JPS5840905A - Multibeam antenna - Google Patents

Abstract

PURPOSE:To increase the side lobe level and to decrease the gain, by having an offset type mirror surface system to get rid of the blocking of a secondary reflector as well as a nonsecondary curved mirror surface to reduce the aberration within all faces. CONSTITUTION:A ray having a thetaS inclination to an axis Z within a horizontal face is made incident to a mirror surface curve M1M4. A mirror curves T1T5 of a secondary reflector 9 is decided under the conditions of a certain length of the optical path so that the ray goes toward the phase center F3 of a horn 1f after reflected at the curve T1T5. If the ray is made incident to the curve T1T5 from the phase center F2, a mirror curve N1N4 of a main reflector 10 can be decided. Then a mirror curve N1'N4' of the reflector 10 can be decided when the ray is made incident from the phase center F1. Furthermore a ray having a thetaS inclination is made incident to the curves N1N4 and N1'N4', and the mirror curve of the reflector 9 can be decided so as to have the convergence to the center F3 respectively. The above-mentioned procedures are successively repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a double-reflector type multi-beam antenna consisting of a plurality of feeding horns, a sub-reflector, and a main reflector.

As shown in Fig. 1, a conventional antenna of this type includes a plurality of feeding horns (1), a rotationally symmetrical hyperboloid mirror (2),
It consisted of a parabolic mirror (3). ζ Here, each mirror surface is rotationally symmetrical with respect to the mirror axis (4).

When the phase center of the feeding horn (1a) coincides with the focal point fo of the hyperboloid mirror (2), radio waves can be emitted in the direction of the mirror axis (center direction) without aberration, as shown by the 9-dotted line in Figure 1. Next, if the feeding horn (1b) is placed at a point fl away from +fo, the radiation direction will change as shown by the broken line in Figure 9, and the radiation direction will change, making it possible to form a multi-beam, but aberrations will occur and the side rope level will change. This has the disadvantage of causing performance deterioration such as increase in light intensity and decrease in gain.For this reason, a method was developed to obtain a special mirror surface shape with a 1iL focal point Fl*r using the Ray Lattice Method, as shown in Fig. 2. Here, both the sub-reflector (5) and the main reflector (6) are rotationally symmetrical with respect to the mirror axis (4) K, and the points I's and F* are symmetrical with respect to the mirror axis (4). .Therefore, if the radio waves from one point F1 can be radiated in the θS direction without aberration, the radio waves from one point F can be radiated in the θS direction without aberration.However, the sub-reflector (5) is in the direction in which the radio waves travel. This becomes an obstacle, causing an increase in the sidelobe level and a decrease in gain.It is known that this drawback can be eliminated by making the mirror surface an offset type, as shown in Figure 8.Here, an offset type sub-reflector ( 5
a).

The main reflecting mirror (6a) uses a part of the rotationally symmetrical mirror surface shown in Fig. 2, and the bowl surface metal used is selected so that the protrusion caused by the sub-reflecting mirror (5a) is eliminated. . In this antenna, when a plurality of feeding horns are provided in a plane perpendicular to the paper, multiple beams cannot be formed by selecting the mirror surface described above. Furthermore, in the case of multiple beams on one sheet of paper, the bifocals F, , P are symmetrical with respect to the mirror axis, which imposes restrictions on the placement of the feeding horn.

The present invention aims to eliminate this drawback.

and each has a bifocal point in a plane perpendicular to it.

It forms multi-beams in a wide angular range with a total of four focal points, and will be described in detail below with reference to the drawings.

FIG. 4 shows a mirror surface shape within the plane of the paper in an embodiment of the present invention. ()) is the mirror surface curve of the offset type sub-reflector, and (8) is the mirror surface curve of the offset type main reflector.

These mirror curves 471 (71, (8) are bifocal P,
It can be designed to have F. First, curve (7),
(8) Each point above is 81. M, and give these as initial values. Also, the radiation direction after passing through points 9, F, and 8, . . . , Ml is here parallel to the mirror axis (4). Therefore, M+Ps h is parallel to the mirror axis (4). Here, one point P1 is a point on the aperture plane of the main reflecting mirror (8). Next, the ray tilted by 6 with respect to the mirror axis (4) is the point M+
Inject it into the This aperture surface tilted by O1 and the above ray
Let the intersection point be 91. The reflection direction of r O7Qt Mt is determined using the already determined normal vector of the point pigeon. Point S on curve (7) from point Q+ to point F+ because of the condition of the optical path length from point Q+1 and because it is a point on the above-mentioned reflection direction,
is found. Next, start yay from point F, point s,
Let K go. Since the normal vector of point S is fixed, the reflection direction of e r O7F g 8 g can be determined.

The point M on the curve (8) is based on the condition that the point is on the reflection direction and the optical path length from the point F to the point P on the aperture surface.

is found. Hereafter, this process is repeated until the curve (73, (
8) can be determined. In this way, the rays from the bifocals F, F can form multiple beams without aberration in two dimensions. Note that here, the ray from point F is the mirror axis (4
), but it is not limited to this.

FIG. 2 shows a schematic configuration diagram of an embodiment of the present invention. (
ld), (le) are the bifocals P, , P in Fig. 4.

The feeding horn whose phase center is (if), (IG
) is a feeding horn whose phase center is bifocals F, , F on a plane perpendicular to the plane of the paper, (9) is an offset-type sub-reflector, and (9) is an offset-type main reflector. In addition.

17) and (8) are the mirror curves shown in FIG.

Here, the mirror surface (9), the asymmetric surface of H is the zfxf surface,
Coordinate system 0-xF with origin O as the center of the four focal points
Also define z. The mirror surfaces (9) and (11m) can be determined as follows, using the already determined mirror surface curves M, M, in the asymmetric surface as initial values.

First, a 7'Lray with an inclination of 2 axes and O5 in the horizontal plane is incident on the mirror curve MI O4. M, O4
Since the normal vector at is fixed, one reflection direction is determined. The mirror surface curve 'rt'r of the sub-reflector (9).

is reflected by the curves 'r, 'r, and then the horn (1
It is determined based on the condition that the optical path length is constant so that the optical path is directed toward the phase center F of f). Here, the mirror surface (91, (El is −
Since the beam is symmetrical, when a ray tilted by -01 is incident on the mirror surface MIM4, the phase center of the horn (IG) is F4.
can be focused on. Next, the mirror surface curves 'r, 'r of the sub-reflector (9) thus determined.

When a ray from the phase center F is incident on , the mirror surface curve N, N4 of the main reflecting mirror a is given by the condition that the optical path length to the aperture plane P1p4 is constant as shown in Fig. 4. In the case of incident light, the mirror surface curve N1'N of the main reflector α is determined based on the constant optical path length to the aperture surface QIQ4 in Fig. 4.
4F can be determined. Furthermore, the mirror curves NI N4 and N
, ' A ray tilted by 03 is incident on N4t, and the specular curve of the sub-reflector (9) can be determined so that each ray is focused on point F under the condition that the optical path length is constant. By repeating this process in sequence, the mirror surfaces of the sub-reflector (9) and the main reflector (111) can be constructed.Such mirror surface coordinates and the normal vector at that point can be found discretely. It is necessary to examine continuity. First, the two-dimensional case shown in Figure 4 will be explained using Figure 6. Let the discretely determined points be S, , S.

Let the normal vector at this point be nt I nl, respectively. When connecting these two points, it becomes a cubic curve based on the given conditions. In the case of FIG. 6(a), the surface is monotonous, but in the case of FIG. 6(6), there is an inflection curve, and the meaning of forming a mirror surface is lost. In the three-dimensional case of Fig. 6, when 54 adjacent points are connected by a curved surface, if the surface is curved so as to transmit waves, it can be used as a mirror surface.

After much consideration, we selected a curved surface system that would not cause waves.

Moreover, by arranging horns near the four focal points, it is possible to form multiple beams within the angular range shown by the shaded area in Fig. 7 while keeping aberrations small and without blocking the sub-reflector (9). .

In addition, in one or more cases, the sub-reflector was made to have a convex shape.

The invention may also be used in concave geometries.

As described above, according to the present invention, the mirror system is made into an offset type to eliminate blocking of the sub-reflector, and the mirror surface shape is changed to a non-dual shape that reduces aberrations not only in one plane but in all planes. The use of a curved surface has the advantage of obtaining a multi-beam with small increase in side lobe level and small decrease in gain.

[Brief explanation of the drawing]

Figures 1, 2, and 8 are schematic configuration diagrams of a conventional multi-beam antenna, Figure 4 is a diagram explaining an embodiment of the present invention, and Figure 2 is a schematic diagram of an embodiment of the present invention. , FIG. 6, and FIG. 7 are diagrams explaining one embodiment of the present invention. In FIG. 99, (
1) is a power supply horn, (9) is an offset type sub-reflector, and all is an offset type main reflector. Agent Makoto Kuzuno - @Figure 1 w2 Figure 3 @4 Figure 5

Claims (1)

[Claims] The yz plane is a horizontal plane and the zx plane is an asymmetrical plane, and the mirror curve MO of the main reflecting mirror on this asymmetrical plane. The mirror surface curve 8o of the sub-reflector is rotated around the y-axis by θa on the yz plane,
A curve that rotates the plane wave by -θa and focuses the plane wave from the friendly direction on the points Fl, F in the asymmetric plane, and a plane wave from the direction that rotates the zx plane by θS around the X axis to the mirror curve Mo is 12 Determine the mirror surface curve S1 of the sub-reflector to focus on the point F in the horizontal plane, which is a surface, and firstly calculate the point F,
, P. The mirror curves M, , M, of the main reflector are determined so that after this mirror curve 8sK onward wave from the main reflector is reflected by the main reflector, it becomes a plane wave in the θa and -θa directions, respectively.
For M, a mirror configuration is sequentially performed so that the plane wave tilted by θS is focused on point F. In addition, since both the sub-reflector and the main reflector are symmetrical with respect to the asymmetric plane, the plane wave of 1 θS, which is a symmetrical direction with respect to θ3 and the ZX plane, is focused at point F4 on the symmetry table, which is 9 points F. , these four points Fl + Fl e Fl
and a multi-beam antenna characterized in that a plurality of feeding horns are arranged near F4.