JPS63116504A - Antenna system - Google Patents

Abstract

PURPOSE:To suppress the reduction of a gain and to improve a side rope characteristic by making the aperture distribution of a main reflection mirror into a non-rotation symmetry by mirror-correcting the main reflection mirror and a sub-reflection mirror. CONSTITUTION:When an orthogonal coordinate system x-y with a center 0 of an aperture as an original point is determined, an electric field radiated from a primary radiator 1 is reflected by a mirror surface system, and thereafter, the main reflection mirror 5 and a sub-reflection mirror 4 are mirror- corrected so that the amplitude distribution when the field arrives at the aperture surface 6 of the main reflection mirror 5 can be different in the surface of x=0 and in the surface y=0. Consequently, when the surface of x=0 and a uniform distribution and the surface of y=0 is a taper distribution, the uniform distribution contributes to the improvement of the gain and the low side rope in the surface of y=0. The side rope characteristic in the surface of x=0 is deteriorated more than the case of the rotation symmetrical distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reflector antenna used in terrestrial microwave communication and satellite communication.

[Conventional technology]

As shown in FIG. 5, the conventional antenna device has a horn 1. which is a primary radiator. Secondary reflector 2. and a main reflecting mirror 3. The radio waves emitted from the horn 1 are transmitted to the sub-reflector 2, as shown by the broken line in the figure. The light is reflected by the main reflecting mirror 3 and radiated into space. At this time, the relationship between the electric field distribution on the aperture surface of the bone 1 and the electric field distribution on the aperture surface 2 of the main reflecting mirror 3 is shown in FIG. Here, if the bone 1 is a corrugated bone or a multi-mode horn, the isoelectric field lines on the aperture surface will be rotationally symmetrical. In order to realize this rotationally symmetrical distribution in the aperture distribution of the main reflecting mirror 3, it is necessary to adjust the inclination of the bone 1 and the secondary reflecting mirror 2, which is a quadratic curved surface. It is only necessary to satisfy a certain relationship with the specular constant of the main reflecting mirror 3, that is, a so-called cross-polarization cancellation condition. In addition, the mirror axis of the parabola that is the main reflecting mirror 3 is 2 axes, and the aperture plane is x
The center of the y-plane and aperture plane is set to point 0, and the yz-plane is a mirror asymmetric surface.

A radiation pattern due to the rotationally symmetrical aperture distribution on the main reflecting mirror 3 is shown in FIG. The horizontal axis is the observation angle measured from the Z axis, and the vertical axis shows the decibel value of the radiation level. The broken line in the figure shows the envelope pattern of the sidelobe level. In order to change this sidelobe level, the density of the rotationally symmetric distribution of the main reflecting mirror 3 shown in FIG. 6 can be controlled. This density can be controlled by sub-reflector 2. This is made possible by changing the mirror surface shape of the main reflecting mirror 3 from a quadratic curved surface to a modified curved surface. In this mirror surface modification, the modified mirror surface coordinates are strictly determined for an axially symmetrical Cassegrain antenna, but approximate solutions have been studied in various fields for Cassegrain antennas of Offsera 1~ type as shown in Figure 5. There is.

Generally, in order to reduce the sidelobe level, it is sufficient to make the equipotential field lines on the main reflecting mirror 3 in FIG. 6 concentrate at the aperture center O. Therefore, the amplitude level is high at the center and low at the periphery, resulting in a tapered aperture distribution.

[Problem that the invention seeks to solve]

However, in the case of this tapered distribution, although the Zydrobe characteristics are improved, since the power in the peripheral portion is small, the aperture becomes substantially smaller, resulting in a problem that the gain decreases.

The present invention was made to solve this problem, and aims to improve not only the zylobe characteristics but also the gain.

[Means for solving problems]

The antenna device according to the present invention makes the aperture distribution of the main reflecting mirror non-rotationally symmetric by mirror-finishing the main reflecting mirror and the sub-reflecting mirror, thereby suppressing gain reduction and improving site lobe characteristics. The mirror surface correction is as follows. In other words, when we determine an orthogonal coordinate system x-y with the origin at the center point O of the aperture on the aperture surface of the main reflecting mirror, the electric field radiated from the primary radiator is reflected by the mirror system, and then Mirror surface modification is performed so that the amplitude distribution when reaching the aperture surface of the reflecting mirror is different in the plane of x=Q and in the plane of y=o.

