JPH0221166B2 - - 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 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 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 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 a reflected wave and a diffracted wave, so here the reflected wave from a curved surface is 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 set so as to connect the radiation directions of the reflected waves. It is emitted almost uniformly in a constant but continuously changing direction. 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 support column shown in FIG. 7, the reflected waves are concentrated in the directions of Θ=2θ and Φ=0°, and the diffracted waves are emitted in the direction where 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 radio 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 these drawbacks, the present invention provides a special shape for part or all of the surface of the support column, and the purpose of the present invention is to realize 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 support, 5 is a passing plane wave, and 8 is a plane forming the support. Here, in a Cassegrain antenna, part or all of the surface on the main reflector side of the support column, and in the case of a parabolic antenna, the surface on the reflector side of the support column is a plurality of planes perpendicular to a plane including both the longitudinal direction of the support support 4 and the traveling direction of the plane wave 5. The shape of the cross section of the support 4 in any plane parallel to the plane including both the longitudinal direction of the support 4 and the traveling direction of the plane wave 5 is the same as shown in FIGS. 12a and 12b. , it is irregularly uneven with sides longer than the wavelength. That is, the shape of the cross section of the support 4 on the reflecting mirror side in any plane is the same in each arbitrary plane, and the length of each side constituting the shape of this cross section on the reflecting mirror side is smaller than the wavelength. It is long, and the angle between the plane wave's traveling direction and the sides is irregular. With this configuration, the scattered wave by the pillar 4 is represented by a combination of the reflected wave 10 by the plane 8 and the diffracted wave by the edge 7. Since the plane 8 is composed of a plurality of planes oriented in irregular directions and perpendicular to the plane including both the traveling direction of the plane wave 5 and the longitudinal direction of the support column 4, the reflected wave 10 is oriented according to Φ= in FIG. It is scattered on the Θ axis of 0. Furthermore, since the edges 7 are made up of irregular irregularities, the diffracted waves are scattered almost uniformly over a wide area.

Therefore, since the plane wave 5 that is incident on the support column 4 can be scattered in a specific area, the radiation level of the scattered wave in other areas can be reduced.

The diffracted waves from the edges formed between the adjacent planes 8 include the directions of the reflected waves respectively reflected from the two planes forming the edges, and form a cone defined by the direction of the edges and the traveling direction of the incident wave. radiated along the generatrix. According to this invention, the plane 8
Since the inclination of the plane 8 is irregular, the reflected waves from the plane 8 are also irregularly radiated in various directions, and the diffracted waves are also irregularly radiated in various directions. Therefore, both reflected waves and diffracted waves are radiated over a wide area without being radiated in a specific direction, so that the peak level can be lowered. FIG. 13 shows another embodiment of the present invention, in which irregular irregularities have different shapes on the incident side of the plane wave 5 on both surfaces parallel to the plane including the longitudinal direction of the support 4 and the traveling direction of the plane wave 5. It has the same number of vertices, as shown in FIG. 8. Such a large number of planes 8 have various inclinations with respect to the plane wave 5, and direct the reflected waves 10 in various directions having components perpendicular to the plane including the longitudinal direction of the support 4 and the traveling direction of the plane wave 5. Furthermore, since the diffracted waves by the edges 7 are irregularly radiated in various directions as in the case shown in FIG. 11, the radiation level of the scattered waves can be reduced.

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 .

As explained above, by using the present invention, it is possible to reduce the radiation level of scattered waves caused by the pillars, so 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 the pillars, 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. Relationship diagrams, FIG. 5 is an explanatory diagram illustrating the traveling direction of scattered waves from a support made of a curved surface, FIG. 6 is an explanatory diagram showing the traveling direction of diffracted waves,
Fig. 7 is an explanatory diagram illustrating scattered waves 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 patterns of scattered waves by a conventional support. 10 is a configuration diagram of a conventional support column, FIG. 11 is a configuration diagram showing an embodiment of the present invention, and FIGS. 12a and 12b are front and side views of an embodiment of the present invention. FIG. 13 is a block diagram showing another embodiment of the present 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. It should be noted that the same or corresponding parts in the drawings are designated by the same reference numerals.

Claims (1)

[Claims] 1. In an antenna device that is a Cassegrain antenna or a parabolic antenna used in the microwave band or millimeter wave band and has a pillar in its aperture that prevents the passage of radio waves and supports a sub-reflector or primary radiator, The shape of the opposing surfaces of the pillars, including the longitudinal direction and the direction of radio wave propagation, consists of irregular unevenness with sides longer than the wavelength, and the sides connecting the vertices of the opposing unevenness between the opposing surfaces also have the wavelength above. A plurality of planes consisting of this side and the uneven side are placed on the surface of the main reflector side of the above-mentioned support in the above-mentioned Cassegrain antenna, and on the surface of the above-mentioned support on the reflector side of the above-mentioned parabolic antenna. An antenna device characterized in that: