JP2001339227A - Helical antenna and its resonance frequency adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily adjust the resonance frequency of a helical antenna to a desired resonance frequency. SOLUTION: This helical antenna 10 has a hollow cylindrical member 11 made of an insulator whose relative permittivity εr is 2 to 4 and four conductors 12 wound helically around the hollow cylindrical member 1. A screw hole 13 which is cut into a female screw is formed in the inner peripheral wall of the upper end of the hollow cylindrical member 11. This helical antenna 10 has a ceramic bolt 14 which is able to threadably engage the screw hole 13 and has relative permittivity εr of 10 to 100. When the ceramic bolt 14 is inserted into the screw hole 13 of the hollow cylindrical member 11, the length of the hollow cylindrical member 11 can be made equivalently short by wavelength shortening effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives digital radio broadcasts by receiving radio waves from artificial satellites (hereinafter also referred to as "satellite waves") or radio waves on the ground (hereinafter also referred to as "terrestrial waves"). And more particularly to an antenna used in a digital radio receiver.

[0002]

2. Description of the Related Art Recently, a digital radio receiver capable of receiving a radio wave (satellite wave) or a terrestrial wave from an artificial satellite so as to listen to a digital radio broadcast has been developed and is being put to practical use in the United States. This digital radio receiver is mounted on a mobile station such as an automobile and has a frequency of about 2.3G.
It is possible to listen to a radio broadcast by receiving a radio wave of Hz. That is, the digital radio receiver is a radio receiver that can listen to mobile broadcasts. still,
The terrestrial wave is obtained by temporarily receiving a satellite wave at an earth station and then slightly shifting the frequency.

In order to receive such a radio wave of a frequency of about 2.3 GHz, it is necessary to install an antenna outside the automobile. As such an antenna, various antennas can be considered, but a stick type is generally used instead of a flat type (flat type). Also, as is well known, an electromagnetic wave radiated in free space is a transverse wave having an electric field and a magnetic field oscillating in a plane perpendicular to the traveling direction of the wave, and the electric field and the magnetic field change in intensity in the plane. However, this is called polarization. Satellite waves are circularly polarized waves, whereas terrestrial waves are linearly polarized waves.

Hereinafter, an antenna for receiving a satellite wave will be mainly described. A helical antenna is known as one of the stick antennas. The helical antenna has a structure in which at least one conductive wire is wound in a helical (spiral) shape around a cylindrical or cylindrical (hereinafter, referred to as “cylindrical”) member, so that the above-described circularly polarized wave can be efficiently emitted. Can be received. Therefore, the helical antenna is used exclusively for receiving satellite waves. As a material of the cylindrical member, an insulating material such as plastic is used. As the number of conductors, for example, four wires are used. On the other hand, it is actually very difficult to wind a plurality of wires in a helix shape around a cylindrical member. For that reason,
Instead, there has been proposed a sheet in which a plurality of conductor patterns are printed on an insulating sheet (hereinafter, referred to as “insulating sheet with a conductor pattern”) wound around a cylindrical member.

In a helical antenna having such a structure, the resonance frequency is determined by the height (length), diameter, relative permittivity, and the like of the cylindrical member.

FIG. 6 shows frequency characteristics of a helical antenna (hereinafter, also simply referred to as "antenna"). 6, the horizontal axis represents the frequency f, and the vertical axis represents the output return loss. As is clear from FIG. 6, the output return loss is minimized at the resonance point. The resonance point moves (shifts) as indicated by the arrow in FIG. 6 due to the above-mentioned variation in the size of the cylindrical member. Therefore, in order to receive a satellite wave (circularly polarized wave) having a frequency of about 2.3 GHz using a helical antenna, it is necessary to set a resonance point (resonance frequency of the antenna) to a desired resonance frequency (2.3 GHz). There is. However, variations in dimensions are inevitable in the manufacturing process of the antenna, and it is necessary to adjust the resonance frequency of the antenna to a desired resonance frequency by using some adjustment means (adjustment method).

Conventionally, the resonance frequency of the antenna is adjusted to a desired resonance frequency by cutting the tip of the helical antenna and adjusting the length of the antenna. That is, at the time of manufacturing (manufacturing process), the length of the helical antenna is made long in advance so that a frequency lower than the desired resonance frequency can be received,
In the adjustment step (adjustment step), the tip of the helical antenna is cut to adjust the length of the antenna so that the resonance point has a desired resonance frequency. Such an adjustment method will be referred to herein as a “cutting method”.