[Effect]

Therefore, if the x=0 plane has a uniform distribution and the y-0 plane has a tapered distribution, the --like distribution contributes to improving the gain and reducing sidelobes in the y-o plane. Note that x=0
The zydlobe characteristics in the plane of are worse than in the case of rotationally symmetric distribution.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is a horn, 4 is a mirror-modified sub-reflector,
5 is a mirror-modified main reflecting mirror, and 6 is an aperture surface. The operation of this antenna will be explained here again in the case of transmission. It is assumed that a spherical wave is radiated from the phase center F of the horn 1, and (θ, φ) is shown in the figure in a polar coordinate system with the central axis of the horn 1 as the polar axis. Radio waves with constant θ and varying φ are sent to the sub-reflector 4. An incident 1 on the specular curve shown by the broken line of the main reflecting mirror 5
It is assumed that the light is reflected and intersects with the aperture surface 6 on a curve shown by a broken line. FIG. 2 shows how this group of circles with constant θ is mapped on the aperture surface 6, and here an asymmetric aperture distribution is created. FIG. 3 shows the radiation pattern when the asymmetric distribution is made in this way. Here, this asymmetric distribution is made uniform in the zy plane, and tapered in the zx plane to obtain the radiation pattern shown in FIG.

The sidelobe level envelope of Figure 7 is also shown in the figure. Therefore, the zy plane has a rotationally symmetric distribution (the seventh
In the case shown in the figure), the relative rope level has an upper limit, but it has decreased in the zx plane, which is an improvement. In the case of terrestrial microwave communication, the sidelobe level in the horizontal plane determines the amount of radio wave interference, so this plane may be made to correspond to the zx plane.

Incidentally, mirror surface modification methods for obtaining such an asymmetric aperture distribution have been reported in various fields, and examples thereof are as follows.

Karigome, Kakoshima: “Design of an offset double-reflector antenna that improves both sidelobe level and cross-polarization discrimination characteristics”, IEICE Antenna Propagation Study Group Technical Report AP
8147 (July 1984).

In the above embodiment, a double-reflecting mirror type is used, but a three-mirror type as shown in FIG. 4 may be used.

6- Here, 7 is an auxiliary reflecting mirror having a quadratic curved surface, and the other parts are the same as in FIG. If this auxiliary reflecting mirror is used, the bone 1 can be arranged perpendicular to the ground, and there is an advantage that there is no need to use a curved waveguide for the waveguide following the horn 1. In this way, a type in which the auxiliary reflecting mirror 7 is provided between the horn 1 and the auxiliary reflecting mirror 4 can also be used.

〔Effect of the invention〕

As described above, according to the present invention, the mirror surface of the main reflecting mirror and the sub-reflecting mirror is modified to give an asymmetric aperture distribution, so that the side rope level can be lowered and radio wave interference can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the invention, FIGS. 2 and 3 are diagrams for explaining the invention, FIG. 4 is a schematic diagram of another embodiment of the invention, and FIG. is a schematic configuration diagram showing a conventional antenna device, and FIGS. 6 and 7 are diagrams for explaining the conventional antenna device. In addition, 1 is a pawn, 2 is a sub-reflector which is a quadratic curved surface, 3 is a main reflector which is a quadratic curved surface, 4 is a sub-reflector with mirror surface modification,
5 is a mirror-modified main reflecting mirror, 6 is an aperture surface, and 7 is an auxiliary reflecting mirror. Agent Masuo Oiwa (2 idiots) Figure 2 Figure 3 (a) ZY side Figure 6 C) Figure 7

Claims (3)

[Claims] (1) In an antenna device consisting of a mirror system including a main reflector and a sub-reflector and a primary radiator, a rectangular coordinate system x-y with the origin at the center point 0 of the aperture is created on the aperture surface of the main reflector. When determined, the amplitude distribution when the electric field emitted from the primary radiator reaches the aperture surface of the main reflecting mirror after being reflected by the mirror system is within the plane of x=0 and the plane of y=0. An antenna device characterized in that a main reflecting mirror and a sub-reflecting mirror are mirror-finished so that they differ from each other. (2) The amplitude distribution in the plane of x=0 is approximately uniform distribution,
2. The antenna device according to claim 1, wherein the amplitude distribution in the plane of y=0 is a low sidelobe type distribution. (3) Claim 1, characterized in that a plurality of quadratic curved mirrors are provided between the sub-reflector and the primary radiator.
Antenna device as described in section.