JPH0352244B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in cross-polarization characteristics in an antenna device comprising a primary radiator, a sub-reflector consisting of a non-rotating quadratic curved mirror having no focal point, and a main reflector. Conventionally, offset antennas composed of quadratic curved mirrors have had very few cross-polarized components. As an example of its configuration, the first
Figure 1a shows the case of an offset Cassegrain antenna, and Figure 1b shows the case of an offset Gregorian antenna. In the figure, 1 is a conical horn, 2
is a sub-reflector made of a hyperboloid of revolution mirror or an ellipsoid of revolution, and 3 is a main reflector of a paraboloid of revolution,
One focus of the sub-reflector 2 coincides with the phase center F ₀ of the conical horn 1, and the other focus coincides with the focus F ₁ of the main reflector. When considered from a geometrical optics perspective, the points where the light ray radiated along the central axis of the conical horn 1 hits the sub-reflector 2 and the main reflector 3 are R and M, respectively, and the light reflected by the main reflector 3 is When taking point W on the line, F ₀ , R,
When M, W, and F ₁ are in the same plane, the beam radiation direction MW→ of the antenna is the reference direction, and the positive direction of the angle is determined so that the angle RM→ makes with the reference direction is less than 180°. , F ₀ F ₁ ―→ is the angle formed with the reference direction by α,
Let β be the angle that F ₀ R→ forms with the reference direction. At this time, in order for the antenna device not to generate cross-polarized components due to geometrical optics, the eccentricity e of the sub-reflector 2 must satisfy the following condition. e=-Pδsinβ/2/sin(α-β/2)...(1) Here, P and δ are parameters representing the shape of the sub-reflector, P=1 is a rotating hyperboloid mirror, P=-1 represents a spheroidal mirror, δ=1 represents a concave mirror, and δ=-1 represents a convex mirror. However, for example, in the case of an antenna with an elliptical aperture, the two reflecting mirrors are not rotating quadratic mirrors, so α and e cannot be defined, and therefore equation (1) cannot be used. Therefore, it was not possible to construct an antenna with few cross-polarized components. In order to eliminate the above-mentioned drawbacks, this invention reduces the cross-polarized component in the electromagnetic field at the mirror surface part that contributes most to cross-polarized wave generation.
This is an attempt to realize an antenna with a low level of cross-polarization even when the mirror surface is composed of a non-rotating quadratic curved mirror without a focal point. explain. Fig _. 2 shows an embodiment of an elliptical beam antenna that can be constructed according to the present invention. This is the main reflecting mirror. Here, R and M are points at which a ray along the central axis of the conical horn 1 hits the sub-reflector 2 and main reflector 3, respectively, and W is a point on the ray reflected by M. At this time, F ₀ , R, M, and W are in the same plane (reference plane), and the intersection of the reference plane and the outer circumference of the sub-reflector 2 is R ₁ , R ₂ , and R and F ₀ are included. And the intersection of the plane perpendicular to the reference plane and the outer periphery of the sub-reflector 2 is R ₃ ,
R ₄ , and the ray coming out from F ₀ is at the point R ₁ on the sub-reflector 2,
Let the points that hit the main reflecting mirror 3 after being reflected by R ₂ , R ₃ , and R ₄ be M ₁ , M ₂ , M ₃ , and M ₄ , respectively. At this time, in the electromagnetic field distribution above the antenna aperture, the line that contributes most to the generation of cross-polarized components is on the line connecting M ₃ and M ₄ , so consider reducing the cross-polarized components in this area. . Here, if the intersection of the straight line connecting M ₃ and R ₃ and the straight line connecting M ₄ and R ₄ is F ₁ ', then for the cross-polarized component, F ₁ ' is the main reflecting mirror 3.
This is approximately equivalent to a quadratic curved mirror having a common focal point with the sub-reflector 2 and the sub-reflector 2. Therefore, when the beam radiation direction is taken as the reference direction and the positive direction of the angle is determined so that the angle between RM→ and the reference direction is less than 180°,
The angle that F ₀ F ₁ -→' makes with the reference direction is α, the angle that F ₀ R→ makes with the reference direction is β, and F ₁ ' is between the main reflecting mirror 3 and the sub-reflecting mirror 2. P=- 1, if we redefine it as P = 1, then from equation (1), e ² -1 = sin (β - α) sin α / sin ² (β / 2 - α)
...(2) From Table 1, it can be seen that α must be positive. Although the case of an elliptical beam antenna has been described above, the present invention is not limited to this, and may be an antenna made of two non-rotating quadratic mirrors having beams of any shape. Moreover, although the case where a conical horn is used as the primary radiator has been described above, the present invention is not limited to this, and any primary radiator having a central axis may be attached and used.

[Table] As described above, according to the present invention, cross-polarized components can be reduced in the electromagnetic field distribution in the portion that contributes most to the generation of cross-polarized components. An antenna device composed of two non-rotating quadratic curved mirrors has the advantage of being able to realize an antenna with a low cross-polarization level.

[Brief explanation of drawings]

FIGS. 1a and 1b are cross-sectional views of an embodiment of an antenna with little cross-polarization constructed by a rotating quadratic curved mirror, and FIG. 2 is a sectional view of an embodiment of an antenna device obtained by the present invention. It is a schematic diagram. In the figure, 1 is a conical horn, 2 is a sub-reflector, and 3 is a main reflector. It should be noted that the same or corresponding parts in the figures are indicated by the same reference numerals.

Claims (1)

[Claims] 1 It is composed of a primary radiator with a central axis, a sub-reflector, and a main reflector, and when considering the phase center of the primary radiator as F ₀ from a geometrical optics perspective, radiation is emitted along the central axis of the primary radiator. Let the point where the ray hits the sub-reflector be R, the point where it hits the main reflector be M, and take a point W on the ray reflected at point M, then F ₀ , R, M,
W is in the same plane (reference plane), the intersection of the reference plane and the outer periphery of the sub-reflector is R ₁ , R ₂ , and F ₀ , the plane perpendicular to the above-mentioned reference plane including R and the outer periphery of the sub-reflector Let the intersection points be R ₃ and R ₄ , and the ray emitted from F ₀ is R ₁ ,
When the points that hit the main reflecting mirror after being reflected by R ₂ , R ₃ , and R ₄ are M ₁ , M ₂ , M ₃ , and M ₄ , respectively, R ₁ and
Intersection point F 1 between the straight line passing through M ₁ and the straight line passing through R ₂ and M ₂ ; Intersection point F _{1 ′} between the straight line passing through R ₃ and M ₃ and the straight line passing through R ₄ and M ₄ In an antenna device in which F ₁ and F ₁ ' are not the same, and the reference direction is the radiation direction MW→ from the antenna, the angle that RM→ makes with the reference direction is less than 180°. An antenna device characterized in that when the positive direction of the angle is determined as follows, the angle that F ₀ F ₁ ′-→ forms with the reference direction is positive.