In the case of a helical antenna having a structure in which a plurality of conductive wires are wound around a cylindrical member in a helical shape (spiral shape), a satellite wave (circularly polarized wave) received by the helical antenna is phase-shifted. After the phases are matched (adjusted) by shifting the phase by a receiver, the signals are combined, then amplified by a low noise amplifier (LNA), and sent to the receiver body. Here, the combination of the helical antenna (antenna), the phase shifter, and the LNA is called an antenna device. Also,
In the case of a helical antenna having a structure in which only one conducting wire is wound around a cylindrical member in a helix (helical shape), a phase shifter is unnecessary.

[0009]

As described above, in the conventional helical antenna, the tip (upper end) is cut to adjust the resonance frequency to a desired resonance frequency. . However, in such a cutting method, it is necessary to cut the upper end of the helical antenna little by little in order to accurately match the resonance frequency (resonance point) of the helical antenna to a desired resonance frequency, which is very troublesome. It will take time.
This is because once the antenna is cut short, it is no longer possible to return the antenna's resonance frequency to the desired resonance frequency, and the helical antenna becomes useless. . Therefore, the cutting of the upper end portion of the helical antenna requires extreme care, which is a very time-consuming operation.

Therefore, it is desired that the resonance frequency of the helical antenna can be easily adjusted to a desired resonance frequency by an adjustment method (adjustment means) other than the conventional cutting method.

Therefore, an object of the present invention is to provide a helical antenna which can easily adjust the resonance frequency.

Another object of the present invention is to provide an adjustment method capable of easily adjusting the resonance frequency of a helical antenna to a desired resonance frequency.

[0013]

The present inventors have determined what kind of structure (configuration) should be adopted so that the resonance frequency of a helical antenna can be easily adjusted to a desired resonance frequency. I thought variously about. As described above, the resonance frequency of the helical antenna is determined by parameters such as the height (length), diameter, and relative permittivity of the cylindrical member. It is actually very difficult to change the height (length) and diameter of the cylindrical member among these parameters. Therefore, the present inventors came to the conclusion that if the relative dielectric constant of the cylindrical member could be changed, the resonance frequency of the helical antenna should be easily adjusted to a desired resonance frequency. did.

Various methods are conceivable for changing the relative permittivity of the cylindrical member. In the present invention, by inserting a male screw member having a high relative dielectric constant into the cylindrical member, the relative dielectric constant of the cylindrical member can be increased, and the length of the cylindrical member can be adjusted to be equivalently shortened. I did it.

That is, according to the present invention, a helical member composed of a cylindrical member (11) made of an insulator and at least one conductor (12) wound in a helix around the cylindrical member. In the antenna (10), the inner peripheral wall at the upper end of the cylindrical member has a screw hole (1
3), a male screw member (1) that can be screwed into this screw hole and has a relative dielectric constant (εr) equal to or higher than the relative dielectric constant of the cylindrical member.
4, 14A) is obtained.

In the helical antenna (10),
The male screw member is made of, for example, ceramic. The male screw member may be a bolt (14).

Further, according to the present invention, there is provided a method for adjusting the resonance frequency of the helical antenna (14) to a desired resonance frequency, wherein the cylindrical member (11) receives a frequency lower than the desired resonance frequency. A step of slightly increasing the length to be as long as possible and a step of screwing the male screw members (14, 14A) into the screw holes (13) to adjust the resonance frequency of the helical antenna to a desired resonance frequency. Thus, a method for adjusting the resonance frequency of a helical antenna is obtained.

Note that the reference numerals in parentheses are provided for easy understanding of the present invention, and are merely examples, and it is a matter of course that the present invention is not limited to these.

[0019]

The relative permittivity of the male screw member is equal to or greater than the relative permittivity of the cylindrical member. Therefore, when the male screw member is inserted into the screw hole of the cylindrical member, the equivalent length of the cylindrical member is reduced due to the wavelength shortening effect. Can be shortened. That is, the length of the cylindrical member can be equivalently adjusted according to the insertion amount of the male screw member into the cylindrical member, and as a result, the resonance frequency of the helical antenna can be easily adjusted to a desired resonance frequency. Becomes possible.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Referring to FIG. 1, a helical antenna 10 according to one embodiment of the present invention will be described. The illustrated helical antenna 10 includes a hollow cylindrical member 11 made of an insulator having a relative dielectric constant εr of 2 to 4;
1 and four conductive wires 12 wound in a helix. The material of the hollow circular upper member 11 is made of, for example, plastic.

Here, instead of winding the four conductive wires 12 in a helical shape around the hollow cylindrical member 11, the above-described insulating sheet with a conductor pattern (not shown) may be wound around the hollow cylindrical member 11. .

