JPH0332086Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to a central loading impedance device for a helical antenna, which allows adjustment of the loading position and impedance at the center of the helical antenna.

(Conventional technology) Because the helical antenna has a short antenna length,
It is used as an antenna for car phones, etc.
An impedance device is loaded in the center of the helical antenna. As shown in Fig. 4, by loading an impedance device 2 as a phase modulator in the center of the helical antenna 1, the phases of the currents flowing through the upper and lower elements 3 and 4 are adjusted to be in the same phase. This is to improve gain. In addition, the broken line in FIG. 4 shows the current distribution. Furthermore, as shown in Fig. 5, if the impedance device 2 as a trap for frequency 1 is loaded at the center of the helical antenna 1, and the lower element 4 is set to 1/4 of the wavelength of frequency 1, then the lower element 4 will be set at frequency 1. Resonating, the upper and lower elements 3,
4 and the impedance device 2 as a whole resonate at another frequency 2, and can act as an antenna for two frequencies. Conventional examples of a center-loaded impedance device loaded at the center of such a helical antenna are shown in FIGS. 6 to 8.

The one in Figure 6 is the upper and lower elements 3,
4, and a lumped capacitor C is arranged in parallel on the outside of this coil L. In addition, the one shown in FIG. 7 has a lumped capacitor C arranged in parallel inside the coil L. Furthermore, in the one shown in FIG. 8, metal members 5 and 6 are provided opposite the ends of the upper and lower elements 3 and 4, and a coil L is interposed between the metal members 5 and 6. The impedance is formed by the stray capacitance CS between the metal members 5 and 6.

(Problems to be solved by the invention) By the way, in the above-mentioned conventional centrally loaded impedance device, the lengths of the upper and lower elements 3 and 4 cannot be adjusted, and the lengths of the upper and lower elements 3 and 4 cannot be adjusted. There is a problem in that the length cannot be set to an optimum value for the desired resonance frequency. Further, as shown in FIG. 6, a device in which a lumped capacitance C is provided outside the coil L has a problem in that its shape becomes large.

The purpose of the present invention was to solve the above-mentioned problems with the center-loaded impedance device of the conventional helical antenna. An object of the present invention is to provide a center-loaded impedance device for a helical antenna.

(Means for Solving the Problem) In order to achieve the above object, the center-loaded impedance device for a helical antenna of the present invention is provided with a centrally loaded impedance device for a helical antenna that is screwed into the helical element and axially Two conductive members are movably disposed, one end of a central shaft member made of a conductor is electrically connected to one of the conductive members, and the other end is electrically insulated from the other conductive member. The central shaft member is fitted into the two electrically conductive members and movably disposed in the axial direction.

(Function) Two conductive members are screwed together inside the element,
One end of the central shaft member is electrically connected to one conductive member, and the other end of the central shaft member is fitted into the other conductive member in an electrically insulated state, so that the element sandwiched between the two conductive members has an inductance. A distributed capacitance is generated between the central shaft member and the conductive member into which the central shaft member is fitted in an electrically insulated state. By rotating the two conductive members and moving them up and down, the lengths of the upper and lower elements can be adjusted, and the inductance can also be adjusted by adjusting the length of the element between the two conductive members. Further, the distributed capacitance can be adjusted by adjusting the amount by which the central shaft member is fitted into the conductive member in an electrically insulated state, and the impedance can be arbitrarily adjusted.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of an embodiment of a centrally loaded impedance device for a helical antenna of the present invention, and FIG. 2 is an external view of a helical antenna in which the centrally loaded impedance device of FIG. 1 is used. FIG. 3 is an equivalent circuit diagram of FIG. 2.

