JPH0221167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna device having excellent wide-angle radiation characteristics in an aperture antenna used in microwave and millimeter wave bands.

FIG. 1 shows the configuration of a Cassegrain antenna as an example of a conventional aperture antenna. In FIG. 1, 1 is a main reflector, 2 is a sub-reflector, 3 is a primary radiator, and 4 is a support supporting the sub-reflector. In the aperture antenna with such a configuration, the primary radiator 3
After being reflected by the sub-reflector 2 and the main reflector 1, the spherical wave radiated from the spherical wave becomes a plane wave and is radiated to the outside. At this time, the plane wave 5 reflected by the main reflecting mirror 1 hits the support 4 supporting the sub-reflector 2 and is scattered by this support. In this case, the scattered waves 6 are composed of a reflected wave that travels in a direction that satisfies Snell's law in terms of geometrical optics, and a diffracted wave that has a strong electric field strength in the traveling direction of the reflected wave and gradually weakens as it moves away from the reflected wave.

First, the relationship between the pillar 4 and the traveling direction of reflected waves will be explained. In the conventional support column 4, the shape on the main reflecting mirror side may be a flat surface or a curved surface.

For this reason, a case will be described in which the support column 4 is configured as a plane.

First, as shown in FIG. 2, a support 4 is set which is composed of an orthogonal coordinate system XYZ and planes Q ₁ and Q ₂ .
Let i, j, and k be unit vectors along each axis of XYZ in the orthogonal coordinate system. The line of intersection between the plane Q ₁ and the plane Q ₂ that constitutes the pillar 4 exists within Z-X, the angle between the above line of intersection and the Z-axis is given by θ, and the angle between the plane Q ₁ and the Z-X plane is given by θ. Suppose that is given by . Here, assuming that the surface of the support is a plane, the unit vector a parallel to the longitudinal direction of the support and the unit vector b perpendicular to this, which are vectors existing in the plane _Q1 , are expressed by the following equation. .

a=sinθi+cosθk b=cos cosθi+sinj +cos sinθk …(1) Next, if the observation point P is given by the polar coordinate system Θ, Φ as shown in Figure 3a, and the plane wave travels in the Z-axis direction, then the plane Q The traveling direction e _r of the reflected wave reflected at ₁ is given by the following equation.

e _r =k−2(n・k)n n=a×b …(2) On the other hand, if e _r is expressed as a polar coordinate component, e _r =sinΘ cosΦi+sinΘ sinΦj+cosΘk…(3), so equation (1) and ( From the relationship between e _r obtained from equation 2) and e _r from equation (3), the relationship between Θ, Φ, and θ is expressed by the following equation.

The observation point P exists regardless of the traveling direction of the reflected wave, and the polar coordinates of the point P are given by Θ and Φ. Then, the traveling direction of the reflected wave is given by a value that satisfies equation (4). Figure 4 shows the relationship between the parameter θ, which represents the shape of the pillar 4, and the traveling directions Θ and Φ of the reflected waves.When the value of θ, which represents the shape of the pillar 4, is given, Figure 3 This shows the direction in which the reflected wave from the pillar 4 is radiated in polar coordinates (Θ, Φ) with parameters Θ and Φ representing the traveling direction of the reflected wave shown in Figure 3b. .

Further, a case where the support column 4 has a curved surface will be explained using FIG. 5. When the cross-sectional shape of the pillar 4 is given by a curved surface, the traveling direction of the waves reflected by the pillar 4 can be roughly considered as a collection of reflected waves from the flat surface by locally replacing the curved surface with a flat surface. . In other words, as shown in Figure 5, the reflection direction of the plane wave incident on point _A1 is
Assuming a tangential plane P ₁ at A ₁ , it can be expressed by the reflection direction when a plane wave is incident on this tangential plane P ₁ . In this case, assuming that the support 4 is provided at an angle of θ with respect to the Z axis as in FIG. 1, the reflection direction includes θ, which is the inclination angle of the support 4, the tangential plane _P1 , and the traveling direction of the plane wave. It is given by ₁ of the face. When the wave is incident on point A ₂ , it is similarly given by angle ₂ formed by the tangential plane P ₂ and the plane that includes the traveling direction of the plane wave.

In this way, if the support is a curved surface and the curved surface is replaced with a polyhedron, there will be reflected waves corresponding to each plane, and diffracted waves will exist from the connection of each plane,
The diffracted waves connect the reflected waves in the radiation direction. Next, if we increase the number of planes of this polyhedron as much as possible, it becomes a curved surface. In this case, it is difficult to clearly distinguish between reflected waves and diffracted waves, so here the reflected waves from a curved surface are represented by a set of reflected waves from each tangential plane.

Next, the relationship between the shape of the support 4 and the traveling direction of the diffracted waves will be explained using FIG. 6. As shown in FIG. 6, given the traveling direction of the plane wave shown by the arrow and the shape of the support 4, the plane that constitutes the support 4 is
If the angle between the intersection line 7 of Q ₁ and Q ₂ (hereinafter referred to as edge) and the Z axis, which is the traveling direction of the plane wave, is θ, then the traveling direction of the diffracted wave is centered around edge E, and
It is given in the direction along the generating line B of the cone whose half apex angle is given by θ. As shown in FIG. 6, this half-vertex angle θ is equal to the inclination of the edge 7 with respect to the traveling direction of the plane wave. Therefore, in the conventional support column 4 as shown in FIG. is expressed by θ and (=90°), so from equation (4), the traveling direction of the reflected wave is Θ=
It is radiated in the direction given by 2θ, Φ = 0°. Furthermore, as shown in FIG. 8, the diffracted waves are radiated in a direction in which θ is constant and continuously varied. here,
The readings of Θ and Φ are as shown in FIG. 3b, and are the same as in the case of FIG.

In the case of the pillar shown in Figure 5, the reflected waves are not concentrated in a specific direction, but when the diffracted waves are made into a polyhedron as described above, θ is constant so that the radiation directions of the reflected waves are connected. It is emitted almost uniformly in a direction that changes continuously. However, if the number of polyhedrons is increased to an infinitely large number, it can be expressed as a collection of reflected waves as described above, and the contribution of diffraction disappears. Furthermore, in the direction where θ is zero, a direct wave exists, so the radiation level becomes stronger. In the case of the pillar shown in Figure 7, the reflected waves are concentrated in the direction of Θ = 20θ, Φ = 0°,
The diffracted waves are emitted in a direction in which θ is constant but continuously changes. Further, in the case of the support shown in FIG. 7, as in the case of the support shown in FIG. 5, direct waves exist in the direction where Θ is zero, so the radiation level becomes strong.

Radiation patterns by the pillars shown in FIGS. 5 and 7 are shown in FIGS. 9a and 9b, respectively. In contrast to the radiation level of the pillar in Figure 5 shown in Figure 9a, the radiation level of the pillar in Figure 7 shown in Figure 9b is that reflected waves exist in the directions of Θ = 2θ and Φ = 0°. However, in other directions where θ is constant but changes continuously, only diffracted waves exist, so it becomes low.

In FIGS. 9a and 9b, it is assumed that the higher the line density, the higher the radiation level. In this way, when using the conventional struts having the shapes shown in Figs. 5 and 7, the radiation level is high throughout the conical shape as shown in Figs. 9a and b, and even in areas where the value of Θ is large The level is not reduced and becomes a cause of deterioration of wide-angle radiation characteristics. Therefore, when such an antenna is used, it has the disadvantage of causing interference with other wireless lines.

In order to eliminate these drawbacks, conventional methods of attaching a radio wave absorber to the surface of the pillar, such as the 10th method, have been proposed.
As shown in the figure, a method of arranging metal plates 9 having a constant period on the support 4, or a method smaller than the wavelength,
There is also a method of arranging a metal body with irregular irregularities, but the first method has the drawback that it is difficult to completely eliminate scattered waves with a radio wave absorber, and it is also difficult to obtain materials with good weather resistance. It was hot. The second method had a drawback in that grating lobes appeared in accordance with the period of the metal plates arranged at a constant period. Furthermore, the third method has the disadvantage that although it is possible to scatter the reflected waves, it is difficult to scatter the diffracted waves.

In order to eliminate such drawbacks, this invention
A structure that is a flat plate with a thickness smaller than the wavelength and has a specific shape is attached to part or all of the surface of the support column, and its purpose is to create an antenna with excellent wide-angle radiation characteristics. . The drawings will be explained in detail below.

FIGS. 11a and 11b show an embodiment of the present invention, and are a perspective view and a side view. In FIG. 11, 4 is a column, 5 is a passing plane wave, and 10 is a structure. Here, the structure 10 is a flat plate whose thickness is smaller than the wavelength, and one end of the flat plate is connected to the support column 4.
are connected along the longitudinal direction, and the other ends form irregular irregularities with sides longer than the wavelength. The structure 10 is parallel to a plane that includes both the longitudinal direction of the support 4 and the traveling direction of the plane wave 5, on the main reflector side of the support 4 in a Cassegrain antenna, and on the reflector side of the support 4 in a parabolic antenna. It is installed so that With such a configuration, the plane wave 5 incident on the structure 10 becomes a diffracted wave by the edge 7 and is scattered. Here, since the edges 7 are irregular irregularities having sides longer than the wavelength, the diffracted waves by the edges 7 are scattered over a wide area.

Here, it is assumed that the length of the side made of irregular unevenness is sufficiently long compared to the wavelength.

This is based on the geometric optical diffraction theory, and this logic is a high-frequency approximation method that can be applied when the dimensions of the object are sufficiently large compared to the wavelength.

Therefore, when the dimension of the edge 7 is smaller than the wavelength, the effect of this "edge" is small, and the diffracted wave travels in a direction determined by the overall slope, ignoring the small "edge".

However, by making the dimension of the edge 7 longer than the wavelength, the refracted wave will actually be radiated in the direction along the generating line of the cone as shown in Figure 6, and the desired direction determined by the inclination of the edge 7 will be emitted. Diffracted waves can be emitted in the direction of . Furthermore, by combining a large number of edges 7 having different inclination angles, diffracted waves can be radiated in various directions. Therefore, the radiation level of the diffracted waves can be reduced. Furthermore, as shown in Fig. 12a and b, the same effect can be obtained by irregularly arranging multiple types of convex shapes with different side lengths or sizes as irregular irregularities. can. Therefore, the incident plane wave 5
Since some of the waves can be scattered over a wide area, the radiation level of scattered waves by the pillars can be reduced.

In addition, the effect of setting the thickness of the structure 10 on the wavelength order, and the reason why it is composed of a flat plate whose thickness is smaller than the wavelength, are that the thickness is almost ignored by wave dynamics, and the reason is that the thickness is almost ignored by waves, and the reason is that This is to prevent reflected waves from the plane from being radiated into the plane of Φ=0. That is, by doing so, the scattered waves from this flat plate can be represented only by diffracted waves.

Although FIG. 12 shows the case where a triangular shape is used as the convex shape, the same effect can be obtained by using not only a rectangular shape but also a rectangular shape or a combination thereof. A similar effect can also be obtained by rounding some or all of the corners of the irregular irregularities.

As described above, by using the present invention, the radiation level of scattered waves by the pillars can be reduced, so an antenna with good wide-angle radiation characteristics can be realized.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional antenna device, Figure 2 is a diagram of the arrangement relationship between the orthogonal coordinate system XYZ and columns, and Figure 3
Figures a and b are polar coordinate system diagrams showing the observation points and explanatory diagrams showing the readings of the traveling directions Θ and Φ of the reflected waves, respectively. A relationship diagram, FIG. 5 is an explanatory diagram illustrating the traveling direction of scattered waves from a support made of a curved surface, and FIG. 6 is an explanatory diagram showing the traveling direction of diffracted waves.
Fig. 7 is an explanatory diagram illustrating scattering by a planar support, Fig. 8 is an explanatory diagram showing the radiation direction of reflected waves and diffracted waves, and Fig. 9 a and b are radiation pattern diagrams of scattered waves by a conventional support. , FIG. 10 is a configuration diagram of a conventional support column, FIGS. 11a and 11b are perspective views and side views showing an embodiment of the present invention, and FIGS. 12a and 12b are perspective views and side views showing an embodiment of the present invention. FIG. In the figure, 1 is the main reflector, 2 is the sub-reflector, 3 is the primary radiator, 4 is the column, 5 is the plane wave, 6 is the scattered wave, and 7
is an edge, 8 is a reflective surface, 9 is a metal plate, 10 is a reflected wave, and P is an observation point. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Scope of Claims] 1. An antenna device that is an aperture antenna used in the microwave band or millimeter wave band and has a pillar within the aperture that prevents the passage of radio waves and supports a primary radiator or sub-reflector. , a flat plate having a thickness smaller than the wavelength is connected to the surface of the pillar on the main reflector side or the reflecting mirror side of the aperture antenna, one end of the flat plate is connected along the longitudinal direction of the pillar, and the other A structure having irregular irregularities whose ends are longer than the wavelength is attached so as to be parallel to a plane including both the longitudinal direction of the support and the direction of propagation of the radio waves. antenna device. 2 Claim 1 characterized in that some or all of the corners of the irregular irregularities are rounded.
Antenna device as described in section.