On the inner peripheral wall at the upper end of the hollow cylindrical member 11, a screw hole 13 having a female thread is provided. The helical antenna 10 further includes a male screw member 14 that can be screwed into the screw hole 13. This male screw member 1
Reference numeral 4 has a relative permittivity equal to or higher than the relative permittivity of the hollow cylindrical member 11. In the present embodiment, the male screw member 14 is made of a ceramic bolt having a relative dielectric constant εr of 10 to 100. The ceramic bolt 14 includes a screw portion 141 screwed into the screw hole 13 and a head portion 142 at the tip thereof.

Next, a method of adjusting the resonance frequency of the helical antenna 10 shown in FIG. 1 to a desired resonance frequency will be described with reference to FIG.

First, the hollow cylindrical member 11 is made slightly longer so that it can receive a frequency lower than a desired resonance frequency. Then, the male screw member (ceramic bolt) 14 is screwed into the screw hole 13 (FIG. 1) to adjust the resonance frequency of the helical antenna 10 to a desired resonance frequency. Here, the insertion distance of the ceramic bolt 14 can be easily adjusted with respect to the screw hole 13 as shown by an arrow A in FIG.

Since the relative permittivity εr of the ceramic bolt 14 is higher than the relative permittivity εr of the hollow cylindrical member 11, when the ceramic bolt 14 is inserted into the screw hole 13 of the hollow cylindrical member 11, the equivalent is obtained due to the wavelength shortening effect. Thus, the length of the hollow cylindrical member 11 can be shortened. That is, the length of the hollow cylindrical member 11 can be equivalently adjusted according to the insertion amount of the ceramic bolt 14 into the hollow cylindrical member 11. More specifically, if the insertion amount is large, the length of the hollow cylindrical member 11 is equivalently short, and if the insertion amount is small, the length of the hollow cylindrical member 11 is equivalently long. As a result, the resonance frequency of the helical antenna 10 can be easily adjusted to a desired resonance frequency.

Although the present invention has been described with reference to the preferred embodiments, the present invention is, of course, not limited to the above-described embodiments. For example, in the above-described embodiment, the ceramic bolt 14 is used as the male screw member. However, the present invention is not limited to this, and a male screw 14A as shown in FIG. 3 may be used. Further, the shape of the head of the male screw 14A may be not only a hexagonal concave portion as shown in FIG. 4 but also a cross-shaped groove as shown in FIG. Further, the material of the male screw member is not limited to ceramic, and any material having a relative dielectric constant εr equal to or higher than the relative dielectric constant εr of the hollow circular member 11 may be used. Further, the number of conductors wound in a helix around the cylindrical member is not limited to four, and may be at least one.
I just need a book.

[0028]

As is apparent from the above description, according to the present invention, a screw hole with a female screw is provided in the inner peripheral wall at the upper end of the cylindrical member, and the screw hole can be screwed into the cylindrical hole. Since it has a male screw member having a relative dielectric constant equal to or higher than the relative dielectric constant of the member, the length of the cylindrical member can be equivalently adjusted according to the insertion distance of the male screw member into the cylindrical member, and as a result, The resonance frequency of the helical antenna can be easily adjusted to a desired resonance frequency.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a helical antenna according to one embodiment of the present invention.

FIG. 2 is a perspective view for explaining a method of adjusting a resonance frequency of the helical antenna shown in FIG.

FIG. 3 is a sectional view showing a male screw that can be used in place of the ceramic bolt of the helical antenna shown in FIG. 1;

FIG. 4 is a plan view showing an example of the shape of a head constituting the male screw shown in FIG. 3;

FIG. 5 is a plan view showing another example of the shape of the head constituting the male screw shown in FIG. 3;

FIG. 6 is a diagram illustrating frequency characteristics of a helical antenna.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Helical antenna 11 Hollow cylindrical member 12 Lead wire 13 Screw hole 14 Ceramic bolt (male screw member) 14A Male screw

Claims (4)

[Claims] 1. A helical antenna comprising a cylindrical member made of an insulator and at least one conductive wire wound in a helical shape around the cylindrical member, wherein an upper end of the cylindrical member is provided. A helical thread provided with a threaded hole provided with an internal thread on an inner peripheral wall of the helical member, the male threaded member being capable of being screwed into the threaded hole and having a dielectric constant greater than or equal to the dielectric constant of the cylindrical member. antenna. 2. The male screw member is made of ceramic.
The helical antenna according to claim 1. 3. The helical antenna according to claim 1, wherein said male screw member is a bolt. 4. A method for adjusting a resonance frequency of a helical antenna to a desired resonance frequency according to claim 1, wherein the cylindrical member has a length capable of receiving a frequency lower than the desired resonance frequency. And a step of adjusting the resonance frequency of the helical antenna to the desired resonance frequency by screwing the male screw member into the screw hole. Resonance frequency adjustment method.