JPH04253404A - Double reflector for antenna - Google Patents

Abstract

PURPOSE: To form an antenna reflector for reflecting two mutually crossing linearly polarized radio waves with the same frequency at low manufacturing cost and with satisfactory stability. CONSTITUTION: This double reflector 24 includes one front reflector 26 equipped with a grid for reflecting a linearly polarized radio wave, one rear reflector 28 which can reflect all radio radiation unrelated with the bias of the radio wave, and attaching device 30 which can hold the front reflector with a constant distance from the rear reflector. The front reflector 26 is at least partially overlapped on the rear part reflector 28. Also, one filtering device is arranged between the front reflector and the rear reflector. The rear reflector is constituted of two outer branches and a honeycomb structure between them, and at least one outer branch is made of conductive materials.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a double reflector with a grid for using a plurality of pairs of radio waves of the same frequency, the two radio waves of each pair having polarizations orthogonal to each other. It involves one structure containing two antenna reflectors.

0002

BACKGROUND OF THE INVENTION There are antenna systems that allow the reuse of the same frequency using multiple sources and reflectors that are perpendicularly polarized to each other. Such systems are widely used in satellite applications. At a given frequency, two mutually perpendicularly polarized radio waves are generated by separate, uncoupled sources. Therefore, even with a small and lightweight antenna system, its transmission capacity is doubled.

French Patent Application No. 2 571 898 filed on October 15, 1985 and French Patent Application No. 2 5 filed on November 12, 1986.
No. 90 081 describes an example of this type of frequency reuse antenna.

Generally, such known devices have two reflectors in the form of parabolic dishes. FIG. 1 shows one embodiment of such a device according to the prior art, which is also similar to the antenna reflector described in patent document GB-A-2 125 633.

Two parabolic reflectors 10, 12 are superimposed. A first reflector 10 overlies a second reflector.

[0006] Each plate of reflectors 10, 12 has a Kevl
Sandwiched between two outer panels made of ar.
It can be constructed by a honeycomb core formed of Kevlar fabric (Kevlar is E.I.
．． (a registered trademark of DuPont).

[0007] On the inside of the pan, a grid 14, 16 is mounted on an overlying skin. These grids are made of parallel conductors brought close together and oriented such that each of the reflectors reflects two waves polarized perpendicularly to each other.

The two reflectors 10 and 12 have two Kev
1 Kevla sandwiched between lar skins
It is held together by fixing means comprising an outer annular structure 18, such as a honeycomb core, and support ribs 20 formed in the same manner as this structure.

Kevlar is chosen because of its transparency to radio waves. However, Kevlar is an expensive material and difficult to process. Therefore, a long and difficult process is necessary to obtain a honeycomb structure.

On the one hand, such known devices have two reflectors with separate grids. However, the fabrication of these grids requires a very delicate machining process.

[0011] The document FR-A-1 141 476
An antenna system with two return reflectors, front and rear, is also described, the rear reflector made of a single steel plate having no selective properties with respect to the polarization direction of the reflected radiation. . However, this document does not describe any device for filtering between said two reflectors in order to remove any residual components of the polarized radiation due to the first reflector.

0012

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate these drawbacks, namely to reduce manufacturing costs by reducing the need for Kevler and to The second without
and to simplify the fabrication of frequency reusing reflector systems.

[0013]

SUMMARY OF THE INVENTION To achieve this object, the present invention provides a single front panel with a grid oriented to reflect linearly polarized radio waves along a particular polarization direction. It is proposed to use a partial reflector and one rear reflector capable of reflecting all radio waves regardless of their polarization.

[0014] The rear reflector therefore requires only one continuous reflective surface without any grid; this surface is
Made of cheaper materials than Kevler, Kevler
have better mechanical properties (especially better stiffness) than

More specifically, the invention comprises: - a front reflector made of a shell supporting a conductive grid arranged to reflect linearly polarized radio radiation; - a polarization of the radio waves; - one rear reflector capable of reflecting all radio radiation regardless of the radio wave radiation; and - a filtering device arranged between said front reflector and said rear reflector.

Other features and advantages of the invention will be more easily understood from the following description, given by way of non-limiting example only and with reference to the accompanying drawings, in which: FIG.

[0017]

2 shows a schematic diagram of an antenna system with one double reflector according to the invention.

Two radiation sources S1 and S2 radiate two linearly polarized radio waves having the same frequency orthogonal to each other. These sources S1, S2 are arranged on a support 22, which also supports a double reflector 24. The double reflector 24 includes two reflectors 2 each having a truncated cross section of a parabola of revolution.
6 and 28.

In the embodiment shown in FIG. 2, the front reflector 2
6 completely overlaps the rear reflector 28 and is held at a constant distance therefrom by attachment means 30. However, the overlap between the front reflector 26 and the rear reflector 28 may be partial.

The spacing between the front reflector 26 and the rear reflector 28 is such that the focal axes of each of these two reflectors are parallel to each other and do not intersect. In this more specifically illustrated embodiment, two reflectors in the shape of a parabola of revolution are centered and their centers (commonly known as "vertices") are offset from each other.

The front reflector 26 receives one radio wave radiation signal (
In this embodiment, it is arranged to reflect the radio signal emitted by the radiation source S1) and to be transparent to the other radio signal. The rear reflector 28 is capable of reflecting all radio radiation without any particular polarization distinction.

FIG. 3 is a schematic exploded view of a portion of the front reflector. The front reflector has a shell 32 formed by a honeycomb structure, for example made of Kevler or other materials, which is transparent to radio waves and has suitable stiffness qualities. The shell 32 has a thickness eK selected to optimize the radio performance of the double reflector. In the illustrated example, for the frequency range of 10-14 GHz, the thickness of the Kevler structure is 6.3
It is chosen to be equal to 5mm. In practice, the reflection coefficient of the structure has approximately a maximum value for this value. The front surface of the shell 32 is covered with a skin 34, which can also be made of Kevler.

The outer panel 34 is covered with a grid 36. This grid 36 is made up of a plurality of electrical conductors 38 spaced from each other in such a way that their projections onto a plane perpendicular to the focal axis of the front reflector are parallel to each other. In addition, the length and pitch of these conductors are not constant when projected onto this plane. These conductors 3
8 may be a copper strip. These conductors are either fixed in a medium such as polymide, which is transparent to radio frequencies, or bonded directly using an epoxy-type adhesive that does not outgas even under vacuum.

[0024] In one advantageous embodiment, the double reflector is provided with a filtering device. The filtering device makes it possible to remove any residual components of the linearly polarized radiation reflected by the front reflector in order to prevent them from being reflected by the rear reflector.

In the embodiment shown in FIG. 3, the filtering device comprises a plurality of filters arranged to reflect linearly polarized radio radiation parallel to the linearly polarized radio radiation reflected by the front reflector 26. It is formed by a grid 40 made of conductors. This grid 40 is supported by the back surface of the front reflector shell 32. The projections of the filter conductors in the plane perpendicular to the focal axis of the reflector are parallel to each other and to the projection of the front grid 36. This second grid 40 is formed in a similar manner as the front grid 36.

[0026] The second part that can be made with Kevler
A skin 42 covers the filtering grid 40.

In addition to making it possible to remove any residual components of the radio waves reflected by the front reflector 26, the filtering grid 40 introduces a certain symmetry to the structure of the front reflector 26, This has the advantage of improving the mechanical properties and stiffness of the front reflector 26.

The radio radiation emitted by the radiation source S1 is therefore completely reflected by the front reflector 26. On the other hand, the front reflector 26 is substantially transparent (by its construction, ie by the selection of the material and the positioning of the grid) for the radio radiation by the radiation source S2 which is reflected by the rear reflector.

FIG. 4 is a schematic exploded view of a portion of the rear reflector. The rear reflector is capable of reflecting any radio radiation regardless of the polarization of the radio waves. For this purpose, it is sufficient that this reflector has a continuous surface that reflects radio waves. The rear reflector therefore does not require a grid and can be made using a cheaper material that is much easier to process than Kevler and has better thermostructural properties.

In the embodiment shown in FIG. 4, the rear reflector 2
8 is made of shell 44. The shell has a honeycomb structure made of a conductive material, such as aluminum, sandwiched between two identical skins 46, each formed with four layers 48, such as carbon fiber layers. The shell 44 has a thickness eA selected to ensure good thermomechanical properties of the double reflector. In the case of an aluminum shell, this thickness eA is between 20 and 40 m.
m. In the example described here, eA is equal to 25 mm.

The number of layers 48 forming the skin 46 is also selected to provide good thermomechanical properties to the assembly.

The orientation of the carbon fibers in each layer of layer 48 is determined, firstly, to give the rear reflector good mechanical properties, and secondly, to ensure that the rear reflector has a nearly chosen to ensure that it has an expansion coefficient of zero.

FIG. 5 schematically shows a mounting arrangement for integrating the two reflectors with each other.

This combination device makes it possible to maintain a spacing between the two reflectors. This interval is 1
Depending on the position of the two reflectors on their circumference, the distance varies from their minimum spacing to their diametrically opposite maximum spacing.

In the illustrated embodiment, the attachment device is formed by an outer annular structure 50, two parallel rib-like internal support stiffeners 52, and a plurality of braces 54. . These elements are part of the rear reflector 28
It is held on the rear reflector 28 by gluing it onto a plurality of wedges 56 that are secured to the rear reflector 28 . These wedges 56 are made of Kevler or any other material that is transparent to radio waves and has the required thermomechanical characteristics.

[0036] These wedges are secured by optionally removable mechanical fastening means (not shown).
It is possible to be fixed to the rear reflector.

Wedges 56 are distributed along the outer annular structure 50 , on both sides of the internal stiffener 52 , and further on both sides of the brace 54 .

The elements constituting the mounting device are glued onto the back surface of the front reflector 26 using a non-static, insulating adhesive.

The outer annular structure 50 is made of, for example, Kevler.
It is a honeycomb-like structure made of The internal stiffener 52 also has a honeycomb structure, for example made of Kevler. The internal stiffener 52 is fretworked to reduce its weight. The internal stiffener 52 is arranged in such a way as to cause as little disturbance to the radiation patterns of both reflectors as possible.

In the embodiment shown in FIG. 6A, the stiffener 52 with respect to the plane P perpendicular to the focal axis AF of both reflectors.
The projection PR of is parallel to the projection PC of the conductor of the grid 38 of the front reflector 26.

In the embodiment shown in FIG. 6B, the stiffener 52 with respect to the plane P perpendicular to the focal axis AF of both reflectors.
The projection PR of is perpendicular to the projection PC of the conductor of the grid 38 of the front reflector 26.

The internal stiffener 52, on the other hand, is fixed perpendicularly to the back surface of the front reflector 26 in both cases.

Correction of the deformation of the front reflector due to temperature changes is obtained by a plurality of braces 54 made of Kevler or any other material, transparent to radio waves and having the necessary stiffness. It will be done. these braces 5
4 are arranged at regular intervals from each other on an axis parallel to the internal stiffener 52 and passing through the apex of the rear reflector. A brace 54 fixed to each of both reflectors reduces the thermomechanical deformation of the front reflector due to the stress of being supported on the rear reflector, which has an approximately zero coefficient of expansion.

The double reflector according to the present invention simplifies the structure of its assembly and reduces its manufacturing cost by using a rear reflector that is capable of reflecting all radio waves regardless of the polarization of the radio waves. and enable lowering. On the one hand, the materials used make it possible to achieve an improvement in the thermomechanical stability of the assembly.

[Brief explanation of the drawing]

1 is a schematic diagram showing a dual reflector system for frequency reuse according to the prior art; FIG.

FIG. 2 is a schematic diagram showing an antenna system with dual reflectors according to the invention;

FIG. 3 is a schematic exploded view of a portion of a front reflector according to the invention;

FIG. 4 is a schematic exploded view of a portion of a rear reflector according to the invention;

FIG. 5 is a schematic illustration of a device for attaching a front reflector and a rear reflector according to the invention;

FIG. 6A is a schematic diagram illustrating the positioning of an internal stiffener according to the present invention.

FIG. 6B is a schematic diagram illustrating the positioning of internal stiffeners according to the invention.

[Explanation of symbols]

S1, S2 Radiation source 22 Support 26 Front reflector 28 Rear reflector 32, 44 shell 34, 42, 46 outer panel 38 Conductor 36, 40 grid 48 Outer panel layer 50 Outer annular structure 52 Internal stiffener 54 Brace 56 Wedge

Claims (8)

[Claims] 1. A dual reflector for an antenna, comprising one front reflector that supports a conductor grid arranged to reflect linearly polarized radio radiation and a specific polarization of the radio waves. one rear reflector capable of reflecting all radio waves irrespective of the radio waves; and one rear reflector separated from the rear reflector in such a way that the front reflector at least partially overlaps the rear reflector. a mounting device capable of being held at a fixed distance;
1 disposed between the front reflector and the rear reflector.
a filtering device, the filtering device being capable of removing any residual component of the linearly polarized radiation reflected by the front reflector; a honeycomb formed by a multi-conductor grid arranged to reflect linearly polarized radio radiation parallel to the reflected linearly polarized radio radiation, said rear reflector being sandwiched between two skins; A dual reflector having a shaped structure, at least one of said skins being made of a conductive material. 2. The dual reflector of claim 1, wherein the filtering grid is supported by a back surface of the front reflector shell. 3. The dual reflector of claim 1, wherein said back reflector has an expansion coefficient of approximately zero. 4. The dual reflector of claim 1, wherein the honeycomb structure of the rear reflector has a thickness selected to optimize thermomechanical properties of the dual reflector. 5. The honeycomb structure has a thickness of 20 to 40 mm.
2. A double reflector as claimed in claim 1, made of aluminum with a thickness between. 6. The mounting device is first fixed on the rear surface of the front reflector and secondly fixed on the front surface of the rear reflector, and includes one outer annular shape. structure and
at least two rib-like internal support stiffeners, the mounting device further comprising a device for compensating for any deformation of the front reflector due to temperature changes; the device has a plurality of braces made of a material that is substantially transparent to radio waves, each of the braces being first secured onto a back surface of the front reflector; 2. A double reflector as claimed in claim 1, wherein the reflector is secondly fixed on the front surface of the rear reflector. 7. The internal stiffener has a projection onto a plane perpendicular to the focal axis of both reflectors, the projection being a projection of the conductors of the grid of the front reflector. 7. The dual reflector of claim 6, wherein the internal stiffener is fixed perpendicularly to the rear surface of the front reflector. 8. The internal stiffener has a projection onto a plane perpendicular to the focal axis of both reflectors, the projection being a projection of the conductors of the grid of the front reflector. 7. The double reflector of claim 6, wherein the internal stiffener is fixed perpendicularly to the rear surface of the front reflector.