JPS62281604A - Double reflector antenna - Google Patents

Abstract

PURPOSE:To reduce the interference between satellite communication systems by setting a supporting structure so that plural posts are asymmetrical to a vertical plane including an antenna reflector axis. CONSTITUTION:A supporting structure 4 consists of a column 41 which is not parallel with a vertical plane L including an antenna reflector axis M and two columns 42 and 43 which are symmetrical to the plane L. When this structure 4 is used as an antenna of an earth station opposite to a satellite within the same meridian as the earth station, a plane orthogonal to the column 41 having the largest deterioration of the antenna side lobe characteristics due to the shade formed by the column 41 can be separated from the plane orthogonal to the plane L, i.e., a satellite track plane G since the column 41 has the gradient to the plane L. Thus it is possible to improve the side lobe characteristics within the track plane of a satellite by giving the gradient to the column 41 against the column 41 and setting the structure 4 asymmetrically to the plane L. Then the interference level is reduced between the satellites adjacent to each other on a track.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a double-reflector antenna, and particularly to a double-reflector antenna in which the plane where the side rope level is high is shifted from the satellite orbit plane. Regarding.

[Conventional technology]

BACKGROUND ART A double-reflector antenna having a Cassegrain-type double reflector or a Gregorian-type double-reflector, for example, is used as an antenna for an earth station in a satellite communication system in which a high frequency band higher than microwaves is used.

Figures 6 (a) and (b) show a Cassegrain type double-reflector antenna, where 1 is the main reflector, 2 is the primary radiator that transmits and receives radio waves, and 3 is the Cassegrain type antenna placed in front of the main reflector 1. 4 indicates a support structure for supporting the double reflector 3. From the viewpoint of mechanical balance and economy of the antenna, the support structure 4 has a support 41 that is parallel to a vertical plane that includes the mirror axis M of the antenna, and two supports 42 that are symmetrical with respect to the vertical plane.
．． It consists of 43.

This multi-reflector antenna can be designed with high efficiency through mirror surface modification, and the input/output terminals of the -order radiator are placed near the apex of the main reflector to reduce loss in the feeder line connecting the transmitter/receiver and the primary radiator. Therefore, it is widely used as an antenna for earth stations in satellite communication systems.

On the other hand, with the development of new media, communication demand is rapidly increasing and diversifying, and in the field of satellite communication,
The spacing between adjacent satellites in satellite orbits is becoming increasingly narrow.In order to make effective use of limited satellite orbits and reduce interference between satellite communication systems, earth stations are equipped with lower sidelobe characteristics. There is a strong demand for the installation of antennas that provide

Therefore, we will examine the side lobe characteristics of this type of multi-reflector antenna. As mentioned above, the main reflector 1
Since the double-reflector 3 and the support structure 4 are arranged in the radio wave path in front of the antenna, it is possible that these will block the radio waves and cause a geometric optical shadow (hereinafter referred to as "dark shadow") on the aperture surface A of the antenna. Inevitable. FIG. 7 shows this dark shadow, where the double reflecting mirror 3 causes a dark shadow S0, and the plane wave R between the main reflecting mirror 1 and the aperture A.

is blocked by the support structure 4, resulting in a dark shadow S.

However, in addition, the spherical wave R2 between the double reflecting mirror 3 and the main reflecting mirror 1
is blocked by the support structure 4, resulting in a dark shadow S2.

On the other hand, dark shadows on the aperture plane are one of the major factors that degrade the sidelobe characteristics of the antenna. FIG. 8 shows calculated values estimated by the aperture method of the side lobe level due to the dark shadow created by one pillar constituting the support structure. The dark shadow S in FIG. 8 is a fan-shaped model of the dark shadows S+ and Sz in FIG. 7 (fan angle α=4°).

From Fig. 8, the sidelobe level due to the dark shadow has directionality, and in the plane perpendicular to the dark shadow S (φ-90' plane), the sidelobe level is high in a wide angular range (0, θ, 9°); It can be seen that a surface that is not orthogonal to the dark shadow S but slightly oblique, that is, in the case of this calculation example, the φ=75° surface has a sidelobe characteristic in which the level sharply decreases with respect to the angle θ.

From this, it can be seen that in an antenna having a support structure 4 having pillars 41 parallel to the vertical plane as shown in FIGS. It is expected that the sidelobe level will be low in a plane that is higher and slightly oblique than this. FIG. 9 shows the results of actually measuring the side lobe level of the double-reflector antenna shown in FIGS. 6(a) and 6(b). As is clear from this result, the sidelobe level is high on the φ=90° plane perpendicular to the vertical plane, and the side lobe level is high on the φ=90° plane that is perpendicular to the vertical plane.
It can be seen that the sidelobe characteristics are improved within the 5° plane.

[Problem that the invention seeks to solve]

However, with conventional double-reflector antennas, if the opposing satellite is on a satellite orbit in the same meridian as the earth station, the φ = 90° plane with a high sidelobe level has a large number of satellites spaced closely apart. Since it corresponds to the orbital plane of satellites lined up, it has the disadvantage of causing a high level of interference with adjacent satellites in orbit.

[Means for solving problems]

The present invention has been made in view of the above, and in order to reduce interference between satellite communication systems, a double reflection mirror is provided in which a support structure supporting a double reflection mirror is disposed asymmetrically with respect to the vertical plane of the antenna. This provides a mirror antenna.

Hereinafter, the double reflector antenna of the present invention will be explained in detail.

〔Example〕

1(a) and (b) show an embodiment of the present invention, in which 1 is a main reflecting mirror, 2 is an r-order radiator that transmits and receives radio waves, and 3 is a radio wave path in front of the main reflecting mirror 1. The Cassegrain double-reflecting mirrors 4 are arranged, and numeral 4 indicates a support structure for supporting the double-reflecting mirrors 3. The support structure 4 is composed of three pillars: a pillar 41 that is non-parallel to a vertical plane that includes the mirror axis M of the antenna, and pillars 42 and 43 that are symmetrical to the vertical plane.

In the above configuration, when used as an earth station antenna facing a satellite in the same meridian as the earth station, since the support 41 is inclined with respect to the vertical plane, antenna side lobes due to the dark shadow created by the support 41 are generated. It is possible to avoid the plane perpendicular to the pillar 41, where the deterioration of characteristics is most remarkable, from the plane perpendicular to the vertical plane, that is, the satellite orbit plane G. In this way, by tilting the column 41 with respect to the vertical plane and arranging the support structure 4 asymmetrically with respect to the vertical plane, the side lobe characteristics in the satellite orbit plane are improved, and the side lobe characteristics in the satellite orbit are improved. A multi-reflector antenna for an earth station can be constructed that reduces the level of interference to other satellites.

FIG. 2 shows a second embodiment of the invention, in which the support structure 4 is composed of three columns 41, 42, 43 arranged at equal angular intervals around the mirror axis M of the antenna. are arranged asymmetrically with respect to the vertical plane by being inclined with respect to the vertical plane including the mirror axis M. Also in this embodiment, since the plane perpendicular to the support 41 does not coincide with the satellite orbital plane G,
Similar to the first embodiment, the side rope characteristics within the satellite orbit plane can be improved. In this embodiment, since the support structure 4 is rotationally symmetrical, there are economical advantages in its manufacture and in the workability of attaching it to the main reflecting mirror 1.

FIG. 3 shows a third embodiment of the present invention, which is an effective example of application as an earth station antenna facing a satellite located on a different meridian from that of the earth station. When the meridians of the earth station and the satellite are different, and the supports 41, 42, 43゛, which are arranged at equal angular intervals around the mirror axis M of the antenna, are arranged symmetrically in a vertical plane that includes the mirror axis M, There may be cases where the satellite orbital plane G is perpendicular to the pillar 43'. The present invention is also applicable to such cases, and by replacing the support 43' with a support 43 that is not perpendicular to the satellite orbital plane G, it is possible to construct a support structure 4 that is asymmetrical in the vertical plane. .

Although the above embodiment has been described assuming that the support structure is composed of three columns, the present invention can also be applied to a case where the support structure is composed of four columns, which are also widely used. Fourth
Figures 4 and 5 show that the support structure 4 consists of four columns 44.45.
．． 46.47.

Figure 4 shows pillars 45' and 47' perpendicular to the satellite orbital plane G.
By replacing the support structures 45 and 47 with support columns 45 and 47 that are not perpendicular to the satellite orbital plane 9, a vertically asymmetric support structure 4 is constructed.

FIG. 5 shows that the support structure 4, which is composed of four pillars 44, 45, 46, and 47 arranged at equal angular intervals around the mirror axis M of the antenna, is arranged asymmetrically in the vertical plane. This is to avoid perpendicularity to the satellite orbital plane G of the pillars 45 and 47.

In the case of the antenna of the embodiment shown in FIG. 5, the antenna described in the embodiment of FIG. 2 is economically effective.

Although the above-described embodiments are based on the case where the double reflector is a Cassegrain type, it goes without saying that the present invention can be similarly implemented in a double reflector antenna having a Gregorian type double reflector.

[Effects of the Invention] As explained above, according to the double-reflector antenna of the present invention, the support structure that supports the double-reflector is disposed asymmetrically with respect to the vertical plane of the antenna, so interference can be reduced.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) show a first embodiment of the present invention,
(A) is a side view, (B) is a front view, FIGS. 2 to 5 are front views showing the second to fifth embodiments of the present invention, and FIG.
A) and (B) show conventional double-reflector antennas, and (A)
is a side view, (b) is a front view, FIG. 7 is an explanatory diagram showing the dark shadow that occurs on the aperture surface of the double reflector antenna, and FIG. 8 is a diagram showing the dark shadow caused by the support structure that supports the double reflector. FIG. 9 is an explanatory diagram showing an example of calculation of a side lobe level based on dark shadows; FIG. 9 is an explanatory diagram showing actual measurement results of side lobe characteristics of an antenna having a support structure supporting a double reflecting mirror; Explanation of symbols 1-111・-Main reflector 2-・・−・−Secondary radiator 3−−−−−Return reflector 4−・−・
Support structure 41.42.43 ・ - ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・

Claims (1)

[Scope of Claims] A retroreflector supported by a support structure having a plurality of columns is disposed in a radio wave path in front of the main reflector, and the main reflector is connected to the primary radiation via the retroreflector. A double-reflector antenna for transmitting and receiving radio waves between mirrors, wherein the support structure has the plurality of support columns at asymmetric positions with respect to a vertical plane that includes the antenna mirror axis.