JPH0728176B2 - Spherical mirror antenna - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a spherical mirror antenna, and more particularly, to providing two auxiliary reflecting mirrors to eliminate spherical aberration and improve beam deflection characteristics. It is a feature.

[Conventional technology]

FIG. 2 is an explanatory diagram of an example of a conventional spherical mirror antenna.
In the figure, 1 is a spherical mirror, 2 is an auxiliary reflecting mirror, and 3 is a horn.

The operating principle of this antenna in the transmitting state will be described. The spherical wave emitted from the phase center O of the horn 3 is reflected by the auxiliary reflecting mirror 2 and the spherical mirror 1 and heads for the space. Here, the mirror surface coordinates of the auxiliary reflecting mirror 2 are determined so that the radio wave traveling to the space becomes a plane wave. In this way, the auxiliary reflecting mirror 2 can eliminate the spherical aberration of the spherical mirror 1 and obtain high gain and low side lobe characteristics.

In FIG. 2, a ray tracing result of a ray group at equal angular intervals from the point O is shown by a broken line. On the opening surface of the spherical mirror 1, light rays are concentrated in the peripheral area rather than in the central area. Here, the radiation pattern of the horn 3 usually has a maximum taper distribution in the front direction, and when the auxiliary reflection mirror irradiates with this radiation pattern, the electric field level of the peripheral portion of the opening surface by the above-mentioned auxiliary reflection mirror 2 rises. Are canceled out, resulting in a substantially uniform electric field level over the entire opening surface.

Next, consider a case where a plurality of horns are arranged in the vicinity of the point O in this type of antenna to obtain a multi-beam. In order not to deteriorate the beam deflection characteristics of this multi-beam, that is, the performance such as the gain reduction and the sidelobe level increase due to the deflection, it is necessary to satisfy the Abbe sine condition shown in FIG. is there. This sine condition can be explained as follows using FIG.

First, the reflecting mirror system 4 of FIG. 3 is provided between the spherical mirror 1 and the horn 3, and it may be composed of any number of reflecting mirrors.

In addition, light rays emitted from the feeding point O of the horn 3 and traveling in a direction forming an angle of θ with the x-axis successively hit the reflecting mirrors constituting the reflecting mirror type 4, and finally hit the spherical mirror (main reflecting mirror) 1. Is denoted by M, the y coordinate of this point M is denoted by H. Therefore, this H is a function of θ.

Also, this function is determined depending on the reflecting mirror system 4,
Here, as already mentioned, it is assumed that the sine condition of H = Const. · Sin θ (Const. Is a constant) is satisfied.

Further, by displacing the position of the horn 3 by d in the y-axis direction, a plane wavefront forming an angle of ψ with the x-axis is created. Therefore, both d and ψ are constants.

Under such a premise, when the feeding point O is displaced by d, the optical path length Δp is shortened by Δp = dsinθ (1) as compared with the case where it is not displaced.

On the other hand, if the main beam is directed in a direction inclined by ψ due to the displacement of d, in order to obtain the same amount of optical path length difference Δp in the aperture surface 5 of the main reflecting mirror 1, Δp = Htanψ (2) Holds. Therefore, the following equation is obtained from the equations (1) and (2).

Here, since d and ψ are known and constant, H / sin θ is constant.

[Problems to be solved by the invention]

This expression (3) is the sine condition of Abbe, but in the mirror surface system that satisfies this condition, the light rays do not concentrate on the peripheral portion at the aperture surface. The reason is as follows.

That is, by displacing the position of the horn 3 by d in the y-axis direction, the optical path length difference Δp represented by the equation (1) is generated, and thereby a parallel wavefront forming an angle of ψ with the x-axis is formed. In order to realize the optical path length difference Δp (represented by equation (2)) necessary for the aperture surface 5 of the spherical mirror 1, the sine condition in which the relationship between H and θ is represented by equation (3) is satisfied. To be satisfied,
It suffices to determine the reflecting mirror system 4.

In other words, if the reflecting mirror system 4 is determined so as to satisfy the sine condition expressed by the equation (3), a parallel wavefront forming an angle of ψ with the x axis can be realized without aberration, so that the beam deflection characteristic is improved. Will be improved.

In addition, H indicates where on the spherical mirror 1 the light ray emitted from the feeding point O and traveling in the direction forming an angle of ψ with the x-axis finally hits.
That is, it also shows how the light rays are concentrated on the aperture surface 5, which is expressed by H = Const. · Sin θ, which means that within a small range of θ,
As shown in FIG. 1, the light rays emitted from the feeding point O in the direction at equal intervals have substantially equal intervals even on the aperture, and do not concentrate on the periphery of the aperture as in FIG.

However, since the conventional spherical mirror antenna does not satisfy the sine condition, as shown in FIG. 2, light rays are concentrated in the peripheral portion, aberration occurs at the aperture surface, and there is a problem that the beam deflection characteristic is poor. .

