JPH06244618A - Loop antenna - Google Patents

Abstract

PURPOSE:To form a loop antenna in small size without lowering antenna gain by forming a short-circuit conductor in the shape of plate and setting the width so as to show a specified impedance. CONSTITUTION:Two conductor boards 21 and 22 are almost parallelly arranged so that their planes can be faced each other, and a power feeding terminal 23 is provided between the respectively mutually faced points of those two conductor boards 21 and 22. Then, a short-circuit conductor 24 to short-circuit those two conductor boards 21 and 22 are connected at a certain position away from the power feeding terminal 23. The two conductor boards 21 and 22 are respectively rectangular, the power feeding terminal 23 is set near one apex of the rectangle, the short-circuit conductor 24 is connected near the apex farest from the power feeding terminal 23, and the short-circuit conductor 24 is plate- shaped while setting the width so as to show the impedance sufficiently small in comparison with the length of the side and sufficiently low with the wavelength to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used as an antenna for a wireless communication device. The present invention is suitable for use in a small wireless communication device carried by a user. The present invention relates to an antenna particularly suitable for use in a selective call receiver.

[0002]

2. Description of the Related Art Conventionally, it has been known to use a loop antenna for a portable radio communication device whose shape is smaller than the wavelength used. For example, the frequency used by the radio selective call receiver is several hundred MHz (wavelength is 1 m when the frequency is 300 MHz), and the shape of the receiver main body is several cm even in the longitudinal direction. It is not possible to mount an antenna of several tens of centimeters protruding from the receiver body because it is inconvenient to carry and use. When a loop antenna is adopted as an antenna in such a device, a practical antenna gain can be obtained with the loop passing over several% of the used wavelength (that is, several cm). Therefore, it is rational to use a loop antenna and mount it around the receiver housing.

The basic shape of the loop antenna is that a conductor wire is formed in a circular shape and one portion on the circumference thereof is cut open to be a feeding end. The circular shape need not be a perfect circle but may be an ellipse or any other shape as long as the conductor forms a loop shape and can be used as a loop antenna. As a deformed shape of this shape, a metal plate formed to have a U-shaped cross section as shown in FIG. 10 is known. This is a structure in which two rectangular metal plates are arranged in parallel so that their planes face each other, a feeding end is provided at approximately the center of its long side, and a short-circuit conductor is connected to the opposite side by an elongated metal plate. .

[0004]

The loop antenna having the structure shown in FIG. 10 is used in a radio selective call receiver. This structure is an excellent shape that matches well with the shape of the receiver housing. However, the loop antenna with this structure
It must be fairly large to get a satisfactory antenna gain. That is, the electronic circuit of the receiver can be miniaturized by the progress of integration technology, but the antenna cannot be made smaller accordingly.

The present invention has been made against such a background, and an object of the present invention is to improve the antenna gain of a loop antenna having a shape in which two conductor plates are arranged so that their planes face each other. And It is an object of the present invention to provide a loop antenna having a large antenna gain, which has a shape capable of mounting an electronic circuit of a wireless communication device inside an antenna structure.

[0006]

According to the present invention, two conductor plates are arranged such that their planes face each other and are substantially parallel to each other, and a feeding end is provided between points of the two conductor plates facing each other. In a loop antenna in which a short-circuit conductor for short-circuiting the two conductor plates is provided at a position distant from the feeding end, the two conductor plates are rectangular, and the feeding end is one of the squares. The short-circuit conductor is set near the apex, and the short-circuit conductor is connected near the apex farthest from the feeding end, and the short-circuit conductor is plate-shaped and its width is sufficiently smaller than the length of the side and the wavelength used is sufficient. It is characterized in that it is set to exhibit a low impedance.

The length of one side of the two conductor plates is 2 to 15% of the used wavelength, and the width of the short-circuit conductor is 0.5 to 3.5% of the used wavelength. The part between the conductor plates of the wireless communication device forms part of the housing of the wireless communication device, the electric circuit of the wireless communication device is arranged between the two conductive plates, and the operating end or display end of the wireless communication device is attached to the conductive plate. Is desirable.

[0008]

[Function] A square that has a side length of 2 of the used wavelength
Make the planes of two conductor plates shorter than 1/10 face each other, set the feeding end near one vertex of the two conductor plates, and have a plate shape whose width is the length of one side of the conductor plate. By connecting a short-circuit conductor configured to have a sufficiently small impedance and a sufficiently low impedance at the used wavelength in the vicinity of the apex farthest from the feeding end, the opening area increases and the radiation resistance increases. In addition, since the short-circuit conductor has a width, the electric resistance is reduced, radiation efficiency is improved, and a large gain can be obtained in the same volume.

