JP2011087148A - Choke member, and waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such the problem that axial symmetry deteriorates by diffraction caused at a projected part at the center of a subreflector even when directivity of a feed waveguide is axially symmetrical in the conventional ADE antenna. <P>SOLUTION: The feed waveguide is provided with a choke, and the position and size of the choke are adjusted to control radiation directivity of the feed waveguide. Specifically, the diffraction at the apex of the subreflector is suppressed to obtain a feed antenna of the ADE antenna having the axial symmetrical directivity by suppressing a radiation level in the apex direction at the center of the subreflector by control of the directivity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to an antenna device including a plurality of reflectors, which is used when a good directivity characteristic is required in a satellite communication device, a radar device, or the like.

As a large antenna, a Cassegrain antenna as shown in FIG. 1 is most widely used at present. This antenna achieves gain improvement by using two reflecting mirrors. The radio wave applied to the sub-reflecting mirror 105 from the feeding waveguide 103 installed at the apex of the main reflecting mirror 101 is reflected by the sub-reflecting mirror and applied to the main reflecting mirror.

Then, it is further reflected by the main reflector and radiates out. The point here is that the reflecting surface of the sub-reflecting mirror is a curved surface. By designing this shape well, the illuminance distribution of radio waves radiated in parallel from the antenna can be made constant and the gain can be maximized.

FIG. 2 is a further simplification of FIG. In order to solve the problems caused by the shape of the sub-reflecting mirror 105 in FIG. 2, an antenna having an ADE (Axially) with the center portion close to the main reflecting mirror in the shape of the sub-reflecting mirror as shown by 301 in FIG. It is called a Displaced Ellipse antenna (Non-Patent Document 1).

The problem of the shape of the sub-reflecting mirror 105 is shown in FIG. That is, when the radio wave radiated from the feeding waveguide is reflected by the central portion of the sub-reflecting mirror 105, the component returns to the feeding waveguide 103 as indicated by 401, and the reflection characteristics deteriorate. is there.

However, when the sub-reflecting mirror is shaped as shown by 301 in FIG. 5, the component returning to the feed waveguide 103 is remarkably reduced with respect to the reflected wave from the sub-reflecting mirror, so that deterioration of the reflection characteristics can be suppressed.

Of the radio waves from the power supply waveguide 103 as shown by 403 in FIG. 4, the radiated waves that are not reflected by the sub-reflecting mirror 105 and are radiated as they are into the space are called spillover. Due to the spillover, the gain of the antenna is lowered and the side lobe is deteriorated.

Generally, in order to reduce spillover, the distance between the feeding waveguide 103 and the sub-reflecting mirror 105 is shortened. However, in the conventional Cassegrain antenna, the radio wave returning to the feeding waveguide 103 by shortening the distance. (401) increases.

In other words, in the Cassegrain antenna, when the distance between the feeding waveguide and the sub-reflecting mirror is shortened in order to reduce spillover, the reflected wave from the sub-reflecting mirror returns to the feeding waveguide and deteriorates the characteristics. The ADE antenna is effective in solving this problem.

Aluizio Prata, Jr., Fernando J.S.Moreira, and Luis R. Amaro "Displaced-Axis-EllipseReflector Antenna for Spacecraft Communications" IEEE Microwave and Optoelectronics Conference, 2003.

However, the sub reflector of the ADE antenna is a spheroidal surface as described above, and has a vertex at the center of the sub reflector. Since there is a vertex in the front direction of the feed waveguide, the influence of diffraction at the vertex cannot be ignored.

On the other hand, in the Cassegrain antenna, it is a well-known method to set the diameter of the feeding waveguide to about 1λ in order to obtain axial directivity (symmetric with respect to the Z axis in FIG. 3). However, even in this case, the ADE antenna still has a problem that the axial symmetry of the feeding antenna is broken due to the influence of diffraction by the central part in the reflection of the sub-reflecting mirror.

In other words, even if the diameter of the feed waveguide is about 1λ and the directivity of the feed waveguide is axially symmetric, the axial symmetry deteriorates due to the influence of diffraction when reflected by the sub-reflecting mirror.

An example in which the axial symmetry is broken by the sub reflector of the ADE antenna is shown in FIGS. 6 and 7 together with the simulation results. FIG. 6 shows the directivity of the feed waveguide, and FIG. 7 shows the directivity when the feed waveguide and the sub-reflector are used together. In FIG. 7, as a criterion for determining that this is not axially symmetric, the shape of the electric field surface (E-PLANE) and the magnetic field surface (H-PLANE) are not similar.

In addition, the large dBi value of the 45-degree cross-polarized wave in FIG. 7 is also a criterion for determining whether or not the directivity axial symmetry is good.

As described above, the present invention implements the following means in order to reduce the diffraction caused by the convex portion at the center of the sub-reflecting mirror.

In the ADE antenna, a choke member is disposed around the opening portion of the waveguide of the aperture antenna including the main reflection mirror and the sub-reflection mirror, and makes the directivity of the waveguide concave.

According to the present invention, in the ADE antenna, the aperture antenna having a main reflector and a sub-reflector has a choke member that makes the directivity of the waveguide concave, and is disposed at a feeding point of the aperture antenna, and The waveguide has the choke member disposed around the opening.

By using such a choke material and a waveguide, the radio wave applied to the convex portion at the center of the sub-reflecting mirror is reduced, and the diffracted wave at the convex portion can be suppressed.

According to the present invention, since the directivity of the feed waveguide can be controlled by the position and size of the choke, the radiation level in the front direction of the feed waveguide can be controlled while maintaining the axial symmetry. It is possible to lower.