The present invention has been made to solve the above problems, and an object thereof is to obtain a spherical mirror antenna capable of forming a multi-beam having good beam deflection characteristics by satisfying not only phase correction but also a sine condition. And

[Means for solving problems]

In the spherical mirror antenna according to the present invention, the main reflecting mirror is a spherical mirror, and two auxiliary reflecting mirrors are provided between the horn and the spherical mirror, and the mirror surface coordinates of the auxiliary reflecting mirror are the reflection condition that is a geometric method. , Power condition, and constant optical path length.

Here, the sine condition of Expression (3) is used as the power condition.

[Action]

In the present invention, in the multi-reflecting mirror antenna consisting of the main reflecting mirror and the two auxiliary reflecting mirrors, the two auxiliary reflecting mirrors satisfy the sine condition, so that a plurality of primary radiators are also preferable. Beam deflection characteristics can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
The figure shows a spherical mirror antenna according to an embodiment of the present invention. In the figure, 1 is a spherical mirror which is a main reflecting mirror, 3 is a feeding horn as a primary radiator, 6 and 7 are auxiliary reflecting mirrors, and θ is a horn 3.
Is the angle from the central axis of H, and H is the x-axis of the point M when the light rays emitted in the direction of the angle θ from the central axis of the horn 3 are reflected by the auxiliary reflecting mirrors 7 and 6 and hit the spherical mirror 1. Is the distance from.

When this antenna is used as a multi-beam antenna, a plurality of horns may be arranged near the horn 3, but they are omitted in the figure. In FIG. 1, the spherical mirror 1 and the auxiliary reflecting mirror 6 are rotationally symmetrical, and the auxiliary reflecting mirror 7 is an asymmetric mirror surface. Here again, the result of ray tracing in the transmitting state is shown, but in the figure, the phase center O of the horn 3
The rays from to the auxiliary reflecting mirror 6 are shown by dotted lines, and the rays from the auxiliary reflecting mirror 6 to the main reflecting mirror opening surface are shown by broken lines. As compared with FIG. 2, it can be seen that the light rays do not concentrate around the aperture surface and the sine condition is satisfied.

Further, in the above embodiment, the feeding horn was used as the primary radiator, but it may be constituted by at least one reflecting mirror and a focused beam feeding system composed of the feeding horn.

Further, in the above-mentioned embodiment, the main reflecting mirror 1 and the auxiliary reflecting mirror 6 use rotationally symmetric mirror surfaces, but they may be constituted by offset type mirror surface systems.

When the two auxiliary reflecting mirrors, including the main reflecting mirror, are rotationally symmetric mirror surfaces, the mirror surface coordinates satisfying the above conditions of constant reflection, sine and constant optical path length can be obtained, but even one of them is asymmetrical. In the case of a mirror surface, the mirror surface coordinates cannot be determined exactly.
However, an approximation method has been developed in which the error does not pose a problem in practical use, and the literature that describes one example is shown below.

Urasaki, Kataki, Mizusawa: "Mirror Reflector Adjustment of Offset Cassegrain Antenna Fed by Horn Reflector", Sho 53 No. 5
28 Here, the error is how much the sine condition is broken when the conditions of constant reflection and optical path length are satisfied.

〔The invention's effect〕

As described above, according to the spherical mirror antenna of the present invention, by adding another auxiliary reflecting mirror, the degree of freedom in design is increased, and not only the conventional phase distribution control but also the amplitude distribution control becomes possible. This has the effect of obtaining a multi-beam with high gain and low side lobes.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a spherical mirror antenna according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a conventional spherical mirror antenna, and FIG. 3 is a diagram explaining the effect of the present invention. In the figure, 1 is a spherical mirror (main reflecting mirror), 2 is a phase correction type auxiliary reflecting mirror, 3 is a horn (primary radiator), 4 is a reflecting mirror system, 5 is an aperture surface, and 6 and 7 are auxiliary reflecting of the present invention. It's a mirror.

Claims (3)

[Claims] 1. A multi-reflecting mirror antenna comprising a main reflecting mirror, an auxiliary reflecting mirror, and a primary radiator, wherein a spherical mirror is used as the main reflecting mirror, two auxiliary reflecting mirrors are provided, and two auxiliary reflecting mirrors are provided. , The plane wave incident from the direction of the radiation beam is reflected by the main reflecting mirror and then by the two auxiliary reflecting mirrors, and is focused on the phase center of the primary radiator. A spherical mirror antenna characterized in that the auxiliary reflecting mirror satisfies the sine condition of Abbe so that aberrations other than those contributing to beam deflection which are generated at the time of deviation feeding are reduced. 2. The mirror surface coordinates of the two auxiliary reflecting mirrors satisfy not only the sine condition but also the condition of reflection and the condition of constant optical path length as set forth in claim 1.
The spherical mirror antenna according to the item. 3. The spherical mirror antenna according to claim 1, wherein an offset type reflecting mirror system is used as the reflecting mirror system including the main reflecting mirror and the auxiliary reflecting mirror.