JP2004015246A - Plate antenna and communication terminal equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate antenna IMT-2000 for a communication terminal, which has a sufficient band width for application to Bluetooth and wireless LANs with the band widths of 2.4GHz and 5.2GHz, high gain, and stable input and output characteristics. <P>SOLUTION: A plate antenna 1 comprises a first and a second antenna elements. The first antenna element comprises a copper foil 12, which is formed as a rectangle window 14 and is located at one side of a dielectric plate 11. The second antenna element comprises copper foils 15 and 16, which are formed at the other side of the dielectric plate 11. The copper foils 15 and 16 are of rectangular shape and are located symmetric with respect to the center line of a gap 17, sandwiching the gap 17. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a communication terminal such as a mobile phone, a personal digital assistant (PDA), and an antenna related to a wireless LAN (Local Area Network) system including the communication terminal.
[0002]
[Prior art]
2. Description of the Related Art A whip-type half-wavelength dipole antenna is often used as an antenna of a mobile communication terminal such as a conventional mobile phone.
[0003]
The frequency bandwidth of the whip-type half-wave dipole antenna is, for example, a center frequency of 2080 MHz, about 200 MHz in a free space, and about 160 MHz in the vicinity of a human body.
[0004]
However, the frequency band used in the third generation mobile phone system IMT-2000 (International Mobile Telecommunication-2000), which was put into practical use in 2001 AD, is 1920 MHz to 2170 MHz, 250 MHz, and the modulation method is W-CDMA. Since the entire frequency band of 1920 MHz to 2170 MHz is used in the IMT-2000 W-CDMA modulation method, the antenna of the mobile phone for the IMT-2000 requires a frequency band of 250 MHz.
[0005]
As described above, the whip-type half-wave dipole antenna employed in the conventional mobile phone has a bandwidth of about 160 MHz in an environment near a human body (with human body), and is insufficient in bandwidth for IMT-2000. Was. Also, with IMT-2000, it is predicted that there will be more opportunities to connect a mobile phone to the Internet and download data at high speed. A high-gain antenna is advantageous for realizing the high-speed downloading, but an absolute gain of the half-wavelength dipole antenna is 2.15 dB, and an antenna having a larger gain is required.
[0006]
In order to expand the frequency band and increase the antenna gain, it is temporarily advantageous to use the housing of the mobile phone as an antenna element in addition to the half-wavelength dipole antenna provided in the mobile phone. However, when the housing of the mobile phone is used as an antenna element, when the antenna is held near the human body, the input / output characteristics of the antenna, that is, the bandwidth and gain, depend on the posture of the antenna and the position of the housing held by hand. Greatly fluctuates, and the communication quality is not stable. In addition, using a housing as a part of an antenna causes a current to flow through a human body and increases the exposure of radio waves to the human body. Therefore, it is desirable to avoid using the housing from the viewpoint of EMC (Electro Magnetic Compatibility).
[0007]
The present inventor has proposed a plate antenna (Patent Application No. 2001-037777; hereinafter, referred to as a prior invention) as an antenna sufficiently applicable to this IMT-2000 system. In the plate antenna of the prior application, the bandwidth and gain required for the IMT-2000 system can be obtained without depending on the housing, and the input / output characteristics are stable even near the human body. As shown in FIGS. 6 (A), 6 (B) and 6 (C), the plate antenna 3 of the invention of the prior application includes a dielectric plate 31 of a printed circuit board and a conductive foil formed on the dielectric plate 31 such as copper. It comprises a foil (vertical width T, horizontal width W) 32, a signal source 33 indicated at the position of the feeding point of the antenna, and a horizontally long rectangular (length L1) window (slit).
[0008]
This plate antenna 3 can be applied not only to the IMT-2000 system, but also to a system called Bluetooth, which has recently emerged (that is, a system in which personal computers PCs or a PC and a general home appliance are wirelessly linked: frequency: Band 2400 MHz to 2500 MHz) or a 2.4 GHz band (frequency band 2400 MHz to 2500 MHz) wireless LAN system widely used at present under the name of wireless broadband. An example applied to this Bluetooth system will be described below.
[0009]
In FIG. 6, the thickness of the dielectric plate 31 is 16 mm, the relative permittivity is 3.5, and the conductivity is 0.003 S / m (S is Siemens, 1 / Ω). The thickness of the copper foil 32 is 35 μm, the horizontal width W of the copper foil 32 is 38 mm, the vertical width T is 53 mm, the horizontal rectangular window (slit) 34 has a horizontal width L1 of 37 mm, and a vertical width L2 of 1 mm. The amount of glue around the copper foil 32 is approximately 1 mm. FIG. 7 shows the frequency characteristics of the plate antenna according to this example. The vertical axis S11 is S11 = 10 × common logarithm {(reflected power) / incident power}, and represents the ratio of the reflected power from the antenna to the antenna input. The horizontal axis indicates the frequency [MHz].
[0010]
7, a curve (B1) is a characteristic curve showing the frequency characteristic of the plate antenna shown in FIG. The frequency band (A1) is a frequency band of the third generation mobile phone system IMT-2000, the frequency band (A2) is a Bluetooth or 2.4 GHz wireless LAN frequency band, and the frequency band (A3) is 5. This is a 2 GHz band (5200 MHz to 5300 MHz) wireless LAN frequency band. From this characteristic diagram, assuming that the frequency is in a band where the reflected power is -10 dB or less, as usual, the bandwidth of the plate antenna in FIG. 6 is 890 MHz in the air from 1960 MHz to 2850 MHz.
[0011]
[Problems to be solved by the invention]
Thus, the plate antenna shown in FIG. 6 can be applied to the above-described IMT-2000 system, Bluetooth system (frequency band 2400 MHz to 2500 MHz) and 2.4 GHz band (frequency band 2400 MHz to 2500 MHz) wireless LAN system.
[0012]
However, since the Bluetooth system and the 2.4 GHz band (frequency band 2400 MHz to 2500 MHz) wireless LAN system use the same frequency band, communication tends to spread in the 2400 MHz to 2500 MHz frequency band. Accordingly, there is a growing movement to find the frequency band of the wireless LAN system in the frequency band of 5200 MHz to 5300 MHz, which has few users, mainly in the United States.
[0013]
Since this frequency band 5200 MHz to 5300 MHz (5.2 GHz band) is about twice as high as the center frequency of the band of the plate antenna of the above-mentioned prior invention (FIGS. 6 and 7), the bandwidth of this plate antenna alone is insufficient. ing. Therefore, the above-mentioned plate antenna of the invention of the prior application cannot be applied to a 5.2 GHz band wireless LAN system, and improvement is required.
[0014]
Accordingly, an object of the present invention is to provide a plate antenna or the like having a wide band, high gain, and stable characteristics, which is applicable to a 5.2 GHz band wireless LAN system.
[0015]
[Means for Solving the Problems]
The present invention provides the following means to solve the above-mentioned problems.
[0016]
(1) A first antenna element in which a first thin conductor having a slit cut inward from an outer edge is formed on one surface of a dielectric plate, and two second thin conductors are formed of the dielectric material. A second antenna element disposed on the other surface of the plate with a gap therebetween.
[0017]
(2) The plate antenna according to (1), wherein an opening dimension of the slit at the outer edge is smaller than a depth of the slit cut into the inside.
[0018]
(3) The first thin conductor has a rectangular planar shape, the opening of the slit is located at the center of one side of the rectangle, and the shape of the slit is symmetric with respect to an imaginary line orthogonal to the side. The plate antenna according to the above (1) or (2), wherein
[0019]
(4) The plate antenna according to (1), (2) or (3), wherein the two second thin conductors are formed symmetrically with respect to the gap.
[0020]
(5) The first and second thin conductors are metal foils printed on the front and back surfaces of the dielectric plate, respectively, and the first and second thin conductors and the dielectric plate are formed of one print. The plate antenna according to (1), (2), (3) or (4), which constitutes a substrate.
[0021]
(6) The plate antenna according to (5), wherein the printed circuit board is attached to a housing of the communication terminal by a hinge.
[0022]
(7) The plate antenna according to (6), wherein an opening / closing angle of the printed board by the hinge can be changed.
