JPS61208904A - Helical antenna system - Google Patents

Abstract

PURPOSE:To vary the radiation characteristic by providing a conductor cylinder to the peripheral of a reflecting plate and moving the cylinder in a direction in parallel with the helical center axis. CONSTITUTION:The conductor cylinder 3 is provided to the peripheral of the reflecting plate 2 whose center axis is in common to the center axis Z of the helical element 1 and moved in a direction in parallel with the center axis Z to the reflecting plate 2. The cylinder 3 is fixed at an optional position in the direction of the center axis Z to the element 1 by means of a screw 5. When the cylinder 3 is fixed while being moved upward, the irradiating directivity of the helical antenna is sharpened in comparison with the irradiation directive characteristic when the cylinder 3 is fixed while being moved downward. The directivity is sharpened more as the movement onto the cylinder 3 is increased much. When the cylinder 3 is moved upward, the gain near the major radiation of the antenna is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a helical antenna device, and more particularly to a helical antenna device with variable radiation directivity characteristics.

<Prior Art> Helical antennas, spiral antennas, cross dipole antennas, and the like are well known as linear antennas that can obtain circularly polarized wave characteristics. The above-mentioned helical antenna is used as one of the circularly polarized antennas with relatively high gain.

Radiation having a main radiation direction in the direction of the main axis is called axial mode radiation, and the radiation directivity characteristics of a helical antenna that emits axial mode has conventionally been controlled by the number of turns, pitch, circumference, etc. of the helical element. An important value representing the radiation directivity characteristic is the power half width. This power half width β is
The number of turns of the helical element is n, the pitch is S9, the peripheral length is C1
It is known that when the wavelength is λ, it can be approximately expressed by the following equation.

However, this is only an approximation, and
Helical elements are difficult to analyze, and therefore, specific radiation directivity characteristics must be measured by actually manufacturing a helical element. In this case, it is difficult to change the number of turns, pitch, circumference, etc. of the helical element after the helical element is manufactured, and the radiation directivity characteristics cannot be changed after the helical element is manufactured. For this reason, there is a problem in that a desired radiation directivity characteristic may not be obtained after the helical antenna is assembled.

Furthermore, conventionally, when this helical element is used as the primary radiator of a reflector antenna such as a parabolic antenna, if the same primary radiator is used with reflectors of different sizes, the directivity of this primary radiator Since the characteristics are fixed, the curved shape of the reflector must be changed, and the focal length etc. also change, making it time-consuming to design the entire antenna and making it difficult to standardize parts.

<Objective of the Invention> The present invention has been made in view of the above circumstances, and its object is to provide a helical antenna device with variable radiation directivity characteristics.

<Structure of the Invention> The present invention includes a helical element having a main radiation direction in the direction of the main axis, a reflecting plate made of a metal conductor, and a cylinder made of a conductor. The cylinder is a plate, and the cylinder has a helical center axis and a center axis common to the outer periphery of the reflector, and is movable in a direction parallel to the helical center axis, and by moving the cylinder, the radiation directivity characteristics can be changed. It is characterized by being configured to change.

<Principle of the Invention> The present invention provides a helical antenna device in which, when the shape of the reflecting plate of the helical element is, for example, a disk, an annular metal plate is installed on the disk or on the outer periphery of the disk. By attaching a conductive cylinder to the outer periphery of the reflector and moving this cylinder in a direction parallel to the helical central axis,
The aim is to change the radiation directivity characteristics to obtain desired beam width, gain, sidelobe level, etc.

<Example> An embodiment of the present invention will be described below.

FIG. 1 shows a planar configuration of a helical antenna device according to an embodiment of the present invention, and FIG. 2 shows a side configuration thereof.

Reference numeral 1 denotes a helical element having its main radiation direction in the direction of its main axis, and reference numeral 2 denotes a reflecting plate made of a circular plate of a metal conductor whose central axis is common to the central axis 2 of this helical element 1. The lower end of the helical element 1 is fixed to the axial center of the reflector 2. 3 is a conductor cylinder, and this conductor cylinder 3 has a helical center axis Z.
and a central axis are provided in common on the outer periphery of the reflector 2, and the reflector 2
It is movable in a direction parallel to the helical center axis Z.

FIG. 3 shows the cross-sectional structure of the reflecting plate 2 and the conductor cylinder 3. The reflecting plate 2 is formed into a circular shape so as not to destroy the symmetry of the radiation directivity characteristics, and a plurality of small diameter screw holes 6 are provided on the outer circumference of the reflecting plate 2. As shown in FIG. 2, the conductor cylinder 3 is provided with a plurality of elongated holes 4 in the same direction as the helical central axis Z, and screws 5 are inserted through the elongated holes 4.
is fitted into the screw hole 6 of the reflection plate 2. After moving the conductor cylinder 3 in a direction parallel to the helical central axis 2 with the screw 5 passing through the elongated hole 4, by tightening the screw 5,
The conductor cylinder 3 is aligned with the helical center axis Z with respect to the helical element 1.
It can be fixed in any position in the direction of.

The height of the conductor cylinder 3 needs to be sufficiently larger than the thickness of the reflector 2, and the elongated hole 4 does not allow the screw 5 to move even when the conductor cylinder 3 is moved in a direction parallel to the helical center axis Z. must be as small as possible so that it can be inserted into the screw hole 6 and the axial symmetry of the radiation directivity characteristics is not destroyed.

Hereinafter, the operation when receiving radio waves using the above-mentioned helical antenna device will be explained. Here, the conductor cylinder 3
The movement in a direction parallel to the helical central axis Z to cover the helical element 1 is referred to as upward movement, and the movement in the opposite direction is referred to as downward movement.

FIG. 4 shows the configuration of a side cross section when the conductor cylinder 3 is fixed to the reflector plate 2 in a downwardly moved state. In this case, radio waves arrive at the entire helical element 1, and radio waves arrive from the direction of the arrow a, which is almost orthogonal to the helical center axis 2, and radio waves arrive from the direction of the arrow, which is diagonal to the helical center axis Z. Both can be received.

FIG. 5 shows the configuration of a side cross section when the conductor cylinder 3 is fixed to the reflector plate 2 in an upwardly moved state. In this case, a portion of the radio waves arriving from the direction of arrow C oblique to the helical center axis Z is reflected by the conductor cylinder 3, and the radio waves are concentrated on the helical element 1. On the other hand, a part of the radio waves arriving from the direction of arrow d, which is substantially perpendicular to the helical center axis Z, is reflected by the conductor cylinder 3 and does not reach the helical element 1.

That is, when the conductor cylinder 3 is moved upward and fixed, the radiation directivity of the helical antenna is less directional than when the conductor cylinder 3 is moved downward and fixed. Become sharp. This directivity becomes sharper as the amount of movement above the conductor cylinder 3 increases. Furthermore, when the conductor cylinder 3 is moved upward and fixed,
The gain near the main radiation direction of the helical antenna increases.

Figure 6 shows measurement results that demonstrate the above operation.

This measurement result shows the directivity characteristic at a frequency of 11.95 GHz in the ZX plane of the coordinate system of the helical antenna shown in FIG. 7, where the vertical axis represents the received power and the horizontal axis represents the angle from the Z axis. In this case, the number of turns of the helical element 1 is 6.5 turns, and the diameter of the reflection plate 2 is 74 m.

In FIG. 6, a solid line A shows the radiation directivity characteristic when the distance in FIG. 7, which indicates the amount that the conductor cylinder 3 has moved downward, ie, the amount that the conductor cylinder 3 has moved upward, is zero. Also,
Solid line B shows the radiation directivity characteristic when the conductor cylinder 3 moves upward and the distance is 20 m, and solid line C shows the radiation directivity characteristic when the conductor cylinder 3 moves further upward and the distance is 25 m. shows. As is clear from this measurement result, the conductor cylinder 3
It can be seen that the radiation directivity characteristics change with the movement of .

FIG. 8 shows the structure of another embodiment of the present invention, in which 7 is a helical element, 8 is a reflecting plate, and 9 is a conductor cylinder. FIG. 9 shows the configuration of the II' cross section in FIG. 8, in which a screw 10 formed on the outer circumferential surface of the reflective plate 8 made of a metal conductor disk is connected to a screw 11 formed on the inner surface of the conductor cylinder 9. Engage, reflector 8
A conductor cylinder 9 is provided on the outer periphery of the conductor cylinder 9.

In this case, the conductor cylinder 9 is aligned with the helical axis Z with respect to the reflector 8.
By rotating around the center, the conductor cylinder 9 slides in a direction parallel to the helical central axis 2 due to the effect of the screw, and the same effect as in the above embodiment can be achieved. Furthermore, in this case, since the conductor cylinder 9 is not provided with a through hole or the like, it becomes completely axially symmetrical, and it is easy to maintain the axially symmetrical nature of the radiation directivity characteristics. Moreover, the operability of the conductor cylinder is improved.

<Effects of the Invention> As explained above, in the present invention, the radiation directivity characteristics of a helical antenna are changed by installing an annular metal plate on the reflector, and the conductor cylinder is placed in the center of the reflector. A desired beam width, gain, sidelobe level, etc. can be obtained by combining the axes in common and making this conductor cylinder movable in a direction parallel to the helical center axis.

The helical antenna device according to the present invention is effective when finely adjusting directivity after being assembled as an antenna device. In particular, when the helical antenna device of the present invention is used as the primary radiator of a reflector antenna such as an offset parabolic antenna, by changing the characteristics of the primary radiator, it is possible to improve the focal length without changing the curved shape of the reflector. This primary radiator can be used in common with reflecting mirrors having different aperture diameters without changing the antenna structure, etc., making it easy to design the entire antenna and making parts common. Furthermore, since directivity can be finely adjusted after assembly, efficient reception can be achieved. Furthermore, since this primary radiator can be mass-produced, the price of the primary radiator can be reduced.

[Brief explanation of drawings]

Fig. 1 is a plan view of the embodiment of the present invention, Fig. 2 is a side view of Fig. 1, Fig. 3 is a partial sectional view of Fig. 2, and Figs. 4 and 5 are explanations of the operation of the embodiment of the present invention. 6 is a graph showing the measurement results of the embodiment of the present invention, FIG. 7 is a diagram showing the coordinate system and parameters of the embodiment of the present invention, and FIG. 8 is a perspective view of another embodiment of the present invention. FIG. 9 is a partial sectional view of FIG. 8. 1.7...Helical element 2.8...Reflector plate 3.9...Conductor cylinder 2...Helical center axis Patent applicant Sharp Corporation Representative Patent attorney Nishi 1) New construction 5 Figure 8 Figure 8 Figure 2 Figure 4

Claims (1)

[Claims] A helical element having a main radiation direction in the main axis direction, a reflecting plate made of a metal conductor, and a cylinder made of a conductor, the reflecting plate being a disk whose central axis is common to the helical central axis, and the cylinder having the helical central axis and a central axis is provided in common on the outer periphery of the reflecting plate and is movable in a direction parallel to the helical central axis, and the radiation directivity characteristics are changed by moving the cylinder. Helical antenna device.