JPS5840906A - Multibeam antenna - Google Patents

Abstract

PURPOSE:To suppress a rise of the side lobe level without lowering the gain, by using a columnar surface reflector containing two special sections in place of a parabolic reflector and as a result reducing the aberration which is caused on the surface of an opening. CONSTITUTION:The axis (y) is set toward the bus bar of a columnar surface, and a face (yz) is set horizontal. The section curve of a columnar surface reflector 7 on a (zx) surface and the section curve of a secondary columnar surface reflector 6 are decided so that the planar wave sent from the (z) axis direction and the planar surface from the direction having a theta inclination to the axis (z) are focused at a focus F0 respectively. Then plural linear primary radiators are distributed at the areas near the focus F0. In such way, a multibeam having the reduced deterioration of performance is obtained between -theta and theta. Thus the multibeam can be radiated over a wide-angle range. At the same time, a rise of the side lobe level is suppressed without lowering the gain since the aberration caused on the surface of an opening.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a double-reflector multi-beam antenna consisting of a plurality of linear primary radiators, a cylindrical sub-reflector, and a cylindrical main reflector. .

As shown in FIGS. 1(a) and 1(b), a conventional antenna of this type is composed of a plurality of linear primary radiators (1) and a parabolic cylindrical reflector (2). Here, this reflector (2
There is a focal line P, on the mirror axis (3) of the mirror (3), and the cylindrical wave from this F is reflected by the mirror (movement) and becomes a plane wave in the direction of the mirror axis (3). Radiator (1a), (l
b), the cylindrical waves from the line wave sources F, , F, are reflected by this reflecting mirror (1) and are approximately θ, -〇, as shown by the broken lines and dotted lines in Figure 1. direction, but it does not turn into a complete trance. In other words, this reflector (
2) The wavefront is disordered on the aperture surface. This disturbance of the wavefront has the drawback of deteriorating performance, such as a decrease in gain and an increase in sidelobe level.

In order to eliminate such drawbacks, the present invention employs a double-reflecting mirror and changes the shape of its mirror surface, and will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of this invention.

(3) is a mirror axis, (4) is an offset columnar sub-reflector, and (5) is an offset columnar main reflector.

The direction of the generatrix of each reflecting mirror (4), (51) is perpendicular to the plane of the paper.The cross-sectional curves of these mirror surfaces are s, s, s, s.

and M, M, M, M, M4 bifocal F@ v F
It can be designed to have I. First, a plane wave along the direction of the mirror axis (3) is made incident. The wavefront is Qa QIQ-Q
Let it be a. Let the point Fe=Qo be a point on the mirror axis (3), and let the points on the cross-sectional curves of the sub-reflector (4) and the main reflector (5) on this axis be 8. ,M,. Here, 9 points Qo = Me and Ss - Fo are given as initial conditions. One point next? , is given as a parameter, and this point F,
A ray of light is incident on point S from . Since the normal direction at point S is the mirror axis (3) direction, the reflection direction at point S is 8. M, can be determined. The direction of reflection at this point Ml is assumed to be a direction tilted by 0 from the mirror axis (3). Let the wavefronts of this plane wave heading in the 0 direction be P, P, P, and P4. Given this wavefront as a parameter, 9 points M8 have an optical path length F, 8
0M, p1=can be determined from certain conditions. Next, a light beam QIM1 along the mirror axis (3) is made incident on this point M1.

The normal vector at point M is calculated using the above ray trajectory method F, 8.
Since it is determined at M+Pt, 1 reflection direction M,
8. can be determined. Point 8ta optical path length QIM18+ F
o = can be determined from certain conditions. Next, point F is made to enter point S1, and point M is obtained by the same external operation. Thereafter, the cross-sectional curve can be determined by repeating the same process. Therefore, the cylindrical waves from the focal lines F, , F, pass through the sub-reflector (4) and the main reflector (5), and then reach the mirror axis (3), respectively.
It becomes a plane wave in a direction tilted by θ with respect to this axis.

If multiple primary radiators, which are linear wave sources, are placed near the focal line F, , F obtained in this way, multiple linear wave sources will be placed in the vicinity of the mirror axis and in a direction tilted by an angle θ from the mirror axis. Plane waves can be directed.

However, the disturbance in the wavefront becomes smaller due to the bifocal line. Therefore, a multi-beam antenna with small gain reduction and low side lobe level has the same mirror axis as shown in Fig. 2, sub-reflector (6), and main reflector (7). ), (5), mirror surface (4), +51 symmetrical mirror surface with respect to a plane that includes the mirror axis (3) and is perpendicular to the plane of the paper. Also, the focal line F regarding this perpendicular plane
If the symmetrical straight line of , is F3, due to the symmetry of the mirror surface, F8 of and will also be a focal line that obtains a plane wave in the 10 direction. Here, outside the range between the focal line Fl + F4, the primary radiator does not interfere with the light beam reflected by the sub-reflector (6) and causes performance deterioration, so the -order radiator is placed in the range between Fl + F4. It must be placed within. Note that this failure is explained in the case of a transmitting antenna. This i;',
If multiple primary radiators are placed between t F4, -0
It is possible to obtain multi-beams with little performance deterioration between ~0 and emit multi-beams over a wider range of angles than in Fig. 2.

As described above, according to the present invention, in place of a parabolic cylindrical mirror, two
By using a cylindrical reflection mirror with a special cross-sectional shape, the aberration generated on the aperture surface is reduced, which has the advantage of obtaining a multi-beam antenna with small gain reduction and small increase in side lobe level.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional multi-beam antenna, FIG. 2 is a schematic diagram of an embodiment of the invention, and FIG. 8 is a schematic diagram of another embodiment of the invention. In the figure, (1) is a primary radiator that is a line wave source, (4) is an offset sub-reflector, (5) is an offset main reflector, and (6) is a plane-symmetric sub-reflector. (7) is a plane-symmetric principal reflection or mirror. Agent Shin Kuzuno - Figure 1 (6) θ @2 Figure 4

Claims (2)

[Claims] (1) In a multi-beam antenna consisting of a cylindrical main reflector, a cylindrical sub-reflector, and a plurality of linear primary radiators, the y-axis is the direction of the generating line of the cylindrical surface + the yz plane is the horizontal plane,
The cross-sectional curve of the main reflecting mirror and the cross-sectional curve of the sub-reflecting mirror in the NX plane are a plane wave from the Z-axis direction and a plane wave from a direction tilted by 0 to the two axes, respectively, at the focal point F. A multi-beam antenna characterized in that a plurality of the linear primary radiators are arranged in the vicinity of the focal line determined to be focused on Fl. (2) Regarding the cylindrical main reflecting mirror, the cylindrical sub-reflecting mirror, and the plurality of linear yz planes, a line symmetrical to the focal line F1 is the focal line F.
, In a plane-symmetric multi-beam antenna with additional symmetrical mirror surfaces of a main reflector and a sub-reflector with respect to the I FZ plane, a plurality of linear primary radiators are placed between the focal lines F, , F, A multi-beam antenna characterized by: