JPH04344705A - Omnidirectional antenna - Google Patents

Abstract

PURPOSE:To warrant the ominidirectivity with respect to a circularly polarized wave, to eliminate a fragile mechanical part with a small size and a light weight and to attain ease of manufacture by providing two specific reflectors respectively to the antenna. CONSTITUTION:An axis of a parabola A and an axis of a right circular cone are made coincident to form a Z axis, an angle theta between the Z axis and a conical face B is selected to be 45 deg., the parabola A and the right conical face B are made opposite to each other, a feed horn F is placed at a focus of the parabola A. A radio wave W1 from the feed horn F is reflected in a point A1 of the parabola A and reflected in a pint B1 of a circular cone B in parallel with the Z axis and radiates through a path in a direction C1 perpendicular to the Z axis. Similarly, a radio wave W2 radiates through a path in a direction C2. Then transmission power as a circularly polarized wave radiates from he feed horn F, is reflected on a mirror surface of the parabola A whose radiation phase midpoint is used for a focus, and converted from a spherical wave into a plane wave. The plane wave is reflected by 90 deg. in the circular cone face B and an omnidirectional radio wave in the horizontal direction is obtained when the Z axis is provided in a vertical direction.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is directed to non-directional in the horizontal plane (
Hereinafter referred to as "omnidirectional." ) and is for circularly polarized waves and is suitable for radio waves (electromagnetic waves) with short wavelengths.

0002

2. Description of the Related Art Biconical antennas are examples of antennas that are non-directional in the horizontal plane and have circularly polarized wave characteristics. Such antennas are often used in the microwave band, but if you try to narrow the beam width in the vertical plane, the size of the upper and lower conical shapes will become very large, and the weight will also increase. Therefore, the central slot portion becomes structurally weak. The frequency band is also narrow. The width of the central slot needs to be very narrow compared to the wavelength, for example 2m at 3GHz.
m, but in the 70 GHz band it is about 0.1 mm. Therefore, processing is also extremely difficult. Such factors such as large size, heavy weight, and structurally weak parts are not suitable for use while being mounted on a moving body and subject to vibrations and shocks.

0003

[Purpose of the Invention] The purpose of the present invention is to obtain an omnidirectional antenna for millimeter waves (hereinafter referred to as "millimeter waves") or submillimeter waves (hereinafter referred to as "submillimeter waves") to be mounted on a mobile object. From this point of view, the weight should not be large, the shape should not be large, there should be no structurally weak parts, the completeness of omnidirectionality should not be impaired, and it should be easy to process and manufacture. This is in response to such requests.

0004

[Summary of the Invention] The present invention is a paraboloid of revolution (hereinafter referred to as a "parabola") in which a right circular conical surface having an axis coinciding with the axis of the first reflecting mirror is provided as the second reflecting mirror. be. If the cone is a right cone with a 45° angle between the axis and the cone surface, the axis of the parabola, and therefore the axis of the right cone, is vertical, and the surface of the parabola is opposed to the cone surface, the radio waves entering and exiting the cone surface will be It is omnidirectional in the horizontal plane. The feed horn is installed at the focal point of the parabola.

[0005]

[Effects] The antenna according to the present invention has an extremely simple structure, does not increase in weight or size, and has a simple shape. Furthermore, it does not have any structurally weak parts. It is also easy to manufacture. According to this invention, if the axis of a circularly polarized radio wave is set in the vertical direction, omnidirectionality in the horizontal plane is guaranteed in principle.

[0006] For elliptically polarized radio waves, although omnidirectionality is lost, a characteristic of having a certain degree of directivity in any direction can be obtained. Since a reflecting mirror is used, the frequency band is essentially wide. Therefore,
Suitable for mounting on moving objects, and suitable for millimeter and submillimeter waves.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic arrangement of the antenna structure of the present invention. In this figure, A is a parabola and B is a right circular cone.

In the following explanation, the symbol "A" for a parabola refers to the structure of the parabola as well as the mirror surface of the parabola, and the symbol "B" for a right circular cone.
indicates the structure of a right circular cone and the conical surface (mirror surface) of the right circular cone.
shall also be indicated.

In FIG. 1, the axis of the parabola A and the axis of the right circular cone are aligned and shown as the Z axis. Also, in this diagram, Z
The angle θ between the axis and the conical surface B is 45 degrees. A parabola A and a right circular conical surface B are opposed to each other, and F is a feed horn located at the focal point of the parabola A.

In FIG. 1, the radio wave W1 emitted from the feed horn F is reflected at point A1 of parabola A, travels parallel to the Z-axis, is reflected at point B1 on the surface of cone B, and travels perpendicular to the Z-axis. Exit via the route in the direction of C1. Similarly, the radio wave W2 is reflected at point A2 of parabola A and point B2 of the surface of cone B, and then exits on a path perpendicular to the Z-axis in the direction of C2.

Here, in FIG. 1, transmission power is radiated from the feed horn F as a circularly polarized wave. This is the premise. Furthermore, it is reflected by the mirror surface of the parabola A whose focal point is the radiation phase center of the feed horn F, and the spherical wave is converted into a plane wave. This plane wave is bent by 90 degrees by the reflecting mirror of the conical surface B, and when the Z-axis is vertical, it becomes a horizontal omnidirectional radio wave.

