EP0865097A1 - Method and apparatus for the fabrication of slotted waveguides, particularly usable for millimetric wavelengths - Google Patents

Abstract

The method involves first making a mould with a form conjugate with that of the wave guide. The mould is hollow and includes a number of transverse sectional elements which are conjugate with the intended radiating slots. A dielectric material is injected into the mould, and then the mould is opened to extract the moulded shape having projecting elements. At least one face of the body is metallised, with the metallisation covering the projecting elements. The projecting elements are then cut off in order to open the slots in the body, corresponding to the required radiating slots in the waveguide. The cutting is controlled to the correct level so that the main face of the body is protected so that there is no need to apply supplementary protection to the body.

Description

The present invention relates to the manufacture of antennas in slotted waveguides, in particular usable for millimeter wavelengths.

Slotted waveguide antennas are used in several areas, due to their profile and weight relatively thin and weak, their relatively compact size reduced at high frequency, their effectiveness relatively significant (reduced losses, high gain), their good power handling, and their relatively bandwidth important.

By millimeter waves, we mean the frequencies higher than 30 GHz. They are used more and more, for example in radar systems, communications Obstacle avoidance radars, etc.

We know several methods of manufacturing antennas slotted waveguides. Generally, these processes make use of conventional drawing and foundry techniques ( lost wax for example), or milling.

For example, the milling technique includes a step in which we create a set or network of channels forming waveguides in light aluminum alloy. We plate then on this set, a thin tray where are already cut, or will be cut later, radiant slots by machining techniques, milling followed by deburring. Machining of the slots can also be carried out by laser. EDM is also used to make the radiant slots.

The plate can be attached to the network of channels by soldering (or mechanical welding, or bath welding salt), by bonding with conductive glue, by soldering tin, by soldering with electron beams, or by laser welding.

The formation of networks of slotted guides can be carried out also by assembly according to a weld, a solder or a collage of independent guides with slots.

We also know other processes that reduce the weight of the antenna. These methods consist for example in assemble guides in thin aluminum sheets. The slots are first chemically etched, punched or machined. Then the sheet is folded to form guides individual. The guides are finally assembled to form a network antenna. The flat sheet thus provided with slots can also be reported on waveguide channels like mentioned above.

We also know antennas made of plastic reinforced with metallized carbon fibers.

We also know techniques that implement a electroforming of a slotted tray, which use the photolithography to make a slotted tray, or still that use etching slots on a substrate metallized dielectric.

For millimeter wavelengths, the manufacture of the antennas in waveguides with slots described above require flawless radio behavior antenna components and require accuracy much larger than that required at frequencies lower.

However, this impeccable behavior and this precision translate into practice very expensive operations, in particular due to the numerous operations to be implemented work to make antennas in slotted waveguides, and in particular the precise opening of the slots.

In the document PATENT ABSTRACT OF JAPAN vol. 5, n ° 86 (E-060), June 5, 1981 & JP 56 032807 A (FURUNO ELECTRIC CO. LTD), April 2, 1981, there is described a method of manufacturing a radiofrequency antenna comprising molding steps, metallization and leveling to make a slot antenna radiant.

In this process, it is planned to use an additional layer called "molding layer" to protect the face of the waveguide body of the leveling tool and hold flat said face of the body.

Such an additional layer burdens the process of a additional operation and increases costs accordingly.

The present invention provides a solution to this problem.

It aims at a process having the advantage of performs mechanical, chemical or electrical operations simple for precise opening of radiating slots in waveguides.

It aims to provide a process particularly suitable for millimeter wavelengths where the thickness of metal necessary for current conduction is relatively scaled down.

Finally, it aims to provide a method of manufacturing antennas low cost slotted waveguides.

The present invention thus relates to a manufacturing process at least one slotted waveguide which uses molding, metallization and leveling techniques for realization of at least some of the constituent elements of the waveguide and the opening of the radiating slots.

• a) réaliser un moule de forme conjuguée avec celle du corps du guide d'ondes, le moule comprenant, en creux, une pluralité d'éléments de section transversale conjuguée avec la forme des fentes rayonnantes ;
• b) injecter une matière diélectrique dans le moule ;
• c) démouler pour obtenir un corps en matière diélectrique comprenant au moins des éléments en saillie ;
• d) métalliser au moins la face du corps comprenant des éléments en saillie ;
• e) araser les éléments en saillie de façon à ouvrir des fentes dans ledit corps, correspondant aux fentes rayonnantes dudit guide d'ondes.

The method is of the type comprising the following steps:

• a) producing a mold of shape conjugated with that of the body of the waveguide, the mold comprising, in hollow, a plurality of elements of cross section conjugate with the shape of the radiating slots;
• b) injecting a dielectric material into the mold;
• c) unmolding to obtain a body of dielectric material comprising at least projecting elements;
• d) metallizing at least the face of the body comprising projecting elements;
• e) leveling the projecting elements so as to open slits in said body, corresponding to the radiating slits of said waveguide.

According to a general definition of the invention, leveling according to step e) is carried out at a height chosen relative to the face of the body, which protects said face of the body leveling means without applying a protective layer additional on said face of the body.

Surprisingly, the Applicant has found that the slits thus slightly protruding from the face of the body also reduce the existing parasitic couplings between two adjacent slots and which are related to the spread current on the face of the waveguide body. In effect, this current propagation is now disturbed by the protruding geometry of the slots in accordance with method according to the invention, which limits the couplings between the slots.

The present invention also relates to a method of manufacture of a network antenna arranged in at least two waveguides with radiant slits produced separately or together according to the method mentioned above.

• 1) réaliser un moule de forme conjuguée avec celle du réseau à guides d'ondes, comprenant en creux, une pluralité d'éléments de section transversale conjuguée avec la forme des fentes rayonnantes de chaque guide d'onde ;
• 2) injecter une matière diélectrique dans le moule ;
• 3) démouler pour obtenir un corps en matière diélectrique à la forme du moule ;
• 4) découper le corps au format des guides d'ondes ;
• 5) métalliser au moins la face du corps comprenant les éléments en saillie, ainsi que la face latérale séparant les guides d'ondes ainsi découpée ;
• 6) araser à une hauteur choisie par rapport à la face du corps les éléments en saillie de façon à ouvrir des fentes dans les guides d'ondes formant l'antenne réseau.

According to a preferred embodiment of the invention, the method for manufacturing an array antenna comprising at least two waveguides with radiating slits comprises the following steps:

• 1) produce a mold of shape conjugated with that of the waveguide network, comprising in hollow, a plurality of elements of cross section conjugate with the shape of the radiating slots of each waveguide;
• 2) inject a dielectric material into the mold;
• 3) unmolding to obtain a body of dielectric material in the shape of the mold;
• 4) cut the body in waveguide format;
• 5) metallizing at least the face of the body comprising the projecting elements, as well as the lateral face separating the waveguides thus cut;
• 6) leveling the protruding elements at a height chosen relative to the face of the body so as to open slits in the waveguides forming the array antenna.

In practice, step 1) also consists in making a mold including, in hollow, the common connection of the two guides waves while step 6) is to level off further the projecting element corresponding to the common connection of two waveguides.

The present invention also relates to a waveguide with radiating slits obtained by the process mentioned above.

Similarly, the present invention also relates to a array antenna arranged in at least two waveguides at radiant slits obtained by the process mentioned above.

Advantageously, the antenna produced by the method according to the invention can be used for wavelengths millimeter.

• la figure 1 illustre un exemple de réalisation de l'opération de moulage selon l'invention ;
• la figure 2 illustre schématiquement un exemple de moule selon l'invention ;
• la figure 3 illustre l'étape relative à l'injection de la matière plastique dans le moule selon l'invention ;
• la figure 4 illustre l'étape relative à la métallisation du corps de guide d'ondes selon l'invention ;
• la figure 5 représente une coupe droite théorique effectuée sur l'élément décrit en référence à la figure 4, montrant la matière plastique à l'intérieur et la couche de métal enrobant la pièce plastique ;
• la figure 6 illustre l'étape relative à l'ouverture des fentes rayonnantes par arasement des éléments en saillie ;
• la figure 7 représente un exemple de réseau à deux guides d'ondes rectangulaires accolés selon l'invention et comportant chacun quatre fentes rayonnantes ;
• la figure 8 illustre un autre exemple d'un guide à quatre fentes rayonnantes avec un court-circuit d'un côté et un accès par une bride de l'autre côté ;
• la figure 9 illustre encore un autre exemple d'un guide d'ondes à quatre fentes rayonnantes avec un coude au niveau du point d'excitation, accessible par une bride ;
• les figures 10A, 10B et 10C représentent différents moyens pour réaliser des courts-circuits dans des guides d'ondes traditionnels ;
• la figure 11 illustre schématiquement une autre technique de réalisation des éléments terminaux des guides d'ondes représentés sur la figure 7 ;
• les figures 12 et 13 illustrent l'utilisation de courts-circuits à l'intérieur d'un guide d'onde ;
• la figure 14 illustre schématiquement une antenne réseau pour radar, utilisable pour les longueurs d'ondes millimétriques, et obtenue selon le procédé selon l'invention ; et
• la figure 15 illustre une variante de la pièce décrite en référence à la figure 11 et comportant une zone favorisant la fixation de l'antenne sur un support mécanique.

Other characteristics and advantages of the invention will become apparent in the light of the detailed description below and the appended drawings in which:

• FIG. 1 illustrates an exemplary embodiment of the molding operation according to the invention;
• FIG. 2 schematically illustrates an example of a mold according to the invention;
• FIG. 3 illustrates the step relating to the injection of the plastic material into the mold according to the invention;
• FIG. 4 illustrates the step relating to the metallization of the waveguide body according to the invention;
• FIG. 5 represents a theoretical cross-section made on the element described with reference to FIG. 4, showing the plastic material inside and the layer of metal coating the plastic part;
• FIG. 6 illustrates the step relating to the opening of the radiating slots by leveling of the projecting elements;
• FIG. 7 represents an example of a network with two contiguous rectangular waveguides according to the invention and each comprising four radiating slots;
• FIG. 8 illustrates another example of a guide with four radiating slots with a short circuit on one side and access by a flange on the other side;
• FIG. 9 illustrates yet another example of a waveguide with four radiating slots with a bend at the level of the excitation point, accessible by a flange;
• FIGS. 10A, 10B and 10C show different means for producing short circuits in traditional waveguides;
• FIG. 11 schematically illustrates another technique for producing the terminal elements of the waveguides shown in FIG. 7;
• Figures 12 and 13 illustrate the use of short circuits inside a waveguide;
• FIG. 14 schematically illustrates a network antenna for radar, usable for millimeter wavelengths, and obtained according to the method according to the invention; and
• FIG. 15 illustrates a variant of the part described with reference to FIG. 11 and comprising a zone favoring the fixing of the antenna on a mechanical support.

The invention makes it possible to produce at least some of the elements components of a slotted waveguide array antenna by easy molding and metallization operations enforce. In particular, the formation of the slots or the connections between guides, is thus advantageously produced through these molding and metallization operations. The opening of the slots is, in turn, advantageously obtained by a simple leveling of the elements protruding, made at a height chosen with respect to the face of the body comprising the projecting elements.

In FIG. 1, the molding operation uses elements conventionally used in molding.

A hopper 2 is filled with granules of plastic material. These granules fall on an endless screw 4 which is suitable for lead the material to the mold 6. Heating means heat the granules so as to obtain a paste.

The mold 6 consists of two mechanical parts, one of which 8 presents a hollow imprint representing the part to realize that will be described in more detail below.

With reference to FIG. 2, the part 8 comprises in hollow, in particular a plurality of elements 9 of cross section combined with the shape of the radiating slits of each waveguide

For example, the mold is produced by EDM.

The second mechanical part 10 of the mold is preferably plane at the level of the radiating guides so as to avoid deformation on the height of the guide taking into account the feed access geometry (waveguide flange, elbow).

Obviously, this part 10 may also have recessed patterns.

With reference to FIG. 3, the result of injecting the plastic into the mold, after demolding.

The finished set, deburred, corresponds to the internal section of the waveguides. It very advantageously includes extra thickness the elements 9 which will become the radiating slots.

Referring to Figure 4, the plastic form illustrated in reference to Figure 3 is completely metallized. By example, the metallization step is carried out by electroplating.

Referring to Figure 5, a cross section of the whole shows the plastic shape and the metallization in area.

With reference to FIG. 6, the elements in excess thickness or protruding 9 are leveled at a height chosen relative to the body plane, for example 1 or 2 tenths of a millimeter. This leveling allows to open slots 11 which will play the role radiating slots in the waveguides.

The leveling means are for example of the abrasive type (sanding, grinding) or cutting (milling, turning) or similar.

The leveling thus carried out at a height chosen relative to the surface carrying the projecting elements protects said surface of the leveling means without applying a layer additional on said surface.

It should be noted that the method according to the invention modifies slightly the condition of continuity of electromagnetic fields at the interface between the slots and the radiating space since the slots are according to the invention slightly protruding and no longer on the same level as the metal plane constituting the outer wall of the guides waves.

This modification is a second order effect which can be taken into account in simulation models (for example with an analysis implementing a method of calculating "finite elements in the time domain"), or by adjustment with experimental measurements.

Surprisingly, the Applicant has found that the thus slightly protruding slits further reduce the parasitic couplings existing between two adjacent slots, related to a propagation of current on the external wall of feeding guides. Indeed, this propagation of current is now disturbed by the protruding geometry of slots according to the invention, which limits the couplings parasites between the slots.

At the end of step 6, a waveguide is obtained at radiant slots charged with dielectric. If applicable, some elements of the antenna can be made from the installation of overmolded metal inserts in the plastic part.

With reference to FIG. 7, the network 13 comprises two guides of waves 15 and 17, rectangular and contiguous. The two guides waves are produced by molding according to the process according to the invention. Each waveguide includes four slots radiant 20.

The rectangular guides 15 and 17 each include a free end forming short circuit 22. They are excited via a simple T-divider 24 with a flange-type entry access 26.

According to the invention, after an overall metallization, the slots 20 are made by leveling the upper face 28 waveguides.

The separation between the two waveguides is carried out by an open slot 30 made over the entire height of the guides waves.

Advantageously, this open slot 30 is also metallic.

Likewise, the flange-type entry access 24 is obtained, after metallization, by lateral leveling of an extra thickness obtained by molding according to the operations described with reference in Figures 1 to 6.

Alternatively, the flange-type inlet access 24 can be made from the placement on the workpiece plastic of a suitably shaped metal insert.

Terminal short circuits of radiant guides in mode resonant are likely to be achieved by metallization terminal dielectric cross sections 22.

Referring to Figure 10A, in waveguides traditional metal, short circuits can be obtained by metal plates 40 closing completely the guides.

These metal plates represent a configuration similar to the metallization of the cross section 22 described with reference to Figure 7.

Alternatively, in traditional metal waveguides, short circuits can be achieved by metal bars 42 (FIG. 10C), or by a plate 44 partially closing the free end of the waveguide (Figure 10B) without covering the peripheral parts 46.

The role of these short circuits is to prevent the spread the main guided mode beyond the obstacle constituted by the plate or the bars.

These embodiments (FIGS. 10A, 10B and 10C) can be advantageously adapted and produced for the antenna according to the invention.

With reference to FIG. 11, according to the invention, the elements guide terminals shown according to reference 22 on the Figure 7 can thus be produced according to short circuits 50 partially closing the guides, like the plate 44 described in FIG. 10B. Advantageously, the dielectric space 52 corresponding to the available dielectric space 46 described in Figure 10B for guides can also be used to mechanically hold the guides between them.

Referring to Figures 12 and 13, there is shown the use short circuits inside a waveguide, for example example to partition the radiating network by subnet (for example to increase the bands passers-by or in order to perform a deviation measurement function). A slot (not shown) can be opened inside plastic shape over the entire height of the plastic guide and then metallized during the metallization process overall plastic form.

Such an embodiment makes it possible to form an element 58 of the type of the plate described in FIG. 10B. Alternatively, element 58 can be made from the installation in the room made of plastic with a parallelepiped metal insert or cylindrical.

Alternatively, the short circuit can be achieved by a series holes (not shown) made in the section of the guide. This formation of holes can be followed by a metallization in order to produce bars 63 of the short-circuit type as shown in Figure 10C. Alternatively, the elements 63 can be made from the setting place in the plastic part of metal inserts bar type.

Referring to Figure 15, the end part of the part shown in Figure 11 can be changed using open slots on the height of the guides and metallized to form elements similar to elements 58 of the figure 12. One thus constitutes an assembly comprising a zone 59 not used from the radio point of view, but may advantageously ensure the rigidity of the assembly, of a part, and be used for fixing the antenna on a mechanical support for example, on the other hand.

With reference to FIG. 8, another example has been shown. waveguide 100 to four radiating slots 102 with a short circuit 104 on one side and access 106 by flange of the other side.

With reference to FIG. 9, yet another is shown. example of waveguide 200 with four radiating slots 202 with an elbow 206 at the point of excitation, accessible by a flange 208.

It should be noted that the access or entry accesses can be made up of elements other than conventional flanges. For example, they can be made according to the microstrip, triplate or coplanar structure, or even from a classic guide-coaxial transition. The accesses can also be made through cut openings on the side opposite to the radiating slots (inclined slots).

It should also be noted that several pieces made according to the method according to the invention can be assembled by mechanical pressure or by welding (ultrasonic welding for example). Thus, it is possible to make an antenna comprising several levels (or layers) of contiguous guides or superimposed, these guides being coupled for example from inclined slots.

It should also be noted that the slot antenna shown with reference to FIG. 7 is of the network antenna type in longitudinal shunt slot guides on the long side guides.

Obviously, the antenna can also be of a different type and produced according to the technique described above. By example, the guides can be of the slot type on the small side of the waveguides. The slots can also be differently shaped, for example C, Z, I, etc.

The plastic used according to the invention must be preferably easy to use, injectable into a mold and present a good surface condition. She must also be from preferably mechanically stable, for example little expansion with the temperature. In practice, it is metallizable and has electrical characteristics suitable for its use for guiding electromagnetic waves, in term of permittivity and tangent of loss.

For example, the plastic is polycarbonate or similar.

Referring to Figure 14, there is shown an antenna network of slotted guides, obtained according to the method according to the invention. This antenna finds an advantageous application in the radar field and can be used for lengths of millimeter waves. It includes a plurality of guides waves 300, 302, with slots 250 and assembled in pairs. Each pair is connected to the processing and supply means (not shown) according to a chosen AB tree structure and produced from a cascade of CP couplers. The excitement radiant guides can also be performed, depending on the method according to the invention, from a waveguide transverse to the radiating guides and provided with windows coupling to these.

Claims (11)

Method for manufacturing at least one radiating slit waveguide, of the type comprising the following steps: a) producing a mold of shape conjugated with that of the body of the waveguide, the mold comprising, in hollow, at least a plurality of elements of cross section (9) conjugated with the shape of the radiating slots (20), b) injecting a dielectric material into the mold, c) unmolding to obtain a body of dielectric material comprising at least projecting elements, d) metallizing at least the face of the body comprising the projecting elements, and e) leveling the projecting elements so as to open slits in said body, corresponding to the radiating slits of said waveguide, characterized in that the leveling according to step e) is carried out at a height chosen with respect to the face of the body, which makes it possible to protect the face of the body from the leveling means without applying an additional protective layer on said face of the body. Method according to claim 1, characterized in that leveling according to step e) is carried out using means abrasive, cutting, or the like. Method according to claim 1, characterized in that the projecting elements thus leveled correspond, as the case short-circuit, flange-type input access or the like. Method according to one of claims 1 to 3, characterized in that the general shape of the mold is parallelepiped, cylindrical, or whatever. Method according to one of claims 1 to 4, characterized in that the cross section of the projecting elements (9) is long, curvilinear or arbitrary. Method of manufacturing a network antenna arranged in at at least two waveguides (15 and 17) with radiating slits (20) produced separately or together according to one of claims 1 to 5. Method according to claim 6, characterized in that it comprises the following steps: 1) produce a mold of shape conjugated with that of a network with at least two waveguides contiguous to each other (15 and 17), comprising in hollow, at least a plurality of elements (9) of cross section conjugate with the shape of the radiating slots of each waveguide, 2) inject a dielectric material into the mold, 3) unmolding to obtain a network of dielectric material in the shape of the mold, 4) cut the network in the format of the two waveguides, 5) metallizing at least the face of the body comprising the projecting elements, as well as the lateral face separating the two waveguides thus cut, 6) leveling the protruding elements at a height chosen relative to the face of the body so as to open slits in the waveguides forming the array antenna. Method according to claim 7, characterized in that step 1) also consists in making a mold comprising, hollow, the common connection (24, 26) of the two guides waves (15 and 17) while step 6) consists of leveling off in addition to the projecting element corresponding to the connection common of the two waveguides. Radiant slit waveguide obtained by the process according to one of claims 1 to 5. Network antenna arranged in at least two waveguides at radiating slits obtained according to one of claims 6 at 9. Antenna according to claim 10, characterized in that that it can be used for millimeter wavelengths.

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