By lowering the radiation level in the front direction, the influence of the diffracted wave at the apex at the center of the sub-reflecting mirror can be suppressed. Further, the cross polarization level is suppressed by improving the axial symmetry. Furthermore, the side lobe level of E-PLANE can be suppressed without deteriorating the aperture efficiency of the antenna.

General Cassegrain antenna Simplified Cassegrain antenna Simplified ADE antenna State of reflected wave of Cassegrain antenna State of reflected wave of ADE antenna Directivity of feeding waveguide Directivity combining a feed waveguide and a sub-reflector Example 1 of antenna configuration Example 2 of antenna configuration Front directivity is recessed Aperture distribution with concave front directivity and waveguide shape Directivity of a choke-fed waveguide. Directivity combining a choke-fed waveguide and a sub-reflector Results of sidelobe level suppression

A preferred embodiment of the present invention will be described below with reference to the drawings.

In the present invention, a choke is provided in a feed waveguide in order to improve the axial symmetry of the feed antenna with respect to an antenna having a sub-reflector whose center is convex, such as an ADE antenna. An example of the appearance is as shown in FIG.

As shown in FIG. 8, a feeding waveguide 103 is installed at the center of the main reflecting mirror 101, and radio waves radiated from the feeding waveguide are reflected by the sub-reflecting mirror 301 and reflected again by the main reflecting mirror. , Released into space.

The feeding waveguide includes a choke 1001 around it, and suppresses diffraction of radio waves by the apex of the convex portion of the sub-reflecting mirror 301. The sub-reflector is a plurality of struts 1003 installed on the main reflector.
Will support. In addition, the installation method of a strut is not limited to the form of FIG.

Further, when attention is paid to the feeding waveguide and the sub-reflecting mirror, a configuration as shown in FIG. 9 which is an installation method not using the strut 1003 is also conceivable. In this structure, a sub-reflector is fixed by a dielectric 1101 instead of the strut. A choke 1001 is provided around the feed waveguide 103, and the sub-reflector 301, the choke and the feed waveguide are connected to an arbitrary dielectric. 1101 is fixed.

As described above, the present invention does not limit the method of supporting and installing the main reflecting mirror, the sub-reflecting mirror, and the feeding waveguide.

In the ADE antenna, the reason why the axial symmetry of the directivity of the feeding waveguide deteriorates is that the reflection of the radio wave near the center is indefinite due to the convex shape of the center of the sub-reflecting mirror. is there. Therefore, as a solution, regarding the directivity of the feeding waveguide, the central direction seen from the front is made concave, the radio wave irradiated to the convex part of the central part of the sub-reflecting mirror is reduced, and indefinite reflection is caused. It is desirable to remove.

Thus, the directivity of the feed waveguide is desired to be concave as shown in FIG. In the case of having a concave directivity, it is well known that the aperture distribution has a shape as shown in FIG. 11A, and the shape of the feed waveguide that realizes this is as shown in FIG. 11B. Therefore, in the present invention, the choke 1001 is installed in FIG. 11B.

Then, by adjusting the position, depth, or width of the choke, the shape of the aperture distribution in FIG. 11A changes, so that the choke in FIG. 11B has a directivity as shown in FIG. 1001 should be adjusted.

The horizontal arrow in FIG. 11B represents the phase direction, and it can be seen that the phase of the E-PLANE is inverted between the feeding waveguide portion and the choke portion by adjusting the choke.

FIG. 12 shows the directivity of the feeding waveguide provided with a choke, and FIG. 13 shows the ADE antenna. Therefore, the choke when the sub-reflecting mirror having a convex bulge is installed at the center is shown. This shows the directivity of the combined feed waveguide and sub-reflector.

FIG. 7 shows the directivity combining the feeding waveguide without the choke and the sub-reflecting mirror. However, by providing the choke, E-PLANE and H in FIG. The waveform on the -PLANE graph is very similar, and the 45-degree cross-polarized wave is also small, indicating that the axial symmetry is remarkably improved.

In particular, when compared with FIG. 7, the axial symmetry is improved in the range from 90 degrees to 180 degrees, which is the direction radiated to the main reflecting mirror.

If the axial symmetry is poor, a difference occurs between the first side lobe levels of E-PLANE and H-PLANE, leading to an increase in one of the first side lobe levels. FIG. 14 shows a state in which the first side lobe level of E-PLANE is suppressed by improving the axial symmetry.

As described above, according to the present invention, in an aperture antenna such as an ADE antenna in which a diffraction component is mixed in a reflected wave by a sub-reflecting mirror, a choke is installed in a feeding waveguide in order to improve its axial symmetry. As an effect, the influence of diffraction due to the vertex of the sub-reflecting mirror was removed, and the deterioration of axial symmetry could be prevented. In addition, the first side lobe level of E-PLANE could be suppressed.

However, as described above, in the present invention, the position, width, and length of the choke or the adjustment method such as the coupling method with the feeding waveguide is not limited.

In the present invention, the method of installing the sub-reflecting mirror is arbitrary and is not limited.

101: Main reflector 103: Feeding waveguide,
105 ... General sub-reflector,
301 ... Sub reflector of ADE antenna,
401 ... Radiation wave returning to feeding waveguide, 403 ... Spillover,
1001 ... Chalk, 1003 ... Strut,
1101. Dielectric

Claims (2)

In the ADE antenna, a choke member that is disposed around the opening portion of the waveguide of the aperture antenna including the main reflecting mirror and the sub-reflecting mirror and makes the directivity of the waveguide concave. In an ADE antenna, an aperture antenna having a main reflecting mirror and a sub-reflecting mirror has a choke member that makes the directivity of the waveguide concave, and is disposed at a feeding point of the aperture antenna and around the opening. A waveguide in which the choke member is disposed.