In FIGS. 1 to 3, a helical antenna 10 includes an element 1 made of a spiral metal wire.
A cover 12 made of insulating resin or the like is placed on the outer periphery of the element 1, and a cap 13 is provided at the upper end of the cover 12 to prevent rainwater from entering the element 11, and the terminal end of the element 11 is connected to a coaxial cable or the like at the base. A plug 14 is provided for this purpose. The metal conductive members 15 and 16 have grooves corresponding to the spiral element 11 carved on their outer peripheries, are screwed into the inside of the element 11, and can be moved up and down in the axial direction within the element 11 by rotation. It is located in Further, a penetrating female thread is provided at the axial center of one of the conductive members 15, and one end portion of a metal central shaft member 17 is screwed into this female thread. An insulating cylinder 18 made of Teflon (registered trademark), Delrin (registered trademark), etc. is inserted into the other conductive member 16, and the other end of the central shaft member 17 is removably inserted into this insulating cylinder 18. There is. These conductive members 15 and 16, the central shaft member 17, the insulating cylinder 18, and the element 11a sandwiched between the two conductive members 15 and 16 form a centrally loaded impedance device.

In such a configuration, two conductive members 15, 1
6 and move it in the axial direction of the element 11 to separate the upper element 11b and the lower element 11.
The lengths l1 and l2 of c can be adjusted. In addition, an element 11a sandwiched between two conductive members 15 and 16
acts as an inductance, and by adjusting the length between the two conductive members 15 and 16, the inductance
La can be adjusted. Furthermore, the central shaft member 17 is rotated about the axis relative to the conductive member 15 to move the central shaft member 17 in the axial direction, and the other conductive member 16
The distributed capacitance Ca can be adjusted by adjusting the amount of insertion.

Therefore, the impedance as a phase converter or trap can be adjusted as desired, and the length l of the upper element 11b and the lower element 11c can be adjusted as desired.
1 and l2, the resonant frequency of the helical antenna 10 can be easily changed over a wide range. In particular, when the frequency used varies depending on the region, such as in the case of antennas for automobile telephones, this can be accommodated by adjustment without changing the structure or parts.

Further, since the centrally loaded impedance device is housed inside the element 11, the shape is not large and air resistance can be reduced as an antenna for a car phone.

In the above embodiment, the conductive members 15, 16 and the central shaft member 17 are made of metal, but they may also be formed by plating resin or the like with metal, which is useful for reducing weight.

(Effects of the invention) As explained above, the center-loaded impedance device for a helical antenna of the invention has two conductive members screwed together inside the element, and one end of the center shaft member is electrically connected to one of the conductive members. Since the other end of the central shaft member is electrically insulated and inserted into the other conductive member, the element sandwiched between the two conductive members acts as an inductance, and the central shaft member and this central shaft member are electrically connected to each other. Distributed capacitance is generated between the conductive member and the electrically conductive member that is inserted in the electrically insulated state. By rotating the two conductive members and moving them up and down, the lengths of the upper and lower elements can be adjusted, and the inductance can also be adjusted by adjusting the length of the element between the two conductive members. ,
Furthermore, the distributed capacitance can be adjusted by adjusting the amount by which the central shaft member is fitted into the conductive member in an electrically insulated state, and the excellent effect is that the impedance can be adjusted as desired.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of a centrally loaded impedance device for a helical antenna of the present invention, and FIG. 2 is an external view of a helical antenna in which the centrally loaded impedance device of FIG. 1 is used. FIG. 3 is an equivalent circuit diagram of FIG.
The figure is a diagram explaining the effect of loading an impedance device as a phase converter in the center of a helical antenna, and FIG. 5 is a diagram explaining the effect of loading an impedance device as a trap in the center of a helical antenna. 6, 7, and 8 are diagrams of conventional center-loaded impedance devices, respectively. 10: Helical Ante, 11: Element, 1
5, 16: Conductive member, 17: Central shaft member, 18:
Insulating tube.

Claims (1)

[Scope of utility model registration request] Two conductive members are disposed inside the element of the helical antenna so as to be movable in the axial direction by being screwed into the helical element, and one end of the central shaft member made of a conductor is connected to one of the conductive members. The central shaft member is electrically connected, and the other end is fitted into the other conductive member in an electrically insulated state, and the central shaft member is disposed in the two conductive members so as to be movable in the axial direction. Center-loaded impedance device for helical antennas.