[0023]
(8) The plate antenna according to (7), wherein the hinge is provided on one side edge of the rear surface of the housing.
[0024]
(9) The plate antenna according to any one of (3) to (8), wherein an end of the first conductor facing the opening on the side is a feeding point.
[0025]
(10) The first antenna element functions as an antenna for a frequency band of a third-generation mobile phone system (IMT-2000), Bluetooth or a 2.4 GHz wireless LAN system, and the second antenna element is used for a 5.2 GHz band. The plate antenna according to any one of (1) to (9), wherein the plate antenna functions as an antenna for a frequency band of a wireless LAN system.
[0026]
(11) A communication terminal comprising the plate antenna according to any one of (1) to (5).
[0027]
(12) A first antenna element in which a first thin conductor having a slit cut inward from the outer edge is formed on one surface of a dielectric plate, and two second thin conductors are formed of the dielectric. A communication terminal, comprising: a plate antenna having a second antenna element disposed on the other surface of the plate with a gap therebetween.
[0028]
(13) The first antenna element functions as an antenna for a frequency band of a third-generation mobile phone system (IMT-2000), Bluetooth or 2.4 GHz wireless LAN system, and the second antenna element is used for a 5.2 GHz band. The communication terminal according to the above (12), which functions as a frequency band antenna of a wireless LAN system.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
[0030]
FIG. 1 is a diagram showing a plate antenna according to an embodiment of the present invention, and FIGS. 1A and 1B are perspective views of the front side and the back side of the plate antenna, respectively. In the drawings, reference numeral 1 denotes a plate antenna according to an embodiment of the present invention, 11 denotes a dielectric plate of a printed circuit board, and 12 denotes a thin conductor or a conductor foil printed on one surface of the dielectric plate 11, for example. Copper foil (corresponding to 32 in FIG. 6), 13 is a signal source at the feeding point of the antenna, 14 is a horizontally long rectangular (corresponding to 34 in FIG. 6) window (slit), and 15 and 16 are the other of the dielectric plate 11 And 17 are a gap between the copper foils 15 and 16. One printed circuit board is constituted by the dielectric plate 11 and the copper foils 12, 15 and 16 printed on the dielectric plate 11.
[0031]
The planar shape of the dielectric plate 11 is rectangular. The copper foil 12 has a rectangular planar shape similar to the dielectric plate 11. However, since the copper foil 12 is provided with the window 14, to be precise, it means that the planar shape of the copper foil 12 is rectangular when it is assumed that the window 14 is not provided. The four sides of the copper foil 12 similar to the dielectric plate 11 are slightly closer to the inside than the four sides of the dielectric plate 11. The planar shapes of the copper foils 15 and 16 are rectangles of the same size.
[0032]
The opening of the window 14 of the plate antenna is located at the center of one side 12 a in the rectangular plane of the copper foil 12. The plane shape of the window 14 is also an elongated rectangle. The longitudinal center line (virtual line) of the window 14 is orthogonal to the side 12a. The virtual center line bisects the copper foil 12 and the window 14. Each of the bisected windows 14 is symmetric about its center line. The sides of the copper foils 15 and 16 desired for the gap 17 are parallel to each other. The plane shapes of the copper foils 15 and 16 are symmetric with respect to the center line (virtual line) of the gap 17. The center line of the gap 17 is in a plane passing through the center line in the longitudinal direction of the window 14 and orthogonal to the surface of the dielectric plate 11.
[0033]
In this plate antenna 1, as shown in FIG. 1A, a first antenna element (plate antenna in FIG. 6) made of a copper foil 12 provided with a window 14 is formed on the front side of a dielectric plate 11, Further, as shown in FIG. 1B, a second antenna element including copper foils 15 and 16 arranged with a gap 17 therebetween is formed on the back side of the dielectric plate 11. A signal source (for example, a transceiver) 13 is connected to a feeding point of the antenna.
[0034]
In the embodiment of FIGS. 1A and 1B, the dimensions of the first antenna element on the front side are the same as those of the embodiment of the plate antenna 3 of the prior application in FIG. E1 is 5 mm, vertical width E2 is 14 mm, and thickness is about 35 μm, which is the same as the thickness of the copper foil 32. The width of the gap 17 is 1 mm, which is the same as the width of the horizontally long rectangular window 14. The distance D1 of the second antenna element from the end of the printed circuit board is 13.5 mm. The length ES of the gap 17 is 5 mm like E1.
[0035]
FIG. 2 shows the frequency characteristics of the plate antenna 1 having such dimensions. Note that the vertical axis S11 is S11 = 10 × common logarithm {(reflected power) / (incident power)}, and indicates the ratio of the reflected power from the antenna to the antenna input. The horizontal axis indicates the frequency [MHz].
[0036]
In FIG. 2, a curve (B1) is a characteristic curve showing the frequency characteristic of the plate antenna of the invention of the prior application relating to FIG. Further, a curve (B2) is a characteristic curve showing the frequency characteristic of the plate antenna of the present invention related to FIG. The frequency band (A1) is a frequency band of the third generation mobile phone system IMT-2000, the frequency band (A2) is a Bluetooth or 2.4 GHz wireless LAN frequency band, and the frequency band (A3) is 5. This is a 2 GHz band wireless LAN frequency band.
[0037]
From this characteristic diagram, assuming that the frequency is a band where the reflected power is -10 dB or less as usual, the bandwidth of the plate antenna in FIG. 1 is 780 MHz from 1920 MHz to 2700 MHz and 550 MHz from 5000 MHz to 5550 MHz in air. That is, as shown in FIG. 2, the plate antenna 1 including the first and second antenna elements shown in FIG. 1 is a third-generation mobile phone system (IMT-2000), a Bluetooth and a 2.4 GHz wireless LAN system, and .2 GHz band can cover the entire frequency band of a wireless LAN (compliant with the IEEE802.11a standard) system.
[0038]
FIG. 3 shows radiation characteristics in free space of the plate antenna of the present invention shown in FIG. FIG. 3A shows the positioning when the plate antenna is developed on the XYZ three-dimensional coordinate axes. FIG. 3B shows the intensity of the electric field component parallel to the Z axis in the electric field radiated from the antenna over 360 ° in the Y axis direction, with the azimuth indicated by the X axis arrow being 0 °. Things. The index [dB] of the electric field intensity is based on the maximum radiated electric field intensity of the most common half-wavelength dipole antenna, and a common logarithm ｛(radiated electric field intensity of the antenna of the present invention) / (maximum radiated electric field intensity of the half-wavelength dipole antenna). )｝
[0039]
In FIG. 3B, at 0 [dB], the radiated electric field strength of the antenna of the present invention is equal to the maximum radiated electric field strength of the half-wave dipole antenna. In general, it is said that it is sufficient if the electric field strength in the maximum radiation direction is 0 [dB] or more. Therefore, the antenna gain according to the present invention is sufficiently practical for any frequency of 2 GHz, 2.4 GHz and 5.2 GHz. This is a value that can be provided.
[0040]
FIG. 4 is a plan view showing an example of the second antenna element in the plate antenna 1a according to the second embodiment of the present invention. The second antenna element in FIG. 4 is a modified example of the second antenna element that generates the 5.2 GHz frequency component illustrated in FIG. The first antenna element according to the second embodiment is the same as that shown in FIG.
[0041]
The shape of the second antenna element in the present invention is not limited to a rectangle as shown in FIG. 1B, but may be a trapezoid as shown in FIG. The second antenna element shown in FIG. 4 has copper foils 18 and 19 arranged with a gap 20 therebetween. The second antenna element can also generate a 5.2 GHz frequency component. The first antenna element on the printed circuit board of the play antenna 1a, that is, the antenna element (copper foil 12 and window 14) that generates the frequency components of 2 GHz and 2.4 GHz shown in FIG. Shown by broken lines.
