JP2823644B2 - Helical antenna - Google Patents

Description

The present invention relates to a method for configuring a helical antenna having a circularly polarized conical beam.

[Prior Art] In mobile communication, a mobile satellite communication system, which is a mobile communication system using a satellite, has recently attracted attention because a large area can be made a service area by using a satellite in mobile communication. In order to reduce the cost of the mobile satellite communication system, it is important to reduce the size and cost of a mobile station installed in a mobile body such as an automobile.

Among conventional mobile station antennas, what has hindered economical and miniaturization is a satellite tracking mechanism for always directing the main beam direction of the circularly polarized antenna to the satellite direction.

One method of simplifying the tracking mechanism is to realize a circularly polarized conical beam. The circularly polarized conical beam has a radiation directivity symmetrical with respect to the zenith axis as shown in FIG. 2, and the main radiation direction is set to the angle of suppression of the satellite 10 so that the mobile station antenna without tracking can be used. It is possible to configure.

[Problems to be Solved by the Invention] One of the antennas for realizing this directivity is a four-wire helical antenna, which usually supplies unbalanced current from a coaxial line to feed power from a coaxial line. It requires a balun, which is a circuit for converting to a balanced current,
It was necessary to provide a matching circuit for impedance matching. Therefore, there is a problem that the power supply circuit becomes complicated.

The present invention solves such a conventional problem,
An object of the present invention is to provide an antenna capable of simplifying a feed circuit by appropriately configuring a helical antenna that is a circularly polarized antenna.

[Means for Solving the Problems] According to the present invention, the above-mentioned object is achieved by the means described in the claims.

That is, the present invention relates to a helical antenna having a radiating portion composed of a pair of two conductor wires, a terminal having a feed point at one end of the antenna and capable of extracting a transmission / reception signal by a feed coaxial line at the other end. One of the conductor lines of the radiating portion of the antenna is formed of a coaxial line, and the other conductor line is electrically connected to the center conductor of the coaxial line at the feeding point. As well as
A helical antenna having a structure in which each conductor wire is wound at the same pitch and one of the conductor wires and the outer conductor of the coaxial conductor wire are electrically short-circuited on the feed terminal side of the helical antenna. It is.

[Operation] Among mobile satellite communication antennas, a helical antenna represented by a conical spiral antenna or the like can generate a circularly polarized conical beam. At this time, as parameters for generating a circularly polarized conical beam, shape parameters of the spiral conductor such as a diameter and a pitch are greatly related, but it is necessary to supply power to other plural spiral conductors with an appropriate phase difference. .

For example, in a helical antenna composed of four conductor wires 1 shown in FIG. 3, it is necessary to feed power with a phase difference of 90 ° which is 360 ° / 4 of each conductor wire. The current can be divided into two sets of radiating parts of a balanced system in which the current flows in the opposite direction. If the feed lines, which are unbalanced systems of the respective radiating parts, are directly connected, the current will flow through the outer conductor of the coaxial line 2. Needed a balun.

In the present invention, as shown in FIG. 1, one of a set of conductor wires is constituted by a coaxial line 6, and the other conductor line 5 is provided with a structure symmetrical to the coaxial line, so that the conductor line 5 is supplied from the coaxial line. The high-frequency current flowing through the center conductor flows through the other conductor 5 as it is at the feeding point 4, and the current of the same magnitude in the opposite direction flowing inside the outer conductor flows outside the coaxial line 6. At this time, if both the conductor and the outer conductor of the coaxial conductor are connected at the end of the winding of the helical, the currents are equal in magnitude and opposite to each other, and then flow on the conductor thereafter. Is terminated without
The high-frequency current flows only through the necessary radiating section.

However, since the standing wave distribution of the voltage and current distribution on the helical shown in FIG. 4 is determined by the number of turns and pitch of the helical, impedance matching may not be sufficient at the feeding point. In such a case, an appropriate impedance element is loaded on both one of the conductor lines and the conductor line formed of a coaxial line to change the standing wave distribution of the voltage and current, thereby achieving matching. . Also, by connecting both conductors via an appropriate impedance element at the end of winding, the voltage / current distribution can be changed, so that the input characteristics can be improved.

Embodiment FIG. 5 is a diagram showing a first embodiment of the present invention,
This is an example in which a conductor impedance is added by winding a conductor wire in a coil shape in the vicinity of a feeding point 4. Also,
FIG. 6 is a view showing a second embodiment of the present invention, in which a metal cylinder 8 is arranged near a feeding point to add a capacitive impedance. FIG. 7 is a view showing a third embodiment of the present invention, in which an impedance element 9 is inserted at the end of the helical winding. The impedance characteristics can be improved by inserting an appropriate stub or the like here.

FIG. 8 shows an actual measurement example of the improvement characteristic of the input impedance when the metal cylinder is added. In the figure, it can be seen that the input characteristics have been improved. At this time, the measured values of the radiation directivity on the plane including the antenna axis when the metal cylinder is not added are shown in FIG. 9, and the measured values of the radiation directivity on the plane including the antenna axis when the metal cylinder is added are shown in FIG. Is shown in FIG.
As can be seen from the figure, the radiation directivity hardly changes due to the addition of the metal cylinder, indicating that the input characteristics have been improved.

Here, a helical antenna wound on a cylinder has been described, but it goes without saying that the same can be said for an antenna wound on a polygonal prism or a cone.

According to the present invention, in a circularly polarized helical antenna,
There is an advantage that a balanced / unbalanced conversion circuit is not required, a simple power supply system can be realized, and the same characteristics can be realized with a shorter antenna length than the conventional one by reducing the size of the antenna power supply circuit.

[Brief description of the drawings]

FIG. 1 is a view for explaining the configuration of the present invention, FIG. 2 is a view for explaining a conical beam, FIG. 3 is a view for explaining a power supply method of a conventional 4-wire helical antenna, and FIG. FIG. 5 is a diagram for explaining voltage and current distribution, FIG. 5 is a diagram showing a first embodiment of the present invention, FIG. 6 is a diagram showing a second embodiment of the present invention, and FIG. FIG. 8 is a diagram showing an actual measurement example of input characteristics in the embodiment of the present invention, and FIGS. 9 and 10 show actual measurement values of the radiation directivity of the circularly polarized antenna of the embodiment. FIG. DESCRIPTION OF SYMBOLS 1 ... Helical antenna, 2 ... Coaxial line, 3 ... Matching circuit, 4 ... Feeding point, 5 ... Helical radiation part conductor in the present invention, 6 ... Coaxial line serving as helical radiation part in the present invention, 7 …… Inductance inserted near the feeding point, 8
…… a metal cylinder placed near the feeding point, 9 …… impedance inserted at the end of the helical winding, 10 …… satellite,
... Balun

Claims (1)

(57) [Claims] 1. A helical antenna having a radiating portion composed of a pair of two conductor wires, comprising a feed point at one end of the antenna and a terminal capable of extracting a transmission / reception signal by a feed coaxial line at the other end. One of the conductor lines of the radiating portion of the antenna is composed of a coaxial line, and the other conductor line is electrically connected to a center conductor of the coaxial line at a feeding point. The conductor wires are wound at the same pitch, and one of the conductor wires and the outer conductor of the coaxial conductor wire are electrically short-circuited on the feed terminal side of the helical antenna. A helical antenna, comprising: