JPH0221171B2 - - 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.

This way of thinking is called the geometric diffraction theory, and the following explanation will be based on this theory.

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=sinθj+cosθk b=-cos cosθj+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 The traveling direction e _r of the reflected wave reflected at Q 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 cosΦj+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 the angle ₁ between the faces. Similarly, when incident on point A ₂ , the tangent plane P ₂
and the angle ₂ formed by the plane including the direction of travel 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 4 as shown in FIG. 7, there are waves reflected by the reflecting surface 8 and diffracted waves by the edge 7, where the value of in FIG. 5 is 90 degrees, and the shape of the support 4 is θ. and (=90°), so from equation (4), the traveling direction of the reflected wave is Θ=2θ,
It is radiated in the direction given by 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, Θ,
The reading of Φ is as shown in FIG. 3b, and is the same as in 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, direct waves exist, 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 conventional pillars with shapes as shown in Figures 5 and 7, the radiation level is high throughout the conical shape, even in areas where the value of Θ is large, as shown in Figures 9a and b. The radiation level does not decrease 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 triangular prism with a triangular cross section and a length along the longitudinal direction of the pillar is longer than the wavelength is attached to part or all of the surface of the support, and the thickness is The antenna is equipped with a plate-like structure whose wavelength is smaller than the wavelength, and its purpose is to create an antenna with excellent wide-angle radiation characteristics. The drawings will be explained in detail below.

FIG. 11 shows an embodiment of this invention.
In the figure, 4 is a column, 5 is a passing plane wave, 1
0 is a triangular prism, and 11 is a structure. Here, the shape of the cross section perpendicular to the longitudinal direction of the support 4 of the triangular prism 10 is triangular, the length of the side connecting to the support 4 of the above-mentioned triangle is equal to the width of the support 4, and the length of the other two sides are each the wavelength. The length along the longitudinal direction of the support of the triangular prism 10 is longer than the wavelength. Further, the structure 11 is a flat plate whose thickness is smaller than the wavelength, and one end of the flat plate is connected to the triangular prism 1.
0 along the longitudinal direction, and the other end is irregularly uneven with sides longer than the wavelength. The triangular prism 10 is attached to the main reflector side of the prop in a Cassegrain antenna, and to the surface of the reflector side of the prop in a parabolic antenna. The triangular prism 10 is attached along each of the three longitudinal sides of the triangular prism 10 so as to be parallel to a plane containing both of the triangular prisms 10 and 10. Edge 7
a, 7b, and 7c are structures 11a and 11, respectively.
b, 11c, and edge 7d is the structure 11
a and the triangular prism 10, and the planes 8a and 8b
is the side surface of the triangular prism 10. With this configuration, the scattered wave of the plane wave 5 is expressed as a combination of the diffracted waves 12 by the edges 7a, 7b, 7c, and 7d and the reflected waves 13 by the planes 8a and 8b, as shown in FIG. be done. The waves reflected by the planes 8a and 8b are radiated in the direction determined by θ according to equation (4), and in the case of a support as shown in Fig. 11, when θ is constant, the signs corresponding to the planes 8a and 8b are constant with opposite signs. value, so it will have a peak in the direction determined by θ, but a part of this reflected wave will be reflected by the structures 11b and 1
The reflected waves reflected by the structures 11b and 11c are scattered in various directions. In addition, in FIG. 11, the edges (
When a plane wave is incident on the side surface of the support with the edge 7a at the connection part b, the diffracted wave is radiated along the generatrix of the cone determined by the direction of the edge and the direction of propagation of the incident wave, and is emitted from the structures 11a, 11b, 11c. Since the edges 7a, 7b, and 7c are made of irregular irregularities with sides longer than the wavelength, the diffracted waves from these edges are scattered in a ring shape defined by the inclination angle θ of each edge. Since the angle is zero, it has a peak in the traveling direction of the plane wave, and the waves reflected by the structures 11b and 11c are also diffracted by these edges and scattered over a wide area because the edges are irregularly uneven. and have different phases, it is possible to reduce the radiation level of the scattered waves.

FIG. 13 shows another embodiment of the present invention, in which the surface shape of the support 4 to which the triangular prism 10 and the structures 11a, 11b, 11c are attached is a plane that includes both the longitudinal direction of the support 4 and the traveling direction of the plane wave 5. It is composed of multiple planes perpendicular to the plane. By adopting such a configuration, the direction and phase of the reflected wave and the diffracted wave can be changed, so that the radiation level of the scattered wave can be further reduced.

Furthermore, the same effect can be obtained by irregularly arranging a plurality of triangles or rectangles of different side lengths or sizes as the irregular irregularities of the structure. Furthermore, the same effect can be obtained by rounding some or all of the corners of the irregular irregularities.

Here, it is assumed that the lengths of the edges shown in FIGS. 11, 14, and 15 are 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 size of the edge is smaller than the wavelength, the effect of this "edge" is small, and the diffracted wave proceeds in a direction determined by the overall slope, ignoring the small "edge."

However, by making the edge dimension longer than the wavelength, the refracted wave will actually be radiated in the direction along the generatrix of the cone as shown in Figure 6, and the desired wave determined by the inclination of edge 7 will be emitted. It is possible to radiate diffracted waves in the direction.

As explained above, by using the present invention, it is possible to reduce the radiation level of scattered waves by the pillars, and therefore it is possible to realize an antenna with good wide-angle radiation characteristics.

[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 scattered waves caused by planar supports, Fig. 8 is an explanatory diagram showing the radiation directions of reflected waves and diffracted waves, and Figs. 9 a and b are radiation patterns of scattered waves caused by conventional supports. Fig. 10 is a block diagram of a conventional support, Fig. 11 is a block diagram showing an embodiment of the present invention, Fig. 12 is an explanatory diagram of diffracted waves due to edges and reflected waves by planes, and Fig. 13 is a block diagram showing an embodiment of the present invention. It is a block diagram which shows another Example of this invention. 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. In the drawings, the same or corresponding parts are denoted 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. , in a Cassegrain antenna, the surface of the main reflector side of the prop, and in a parabolic antenna, the surface of the prop on the reflector side has a triangular cross section perpendicular to the longitudinal direction of the column, and the length of one side connected to the triangular column is the length of the column. A triangular prism whose width is equal to the length of the other two sides is longer than the wavelength, and whose length along the longitudinal direction of the support is longer than the wavelength, and whose thickness is smaller than the wavelength. , one end of the flat plate has an irregularly uneven structure with a side longer than the wavelength, so that it is parallel to a plane that includes both the longitudinal direction of the support and the direction of propagation of the radio wave, An antenna device characterized in that the other end of the structure is attached to each of the three longitudinal sides of the triangular prism. 2. Claims characterized in that the shape of the surface of the triangular prism and the support to which the structure is attached consists of a single or multiple planes orthogonal to a plane that includes both the longitudinal direction of the support and the propagation direction of radio waves. The antenna device according to item 1. 3 Claim 1 characterized in that some or all of the corners of the irregular irregularities are rounded.
2. The antenna device according to any one of item 1 and 2.