JP2560819B2 - Double reflector antenna - Google Patents

Description

TECHNICAL FIELD The present invention relates to a double reflector antenna, and more particularly to a double reflector antenna with improved sidelobe characteristics.

[Conventional technology]

One of the most commonly used double-reflector antennas with a rotationally symmetric main reflector, a sub-reflector placed on the antenna axis in front of this main reflector and a primary radiator on the antenna axis. As one example, there are a cassegrain antenna as shown in FIG. 7 and a mirror surface modified cassegrain antenna in which mirror surface modification is added.

FIG. 7 is a joint sectional view showing an example of a conventional double reflector antenna.

The cassegrain antenna has a mirror surface system composed of a main reflecting mirror 13 having a paraboloid of revolution and a sub reflecting mirror 14 having a hyperboloid of revolution.
The electromagnetic wave incident parallel to the antenna axis 11 is focused on the focal point 12 of the Cassegrain mirror surface system. The primary radiator 15 is arranged so that its phase center substantially coincides with the focal point 12. Note that θs
Is the angle from the focal point 12 to the edge of the sub-reflecting mirror 14 (viewing angle)
Is.

On the other hand, the mirror-modified cassegrain antenna is a mirror-system curved surface modified to improve the irradiation efficiency in consideration of the radiation characteristics of the primary radiator.

[Problems to be Solved by the Invention]

In a conventional double reflector antenna such as the cassegrain antenna described above, the spillover power from the subreflector, that is, the end of the subreflector is seen from the inner focus of the power radiated from the primary radiator toward the subreflector. Angle (angle of view) θ
There is a problem that the power radiated outside s deteriorates the side lobe characteristic of the antenna. In order to improve this, the electric field strength (edge level) at the end of the sub-reflector is reduced by increasing the sub-reflector to widen its angle of view θs or by sharpening the radiation characteristic of the primary radiator. It is sufficient to reduce the spillover power, but in this case, the edge level on the aperture surface of the main reflecting mirror is also lowered, so that the irradiation efficiency is lowered and the antenna gain is reduced.
Further, when the size of the sub-reflecting mirror is increased, the blocking area of the sub-reflecting mirror also increases, and thus the blocking efficiency also decreases.

As a method of improving this efficiency decrease, for example, a method of extending the sub-reflecting mirror and attaching the hem can be considered, but in this case the blocking area increases and the spillover power reflected by the hem increases at other angles. There was a problem of degrading the side lobe characteristic in the direction. There is also a method in which a shield plate is attached to the outer circumference of the sub-reflecting mirror and a radio wave absorber or the like is attached thereto, but this has a problem of increasing the antenna noise temperature in addition to increasing the blocking area.

[Means for solving the problem]

The double-reflecting mirror antenna of the present invention includes a primary radiator arranged on the antenna axis, a sub-reflecting mirror which is arranged so that its reflecting surface faces the primary radiator, and which is rotationally symmetric with respect to the antenna axis, and a reflecting surface. In a multi-reflector antenna having a sub-reflector and a main reflector that is rotationally symmetric with respect to the antenna axis and is arranged to face the sub-reflector, the primary radiator radiates at an angle larger than the angle at which the end of the sub-reflector is seen In order to reflect the electromagnetic wave from the primary radiator to the front of the reflecting surface of the main reflector,
Containing at least one conductor ring or an arc-shaped part thereof which is concentric with the sub-reflector and has an arbitrary width in the direction parallel to the antenna axis and is sufficiently thinner than the wavelength in the vertical direction on the outer periphery of the sub-reflector. Is.

[Action]

In the present invention, as an example, in the case of an antenna using circular polarization, the power reflected by the sub-reflecting mirror and the main reflecting mirror and radiated as a plane wave is reflected twice. Since the power that hits the ring is reflected once by the conductor ring, they are circularly polarized waves that are opposite to each other. Therefore, the power reflected by the conductor ring does not affect the side lobe characteristics of the main polarization and appears in the cross polarization characteristics.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a vertical sectional view showing an embodiment of a double reflector antenna according to the present invention.

In FIG. 1, 1 is an antenna axis, 2 is a focus, 3 and 4 are rotationally symmetric main and sub-reflecting mirrors, 5 is a primary radiator on the antenna axis 1, and 6 is a conductor ring.

The multi-reflecting mirror antenna has a mirror surface system composed of a main reflecting mirror 3 and a sub-reflecting mirror 4 which are rotationally symmetric with respect to the antenna axis 1. Electromagnetic waves incident in parallel to the antenna axis 1 are reflected by the mirror surface system.
It is reflected once and converges on the focal point 2. The primary radiator 5 is arranged at a position where its phase center substantially coincides with the focal point 2.
A conductor ring 6 having a width in the antenna axial direction is concentrically attached to the outer circumference of the sub-reflecting mirror 4.

Further, a conductor ring 6 which is concentric with the sub-reflecting mirror 4 and has an arbitrary width in the direction parallel to the antenna axis 1 and which is sufficiently thinner than the wavelength in the vertical direction is provided on the outer peripheral portion of the sub-reflecting mirror 4. It is also possible to have one or more arc-shaped portions of the conductor ring 6.

FIG. 2 is a front view of a double reflector antenna according to the present invention.

In FIG. 2, the same reference numerals as those in FIG. 1 indicate corresponding parts.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

The power radiated from the primary radiator 1 toward the sub-radiation mirror 4 inside the angle of view θs of the inner sub-reflection mirror 4 is reflected by the sub-reflection mirror 4 toward the main reflection mirror 3. Further, it is reflected by the main reflecting mirror 3 and emitted as a plane wave in the antenna axial direction. Here, in the case where the conductor ring 6 is not provided, the spillover power radiated outside the view angle θs of the sub-reflecting mirror 4 is one of the factors that deteriorate the side lobe characteristics of the antenna.

FIG. 3 is an explanatory diagram showing the radiation characteristic of the primary radiator 5, and the hatched portion (a) shows the spillover voltage. Note that (B) indicates the electric power reflected by the conductor ring 6.

FIG. 4 is an explanatory diagram showing the antenna side lobe characteristics,
The solid line I shows the case with a conductor ring, and the dotted line II shows the case without a conductor ring. In this case, side lobes due to the spillover power and those due to other factors are added in the vicinity of θs, and the level is significantly increased. The alternate long and short dash line (c) indicates the sidelobe standard 29-25logθdBi.

Next, the improvement effect when the conductor ring is provided will be described.

As an example, in the case of an antenna using circular polarization, the power reflected by the sub-reflection mirror 4 and the main reflection mirror 3 and radiated as a plane wave is reflected twice, but hits the inner conductor ring 6 of the spillover power. Since the electric power is reflected once by the conductor ring 6, they are circularly polarized waves which are reverse to each other. Therefore, the electric power reflected by the conductor ring 6 does not affect the side lobe characteristic of the main polarization and appears in the cross polarization characteristic. The side lobe characteristic of the main polarization is greatly improved as shown by the solid line I in FIG.

On the other hand, since the side lobe level due to factors other than spillover in the cross polarization side lobe characteristic is lower than that in the case of main polarization, it is easy to satisfy the standard even if the influence of spillover power is added.

FIG. 5 is a vertical sectional view showing a reference example of the present invention, and FIG. 6 is a vertical sectional view showing another embodiment of the present invention.

In FIGS. 5 and 6, the same reference numerals as those in FIG. 1 indicate corresponding parts.

Then, as shown in FIG. 5, a method for dispersing spillover power in a wide angle direction by providing projections or the like that cause irregular reflection on the reflecting surface of the conductor ring 6, and as shown in FIG. A method of giving an appropriate inclination to the ring 6 to shift the angle at which the side lobes are generated by the spillover power is also possible, and a sufficient effect can be obtained even in the case of linear polarization.

Further, in the present invention, since the thickness of the conductor ring in the direction perpendicular to the antenna axis can be made sufficiently thin, there is an advantage that the blocking area on the opening surface hardly increases. Further, since the spillover power is directed to the front of the antenna, that is, to the sky direction where it is less susceptible to ground noise even after being reflected by the conductor ring, it is considered that the antenna noise temperature hardly increases.

The same effects as described above can be expected by using a plurality of conductor rings or by using a part of a partially arcuate conductor ring as necessary.

〔The invention's effect〕

As described above, the present invention reduces the deterioration of the side lobe characteristics due to the spillover power from the sub-reflecting mirror by the simple configuration in which one or more conductor rings or a part of the arc shape thereof is attached to the outer periphery of the sub-reflecting mirror. There is an advantage that it is possible to do so, and it does not cause other characteristic deterioration such as increase of blocking and increase of noise temperature. Therefore, when the present invention is used, the edge level of the sub-reflecting mirror does not need to be reduced as compared with the case where the conductor ring is not provided, so that there is an effect that the gain of the antenna can be improved. There is also an economic effect that the size of the sub-reflector or the primary radiator can be reduced.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a double reflector antenna according to the present invention, FIG. 2 is a front view showing an embodiment of a double reflector antenna according to the present invention, and FIG. 3 is a radiation characteristic of a primary radiator. FIG. 4 is an explanatory view showing an example, FIG. 4 is an explanatory view showing an example of antenna side lobe characteristics, FIG. 5 is a longitudinal sectional view showing a reference example of the present invention, and FIG. 6 is a vertical section showing another embodiment of the present invention. FIG. 7 is a vertical sectional view showing an example of a conventional double-reflecting mirror antenna. 1 ... Antenna axis, 2 ... Focus, 3 ... Main reflector, 4 ...
… Sub-reflector, 5 …… Primary radiator, 6 …… Conductor ring.

Claims (1)

(57) [Claims] 1. A primary radiator disposed on an antenna axis,
A sub-reflecting mirror that is rotationally symmetric with respect to the antenna axis and has a reflecting surface that faces the primary radiator, and a main reflecting mirror that is rotationally symmetric with respect to the antenna axis that has a reflecting surface that faces the sub-reflecting mirror. In the multi-reflecting mirror antenna having, in order to reflect the electromagnetic wave from the primary radiator, which is radiated from the primary radiator at an angle larger than the angle looking into the end of the sub-reflecting mirror, to the front of the reflecting surface of the main reflecting mirror, On the outer periphery of the sub-reflector, one or more conductor rings or arc-shaped parts of which are concentric with the sub-reflector and have an arbitrary width in the direction parallel to the antenna axis and are sufficiently thinner than the wavelength in the vertical direction. Is a double reflector antenna.