Thus, the electronic circuit of the wireless communication device can be mounted inside the antenna structure without lowering the antenna gain, and the size can be reduced.

[0010]

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

(First Embodiment) FIG. 1 is a perspective view showing a structure of a first embodiment of the present invention, and FIG. 2 is a structural example of a matching circuit between an antenna side and a radio circuit in the first embodiment of the present invention. FIG.

In the first embodiment of the present invention, the two conductor plates 21 and 22 are arranged so that their planes face each other and are substantially parallel to each other, and the two conductor plates 21 and 22 have a point-to-point relation facing each other. Is provided with a feeding end 23, and a short-circuit conductor 24 that short-circuits the two conductor plates 21 and 22 is connected to a position distant from the feeding end 23, and the two conductor plates 21 and 22 are rectangular, respectively. Edge 23
Is set near one apex of the rectangle, and its feeding end 2
The short-circuit conductor 24 is connected near the apex farthest from the No. 3, and the short-circuit conductor 24 has a plate-like shape whose width is sufficiently smaller than the length of the side and exhibits sufficiently low impedance at the wavelength used. Is set.

Further, the length of one side of the two conductor plates 21 and 22 is 2 to 15% of the operating wavelength, and the width of the short-circuit conductor 24 is 0.5 to 3.5% of the operating wavelength. The part between the two conductor plates 21 and 22 constitutes a part or the whole of the casing of the wireless communication device, and the electric circuit of the wireless communication device is arranged between the two conductor plates 21 and 22. Conductor plate 2
The operating end or display end of the wireless communication device is attached to 1 and 22.

In FIG. 1, L × d represents the opening area of the conductor plates 21 and 22 forming the loop antenna, and A represents the total width of the short-circuit conductor 24. The short-circuit conductor 24 is L that extends over two sides
Since the shape is formed, the width on one side is A / 2.

FIG. 3 is an exploded perspective view of a radio communication device equipped with a loop antenna according to the first embodiment of the present invention, and FIG. 4 is a state in which the loop antenna according to the first embodiment of the present invention is installed as a casing of a selective call receiver. 5A is a cross-sectional view of a portion where the switch shown in FIG. 3 is arranged, and FIG. 5B is a cross-sectional view of a portion where the display shown in FIG. 3 is arranged.

A circuit board 31 is arranged between the two conductor plates 21 and 22 of the loop antenna of the first embodiment of the present invention, and the switch body 32 and the indicator 3 are disposed on the circuit board 31.
3 is placed and housed in the housing 34. The switch body 32 is operated from the outside of the housing 32 by the switch knob 35, and the display portion of the display 33 is configured to be visible from the outside of the housing 32.

Generally, it is known that the efficiency η of a loop antenna, which is smaller than the wavelength, is expressed by η = Rr / (Rr + Rloss) (1) where Rr is the radiation resistance of the antenna and Rloss is the electrical resistance on the loop circumference. Has been. Here, as one of the methods for increasing the antenna efficiency, a method for increasing the radiation resistance Rr can be considered. Radiation resistance Rr is defined as s, where s is the cross-sectional area of the loop antenna.

[0018]

[Equation 1] Can be expressed as

At this time, the loop cross-sectional area s is given by a and b of the parallel plate sides and the loop height of d.

[0020]

[Equation 2] Can be expressed as

From the equation (2), the radiation resistance Rr is proportional to the square of the cross-sectional area of the loop antenna. Therefore, the loop antennas are arranged diagonally as shown in FIG.
The radiation resistance Rr can be increased by increasing the cross-sectional area of the loop antenna as well as connecting with the line antennas 22 and 22.

FIG. 5 shows theoretical values when there is no loss, which is obtained by changing the width of the short-circuit conductor 24 and changing the cross-sectional area using the formulas (1) to (3). The horizontal axis represents the total width of the two short-circuit conductors 24. The electric resistance Rloos is the same as that of the conventional antenna shown in FIG. It can be seen that the gain is improved by narrowing the width of the short-circuit conductor 24 and increasing the loop opening area.

However, at frequencies higher than the ultra-high frequency band in which portable radios are used, the electric current flows on the surface of the conductor due to the skin effect, so that the electric resistance R of the portions having the same width is
loss is the area w of the conductor surface as shown in equation (4).
Inversely proportional to.

[0024]

[Equation 3] Here, μ is the magnetic permeability, σ is the conductivity, f is the frequency, and c is the total length of the elements having the same width.

For this reason, if the width of the short-circuit conductor 24 is made thin and linear in order to maximize the loop cross-sectional area, the radiation resistance Rr increases, but the electrical resistance Rloss increases, and the efficiency η is eventually increased. Not improved.

