EP0274074B1 - Feeding radiator for a communications antenna - Google Patents

Description

The present invention relates to an illumination source for a telecommunications antenna.

The development of telecommunications, in particular by satellite (Reception and Transmission of data, Reception TV) requires antennas of excellent performances.

To ensure these overall performances, an illumination source with symmetry of revolution and having good polarization characteristics is required.

However, the multiplication of potential users leads to the design of very low cost products.

Conventional sources of illumination, offering diagrams with good symmetry of revolution of the corrugated horn type, have the drawback of being very expensive to produce.

The sources of illumination with conventional traps which have the advantage of being more economical to produce are of low directivity but sufficient to illuminate a reflector of the parabolic type. They are made up of parts with an axis of symmetry (circular guide, trap, etc.) and must be supplied by a standard rectangular waveguide. This feeding is carried out by a transition either continuous or by step.

Thus a French patent application published under the number 2 096 684 describes a device for coupling a circular waveguide to a parabolic reflector of revolution which comprises a circular guide, excited according to TE11 mode, a first end of which is at the focus of this reflector, and the other end of which is connected to a rectangular waveguide. An incomplete cylindrical annular cavity surrounds the first end of the guide. A transition element, formed of a series of waveguide sections of gradually varying shapes and dimensions, connects to the rectangular waveguide.
But a continuous transition must be long to have good adaptation characteristics. A step transition, as described in the document cited above, makes it possible to reduce the length but is difficult to manufacture by technologies at low cost.

The present invention aims to overcome these drawbacks.

• une partie rayonnante ayant une ouverture circulaire ;
• une transition formée de tronçons de guide d'onde variant progressivement ;
• une bride de liaison à un guide rectangulaire ;

caractérisée en ce que ladite source est réalisée en matière moulable, en ce que la partie rayonnante est formée d'une collerette munie d'au moins deux sillons concentriques formant deux pièges, et en ce que ladite source comprend des moyens de fixation dans un support.To this end, it offers a source of illumination for telecommunication antenna comprising:

• a radiating part having a circular opening;
• a transition formed by gradually varying waveguide sections;
• a connection flange to a rectangular guide;

characterized in that said source is made of moldable material, in that the radiating part is formed by a collar provided with at least two concentric grooves forming two traps, and in that said source comprises means for fixing in a support .

Such a source has the great advantage of being a broadband illumination source (10.7 - 12.75 GHz) designed to illuminate an antenna reflector and this, with very high level radio performance, mechanical performance and climatic conditions that meet very severe requirements and whose industrial development calls for economic technologies. The invention makes it possible, in fact, to produce, by molding, a fully integrated part and therefore has a much lower cost compared to the sources of the prior art obtained by electroforming or EDM.

• la figure 1 représente une vue moitié en coupe, moitié en élévation de la source selon l'invention ;
• la figure 2 représente une vue en coupe transversale, selon le plan II-II de la figure 1, de la source selon l'invention ;
• la figure 3 représente une vue en coupe transversale, selon le plan III-III de la figure 1, de la source selon l'invention.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of nonlimiting example, with reference to the appended figures in which:

• Figure 1 shows a half sectional view, half in elevation of the source according to the invention;
• 2 shows a cross-sectional view, along the plane II-II of Figure 1, of the source according to the invention;
• 3 shows a cross-sectional view, along the plane III-III of Figure 1, of the source according to the invention.

The source 10 according to the invention is a guide which, at its first end, has a circular opening 11, and, at its other end, has a rectangular opening 12.

• une partie rayonnante 13 munie de deux pièges 14 et 15 et de l'ouverture 11 dont le diamètre détermine la fréquence de fonctionnement ;
• une transition 16 entre cette partie 13 et un guide d'onde rectangulaire standard, non représenté sur la figure, qui permet le raccordement à une tête hyperfréquence ;
• une bride 17, qui termine cette transition 16, qui permet la liaison à ce guide rectangulaire.

She understands :

• a radiating part 13 provided with two traps 14 and 15 and with the opening 11 whose diameter determines the operating frequency;
• a transition 16 between this part 13 and a rectangular waveguide standard, not shown in the figure, which allows connection to a microwave head;
• a flange 17, which ends this transition 16, which allows the connection to this rectangular guide.

This source will be described more precisely going from its first end to its second end.

• une collerette cylindrique 21, située dans un endroit poche de cette première extrémité, dont l'axe est l'axe de symétrie Δ de la source 10 et qui est munie sur sa face située du côté de la première ouverture de deux sillons circulaires concentriques 14 et 15 qui réalisent les deux pièges ;
• deux collerettes 18 et 19 cylindriques concentriques situées dans sa partie médiane, dont l'axe est l'axe de symétrie Δ de la source 10, ces collerettes étant des collerettes de fixation de la source 10 dans son support ;
• un embout de pressurisation 20 ;
• la bride de raccordement 17 située à la deuxième extrémité de la source 10.

Externally this source 10 includes:

• a cylindrical collar 21, located in a pocket location of this first end, the axis of which is the axis of symmetry Δ of the source 10 and which is provided on its face situated on the side of the first opening with two concentric circular grooves 14 and 15 which perform the two traps;
• two concentric cylindrical flanges 18 and 19 located in its middle part, whose axis is the axis of symmetry Δ of the source 10, these flanges being flanges for fixing the source 10 in its support;
• a pressurization nozzle 20;
• the connection flange 17 located at the second end of the source 10.

• deux premiers pas 22 et 23 en guide circulaire ;
• trois pas 24, 25 et 26 en guide rectangulaire dont les coins auraient été arrondis ;
• un dernier pas 27 en guide rectangulaire.

Internally, this source 10 comprises six steps 22, 23, 24, 25, 25 and 27 which are symmetrical with respect to two planes P1 and P2 of perpendicular section and the size of which decreases progressively from the circular opening 11 to reach that of the second rectangular end 12. It therefore comprises:

• first two steps 22 and 23 in circular guide;
• three steps 24, 25 and 26 in a rectangular guide whose corners have been rounded;
• a last step 27 in rectangular guide.

The part 28 external to the source corresponds to the place where the material is poured between two forms used for molding.

• le coulage d'une matière moulable, par exemple un alliage d'aluminium, ou un matériau diélectrique tel qu'une résine époxy, dans un moule formé de deux formes accolées ;
• le séchage de cette matière ;
• le démoulage.

Indeed, this source can be produced according to a manufacturing process comprising:

• the casting of a moldable material, for example an aluminum alloy, or a dielectric material such as an epoxy resin, in a mold formed of two joined shapes;
• drying of this material;
• demolding.

In the case where the moldable material is a dielectric material, there is then a metallization step, for example with nickel.

• deux formes symétriques dont le plan longitudinal de jonction contient l'axe Δ de révolution de la source selon l'invention ;
• un noyau central dont la forme mâle reproduit fidèlement le guide d'onde cylindrique suivi de la transition rectiligne.

The molding tools are, for example, made of special steel. They have several moving parts, the main ones being:

• two symmetrical shapes, the longitudinal junction plane of which contains the axis Δ of revolution of the source according to the invention;
• a central nucleus whose male form faithfully reproduces the cylindrical waveguide followed by the rectilinear transition.

Depending on the molding process chosen, a supply system of moldable material (aluminum or epoxy for example) allows the part to be filled inside the molding tools.

A system of movable parts for ejecting the molded part, known to those skilled in the art, makes it possible to extract this part from the molds without deforming it, thus retaining all of its geometric characteristics.

The invention has the great advantage of requiring no rework in machining. In addition, its radioelectric design and its manufacturing process are suitable for the medium series, even the large series, and thus make it possible to reach low price levels. Such a production method also allows the integration, without additional cost, of a pressurization nozzle.

A protective radome can be fixed on the opening plane of the circular part 13: It can thus oppose the penetration of runoff water into the source. It is also used to plug the source when it is pressurized.

• d'une ouverture circulaire 11 de diamètre 1,2λ, entourée de deux pièges 14 et 15 d'épaisseur 0,085λ situés en arrière de l'ouverture, elles-mêmes espacées de 0,085 λ , λ étant la longueur d'onde correspondant à la fréquence moyenne dans la bande utile (± 15 % autour de la fréquence moyenne) ;
• d'une transition rectiligne par pas comprenant successivement deux pas en guide circulaire puis quatre pas en guide rectangulaire à bouts éventuellement arrondis (6 pas de $\frac{\text{λg}}{\text{4}}$
  
  avec λg = longueur d'onde guidée) dont chaque pas constitue une portion de guide dont la section droite est inscrite dans le cercle constituant le guide circulaire de plus faible diamètre de la partie rayonnante.

In an exemplary embodiment, the illumination source 10, object of the invention, consists of:

• a circular opening 11 of diameter 1.2λ, surrounded by two traps 14 and 15 of thickness 0.085λ situated behind the opening, themselves spaced apart by 0.085 λ, λ being the wavelength corresponding to the average frequency in the useful band (± 15% around the average frequency);
• of a rectilinear transition in steps comprising successively two steps in circular guide then four steps in rectangular guide with possibly rounded ends (6 steps of $\frac{\text{λg}}{\text{4}}$
  
  with λg = wavelength guided) each step of which constitutes a guide portion whose cross section is inscribed in the circle constituting the circular guide of smaller diameter of the radiating part.

• une ouverture circulaire 11 de 31,5 millimètres de diamètre ;
• une ouverture rectangulaire 12 de 9,9 mm x 19,2 mm ;
• une longueur de 76,2 mm.

So we get for example:

• a circular opening 11 of 31.5 millimeters in diameter;
• a rectangular opening 12 of 9.9 mm x 19.2 mm;
• a length of 76.2 mm.

Due to the traps 14 and 15, this source 10 has a well symmetrical radiation pattern: of the order of - 10 dB around 50 °.

Such a source has a very good standing wave ratio (ROS) of the order of 1.07 for frequencies varying from 10.7 to 12.75 GHz, whether made of metallized epoxy or aluminum.

• moulage d'alliage aluminium ;
• moulage de résines époxy métallisables ;
• électroformage à noyau non destructible ;
• électroérosion.

The invention makes it possible to obtain a very compact radiating source which can be directly connected to a standard rectangular guide. It also makes it possible to produce the part by very economical technological means such as:

• aluminum alloy molding;
• molding of metallizable epoxy resins;
• electroforming with non-destructible core;
• EDM.

• en moulage d'alliage aluminium en coquille de précision ;
• en moulage résine époxy avec une métallisation par exemple au nickel.

Illumination sources in accordance with the invention can be produced using mass production technologies, for example:

• in aluminum alloy casting in precision shell;
• in epoxy resin molding with metallization, for example nickel.

It is understood that the present invention has only been described and shown as a preferred example and that its constituent elements can be replaced by equivalent elements without, however, departing from the scope of the invention.

Claims (12)

1. A telecommunications-antenna illumination source, comprising:

   - a radiating portion (13) having a circular aperture (11),

   - a transition (16) formed by progressively varying waveguide sections,

   - a connection flange (17) which provides coupling with a rectangular waveguide,

   characterized in that said source (10) is made of moldable material, in that the radiating portion (13) is formed by a annular collar (21) provided with at least two concentric grooves forming two traps (14, 15), and in that said source (10) includes means (18, 19) for fixing it in a support.
2. A source according to claim 1, characterized in that the annular collar (21) of the radiating portion is cylindrical.
3. A source according to claim 1, characterized in that the fixing means comprise two concentric cylindrical flanges (18, 19) having different diameters and being disposed in the outer middle area of the source.
4. A source according to any one of the preceding claims, characterized in that it is provided with an integrated pressurization nipple (20).
5. A source according to any one of the preceding claims, characterized in that the transition includes at least two circular transitions (22, 23) followed by at least two transitions of rectangular shape (26, 27).
6. A source according to any one of the preceding claims, characterized in that the circular opening (11) has a diameter of 1.2 λ surrounded by two traps (14, 15) having a thickness of 0,085 λ and located behind the aperture, said traps in turn being relatively spaced apart at a distance of 0,085 λ , where λ is the wavelength corresponding to a mean frequency in the useful band, and that the transition comprises successively six steps (22, 23, 24, 25, 26, 27) of λg/4, where λg is the wavelength of the guided wave.
7. A source according to claim 6, characterized in that the transition comprises successively:

   - two steps forming circular waveguides (22, 23),

   - three steps forming rectangular waveguides (24, 25, 26) with rounded corners, and

   - one step forming a rectangular waveguide (27).
8. A source according to any one of the preceding claims, characterized in that the source is manufactured from aluminium alloy.
9. A source according to any one of claims 1 to 7, characterized in that the source is manufactured from dielectric material which has been metal-coated.
10. A source according to claim 9, characterized in that the dielectric material is epoxy resin.
11. A source according to claim 9 or 10, characterized in that the source is coated with nickel.
12. A method of manufacturing a source according to any one of the preceding claims, characterized in that molding tools made of steel are employed, which include:

    - two symmetrical forms, whose longitudinal joint plane contains the axis of revolution (Δ) of the source, and

    - a central core.

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