JPH039375Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a whip antenna having two closely spaced resonant frequencies.

(Prior Art) FIG. 5 shows a vertical cross-sectional view of a conventional antenna that has two resonant frequencies by combining a coil element and a rod-shaped conductor.

In Fig. 5, coil element 2 is connected to connector 1.
A rod-shaped conductor 3 is arranged on the central axis of the coil element 2, and a base end of the rod-shaped conductor 3 is fixed to the plug 1.

In this configuration, the coil element 2 and the rod-shaped conductor 3 each have a resonant frequency, and one antenna has two resonant frequencies.

(Problems to be Solved by the Invention) By the way, in cordless telephones, car telephones, and other devices that perform two-way communication, the transmitting frequency and receiving frequency are set to be slightly different.
Therefore, as an antenna for a cordless telephone or an antenna for a car telephone, it is desired that a single antenna be provided with two slightly different resonant frequencies: a transmitting frequency and a receiving frequency.

Here, regarding the above-mentioned conventional antenna,
Although the coil element 2 and the rod-shaped conductor 3 provide two different resonance frequencies, it is difficult to set these two resonance frequencies close to each other. That is, the length l ₁ of the coil element 2 and the length l ₂ of the rod-shaped conductor 3 are usually set to l ₁ ≧l ₂ . One coil element 2 has a spiral shape, and its electrical length corresponds to many times the length l ₂ . On the other hand, the rod-shaped conductor 3 is linear and has a significantly different electrical length from the coil element 2. As a result, for example, coil element 2
If the resonant frequency is set to 144MHz, the resonant frequency of the rod-shaped conductor 3 will be approximately 430MHz.
Therefore, the antenna described above is inappropriate as an antenna for a cordless telephone or an antenna for a car telephone.

The purpose of the present invention was made in view of the above-mentioned circumstances, and is to provide a whip antenna in which one antenna has two resonant frequencies that are close to each other.

(Means for Solving the Problem) In order to achieve the above object, the whip antenna of the present invention has a loading coil electrically connected coaxially to the tip of a linear element, and an insulating material on the outer periphery. An electrode covered with is inserted into the loading coil, and one end of this electrode is electrically connected to the tip of the element.

(Function) A trap circuit is formed at the tip of the linear element by the inductance of the loading coil and the capacitance generated between the electrode inserted into the loading coil, and the trap frequency of this trap circuit is set by the element. By matching the resonant frequency of the element and the loading coil, it is possible to provide two slightly different resonant frequencies: the resonant frequency of the element and the loading coil, and the resonant frequency of the element itself.

(Explanation of Examples) Below, Figures 1 and 2 will be explained as examples of the present invention.
This will be explained with reference to the figures. FIG. 1 is a vertical cross-sectional view of the main part of the tip of an embodiment of the whip antenna of the present invention, and FIG. 2 is an equivalent circuit diagram of FIG. 1.

In FIG. 1, the base end of an element 4 made of a straight metal pipe is fixed to a plug (not shown), and a connecting fitting 5 is fixed to the tip by soldering, welding, etc. . A loading coil 6 is disposed coaxially with the element 4, with one end fixed to the connecting fitting 5 and electrically connected to the element 4. Further, an electrode 7 is integrally formed and disposed so as to protrude from the connecting fitting 5 onto the central axis of the loading coil 6, and a tube 8 made of an insulating material is placed over the outer periphery of the electrode 7. In addition,
9 is a cap made of resin or the like.

In such a configuration, a stray capacitance C is generated between the electrode 7 and the portion of the loading coil 6 that faces the electrode 7. Therefore, this stray capacitance C and the inductance L of the loading coil 6 facing the electrode 7 form a parallel resonant trap circuit 10 as shown in FIG. In FIG. 2, L ₁ is the inductance caused by the upper loading coil 6 that does not face the electrode 7, and L ₂ is the inductance caused by the element 4.

Here, the trap frequency t of the trap circuit 10
By matching the resonant frequency ₂ of the element 4 itself, two different resonant frequencies are set, the resonant frequency ₂ of the element 4 itself and the resonant frequency ₁ of the element 4 and the entire loading coil 6, as shown in Figure 2. can. Since the trap circuit 10 is disposed at the tip of the element 4, the two resonance frequencies ₁ and ₂ can be set to slightly different values by appropriately setting the inductance of the loading coil 6 to a small value. The trap frequency t may be adjusted by changing the length and diameter of the electrode 7, the dielectric constant of the tube 8, etc.

FIG. 3 is a longitudinal sectional view of the main part of the tip of another embodiment of the hop antenna of the present invention. In FIG. 3, the same members as those in FIG. 1 are given the same reference numerals, and redundant explanations will be omitted.

In FIG. 3, a connecting fitting 15 is fixed to the cable at the tip of an element 14, which is a linear flexible cable covered with an insulating material, by caulking or the like. A loading coil 6 is connected and fixed to a connecting fitting 15 coaxially with the element 14. Furthermore, a through hole 15a is formed on the central axis of the connecting fitting 15, and one end of the braided wire covered with a tube 18 made of an insulating material is bundled and inserted into the through hole 15a, and soldered to the connecting fitting 15. An electrode 17, which is fixed and inserted into the loading coil 6, is electrically connected to the tip of the element 14.

FIG. 4 is a longitudinal sectional view of the main part of the tip of still another embodiment of the whip antenna of the present invention. Fourth
In the drawings, the same members as those in FIGS. 1 and 3 are given the same reference numerals and redundant explanations will be omitted.

In FIG. 4, a connecting fitting 25 is fixed to the tip of an element 24 made of a linear rod by soldering, welding, or the like. A through hole 25a is formed on the central axis of the connecting fitting 25, and the core of the coaxial cable is inserted into this through hole 25a, fixed to the connecting fitting 25 by soldering, and inserted into the loading coil 6. An electrode 27 is arranged and electrically connected to the tip of the element 24.

Note that by setting the two resonant frequencies ₁ and ₂ very close to each other, it is possible to achieve a wide band with one antenna. Furthermore, the trap circuit 9
By providing multiple pieces of in the loading coil 6,
A multi-band whip antenna with two or more resonant frequencies can be constructed. Further, in the above embodiment, a structure is shown in which the loading coil 6 is longer than the electrodes 7, 17, and 27, but it goes without saying that the lengths may be the same.

(Effect of the invention) As explained above, according to the whip antenna of the invention, two slightly different resonance frequencies can be arbitrarily set. One resonance frequency is the resonance frequency of the linear element itself, and the gain is high, especially at 800MHz in the UHF band.
It has excellent effects and is suitable as a 900MHz antenna.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of the main part of the tip of an embodiment of the whip antenna of the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, and FIG. 3 is a hop antenna of the present invention. FIG. 4 is a vertical cross-sectional view of the main part of the tip of still another embodiment of the whip antenna of the present invention, and FIG. FIG. 2 is a vertical cross-sectional view of a conventional antenna that has two resonant frequencies by combining an element and a rod-shaped conductor. 4, 14, 24: element, 6: loading coil, 8, 18: tube made of insulating material,
7, 17, 27: electrode.

Claims (1)

[Scope of utility model registration request] A loading coil is electrically connected coaxially to the tip of a linear element, and an electrode whose outer periphery is covered with an insulating material is inserted into the loading coil, and one end of this electrode is connected to the tip of the element. A whip antenna characterized in that it is electrically connected to and arranged in the antenna.