JPH07176938A - Flexible antenna for mobile communication and its configuration method - Google Patents

Abstract

PURPOSE:To prevent a trouble caused by an unbalanced current by improving an antenna of a structure incorporating a coaxial cable to prevent the unbalanced current with simple and inexpensive configuration without disturbing the flexibility. CONSTITUTION:A center conductor 2 whose electric length is lambda/4 at a tip of a coaxial cable 1 is exposed electrically and a conductor 3 whose electric length is lambda/4 is arranged along the coaxial cable 1 to form a dipole antenna, and a conductive cylindrical member whose electric length is lambda/2 (e.g. a lambda/2 cylindrical conductor 7) is fitted externally to the coaxial cable 1. An unbalanced current produced in the dipole antenna is blocked by the lambda/2 cylindrical conductor 7 and then no adverse effect is caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dipole antenna suitable for mobile communication, and in particular, there is no fear that an unbalanced current generated in the antenna will adversely affect the communication device main circuit, and the antenna is flexible. The present invention relates to a flexible mobile communication antenna that is improved so as not to impair its property, and a method of configuring the same.

[0002]

2. Description of the Related Art As an antenna of a mobile station in mobile communication, it is desired that the antenna be small, lightweight and simple. From this viewpoint, a coaxial antenna or an improved antenna thereof is often used. In the coaxial antenna, for example, a center conductor of a coaxial cable having a characteristic impedance of 50 ohms is extended upward by about 1/4 wavelength to act as an upper half portion of a half-wave antenna, and a lower half portion of a copper of about 1/4 wavelength Alternatively, it is covered with a sleeve made of brass and is connected to the outer conductor of the coaxial cable so as to act as the lower half of the antenna.

FIG. 4 shows a coaxial antenna provided with a quarter-wave conductor, (A) is a schematic view showing an antenna current distribution graph and a coaxial cable external current distribution graph, and (B) is the coaxial antenna. FIG. 3 is a schematic diagram for explaining the mechanism of an unbalanced current that occurs in FIG. Alternating current and voltage are generated in the conducting circuit of the antenna. Considering that one moment, an upward current I ₁ is generated in the central conductor 2 and a downward current I ₂ is generated in the λ / 4 conductor 3. Along with this, electric currents I having different directions are generated in the inner conductor and the central conductor of the coaxial cable 1. An unbalanced current I ₃ caused by the unbalance of the antenna is generated outside the coaxial cable outer conductor. The unbalanced current described above is a high cycle alternating current, and therefore radiation occurs. Since the coaxial cable 1 is connected to the communication device main body, the unbalanced current adversely affects the communication device main circuit. Also,
The unbalanced current not only deteriorates antenna characteristics, but also causes power loss due to radiation. Furthermore, if the length of the coaxial cable changes, the overall characteristics of the antenna including the cable also change.

FIG. 5 is an explanatory view of a conventional technique for preventing an unbalanced current in a dipole antenna having a coaxial cable built therein. A central conductor 2 having a length corresponding to a quarter wavelength is exposed at the tip of the coaxial cable 1. Reference numeral 3 is the aforementioned λ / 4 conductor. A Schbeltoff 5 made of a metal tube is externally fitted to the coaxial cable 1, and a base end side of the Schbeltoff 5 (an opposite side of the dipole antenna 4 formed at the tip end side) to the outer conductor of the coaxial cable 1. Electrical connection 6 is made. When the Schwertoff 5 thus configured is viewed in the direction of arrow a, the impedance is infinite, so that the unbalanced current generated in the dipole antenna 4 is blocked.

[0005]

When the conventional technique shown in FIG. 5 is applied in the process of industrial production of an antenna, the insulating jacket of the coaxial cable 1 is partially stripped to expose the outer conductor. Then, a Schwertoff made of a metal tube must be externally fitted and soldered. Such an operation is very complicated, requires a lot of time and labor, and increases the manufacturing cost. In addition, since the outer conductor of the coaxial cable is heated by the soldering work, there is a constraint that the insulating material in contact with the outer conductor must have heat resistance. Furthermore, the flexibility of the coaxial cable 1 is
There is a problem that the Schwertoff 5 which is a rigid tubular member interferes. Since the location where the schwertoff is disposed corresponds to the portion where the coaxial cable 1 is routed inside the case of the communication device main body, it is very inconvenient and difficult to handle if it is stiffened by λ / 4 length. The present invention has been made in view of the above circumstances, there is no need to solder the outer conductor of the coaxial cable, without impairing the flexibility of the coaxial cable,
It is an object of the present invention to provide a technique capable of preventing various troubles caused by an unbalanced current.