The spread of the conical surface B (spread along the plane perpendicular to the Z-axis) is such that its peripheral edge B0-A0 falls within a line drawn parallel to the Z-axis from the peripheral edge A0-A0 of the parabola A. B
Set the size of 0.

The beam width in the vertical plane is the diameter of parabola A (
Since it is determined by the diameter of the peripheral edge A0-A0 in Fig. 1,
By increasing this diameter, the beam width can be made as narrow as desired. Here, if the diameter of parabola A is D and the wavelength of the radio wave used is λ, then the beam width in the vertical plane is

00
14]

[Math 1]

It is known that it is given by:

For example, when used in the millimeter wave band,
If D=150 mm and λ=3.85 mm (78 GHz), the beam width in the vertical plane is about 3.6 degrees according to the above equation.

(Explanation of why circularly polarized radio waves are omnidirectional) Figure 2 shows the mirror surface of right circular cone B in Figure 1 viewed from above (parabola A side).
This is a diagram seen from. In this figure, the wavefront of the circularly polarized wave reflected from parabola A is parallel to the plane of the paper, and its electric field vector 1
, 2, 3, and 4 are dotted arrows 1A, 2A, 3A, and 4, respectively.
Assume that it is rotating to face A. This is a right-handed twist when viewed from behind the direction of the electric field vector.

[0018]

[Outside 1]

At this time, each electric field vector becomes "A" after reflection due to the promise of rotation as described above.
It rotates from the one with no symbol to the one with the same number "A" symbol. This is a left-handed screw rotation when viewed from behind the progression of the electric field vector. That is, the radio waves reflected at any point on the conical surface B rotate in the same left-handed direction.

[0020] Regarding the elliptically polarized radio wave, after reflection on the conical surface B, the electric field vector rotates as in the case of the circularly polarized wave.

(Explanation when radio waves are linearly polarized waves) If the radio waves are linearly polarized waves (when there are no dotted line arrows 1A, 2A, 3A, and 4A for electric field vectors 1, 2, 3, and 4 in FIG. 2),
Assuming that the Z-axis is vertical, the wavefront is parallel to the plane of the paper, and after electric field vectors 1, 2, 3, and 4 are reflected by conical surface B, vectors 5 and 7 become horizontally polarized waves. 6 and 8 are vertically polarized waves. That is, the plane of polarization is not preserved due to reflection by the conical surface B.

(Considerations on modification of the embodiment) (1) In FIG. 1, the apex of the right circular cone B is shown to be located at the focus of the parabola A and coincide with the feed horn F, but this is not necessary. isn't it. By moving the entire right circular cone along the Z axis, referring to Figure 1, between A1 and B1, A2 and B2
The distance between them may be determined depending on the convenience of implementation.

(2) If it is accepted that the conical surface of the right circular cone B has directionality in the direction of propagation and the electric power, it is not essential that a part of the conical surface is structurally missing. .

(3) If the angle θ between the Z axis and the conical surface is set to an angle other than 45 degrees while keeping the right circular cone, the direction of propagation can be shifted from the direction perpendicular to the Z axis while maintaining omnidirectionality. can be done. When the Z-axis is set vertically, the angle θ can be set smaller than 45 degrees to provide directivity toward the ground surface, or conversely, set larger than 45 degrees to provide directivity toward flying objects in the air. You can do things like give it a gender.

(4) When installed with the Z axis tilted from the vertical line, directivity can be given to the ground surface or upward in a specific direction (azimuth).

(5) Even if the axis is aligned with the vertical line to form an oblique cone, it will not be omnidirectional, but it will be possible to provide directionality toward the ground surface or upward.

(6) The present invention is not limited to the millimeter wave band or submillimeter wave band, and in principle there is no restriction on the wavelength of the wave.

(7) The present invention can be used both as a transmitting antenna and as a receiving antenna.

(8) Discarding the problem of the plane of polarization and talking only about the reflection path, the present invention can also be used for sound waves and ultrasonic waves.

(Summary) The present invention is suitable for being mounted on a moving object and transmitting and receiving radio waves to and from a radio wave lighthouse. Also,
Suitable for transmitting and receiving when installed in a fixed building or mobile station, etc., and communicating with mobile stations on all sides.

[Brief explanation of the drawing]

[Figure 1] Explanatory diagram of the example

[Figure 2] Explanatory diagram of the example

[Explanation of symbols]

A... Parabolic mirror of revolution (parabola) A0... Periphery of parabolic mirror A of revolution B... Right circular cone reflecting mirror
B0 ... Periphery F of right cone reflector B ... Feed horn θ ... Angles 1, 2, 3 between the axis of right cone reflector B and the mirror surface,
4, 1A, 2A, 3A, 4A... Electric field vector of circularly polarized wave 5, 6, 7, 8, 5A, 6A, 7A, 8A... Electric field vector of circularly polarized wave reflected by right cone reflecting mirror B

Claims (3)

[Claims] Claim 1: A first reflector made of a paraboloid of revolution;
An omnidirectional antenna comprising a second reflector made of a right circular conical reflecting surface having an axis that coincides with the axis of the paraboloid of revolution. 2. The omnidirectional antenna according to claim 1, wherein the axis of the paraboloid of revolution is provided in the direction of a vertical line. 3. The omnidirectional antenna according to claim 1, wherein the right circular conical reflecting surface is formed at an angle of 45 degrees with respect to its axis.