller and thus the loss resistance value exceeds the radiation resistance value. Even if the two are equal, the efficiency is 50%, so the loss resistance is doubled and 3
The gain gradually decreases to 3% and 25% at 3 times.

Considering the actual work, it is quite difficult to make a coil having a high Q value, and in a small coil, the Q value is considered to be around 100 at most. For example, if the reactance is j2000Ω, the loss resistance of the coil alone is 2
000/100 = 20Ω. This allows
It must be prepared that the substantial gain of the inductance-loaded antenna (small dipole) decreases considerably as the size decreases. However, in the case of a small loop,
Since only the conductor loss of the loop element has to be considered as the loss resistance, the radiation resistance itself is considerably small, but the conductor loss is below this value. The substantial gain of the micro loop is far more advantageous than the inductance loaded antenna (micro dipole). This invention was researched and developed based on the above concept.

The advantages of the small loop are: No radial or coil required. 2. Highest radiation efficiency among small antennas. 3. Fully tuned within the frequency range used. 4. Excellent voltage standing wave ratio (VSWR) characteristics. 5. Wide range of applications from near / medium distance (high launch angle) to long distance (low launch angle). 6. Gain close to a half-wave dipole. 7. Vertical installation has little effect from the ground. 8. Since the magnetic field component is less affected by buildings than the electric field component, it can be operated indoors. 9. The magnetic field component has less interference with televisions (electric field type antennas). 10. Since it is a non-grounded antenna and does not require a ground plane, it is not affected by convection currents and causes little BCI or TVI.

Next, a preferred embodiment of the sheet-shaped loop antenna device for a mobile phone according to the present invention made based on the above concept will be described with reference to FIGS. Magnetic field detection type micro loop antenna device P of the present invention
Is a pair of loop antennas 1A and 1B that are formed in a planar shape and have a left-right symmetry and that have an opening 11 at each end.
And a feed line 3 that connects the opposite ends of the pair of loop antennas 1A and 1B, which are the opposite ends, through a matching circuit (coupling circuit) 2, and the pair of loop antennas 1A. , 1B are connected with the same feeding impedance. The opening 11 substantially forms a tuning capacitor C to tune the loop antennas 1A and 1B, and the matching circuit 2 raises the feeding impedance of the feeding line 3. The loop antennas 1A and 1B have the same impedance due to the cooperative action of the condenser unit 11 and the matching circuit 2.

The antenna device P including the loop antennas 1A and 1B, the matching circuit 2 and the feeder line 3 is integrally manufactured in a thin plane shape. Then, in consideration of conductivity and thinning, a metal conductor, preferably gold, silver,
A metal foil of copper, aluminum, or the like, or a plastic film hot stamped with the metal foil, a plastic film deposited with the metal, or a plastic film plated with metal is used. All of these are suitable materials that are easily available, and are easy to implement.

As shown in FIG. 3, a loop antenna made of metal foil is provided so that the sheet-like antenna device constructed as described above is not easily damaged in commercialization and can be easily mounted on a mobile phone by a user. The adhesive 4 is applied to one surface of the device, and the release paper 5 having an area larger than that of the antenna device is attached to the upper surface of the device as a mount, and then placed in a packaging bag (not shown). If the loop antenna device P is formed by vapor deposition or plating on the film 6 (see FIG. 3).
(See (B)), after applying the adhesive 4 to the back surface of the film 6, the release paper 5 may be attached. In use, after peeling off the release paper 5, the adhesive layer 4 may be attached to the back surface of the mobile phone body, for example. However, when the antenna device P is formed by directly plating a plastic plate, the antenna device may be directly plated on the back surface of the mobile phone body.

In the above embodiment, the loop antenna 1
Although A and 1B are formed in a slightly rectangular circuit, FIG.
Obviously, it may be formed in a circular shape, a triangular shape, a rectangular shape, a polygonal shape or any other shape as shown in FIGS. In short, it suffices that the material is formed in a compact thin sheet shape with a material having low conduction loss, and the result of tuning to the target frequency can be obtained by appropriately mixing the sizes of the opening 11 and the loop.

In order to apply the sheet-shaped loop antenna device of the present invention to a cell phone for a cellular system currently in use, the size of the entire device is attached to the sub surface (rear surface) of the phone body with a sufficient margin. In order to obtain a frequency that is tuned to the target frequency while designing the size as much as possible, for example, each part 1A, 1B of the loop antenna P,
It is advisable to design 2, 3 according to the procedure as shown in FIG. That is, the widths of the symmetrical loop antennas 1A and 1B are set to, for example, 1 / 8λ to 1 / 10λ, and the distance d between both loops is set to at least 1 / 5λ. The size of the capacitance of the opening 11 that serves as the condenser C can be changed by adjusting the gap g of the opening 11 and the length l (ell). The shape of the opening 11 or the condenser C may not be as shown in the figure. For example, a chip capacitor (not shown) connected to the gap g may be used instead of the pattern. Further, in this embodiment, the symmetrical (balanced) matching circuit 2 is used, but this is to increase the impedance at the feeding point. Actually, a pair of loop antennas 1A having the same impedance,
Since it suffices to connect 1B in parallel, the matching circuit 2 may be removed and both loops 1A and 1B may be directly connected by the feeder line 3.

FIG. 6 is an explanatory view showing the flow of radio waves with the telephone relay station B when the loop antenna device P of the present invention is attached to the mobile telephone M and used. In the figure, M
IA is a transmitting / receiving antenna attached to the mobile phone M, MIB
Is a reception-only antenna attached to the mobile phone M, and 1A and 1B are micro magnetic loop antennas attached to the mobile phone M. As is clear from this figure, the downlink signal radio wave from the relay station B is originally directly received by the antennas MIA and MIB of the mobile phone M as shown by the alternate long and short dash line. After mounting, the radio waves are, as shown by the solid line, loop antenna 1A → loop antenna 1B → antenna MIA, MIB, and loop antenna 1B → loop antenna 1A → antenna MIB,
The signals are received by the antennas MIA and MIB through the two routes with MIA. Further, the uplink radio wave transmitted from the mobile phone M to the relay base B is originally transmitted from the antenna MIA directly to the base B as shown by the two-dot chain line, but the antenna as shown by the dotted line is shown. MIA → loop antenna 1A → loop antenna 1B → base B, and antenna MI
A → loop antenna 1B → loop antenna 1A → base B
It is transmitted to the base B by two routes.

FIG. 7 is a schematic diagram showing the electric field strength measured by a scalar net analyzer when the magnetic loop antenna device according to the present invention is mounted on a mobile phone and used. There are two types of loop antennas used in the measurement, 800 MHZ and 1500 MHZ class.
The measuring instruments used were the standard antenna for transmission, the standard antenna for reception, the preamplifier, and the Wiltron 5
411A type) Scalar net analyzer and coaxial cable.

As the measurement conditions, the measurement distance from the loop antenna to the transmission antenna is set to 4 m, the height of the transmission antenna is set to 2 m, and the height of the reception antenna is set to 1 m, and a marker of the Scalar Net Analyzer is set to 825 M for the 800 type.
HZ, 892MHZ, 960MHZ, 1500 type, 1429MHZ, 1465MHZ, 15
The electric field strength was measured for each of the cases where the loop antenna of the present invention was attached and the case where the loop antenna of the present invention was not attached. For the former, 800 type and 15
For 00 type, (A) Horizontal installation / horizontal polarization, (B) Horizontal (width)
The measurement was performed for each state of vertical installation / vertical polarization, and (C) vertical installation / vertical polarization in the vertical (length) direction.

The following results were obtained from the measured data. Horizontal polarization / horizontal installation (Refer to Loop A) The electric field strength in the slit direction (0 degrees, 180 degrees) is strong, and it is about + compared to when it is not attached (antenna → antenna).
A gain of 1.2 dB was obtained. Vertical polarization / horizontal vertical installation (see Loop B) The electric field strength in the antenna side surface direction (0 degrees, 180 degrees) was strong, and a gain of about 1.8 dB was obtained. Vertical polarization / Vertical installation (see Loop C) The electric field strength in the slit direction (0 degrees, 180 degrees) was strong, and a gain of about 3.6 dB was obtained. As is clear from the above results, by mounting the loop antenna of the present invention on a mobile phone, it is possible to increase the sensitivity and maintain a stable call in a place where the electric field strength is low.

[0028]

Since the present invention is configured as described above, it can be easily attached to the main body of the mobile phone by simply attaching it to the back without modifying the main body of the mobile telephone, and after attachment, it is almost mass-weighted. It is not possible to sense its presence, and the sensitivity of transmission and reception is greatly increased, and stable call quality can be maintained in a place with low electric field strength.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a basic concept of a loop antenna device according to the present invention.

FIG. 2 is a plan view showing an embodiment of the sheet-shaped loop antenna device of the present invention.

FIG. 3 is a sectional view showing another embodiment of the loop antenna of the present invention.

FIG. 4 is a plan view showing a half portion of a modified example of the present invention.

FIG. 5 is an explanatory diagram showing a design example of the present invention.

FIG. 6 is an explanatory diagram showing the flow of radio waves between a mobile phone and a relay station using the loop antenna of the present invention.

FIG. 7 is an explanatory diagram showing the electric field strength of a mobile phone equipped with the loop antenna of the present invention.

[Explanation of symbols]

P ... Loop antenna device, 1A, 1B ... Loop antenna, C, 11 ... Opening part (capacitor part), 2 ... Matching circuit, 3 ... Feed line, 4 ... Adhesive, 5 ... Release paper, 6 ...
the film

Claims (7)

[Claims] 1. A pair of loop antennas, which are formed in a planar shape and are bilaterally symmetric, and each of which has an opening portion acting as a tuning capacitor portion at one end, and an opposite end of each opening portion of the pair of loop antennas. A sheet-shaped loop antenna device for a mobile phone, comprising a pair of feed lines connecting opposite ends, and connecting the pair of loop antennas with the same feed impedance. 2. The sheet-shaped loop for a mobile phone according to claim 1, wherein both ends of the feed line are connected to the pair of loop antennas through matching circuits that raise the feed impedance of the loop antenna, respectively. Antenna device. 3. The sheet-shaped loop for a mobile phone according to claim 1, wherein the loop antenna, the matching circuit, and the power supply line are integrally formed of a metal conductor in a thin sheet shape. Antenna device. 4. The sheet-shaped loop antenna comprises a metal foil of gold, silver, copper, aluminum or the like, or a plastic film hot-stamped with the metal foil, a plastic film vapor-deposited with the metal, Alternatively, the sheet-shaped loop antenna device for a mobile phone according to claim 3, wherein the sheet-shaped loop antenna device is made of a metal plated on plastic. 5. The sheet-shaped loop antenna for a mobile phone according to claim 4, wherein the sheet-shaped loop antenna is formed by applying an adhesive to a back surface of the sheet, and further attaching a release paper to an upper surface of the adhesive layer. Antenna device. 6. The sheet shape for a mobile phone according to claim 1, wherein the pair of loop antennas are formed into an approximate square shape, a circular shape, a rectangular shape, a triangular shape, a polygonal shape, an elliptical shape having an opening at one end, or a modification thereof. Loop antenna device. 7. The sheet-shaped loop antenna device for a mobile phone according to claim 1, wherein the pair of loop antennas have a chip capacitor connected to the opening instead of the opening serving as a capacitor.