[0006]

In order to achieve the above object (easy to manufacture and inexpensive), a flexible mobile communication antenna structure according to the present invention includes a coaxial cable having a center conductor and an outer conductor. It is applied to an antenna, and the outer conductor is removed to electrically expose the center conductor in the range of electrical length λ / 4 of the tip end portion of the coaxial cable, and λ / 4
The electric length λ /
The conductor 4 is arranged along the outer conductor to form a dipole antenna, and the coaxial cable is externally fitted to a portion closer to the main body of the communication device than a portion where the coaxial cable forms the antenna. A cylindrical conductor having a length of λ / 2 is arranged to prevent an unbalanced current generated in the dipole antenna from affecting the communication device main circuit. The method of the present invention created to apply the antenna of the present invention in industrial manufacture is an antenna incorporating a coaxial cable having a central conductor and an outer conductor, wherein the electrical length of the tip of the coaxial cable is The central conductor in the range of λ / 4 is electrically exposed and the electrical length λ / 4
When constructing a dipole antenna in which the conductor of (1) is arranged along the outer conductor, an unbalanced current is blocked by externally fitting the coaxial cable and providing a tubular conductor of electrical length λ / 2. And

Since an antenna generally has a peculiar tuning frequency band, for example, even if it is called a quarter wavelength conductor, it is not necessarily strictly limited to λ / 4 in terms of precision engineering, and it is almost the same. It means λ / 4. Further, since this length changes depending on the presence of the dielectric, when the length dimension of the member is referred to in the present invention with reference to the wavelength λ, it means the electrical length, not necessarily the mechanical engineering length dimension. Does not match. In the following, in the case where there is no ambiguity, the description of the electrical length will be omitted, and the description will be made with the fraction of the wavelength λ.

[0008]

According to the above-mentioned means, when the tubular conductor having the electrical length λ / 2 is externally fitted to the coaxial cable and the tubular conductor is viewed from the antenna side toward the communication device main circuit side, The impedance becomes infinite and the unbalanced current generated in the antenna is blocked. Therefore, the unbalanced current does not deteriorate the antenna characteristics, and the unbalanced current does not flow through the coaxial cable to generate radiation. Therefore, the harmful effect of the radiated wave is prevented, and the energy waste due to the radiated wave is prevented. Then, even if the length from the antenna to the communication device main circuit changes, the overall characteristics including the coaxial cable do not change. Further, the tubular conductor having the electrical length λ / 2 can also be formed of a flexible conductor (for example, a braided body of thin metal wires). With this structure, the antenna and the feed line are flexible. The sex is not lost. Further, the conductor having the electric length of λ / 4 can also be composed of a braided body of electric conductors. With this structure, the lower half of the dipole antenna does not lose its flexibility. Furthermore, the electrical length λ /
The cylindrical conductor of No. 2 does not need to be brought into direct contact with the outer conductor of the coaxial cable for electrical conduction, and since it only needs to be fitted on the outer conductor, it does not require extra time or labor for the assembly work, and is a special skill. Assembling cost is low because it does not require.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a flexible mobile communication antenna according to the present invention, (A) is an external view schematically drawn, and (B) is the same as the above-mentioned external view. It is the figure which added the antenna current distribution graph to the structural drawing drawn to scale. 1
Is a coaxial cable, and in this example, a commercially available product having a characteristic impedance of 50 ohm for communication equipment was used. 2 is its central conductor. In the figure, the upper side is the tip end side of the coaxial cable, and the lower side is the base end side, which are connected to the communication device main circuit (not shown) via the connector 8. Regarding the range of λ / 4 of the tip end of the coaxial cable 1, the center conductor is passed through the tip of the outer conductor made of the braided wire at a portion of the electrical length λ / 4 to be electrically exposed, and The portion from which the central conductor is removed is folded back (toward the base end side), and along the coaxial cable 1, the λ / 4 conductor 3 is formed. Thus, the center conductor 2 in the λ / 4 range where the outer conductor is peeled off is exposed and acts as the upper half of the antenna, and the λ / 4 conductor 3 acts as the lower half of the antenna. Functions as a dipole antenna. From the base end side of the λ / 4 conductor 3 of the dipole antenna to the base end direction (downward in the figure, a cylindrical conductor 7 having an electric length of λ / 2 is gently fitted. The λ / 2 cylindrical conductor 7 is As described below with reference to Fig. 2, it functions as an unbalanced current blocking unit.
The distance g between the / 4 conductor 3 and the λ / 2 cylindrical conductor 7 should theoretically be λ / 4, but the inventors of the present invention have confirmed through repeated experiments that λ / Even if it is not 4, an antenna characteristic having a sufficient practical value can be obtained.
The λ / 4 conductor 3 may be formed of a solid rod-shaped conductor (for example, copper wire) having a wavelength of about ¼ wavelength. However, if the outer conductor of the coaxial cable is used as in the present embodiment, the coaxial cable can be used. This is advantageous because it does not impair the flexibility of the parts, saves material costs, and does not require any additional connection processing (such as soldering work). FIG. 2 shows the vicinity of the λ / 2 cylindrical conductor in the above embodiment, and (A) is a schematic partial external perspective view for explaining the electrical function,
(B) is a perspective view for explaining a specific structure.
As shown in (A), when the λ / 2 cylindrical conductor 7 is viewed from the front end side (upper side in the drawing) to the base end side, the impedance Z becomes infinite, so that the current value I becomes zero. That is,
Unbalanced currents are blocked. Further, as shown in FIG. 6B, the λ / 2 cylindrical conductor 7 of this example is formed by braiding copper wires. With this structure, the λ / 2 cylindrical conductor does not hinder the flexibility of the coaxial cable 1. In carrying out the present invention, the λ / 2 cylindrical conductor 7 does not necessarily have to be a strict cylindrical solid geometrically, and may be a conductive member that cylindrically covers the coaxial cable. Further, in order to easily form the λ / 2 cylindrical conductor, it is preferable to use a braided metal wire as in the above embodiment, but other known flexible materials (for example, conductive composite) Rubber) can also be used.
Reference numeral 9 shown in FIG. 1 is a cover made of electrically insulating flexible synthetic rubber. The center conductor 2 of this embodiment is covered with the above-mentioned cover 9 when viewed mechanically, but is not electromagnetically shielded. In the present invention, such a state is called electrically exposed.

FIG. 3 is a chart showing the tuning characteristics in the above embodiment, (A) is an RFL characteristic chart with a center of 1.9 GHz and a span of 0.5 GHz, and (B) is the same SWR.
It is a characteristic chart. From these figures, it can be seen that the flexible antenna of this example has suitable tuning characteristics for mobile communication at 1.9 GHz. And 1.9GH
In the case of z, the λ / 2 cylindrical conductor has a mechanical length of 50 mm to 60 mm in consideration of the influence of the dielectric material and has flexibility, so that this is used as the main body of the mobile communication device. There is no possibility that another trouble will occur when it is incorporated into the case (not shown).

[0011]

When the present invention is applied, the electrical length λ / 2
When the cylindrical conductor is externally fitted to the coaxial cable and the cylindrical conductor is viewed from the antenna side toward the communication device main circuit side, the impedance becomes infinite and the unbalanced current generated in the antenna is blocked. It Therefore, the unbalanced current does not deteriorate the antenna characteristics, and the unbalanced current does not flow through the coaxial cable to generate radiation. Therefore, the harmful effect of the radiated wave is prevented, and the energy waste due to the radiated wave is prevented. Then, even if the length from the antenna to the communication device main circuit changes, the overall characteristics including the coaxial cable do not change. Further, the tubular conductor having the electrical length λ / 2 can also be formed of a flexible conductor (for example, a braided body of thin metal wires). With this structure, the antenna and the feed line are flexible. The sex is not lost. Further, the conductor having the electric length of λ / 4 can also be composed of a braided body of electric conductors. With this structure, the lower half of the dipole antenna does not lose its flexibility. Further, the cylindrical conductor having the electrical length of λ / 2 does not need to be brought into direct contact with the outer conductor of the coaxial cable for electrical conduction, and it is sufficient to simply fit the outer conductor to the outer conductor of the coaxial cable. Since it does not require labor, labor, or special skill, it has an excellent practical effect that the assembly work cost is low.

