JPH0352242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aperture antenna for wireless communication mainly using frequencies in the microwave band or sub-millimeter wave band.

Conventionally, as aperture antennas for wireless communications, so-called parabolic antennas have been mainly used, in which a main reflector whose reflecting surface is a paraboloid of revolution is fed by a primary radiator, which is a spherical wave source. .
However, due to the structure of this parabolic antenna, there is a primary radiator that blocks the path of the radio waves radiated from the antenna, resulting in so-called blocking of the radio waves, resulting in a decrease in gain and deterioration of the sidelobe level. There were flaws that led to this.

As a way to eliminate the negative effects caused by this blocking, the path of the radio waves radiated from the antenna is
A so-called offset parabolic antenna has been proposed, which has a structure that does not block radio waves. FIG. 1 is a side view showing the configuration of this offset type parabolic antenna. The main reflecting mirror 1 has a reflecting surface formed by a part of a paraboloid of revolution with a point F as a focal point and an axis Z as an axis of rotation. The primary radiator 2 of the spherical wave source has its phase center point coincident with the focal point, and the maximum radiation direction (hereinafter simply referred to as the beam axis) coincides with the axis z that forms a constant angle α (so-called offset angle) with the Z axis. is placed. The angle θ ₀ is a half-angle of the aperture of the main reflecting mirror 1, and is an angle from the z-axis looking from the focal point F to the outer periphery of the main reflecting mirror 1. The coordinate system X-Y-Z and the coordinate system x-y-z are respectively orthogonal coordinate systems centered on point F, and the axes Y and Y are axes that are opposite to each other and perpendicular to the plane of the paper.

As is well known, the spherical wave emitted from the primary reflector 2 is reflected by the reflecting mirror 1 and then emitted as a plane wave with a uniform wavefront within a plane perpendicular to the Z-axis, for example, the X-Y plane in FIG. Hereinafter, the plane on which the wavefronts are aligned will be referred to as the aperture plane. In the antenna of this configuration, as is clear from FIG. 1, there is no blocking of the primary radiator 2 on the path of the radio waves radiated from the antenna, so there is no deterioration in characteristics as occurs with parabolic antennas. However, in the antenna, the main reflector 1 does not have a rotationally asymmetrical configuration, so the rotation on the spherical surface is made up of the intersections of each ray of the spherical wave emitted from the primary radiator 2 and the spherical surface centered at point F. There is a drawback that the symmetrical coordinate system is not rotationally symmetrical on the aperture plane.

Figures 2 and 3 are diagrams for explaining this drawback. Figure 2 shows a spherical surface using variables θ and of a polar coordinate system (γ, θ,) with point F as the center and axis z as the polar axis. This is a diagram showing the above rotationally symmetrical coordinate system on the x-y plane, and each intersection of each light ray emitted from the primary radiator 2 and a spherical surface of radius γ centered on point F is a variable. Trajectories 11, 12, 13 with constant θ,
Variables are represented as intersections with constant trajectories 21, 22, 23. Note that the variable θ is an angle from the z-axis, and the variable is an angle from the x-axis on the xy plane.

FIG. 3 is a diagram showing the trajectory of the intersection of each of the above-mentioned rays with the aperture plane after being reflected by the main reflecting mirror.
are solid lines 31, 32, 33 in Fig. 3 on the aperture plane.
For example, the solid lines 21, 22, 23 in Fig. 2 are not all straight lines, but are non-rotating as a whole, as in the solid lines 41, 42, 43 in Fig. 3. This creates a symmetrical coordinate system. Note that point C in FIG. 3 is the center point of the circle indicated by the solid line 33, that is, the aperture circle of the antenna, and point C ₀ is the X-Y point of intersection 0 between the z-axis and the main reflecting mirror 1, as shown in FIG.
It is a projection point onto a plane.

Therefore, even if the main reflector 1 is fed with linearly polarized waves whose electric field vectors are completely aligned in the x-axis direction, as shown by arrow 8 in FIG. For conversion, the electric field vector is converted into an electric field vector shown by an arrow 9 shown in FIG. 5, which includes an electric field vector component in the X-axis direction and a component in the Y-axis direction, resulting in an electric field vector distribution including so-called cross-polarized components. However, as shown in Figure 5, the distribution is symmetrical only about the X-Y plane, so the only plane in which the cross-polarized components generated by the reflecting mirror 1 cancel each other out is within this X-Z plane; This will degrade the degree of cross-polarization discrimination.