Further, the short-circuit conductor 24 is thickened to make the feeding end 23
If all the two surfaces that are parallel to and are not in contact with each other are short-circuit conductors, the cross-sectional area of the loop antenna will be the same as that of the conventional antenna, and the shortest point of the path in the loop will be only two points at both ends. As the path becomes longer and the electric resistance Rloss increases, the number of current transfer paths in the element becomes large and the antenna has a maximum angle of 90 degrees, so that the radiation characteristic of the antenna spreads. The antenna gain decreases when the width of the short-circuit conductor 24 is set to ½ or more of the length of each of the two sides sandwiching the short-circuit point.

For the antenna according to the present invention, the matching circuit shown in FIG. 2 is used to match the antenna impedance to 50Ω and the width of the short-circuit conductor 24 is changed. The changes are shown in FIG. The model has the same shape as shown in FIG.
At 0 MHz (λ = 1 m), the antenna size is approximately 0.04 × 0.04 × 0.075 (λ), which indicates the antenna gain with reference to the gain of the conventional antenna of the same size shown in FIG. . In addition, the aperture area is increased and the antenna gain is higher than that of the conventional antenna. Further, FIG. 7 shows an antenna directivity pattern when the human body is attached. This shows the pattern when worn in the left chest pocket of clothing, and it can be seen that the overall gain is higher and the antenna efficiency is improved compared to the conventional antenna.

(Second Embodiment) FIG. 8 is a perspective view showing the structure of the second embodiment of the present invention.

In the second embodiment of the present invention, two conductor plates 21 and 22 are connected by a short-circuit conductor 24 'formed on one surface, and other configurations and mounting to a case are the same as those of the first embodiment. It is the same.

FIG. 9 shows the change in the peak gain normalized by the maximum value of the conventional antenna when the width A of the short-circuit conductor 24 'of the second embodiment of the present invention thus constructed is changed. It is a thing. The antenna size used as a model is 0.04 × at 300MHz (λ = 1m).
Although it is 0.04 × 0.075 (λ), the effect of improving the gain can be obtained even if the short-circuit conductor is formed on one surface.

[0031]

As described above, according to the present invention, the antenna gain can be formed in a small size without lowering it, and the electronic circuit of the wireless communication device can be mounted inside the antenna structure. There is an effect that size reduction and power saving can be achieved.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing one configuration example of a matching circuit on the antenna side and the radio circuit side in the first embodiment of the present invention.

FIG. 3 is an exploded perspective view of a wireless communication device equipped with a loop antenna according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a state in which the loop antenna according to the first embodiment of the present invention is mounted as a housing of a wireless communication device.

5A is a sectional view of a portion where the switch shown in FIG. 3 is arranged, and FIG. 5B is a sectional view of a portion where the display shown in FIG. 3 is arranged.

FIG. 6 is a diagram showing changes in gain when the width of the short-circuit conductor is changed in the first embodiment of the present invention.

FIG. 7 is a diagram showing an antenna directivity pattern when a human body is attached according to the first embodiment of the present invention and a conventional example.

FIG. 8 is a perspective view showing a configuration of a second embodiment of the present invention.

FIG. 9 is a diagram showing a change in gain when the width of the short-circuit conductor is changed in the second embodiment of the present invention.

FIG. 10 is a perspective view showing a configuration of a conventional example.

[Explanation of symbols]

 21, 22 Conductor plate 23 Feed end 24, 24 'Short-circuit conductor 31 Circuit board 32 Switch body 33 Indicator 34 Housing 35 Switch knob

Claims (3)

[Claims] 1. Two conductor plates are arranged so that their planes face each other and are substantially parallel to each other, and a power feeding end is provided between points of the two conductor plates facing each other, and are separated from the power feeding end. In a loop antenna in which a short-circuit conductor that short-circuits the two conductor plates is connected at a position, each of the two conductor plates is a square, and the feeding end is set near one vertex of the square, and the feeding The short-circuit conductor is connected in the vicinity of the apex farthest from the end, the short-circuit conductor is plate-shaped, and its width is set to be sufficiently smaller than the length of the side and to exhibit a sufficiently low impedance at the used wavelength. A loop antenna characterized by being made. 2. The length of one side of the two conductor plates is 2 to 15% of the operating wavelength, and the width of the short-circuit conductor is 0.5 to 3.5% of the operating wavelength. 1. The loop antenna according to 1. 3. The part of the casing of the wireless communication device is formed between the two conductor plates, the electric circuit of the wireless communication device is arranged between the two conductor plates, and the wireless communication device is arranged on the conductor plate. The operation end or the display end of is attached.
The described loop antenna.