[0042]
The present invention is also effective when the trapezoidal copper foils 18 and 19 in FIG. 4 are modified into a triangle to form the second antenna element. Further, the two second thin conductors in the second antenna element are not limited to polygons such as trapezoids and triangles, and are effective even if the shape surrounded by a curve is a plane. However, as shown in FIG. 5 (A), the input characteristics are degraded in the arrangement of the elements (21, 22) like the drums in which the trapezoidal elements (18, 19) in FIG. In particular, when the length ES of the gap 23 in FIG. Therefore, as shown in FIG. 5B, an element shape (copper foils 24 and 25) having almost no length ES of the gap 26 is not practical.
[0043]
The plate antenna 1 of FIG. 1 and the plate antenna 1a of FIG. 4 can be attached to the back of the housing of a portable terminal such as a portable telephone or an information terminal. More specifically, for example, the plate antenna 1 or 1a is housed in a rectangular frame (case) made of an insulator such as plastic, and this case is placed on one side edge (ridge) on the back surface of the housing of the mobile phone. The antenna is in a closed state in which the plate surface of the plate antenna 1 or 1a is parallel to the back surface of the housing of the mobile phone, and the antenna is in an open state in which the plate surface of the plate antenna 1 or 1a is perpendicular to the back surface. The plate antenna 1 or 1a is held at an arbitrary angle (the angle of the plate surface with respect to the back surface) between the two postures. The transceiver provided in the housing of the mobile phone is connected to a feeding point of the copper foil 12 of the plate antenna 1 or 1a [the copper foil 12 at the left end position of the window 14 in FIG. You. 1 or 4, a signal source 13 is shown as a transceiver. The feed line at the hinge can be a coated flexible parallel line.
[0044]
In a communication system such as a mobile phone, a call signal usually waits while the antenna is closed. Then, upon receiving the ringing signal and recognizing the ringing sound, the holder of the mobile phone normally sets the antenna to the open state and communicates the signal. Of course, a call signal can be awaited when the antenna is open, and signals can be exchanged even when the antenna is closed.
[0045]
Further, as a plate antenna of the present invention suitable for receiving terrestrial digital television broadcasting, a reflector can be provided in parallel with the plate antenna 1 or 1a to form a high-gain antenna having directivity. .
[0046]
In the description of the embodiments, the structure, dimensions, materials, and the like of the antenna and the like are specifically illustrated for easy understanding. However, the technical scope of the present invention is not limited to this embodiment. For example, the plate antenna of the present invention can be applied not only to a mobile phone but also to a mobile communication terminal such as a personal digital assistant (PDA). In the embodiment, a thin conductor serving as an antenna element (antenna element) in a plate antenna is made of copper foil, and this copper foil is manufactured by printing on a printed circuit board. However, the conductor plate can hold its shape independently. A metal plate having a thickness (usually 0.1 to 0.2 mm) may be used. Furthermore, the plane shape of the window provided in the conductor plate can be various shapes such as a rectangle and a rhombus. In addition, the characteristics of the antenna can be selected in a wide range by selecting the ratio between the length of the window in the vertical direction and the length in the horizontal direction, that is, by selecting the aspect ratio and the ratio of the area of the window to the area of the conductor plate. Although the outer contour of the conductor plate is rectangular in the embodiment, it does not have to be necessarily rectangular as long as the conductor plate substantially acts as a plate antenna. In the embodiments shown in FIGS. 1 and 4, the plate antenna is attached to the side edge of the back surface of the mobile phone by a hinge, but the plate antenna may be provided at an appropriate position according to the outer shape of the mobile communication terminal. Also, the sliding type may be used instead of the hinge. 1 and 4, the opening and closing angle of the plate antenna is set to 90 degrees, but the opening and closing angle can be arbitrarily selected according to design needs. Further, the plate antenna of the present invention is suitable not only for portable communication terminals but also as a receiving antenna for digital terrestrial television broadcasting.
[0047]
【The invention's effect】
As described above in detail, according to the plate antenna of the present invention, the third generation mobile phone system (IMT-2000), Bluetooth and 2.4 GHz wireless LAN system, and 5.2 GHz band wireless LAN (compliant with the IEEE802.11a standard) 2) An antenna for a portable communication terminal having a sufficient bandwidth applicable to the system, a high gain, and stable input / output characteristics can be provided. In addition, the plate antenna of the present invention can realize high gain in a required direction by providing a reflector and enhancing directivity, and is smaller and lighter than a conventional antenna, so that it can be used as a terrestrial digital television broadcast receiving antenna. It is suitable.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams showing a plate antenna according to a first embodiment of the present invention, wherein FIGS. 1A and 1B respectively show a first antenna element on the front side and a second antenna on the back side of the plate antenna; It is a perspective view of an antenna element.
