JPS62154905A - Multibeam antenna - Google Patents

Abstract

PURPOSE:To form a multibeam antenna which is smaller in main reflection mirror size and also smaller in antenna-axial size than a conventional antenna by adding a subordinate reflection mirror which has a torus curved surface to a conventional torus antenna and correcting aberrations by a correcting reflection mirror. CONSTITUTION:An electromagnetic wave radiated by a primary radiator 4 is reflected by the correction mirror 2, and then reflected by the subordinate reflection mirror 2, and then reflected by a main reflection mirror 1, so that the wave is radiated in a beam direction 51. An electromagnetic wave radiated by the primary radiator 42, on the other hand, is reflected by a correcting reflection mirror 32 and reflected by the subordinate reflection mirror 2, and then reflected by the main reflection mirror 1, so that the wave is radiated in a beam direction 52. The main reflection mirror and subordinate reflection mirror 2 are composed of a torus curved surface having its center of rotation at an axis 5 of rotation. The correcting reflection mirrors 31 and 32 are provided so as to correct astigmatism originating from the torus curved surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-beam antenna for simultaneously communicating with a plurality of satellites in a geostationary orbit using one antenna.

[Conventional technology]

Conventionally, some antennas of this type use a torus curved surface as shown in Japanese Patent Laid-Open No. 51-863. As shown in FIGS. 5 and 6 (a) and (b), a torus curved surface 11 formed by rotating a generating curve 15 such as a parabola around the rotation axis 5 is used as the main reflecting mirror. . The radius of rotation at this time is called the torus radius. Here, FIG. 6(,) is a cross-sectional view of the antenna of FIG. 5 along a plane including the two rotational axes 5 and the central axis of the primary radiator 14,
5 is a cross-sectional curve of the main reflecting mirror 11, and 17 is a cross-sectional curve of the correction reflecting mirror 13. ! Also. FIG. 6(1)) is a cross-sectional view taken along a plane perpendicular to the cross-section explained in FIG. 6(a), including one light ray heading from the main reflecting mirror 11 to the correction reflecting mirror 13. This is a cross-sectional curve of the reflecting mirror 11.

18 is a cross-sectional curve of the correction reflecting mirror 13.

As shown in FIG. 6(a), if the cross-sectional curve 15 of the main reflecting mirror is set as a parabola (-), parallel rays incident on the curve 15 in the plane of FIG. 6(a) converge to a focal point 19. do.

However, in the plane of FIG. 6(b), since the cross-sectional curve 16 is a circular arc, parallel rays of light incident on one curve 16 do not converge to one point and have aberrations. The correction reflector 13 is only for correcting this aberration, and the cross-sectional curve 18 allows all the light rays to be at the focal point 2.
It is determined that it converges to 1.

[Problem that the invention seeks to solve]

Although this antenna has the advantage of being able to construct an antenna with arbitrary beam separation, it has the following practical drawbacks.

(1) In order to prevent the plurality of correction reflection mirrors 13 from colliding with each other, the torus radius must be increased and the size of the correction reflection mirrors 13 must be reduced. But only
e To do this, as shown in Fig. 6(b), the quasi-focal point 20 of the arc (1 of the radius of the arc 16 from the torus rotation axis 5) is
The correction reflector 13 must be placed near the point (a point at a distance of /2). Therefore, it becomes a large antenna with a long distance from the main reflecting mirror 11 to the correction reflecting mirror 13.

(2) The main reflector 1] has an oval shape in the direction perpendicular to the torus rotation axis 5 and is larger than the main reflector of a normal single beam antenna. Further, the geostationary orbit of the satellite as seen from the earth is generally inclined with respect to the horizontal plane 64, as shown in FIG. Therefore, in order to simultaneously communicate with the two satellites 61 and 62 on the geostationary orbit, the antenna must be installed with the long axis of the ellipse of the main reflector 11 tilted from the horizontal plane 64. In this case, the back support frame structure of the antenna becomes large and complicated.

(3) As can be seen from the group of rays in Fig. 6(b), the focal point 2 is
The rays leading to 1 are not lined up at equal angles with the focal point 2] as the center. That is, after the axially symmetrical electric field distribution radiated from the primary radiator 4 is reflected by the main reflecting mirror, a deviation occurs. This results in low aperture efficiency and deterioration in cross-polarized wave characteristics. An object of the present invention is to provide a multi-beam antenna that eliminates the above-mentioned drawbacks.

[Means for solving problems]

The antenna according to the present invention includes a main reflecting mirror having a torus curved surface, a sub-reflecting mirror having a torus curved surface, a plurality of correction reflecting mirrors, and a plurality of primary radiation beams each facing at least one of the plurality of correction reflecting mirrors. It is characterized by a predetermined modification applied to each reflecting mirror.

〔Example〕 Next, two embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which one main reflecting mirror 1.
It consists of one sub-reflector 2, two correction reflectors 31.32 and two primary radiators 41.42. The electromagnetic waves radiated from the primary radiator 41 are reflected to the correcting reflector 3, secondarily reflected by the sub-reflector 2, and then reflected to the main reflector and radiated in the beam direction 51. On the other hand, the electromagnetic waves radiated from the primary radiator 42 are reflected by the correction reflector 32, secondarily reflected by the sub-reflector 2, and then reflected to the main reflector and radiated in the beam direction 52. Here, the main reflecting mirror 1 and the sub-reflecting mirror 2 are constituted by a torus curved surface whose rotation center is rotation 1!1115. I cut it. The correction reflecting mirrors 31 and 32 are provided for the purpose of correcting astigmatism due to the torus curved surface.

In the case of a conventional torus antenna, as shown in FIG. 6(a), a plurality of focal points 21 corresponding to the primary radiators can be arranged only within one plane perpendicular to the 1-rus rotation axis 5. was. If the primary radiator is displaced in a direction perpendicular to the plane, aberrations will occur due to defocus, and the characteristics of the antenna will deteriorate.

When considering the cross section of the antenna in a plane including the torus rotation axis 5 (Fig. 6(a)), for example, if the cross-sectional curve 15 of the main reflector and the cross-sectional curve 17 of the sub-reflector are ellipsoids. , if the parallel rays incident on the cross-sectional curve I5 of the main reflector are parallel to the parabola base 22, the light rays will be focused at the focal point 21, and the parallel rays from other directions will be focused on the cross-sectional curve 15 of the main reflector. This is because the light rays do not converge to one point even when they are incident.

On the other hand, the case of two 'andenas will be explained with reference to FIG. FIG. 2 shows cross-sectional curves 3 and 4.71 of the symmetry plane (Al30) of the correction reflector 3I including the torus rotation axis 5 of the antenna shown in FIG. Cross-sectional curve by plane of symmetry (CDO) 3, 4.72
One of the cross-sectional curves 3 and 4 is included in the same plane.
．． 72 rotated by an angle β around the 1-ras rotation axis 5 and superimposed on each other.

Here, to simplify the explanation, the cross-sectional curve 3 of the main reflecting mirror is assumed to be a parabola, and the cross-sectional curve 4 of the sub-reflecting mirror is assumed to be an ellipse. At this time, if the focus of the parabola is made to coincide with the focus of one of the ellipses, then when a parallel ray enters from the direction 55 parallel to the axis of the parabola 3, it will cause other focus 81
converges to.

Therefore, if the cross-sectional curve 71 of the correction reflector is made into an ellipse with two focal points, for example, the phase center 91 and the focal point 8, the parallel rays incident on the main reflector will be reflected in the cross-section shown in FIG. It is possible to converge on one point 91 with a constant optical path length.

The above is all about the cross section in Figure 2.

When a torus curved surface is formed around the torus rotation axis 5 with the cross-sectional curve 3 of the main reflecting mirror and the cross-sectional curve 4 of the sub-reflecting mirror as generating curves, the light is incident on the main reflecting mirror from the direction 55 at the cross section other than that shown in FIG. Parallel rays do not converge to one point at point 81. The curved surface shape of the correction reflecting mirror 31 other than the section shown in FIG. 2 is defined as a curved surface that corrects this aberration. That is, the parallel rays incident on the main reflecting mirror 1 are reflected by the main reflecting mirror 1. Secondary reflector 2
After being reflected by the correction reflecting mirror 3, the correction reflecting mirror 31
The curved surface shape of is required.