Furthermore, when the antenna shown in Figure 1 is used for circularly polarized waves, for example, the maximum radiation direction of the radiated beam will be different depending on whether it is right-handed circularly polarized or left-handed circularly polarized, due to the influence of the cross-polarized components mentioned above. There were some drawbacks such as being different.

An object of the present invention is to provide an offset antenna in which cross-polarized components are not generated when linearly polarized waves are fed, and the maximum radiation direction of the radiation beam is the same for right-handed circularly polarized waves and left-handed circularly polarized waves. There is a particular thing.

According to this invention, a dielectric lens system is arranged between the main reflector and the primary radiator, and the refraction effect on the dielectric lens surface for the light rays emitted from the primary radiator and the refraction effect of the rays inside the dielectric lens. Using the difference in optical path length at However, it should be converted to a coordinate system that is close to rotational symmetry.

FIG. 6 is a diagram for explaining the principle of the present invention. Reference numerals 4 and 5 are radio wave lenses made of dielectric material. Lenses 4 and 5 are so-called hyperbolic lenses. Each one of the surfaces S1 and 2 is a portion of a hyperboloid of revolution having focal points F1 and F2, respectively, focal lengths f1 and f2, and axes of rotation about axes 6 and 7, respectively.
The axes 6 and 7 are parallel to each other on the same plane and separated by a distance d, and each other surface B1 and B2 of the lenses 4 and 5 is formed by a portion of a plane perpendicular to the axes 6 and 7, respectively. Therefore, the distances 11 and 22 from the focal points F1 and F2 to the lens surfaces S1 and S2 are expressed by the formula
Determined by (1).

11=(n-1)f1/ncosθ ₁ −1 22=(n-1)f2/ncosθ ₂ −1 n=√〓…
...(1) However, ε〓 is the relative dielectric constant of each dielectric material of lenses 4 and 5, and θ ₁ and θ ₂ are 11, 22 and axis 6, respectively.
These are the angles each makes with 7.

In the arrangement of the radio lenses 4 and 5 shown in Fig. 6, the light beam incident on the lens 4 from the focal point F1 is refracted according to the law of refraction, but if 11 is the function shown by equation (1), The rays are all parallel to the axis 6, so the surfaces B1 and B2 are perpendicular to the axis 6.
Then, it travels straight without being refracted and reaches the surface S2 of the lens 5, where it is refracted again according to the law of refraction. Here, when F2P2 is a function shown by equation (1), all the refracted light rays travel as spherical waves centered on the focal point F2. Therefore, the optical path length from the focal point F1 to the spherical surface S3 of radius R centered on the focal point F2 is all constant and can be determined by equation (2).

Optical path length = L + R + (n-1) (T1 + T2) ... (2) As is clear from the above, after converting the spherical waves centered at the focal points F1 of radio lenses 4 and 5 shown in Fig. 6 into plane waves, It has the effect of converting into a spherical wave centered at the focal point F2.

FIG. 7 is an explanatory diagram of a configuration example and operation of the radio wave lens system 3 used in the present invention.
1 and B2 are filled with the same dielectric material to form an integral structure. Of course, even with this configuration, it has the same effect as the combination of radio wave lenses 4 and 5 shown in FIG. The primary radiator 2 shown in FIG. 7 is arranged so that its beam axis is inclined at an angle β with respect to the axis 6. A ray 50 passing through the beam axis of the primary radiator 2 and rays 51 and 52 forming an angle θ with this ray pass through the radio wave lens system 3. After passing through the radio wave lens system 3, the ray 50 forms an angle δ with the axis 7.
rays 51 and 52 are converted into rays 54 and 55, respectively, into a ray 53 forming . In this case, the angles formed by the rays 54 and 55 with respect to the ray 53 are θ ₁ and θ ₂ , respectively.
shall be.

As mentioned with reference to Figures 2 and 3, one of the reasons why the rotationally symmetric coordinate system in Figure 2 becomes rotationally asymmetric as in Figure 3 is that The locus with a constant angle θ does not become a concentric circle on the aperture surface, and the center of the circle moves from point C ₀ in the direction of point C in FIG. 3 as θ increases. In this invention, by utilizing the fact that the angles θ ₁ and θ ₂ in FIG. Make the trajectory approach concentric circles on the aperture plane. Variables for adjusting the angles δ, θ ₁ , and θ ₂ with respect to the angle θ include the focal lengths f1 and f2 of the radio wave lens system 3, the refractive index n, the angle β, and the distance d.

FIG. 8 shows an embodiment of the present invention, in which the main reflecting mirror 1
is a part of a paraboloid of revolution with point F2 as its focal point and Z-axis as its axis of rotational symmetry, and its offset angle is α,
The aperture half angle is θ ₀ . The primary radiator 2 and the radio lens system 3 have the configuration shown in FIG.
is aligned with the focal point of the main reflecting mirror 1, and the axis 7 is arranged at an angle γ with respect to the Z axis. A ray 50 passing through the beam axis of the primary radiator 2 and rays 51 and 52 forming an angle θ with this ray become a ray 53 and a ray 54 and 55, respectively, after passing through the radio lens system 3. Each ray passes through the main reflecting mirror 1. After reflection, all the rays travel in the Z-axis direction, and the aperture planes are at points C and C, respectively.
Intersect at A and B. The condition that point C becomes the center of two points A and B is determined by equation (3).

sin(δ+γ)/1+cos(δ+γ)=sinα/cosα+
cosθ ₀ ...(3) "However, the angle δ is determined by equation (5) according to conditional equation (4) (see Fig. 6).

11sinβ+d=22sinδ...(4) Therefore, each variable f1, f described in FIG.
The primary radiator 2
It is possible to make the locus of a light ray whose angle θ is constant with respect to the beam axis of the aperture plane approximate to a concentric circle on the aperture plane.

Specifically, in the configuration shown in FIG. 8, the ratio of the aperture diameter D to the focal length f of the main reflecting mirror 1 is f/D=
0.73, offset angle α = 56 degrees, aperture half angle θ ₀ = 30
degree, inclination angle β of the beam axis of the primary radiator 2 = 10
When the maximum angle of angle θ is 30 degrees, the conditions of equation (3) are n=1.5, f1/f2=1.1, d/f1=0.1 and γ=
It is almost satisfied when 44 degrees and δ=16 degrees.

The trajectory in which the variable θ of the polar coordinate system whose center is the point F1 and whose polar axis is the beam axis of the primary radiator 2 is 1.
When projected onto a plane perpendicular to the beam axis of the next radiator 2, it becomes rotationally symmetrical as described in connection with Fig. 2, and the locus with constant θ is the solid line 11, 1
2, 13, and the constant trajectory is the solid line 21, 2
It becomes 2,23. θ on the aperture plane when a normal offset parabolic antenna is constructed by placing the primary radiator 2 at point F2, and when an offset antenna with a lens according to the present invention shown in FIG. 8 is constructed. Fig. 9 shows the left half and right half of a comparison of trajectories where the distance is constant. Solid lines 31, 32, 3 showing the trajectory of a normal offset parabolic antenna
3 and solid lines 41, 42, and 43 are as described with respect to FIG. 3, but in the lens-equipped offset antenna according to the present invention, θ is a constant locus, that is, one that reacts with the solid lines 11, 12, and 13 in FIG. are almost concentric circles like the broken lines 34, 35, and 36 in FIG.
2 and 23 correspond to broken lines 44 and 4 in Fig. 9.
It becomes 5,46. Note that the solid line 33 and the broken line 36 are the same circle centered on point C, and the solid line 41 and 4 are the same circle.
4 is a straight line on the X axis. As is clear from the figure, by using the present invention, the non-rotationally symmetric trajectory of the conventional offset parabolic antenna is improved and becomes a nearly rotationally symmetrical trajectory. Therefore, for example, in the aperture plane, the electric field vector indicated by arrow 8 in FIG. 4 becomes arrow 9 in the case of a normal offset parabolic antenna, whereas in the case of the lens-equipped offset antenna of the present invention, the electric field vector is indicated by arrow 8. Then, as shown by arrow 10, the electric field vector becomes almost parallel to the X-axis with few cross-polarized components.

FIG. 10 shows another embodiment of the present invention, specifically f/D=0.74, α=53 degrees, aperture radius 30 degrees,
When β = 0 degrees and the maximum angle of angle θ is 30 degrees,
The conditions of equation (3) are n=1.5, f1/f2=1.0, d/f
It is satisfied when 1 = 0.1, γ = 51 degrees, and δ = 5.7 degrees. FIG. 11 shows a view corresponding to the view on the aperture plane shown in FIG. 9 for the embodiment of FIG. 10.
In this case as well, it is clear that the non-rotationally symmetric trajectory of the conventional offset parabolic antenna is improved.

In the above explanation, as the radio wave lens system 3, as shown in FIG. It is clear that any lens may be used as long as it converts an incoming spherical wave into a plane wave, and the radio wave lens 5 may be any lens that converts a plane wave into a spherical wave.

FIG. 12 shows an example of the configuration of the radio wave lens system 3 when a lens other than a so-called hyperbolic lens is used.
This corresponds to the case where the radio wave lens 4 in FIG. 6 is replaced with a so-called elliptical lens. In this radio wave lens 4, the surface B1 on the opposite side to the lens 5 is formed as a spherical surface centered at the point F1, and the surface S1 on the side of the lens 5 is formed at the point F1.
It consists of an ellipsoid of revolution with focal point F1 and axis 6 as the axis of rotation, and distance 1 from focal point F1 to lens surface S1.
P1 is determined by equation (6).

11=(n-1)f1/n-cosθ ₁ ...(6) The light beam incident on lens 4 from focal point F1 is on surface B1
Since is a spherical surface centered on point F1, it travels straight without refraction and reaches surface S1, and is refracted according to the law of refraction. However, if 11 is the function shown by equation (6), the refracted ray are all incident on the radio wave lens 5 as light rays parallel to the axis 6. The light rays after entering the radio lens 5 are as described in connection with FIG. 6, and formula (2), which indicates the optical path length from the focal point F2 to the spherical surface S3 with radius R, also holds true in the case of FIG. do. Therefore, it is possible to use the radio wave lens system having the configuration shown in FIG. 12 in this invention, and the equations (3) to (4) used in the explanation of FIG. Except as indicated, they apply as is.

For convenience of explanation, all antennas have been described as transmitting antennas, but it goes without saying that the present invention is also applicable to receiving antennas due to the reciprocity of antennas.

As explained above, according to the offset antenna of the present invention, it is possible to reduce cross-polarized components generated by the main reflector without losing the characteristics of an offset-type parabolic antenna. It is possible to realize an antenna with good polarization discrimination, and especially when used in an antenna that shares both left and right circularly polarized waves, it is possible to reduce the maximum radiation direction between polarized waves due to cross-polarized components. Specifically, there are effects such as improved gain in the communication direction and improved cross-polarization discrimination.

[Brief explanation of drawings]

Figure 1 is a side view showing a conventional offset parabolic antenna, Figures 2 and 3 are diagrams showing the trajectory on the x-y plane and the aperture plane, respectively, where the variable θ is constant; 4 and 5 are electric field vector diagrams in the x-y plane and the aperture plane, respectively, FIGS. 6 and 7 are side views showing an example of the configuration of the radio wave lens system 3 used in the present invention, and FIG. FIG. 9 is a side elevational view showing an embodiment of the offset antenna according to the present invention, and FIG. The figure is a side view showing another embodiment of the invention, and FIG.
9 of the antenna shown in FIG. 0, and FIG. 12 are side views showing other examples of the radio wave lens system 3 used in the present invention. 1: Main reflecting mirror, 2: Primary radiator, 3: Radio wave lens system, 4, 5: Radio wave lens, 6, 7: Rotation axis of radio wave lenses 4 and 5, 8, 9, 10: Electric field vector,
11, 12, 13: Locus with constant θ on the x-y plane, 21, 22, 23: Locus with constant θ on the x-y plane, 31, 32, 33, 34, 35, 3
6: Locus with constant θ on the aperture plane, 41,4
2, 43, 44, 45, 46: constant trajectory on the aperture plane.

Claims (1)

[Claims] 1. An offset parabolic reflector whose reflecting surface is a part of a paraboloid of revolution, with an offset angle α and an aperture half angle θ ₀ , and a spherical wave source centered at a point F1 that supplies power to the reflector. a primary radiator, and a radio lens system made of a dielectric located between the reflecting mirror and the primary radiator, and the radio lens system focuses a spherical wave center point F1 of the primary radiator. and the central axis 5 of the primary radiator is
a first lens portion that is made of a rotational quadratic curved surface having a rotational center axis 6 that is not parallel to zero, and that converts a spherical wave emitted from the primary radiator into a plane wave that travels in a direction parallel to the rotational axis 6; , having a rotational center axis 7 that shares a focal point with the focal point F2 of the reflecting mirror and is parallel to the rotational center axis 6, and makes a plane wave traveling in a direction parallel to the rotational center axis 7 centering on the focal point F2. It consists of a second lens part made of a rotational quadratic curved surface that converts into a spherical wave, and the light ray passing through the beam center axis 50 of the primary radiator is expressed by the following formula: sin(δ+γ)/1+cos(δ+γ)=sinα/cosα+
cosθ ₀ However, γ is the angle between the rotation center axis 7 and the rotation center axis of the reflecting mirror, and δ is the angle between the lens rotation center axis 7 and the center axis 7 of the lens after the ray passing through the center axis 50 passes through the second lens portion. An offset antenna with a lens that satisfies the angle of .