FIG. 2 is a graph showing frequency characteristics of the plate antenna 1 of FIG.
FIG. 3 is a diagram showing radiation characteristics of the plate antenna 1 of the embodiment shown in FIG.
FIG. 4 is a diagram showing a second antenna element in a plate antenna 1a according to a second embodiment of the present invention.
5A and 5B are diagrams showing a second antenna element of the plate antenna, and FIGS. 5A and 5B show different antenna element (copper foil) shapes.
FIG. 6 is a view showing a plate antenna according to the invention of the prior application, and FIGS. 6A, 6B and 6C show a front view, a lower side view and a right side view of the plate antenna.
FIG. 7 is a diagram illustrating a frequency characteristic of the plate antenna illustrated in FIG. 6;
[Explanation of symbols]
1, 1a: Plate antenna 11: Dielectric plate 12: Copper foil 13: Signal source 14 connected to the feeding point of plate antenna 14: Rectangular window (slit)
15, 16 ... Copper foil 17 ... Gap 18, 19 ... Copper foil 20 ... Gap 21, 22 ... Copper foil 23 ... Gap 24, 25 ... Copper foil 26 ... Gap 3 plate antenna 31 printed circuit board dielectric plate 32 copper foil 33 signal source 34 connected to the feeding point of plate antenna 34 rectangular window (slit)

Claims (13)

A first antenna element in which a first thin conductor having a slit cut inward from an outer edge is formed on one surface of a dielectric plate, and two second thin conductors are formed on the other side of the dielectric plate; A plate antenna having a second antenna element disposed on a surface thereof with a gap therebetween. The plate antenna according to claim 1, wherein an opening dimension of the slit at the outer edge is smaller than a depth of the slit cut into the inside. The first thin conductor has a rectangular planar shape, the opening of the slit is located at the center of one side of the rectangle, and the shape of the slit is symmetric with respect to an imaginary line orthogonal to the side. The plate antenna according to claim 1 or 2, wherein: 4. The plate antenna according to claim 1, wherein the two second thin conductors are formed line-symmetrically with the gap interposed therebetween. The first and second thin conductors are metal foils printed on the front and back of the dielectric plate, respectively, and the first and second thin conductors and the dielectric plate constitute one printed circuit board. The plate antenna according to claim 1, 2, 3, or 4, wherein The plate antenna according to claim 5, wherein the printed circuit board is attached to a housing of the communication terminal by a hinge. The plate antenna according to claim 6, wherein an opening / closing angle of the printed board by the hinge is changed. The plate antenna according to claim 7, wherein the hinge is provided on one side edge of a rear surface of the housing. The plate antenna according to any one of claims 3 to 8, wherein an end of the first conductor facing the opening on the side is a feed point. The first antenna element functions as an antenna for a frequency band of a third generation mobile phone system (IMT-2000), Bluetooth or a 2.4 GHz wireless LAN system, and the second antenna element functions as a 5.2 GHz band wireless LAN system. The plate antenna according to any one of claims 1 to 9, wherein the plate antenna functions as an antenna for a frequency band. A communication terminal comprising the plate antenna according to any one of claims 1 to 5. A first antenna element in which a first thin conductor having a slit cut inward from an outer edge is formed on one surface of a dielectric plate, and two second thin conductors are formed on the other side of the dielectric plate; A communication terminal comprising: a plate antenna having a second antenna element disposed on a surface of the second antenna with a gap therebetween. The first antenna element functions as an antenna for a frequency band of a third generation mobile phone system (IMT-2000), Bluetooth or a 2.4 GHz wireless LAN system, and the second antenna element is used for a 5.2 GHz band wireless LAN system. The communication terminal according to claim 12, which functions as a frequency band antenna.

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