Next, a method of determining the curved shape of the correction reflecting mirror 32 will be described. In FIG. 2, consider the case where a parallel ray is incident on the cross-sectional curve 3 of the main reflecting mirror from a direction 56 that is different from the first beam direction 55 by an angle α.

At this time, the light beam reflected by the main reflecting mirror heads toward the sub-reflecting mirror cross-sectional curve 4 and is reflected there.

The cross-sectional curve 4 is determined so that parallel rays in the direction of 55 converge at a point 81, so if the correction reflecting mirror 32 is made the same as the correction reflecting mirror 3], the phase center 92 There is aberration even at the position.

However, if the curved surface shape of the correction reflecting mirror 32 is newly determined to correct this aberration, an antenna without aberration can be constructed even for beams in 56 directions.In this way, the mirror surface of each reflecting mirror can be constructed. If the shapes are determined, the correction reflector 32 and the primary radiator 42 can be rotated by any angle around the torus rotation axis 5 while maintaining the relative positions of the correction reflector 32 and the primary radiator 42 without geometric optics. Conditions do not change at all. therefore.

The beam can be deflected by any angle β in the direction of a plane perpendicular to the axis of rotation of the torus.

Now, when communicating with two satellites on a geostationary orbit using the antenna according to the present invention, the procedure is as follows.

When a geostationary orbit is viewed from the ground, it generally appears tilted with respect to the horizontal plane, as shown in Figure 3. In this case, two satellites 61
．． The angle of separation seen from the ground antenna at each of the positions P and Q of 62 is assumed to be δ, and the two angles of separation δ are decomposed into a horizontal separation angle β and a vertical separation angle α. Then, the antenna configuration may be determined so that α and β used in the explanation of FIGS. 1 and 2 correspond to these angles.

At this time, the main reflecting mirror 1 becomes a horizontally elongated ellipse due to the two rotation angles β, but there is no need to incline the long axis of the ellipse by the orbital inclination angle δ as in the conventional 1-rath antenna. Furthermore, since the long axis of the ellipse can be made shorter than in the conventional case, the area of the main reflecting mirror can be reduced. Because with the conventional torus antenna.

As mentioned above, in order to avoid the two correction reflecting mirrors colliding with each other, the distance (referred to as R2) from the main reflecting mirror to the torus rotation axis must be increased. On the other hand, in the two antennas according to the present invention, there is freedom in the arrangement of the correction reflectors 31 and 32.

1--The distance (referred to as R1) from the lath rotation axis 5 to the main reflecting mirror can be shortened. Furthermore, in the conventional torus antenna, the length of the major axis of the main reflector needs to be approximately R25inδ, whereas in the antenna of the present invention, the length of the long axis of the main reflector is approximately R,si
As much as nβ is required. From FIG. 3, since the angle β is smaller than the angle δ, the main reflecting mirror of the antenna of the present invention is smaller. Here, D is the effective aperture diameter of the two reflecting mirrors, that is,
The length of the main reflecting mirror in the short axis JJ direction is measured along the torus rotation axis 5.

The next problem is static [1
, is a method of tracking satellites. Satellites in stationary and geostationary orbits are irregularly moving to the left around their geostationary position. In order to track this minute movement, a normal single beam antenna uses a method of moving the entire antenna. but,
Conventional methods cannot be used to simultaneously track two satellites using a multi-beam antenna because the number of satellites fluctuates independently of each other.

In the multi-beam antenna according to the present invention, the auxiliary reflector 3
Attach a drive device to 1 and 32 respectively.

By making fine adjustments to these independently, the two beams can be made to move slightly independently, making it possible to track two satellites at the same time. To achieve the same effect, a drive device may be attached to the primary radiators 41 and 42 to slightly move only the primary radiators.

Alternatively, both the auxiliary reflector and the primary radiator may be slightly moved.

In the following explanation, the focal point 81 and the focal point 82 in FIG.
are the cross section 4 of the sub-reflector and the cross section 71 or 7 of the correction reflector.
I considered a case between 2.

It is also possible to configure the correcting reflector 7] or 72 to be placed between the focal points 81 and 82 and the cross section 4 of the sub-reflector. Further, in FIG. 2, the sub-reflector cross section 4 is concave. Although it is a so-called Gregorian type, the sub-reflector cross section 4 is convex. A so-called Cassegrain type may also be used.

Furthermore, main reflecting mirror 1. Secondary reflector 2. Correction reflectors 31 and 3
By modifying the mirror surface shape of 2.

The aperture electric field distribution of the main reflecting mirror can be controlled. As a result, it is possible to construct an antenna that is highly efficient and has an unbiased main reflector aperture electric field distribution. In this case, at the focal point 81 the rays do not all converge to these points, but up to the focal point 9, which corresponds to the primary radiator, all the rays can converge to these points.

Furthermore, as is clear from the above description, 9 the present invention provides 3
Multi-beams that form more than 3 beams are also possible.
, Fig. 4 shows an embodiment in which a 31''-) antenna is constructed.

In addition, in the above explanation, an example in which only one primary radiator is arranged with respect to the focal point of the correction reflector is shown, but a plurality of primary radiators are arranged around one focal pointff~ It may be something. It is possible that such an antenna could be used onboard a satellite.

[Effects of the Invention] As can be seen from the above explanation, the present invention introduces a sub-reflector having a 1-raus curved surface into a conventional torus antenna, and corrects the aberration by the correction reflector. By doing so, a multi-beam antenna can be constructed in which the size of the main reflecting mirror is smaller and the size in the antenna axis direction is smaller than that of conventional antennas. Furthermore, when communicating with two satellites on a geostationary orbit, there is no need to tilt the long axis of the main reflector as in conventional torus antennas, which has the effect of simplifying the front frame structure that supports the main reflector. Moreover, it can track two individual satellites independently. Furthermore, by modifying the main reflector, sub-reflector, and correction reflector, an antenna with higher efficiency and better cross-polarization characteristics than the conventional torus antenna can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a multi-beam antenna according to an embodiment of the present invention. FIG. 2 is a sectional view taken along a predetermined plane in FIG. 1. FIG. 3 is a diagram illustrating a case where the antenna of the present invention communicates with two satellites in a geosynchronous orbit. FIG. 4 is a schematic configuration diagram of an embodiment of a three-beam antenna according to the present invention. FIG. 5 is a schematic configuration diagram of a conventional multi-beam antenna. 6(a) and 6(b) are sectional views taken along predetermined planes of FIG. 5, respectively. FIG. 7 is a diagram illustrating a case where a conventional multi-beam antenna is used to communicate with two satellites in a geostationary orbit. ]...Main reflecting mirror, 2...Sub reflecting mirror, 31, 32°3
3... Correction reflector, 41, 42.43... Primary radiator. Figure 2 Figure 3

Claims (2)

[Claims] (1) In a multi-beam antenna consisting of a main reflector, a sub-reflector, a plurality of correction reflectors, and a plurality of primary radiators each facing at least one of the plurality of correction reflectors, the main reflector The mirror consists of a curved surface (torus curved surface) obtained by rotating one generating curve around one straight line, and the above-mentioned sub-reflector also consists of a curved surface (torus curved surface) obtained by rotating one generating curve around one straight line. ), in which a group of light rays emitted from the phase center corresponding to one of the plurality of primary radiators passes through the first correction reflector facing the primary radiator, the sub-reflector and the main reflector. After being reflected one after another by a reflecting mirror according to the law of reflection, they become parallel rays pointing in one direction, and the length measured along each ray from the phase center to a plane perpendicular to the parallel ray. The generating curve of the sub-reflector and the curved surface shape of the first correction reflector are determined so that the light rays emitted from the second phase center corresponding to the second correction reflector are equal. The second group of rays
After being successively reflected by the corrective reflector and the sub-reflector and main reflector defined above according to the law of reflection, the beam becomes a parallel ray pointing in the second direction, and along each ray there is a second parallel ray. The curved shape of the second correction reflecting mirror is determined so that the length measured from the phase center to one plane perpendicular to the second parallel ray is equal for each ray, and the other correction reflecting mirrors are also determined in the same manner as above. Similarly, a multi-beam antenna is characterized in that its curved shape is determined so as to produce parallel rays in different directions. (2) In the multi-beam antenna according to claim 1, a driving device is attached to each correction reflector, each primary radiator, or both, and each correction reflector, each primary radiator, or both are slightly moved. A multi-beam antenna characterized in that the directions of a plurality of beams radiated from a main reflecting mirror can be independently changed by changing the direction of each beam.