[Brief description of drawings]

FIG. 1 shows a flexible mobile communication antenna 1 according to the present invention.
An example is shown, (A) is an external view schematically drawn, (B)
[Fig. 3] is a diagram in which an antenna current distribution graph is added to a structural diagram drawn at the same scale as the schematic external view.

2A and 2B show the vicinity of a λ / 2 cylindrical conductor in the above embodiment, FIG. 2A is a schematic partial external perspective view for explaining an electrical function, and FIG. 2B is for explaining a specific structure. FIG.

FIG. 3 is a chart showing tuning characteristics in the above embodiment, (A) center 1.9 GHz, span 0.5 GH.
The RFL characteristic chart of z and (B) are SWR characteristic charts.

FIG. 4 shows a coaxial antenna provided with a quarter-wave conductor, (A) is a schematic diagram showing an antenna current distribution graph and a coaxial cable external current distribution graph, and (B).
FIG. 3 is a schematic diagram for explaining a mechanism of an unbalanced current generated in the coaxial antenna.

FIG. 5 is an explanatory diagram of a conventional technique for blocking an unbalanced current in a dipole antenna having a built-in coaxial cable.

[Explanation of symbols]

1 ... Coaxial cable, 2 ... Center conductor, 3 ... λ / 4 conductor, 4
... Dipole antenna, 5 ... Schwertoff, 6 ... Electrical connection, 7 ... λ / 2 cylindrical conductor, 8 ... Connector, 9 ... Cover.

Claims (6)

[Claims] 1. An antenna having a built-in coaxial cable composed of a central conductor and an outer conductor, wherein the outer conductor is removed to electrically expose the central conductor in the electrical length λ / 4 range of the tip of the coaxial cable. At the same time, a conductor having an electrical length of λ / 4 is arranged near the tip of the outer conductor from which the λ / 4 range is removed to form a dipole antenna, and the coaxial cable is The electrical length λ / is set by fitting it on the part closer to the communication device main body than the part forming the antenna.
A flexible mobile communication antenna, wherein two cylindrical conductors are arranged to prevent an unbalanced current generated in the dipole antenna from affecting the communication device main circuit. 2. The flexible mobile communication antenna according to claim 1, wherein the conductor having an electrical length of λ / 4 is a braided body made of filaments of a conductor. 3. The cylindrical conductor having an electrical length of λ / 2 is
The flexible mobile communication antenna according to claim 1, wherein the flexible mobile communication antenna is a braided body composed of conductor filaments. 4. An antenna having a built-in coaxial cable having a center conductor and an outer conductor, wherein the center conductor within a range of electrical length λ / 4 at the tip of the coaxial cable is electrically exposed. In the case of constructing a dipole antenna in which a conductor having an electrical length of λ / 4 is arranged along an outer conductor, the dipole antenna is fitted over the coaxial cable to provide a cylindrical conductor having an electrical length of λ / 2. A method of constructing a flexible mobile communication antenna, characterized by blocking a balanced current. 5. The center conductor is passed through at a portion having an electrical length λ / 4 from a tip end portion of an outer conductor formed of a braided wire forming the coaxial cable to be electrically exposed.
The flexible portion according to claim 4, wherein a portion of the outer conductor from which the central conductor is removed is folded back to the proximal end side of the coaxial cable so as to function as the conductor having the electrical length λ / 4. A method of configuring an antenna for mobile communication. 6. The tubular conductor having the electrical length λ / 2,
Characterized by being formed by a braided body of conductor wire,
A method of configuring the flexible mobile communication antenna according to claim 4.