JP2982185B2 - Aperture antenna - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aperture antenna having a reflector, and more particularly to an aperture antenna having improved directivity.

[Conventional technology]

Generally, in an aperture antenna having a reflector, the aperture illumination of the reflector is made as uniform as possible in order to improve the gain. However, in such an aperture distribution close to uniform illumination, the illumination level at the edge of the aperture becomes high and the spillover of the reflector becomes large, deteriorating the antenna directivity in this direction, and causing interference with other communication systems. Easier to do.

For example, FIG. 3 shows a conventional prime focus type antenna, in which 1 is a main reflector and 2 is a primary radiator. In this antenna, an outer part E1 of the radio wave emitted from the primary radiator 2 is separated from the main reflecting mirror 1 and becomes a spillover of the main reflecting mirror.

FIG. 4 shows a conventional double reflector antenna, here a Cassegrain antenna, in which 1 is a main reflector,
2 is a primary radiator and 3 is a sub-reflector. In this case,
There is a radio wave E1 emitted from the primary radiator 2 and reflected by the sub-reflector 3 to be a main reflector spillover, and a radio wave E3 emitted from the primary radiator 2 to be a sub-reflector spillover.

Therefore, in this type of conventional reflector antenna, as shown in FIG. 5, a baffle plate 4 or the like is attached to the opening end of the main reflector 1, or the main and sub reflectors are omitted (not shown). The mirror surface is modified to control the aperture distribution.

[Problems to be solved by the invention]

However, in an antenna provided with a baffle plate or the like as shown in FIG. 5, the baffle plate itself may reflect radio waves and increase the side lobe level in the reflection direction. For this reason, an absorption pair is attached to the reflection surface of the baffle plate, but this absorber has problems in that it is expensive, increases in weight, and further has weather resistance.

Further, in the double reflector antenna, there is a problem that the aperture distribution cannot be sufficiently controlled, particularly in a small aperture antenna, and that the secondary reflector spillover cannot be avoided.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an aperture antenna which prevents the above mentioned spillover of the reflector from adversely affecting the directivity of the antenna.

[Means for solving the problem]

In the aperture antenna of the present invention, two blocking plates for reflecting radio waves are arranged around a reflecting mirror, and these blocking plates are directed in the same direction and reflect the radio waves reflected by each blocking plate. The phase is shifted by an odd multiple of 1/2 wavelength.

These blocking plates are arranged around the main reflector and / or around the sub-reflector, respectively.

[Action]

In this configuration, the radio wave that becomes the spillover of the reflector is reflected by each blocking plate, and at this time, the reflected radio waves of the respective blocking plates are in opposite phases to each other and cancel each other, thereby eliminating the influence on the directivity of the reflecting mirror.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a first embodiment in which the present invention is applied to a prime focus parabolic antenna. In the figure, 1 is a main reflecting mirror and 2 is a primary radiator. Here, two annular blocking plates 5 and 6 are arranged concentrically around the main reflecting mirror 1. These blocking plates 5 and 6 are configured as reflecting mirrors for reflecting radio waves in the same direction, and
The distance between the primary radiator 2 and the primary radiator 2 is shifted by an odd multiple of 1/4 wavelength of the frequency of the radio wave used by the antenna.
Thus, the radio waves reflected by the respective blocking plates 5 and 6 are configured to be out of phase by an odd multiple of 1/2 wavelength.

According to this configuration, of the radio waves emitted from the primary radiator 2, the radio waves E1 and E2 that deviate from the main reflecting mirror 1 and spill over from the main reflecting mirror 1 are reflected by the blocking plates 5 and 6. The radio waves E1 'and E2' reflected by the blocking plates 5 and 6 are directed in the same direction, and the phases of the reflected radio waves are shifted by half a wavelength. And the amplitudes are approximately equal, so that most of them are canceled out.

As a result, the directivity of the antenna due to the spillover of the main reflector is not adversely affected, and a baffle plate or the like is not required, so that weight reduction and cost reduction can be realized.

FIG. 2 is a cross-sectional view of a second embodiment in which the present invention is applied to a double reflector example antenna, here a Cassegrain antenna.
In the figure, 1 is a main reflecting mirror, 2 is a primary radiator, and 3 is a sub-reflecting mirror. In addition, the same blocking plates 5 and 6 as in the first embodiment are provided around the main reflecting mirror 1 and two blocking plates 7 and 8 are further provided around the sub-reflecting mirror 3. . These blocking plates 7, 8 also have the same function as the blocking plates 5, 6.

According to this configuration, of the radio waves emitted from the primary radiator 2, the radio waves E3 and E4 serving as the spillover of the sub-reflector 3 are reflected by the blocking plates 7 and 8, respectively. The reflected radio waves E3 'and E4' are directed in the same direction as each other, and the reflected radio waves are out of phase with each other because their phases are shifted by 1/2 wavelength, and their amplitudes are also substantially equal, so that most of them are canceled out. Will be.

Further, there is a spillover of the main reflecting mirror caused by the fact that the sub-reflecting mirror 2 is finite with respect to the attenuation of the used frequency. , 6.

In this embodiment, it is possible to prevent the directivity from being adversely affected by both the sub-reflector spillover and the main reflector spillover.

Although the above description has been made with respect to the transmitting antenna, it has been shown that the interference given to other communication systems can be greatly reduced. However, the reciprocity of the antenna has the same effect with the receiving antenna. This has the effect of greatly reducing the interference caused by the system. Further, if the blocking plate of the present invention is mounted around the primary radiator, the same effect can be exhibited with a smaller structure.

〔The invention's effect〕

As described above, according to the present invention, the radio wave which becomes the spillover of the reflector is reflected by each blocking plate, and each reflected radio wave is canceled out as an opposite phase, so that the adverse effect on the directivity of the antenna is prevented, and the antenna wide angle directivity is prevented. This has the effect of improving the performance. Further, there is an effect that a baffle plate or the like is not required, and downsizing and cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a first embodiment of the present invention, FIG. 2 is a cross-sectional view of a second embodiment of the present invention, and FIGS. 3 and 4 are cross-sectional views for explaining problems in a conventional antenna. Figure,
FIG. 5 is a sectional view showing a conventional improved antenna. 1 ... Main reflector, 2 ... Primary radiator, 3 ... Sub reflector
4 ... Baffle plate, 5,6,7,8 ... Blocking plate.

Claims (2)

(57) [Claims] 1. A pair of blocking plates for reflecting radio waves are disposed around a reflecting mirror. The blocking plates are directed in the same direction, and the phase of the radio waves reflected by each blocking plate is one. /
An aperture antenna characterized in that it is shifted by an odd multiple of two wavelengths. 2. The aperture antenna according to claim 1, wherein two blocking plates are provided around the main reflector and around the sub-reflector, respectively.