EP1097254B1 - Foam-coating method for making antenna elements - Google Patents

Abstract

The invention concerns a method for making an antenna element (antennae, microwave circuits, shielding, etc.), characterised in that it comprises a step which consists in directly contacting at least part of a synthetic foam block having a pH less than 7 such as PVC with at least a metal coating bath and/or a graphite bath during a sufficient time interval for completely coating said foam block surface part with a metal and/or graphite layer. Said method is particularly suited for making three-dimensional antennae.

Description

The invention relates to the field of manufacturing elements antennas. It will be noted that, in the present description, by the terms "antenna elements", both the antennas themselves, microwave circuits (such as waveguides in particular) associated with these, the heat sinks and the housings of shielding associated with such antennas and circuits microwave.

The present invention particularly finds its application for the realization of antennas in three dimensions.

Studies on printed antennas have shown that these have a relatively low bandwidth (of the order 1 to 2%). This is mainly due to the small thickness of the layer of dielectric material which is typically of the order of millimeter or even less for conventional laminates having a relative dielectric constant of the order of 2 to 3.

Increasing the bandwidth needed for good number of high speed communication systems, can be done by increasing the thickness of the dielectric layer. This solution however is not technically satisfactory for polymers conventional, insofar as part of the energy is guided by surface waves, which results in a decrease in yield and a increase in the weight of the whole. It has therefore already been proposed in the state of the art of using a foam of cellular synthetic material, because such a material has a dielectric constant which prevents surface waves and which allows the whole to remain light. It has also been envisaged to place several metal pads separated by layers insulation and thus increase the bandwidth.

However, until now, foams have been mainly used as shims or stiffening support for circuits.

Furthermore, despite the interest presented by the use of such foams for making antennas, such use is limited with flat antennas.

Indeed, the metallization processes of the foams known in the state of the art does not allow the metallization of blocks of foam on all sides (three-dimensional metallization) especially when their shapes are complex.

• le dépôt des mousses sur semelles métalliques épaisses ;
• la sérigraphie en couches épaisses ;
• le pressage à chaud d'un film plastique tel que du polypropylène préalablement métallisé ;
• la vaporisation à vide en couche mince.

These prior art techniques consist of:

• depositing the foams on thick metal soles;
• screen printing in thick layers;
• hot pressing of a plastic film such as polypropylene previously metallized;
• thin layer vacuum spraying.

JONES H.S .: 'Horn design saves weight without performance loss', MICROWAVES, vol. 12, no. 10 October 1973 describes a horn antenna composed of a block of polyurethane foam or polystyrene. The foam surface is metallized with a layer of copper by chemical reduction.

The main objective of the present invention is to present a process which allows the easy realization of antennas in three dimensions. Such three-dimensional antennas indeed find many applications.

Another object of the present invention is to describe such a process which also allows the deposition of graphite layers on blocks of foam to form coatings that can be used as energy adaptation or dissipation charges residual antenna elements, such as waveguides.

Yet another object of the present invention is to provide such a method which can be implemented at low cost, according to a high reproducibility, and according to simple implementation steps.

These different objectives are achieved by the method of claim 1 and the antenna element according to claim 11. Preferred modes of the process are defined in dependent claims 2 to 10.

The invention therefore proposes to dip all or part of a block of polyvinyl chloride foam in a metallization bath and a graphite bath allowing the deposition of metal and graphite on a given surface of the block.

Metallization baths and graphite baths which can to be used are known from the state of the art and used conventionally for metallization and the deposition of a coating of graphite on metal supports.

It will be noted that these baths exhibit a basic behavior which which implies the need to use a polyvinyl chloride foam alveolar with a pH below 7, therefore acid behavior, for implementing the process according to the invention.

On this subject, it will be noted that such foams are relatively rare on the market.

It will be understood that the method can be implemented on only one side of a block of foam. However, as stated above the method according to the present invention finds all particularly its application for the realization of antennas in three dimensions. Consequently, according to a preferred variant of the invention, the method comprises a step consisting in dipping all of said block of polyvinyl chloride foam in said metallization bath and said graphite bath.

The soaking time of the foam block in the bath metallization and the graphite bath can be easily determined by those skilled in the art depending on the nature of the bath used. However, generally speaking, this soaking time will generally be between 10 minutes and 20 minutes.

As already specified above, the process will find everything particularly its interest for the realization of antennas in three dimensions, especially when these have a shape complex. According to an interesting variant of the method, the block of foam therefore has an irregular shape incorporating at least one non-planar face.

According to another variant, this block of foam will have at least a hole and / or a slot which can, thanks to the process, be fully metallized or coated with graphite. Such holes advantageously have a diameter greater than or equal to 0.2 mm. The treatment bath used can either be a metallization or a graphite bath.

The method according to the invention can be used to carry out antenna elements having certain metallized surfaces and some graphite coated surfaces. This is why according to a interesting variant of the process, it comprises at least one step of soaking at least part of a surface of a block of foam in a metallization bath and at least one step consisting of dipping at least part of a surface of said block of foam in a graphite bath.

According to a variant of the method, the method according to the invention includes a preliminary step of coating one or more parts of the surface of said foam block with one or more elements forming cover (s) and removing said element (s) cover (s) after said soaking step. It will thus be possible to manufacture antenna elements including certain parts will not be metallized, in particular to coat these parts not subsequently metallized of graphite.

According to another variant, the method comprises a step consisting in eliminating said layer of metal deposited on one or more several parts of the surface of said foam block. This step removal of part of the metal layer on one or more parts of the surface of the foam block can be made in also removing part of this foam block.

The metallization baths used will be baths containing a metal preferably chosen from the group consisting of copper, nickel, gold, silver, titanium.

According to the invention, the method comprises also at least one chemical and / or physico-chemical step of preparation of the surface condition of said block of foam aimed at improve the deposition of metal and graphite.

According to another variant, the method according to the invention comprises a subsequent step of depositing a metal by electrochemistry on the part of said block of foam previously metallized.

We can use different foams to implement the method according to the invention from the moment it presents a pH below 7. Such foam is made up by certain foams based on polyvinyl chloride.

The invention also covers any antenna element produced thanks to the process according to the invention characterized in that it consists by a block of foam of which at least part of at least one of faces is coated with a layer of metal in direct contact with said foam.

Said antenna element comprises at least a metallized part and at least a part coated with a layer of graphite.

• la figure 1 représente une vue en perspective d'une antenne 3D métallisée selon le procédé de l'invention ;
• les figures 2 et 3 montrent les courbes d'adaptation en impédance d'une telle antenne;
• la figure 4 montre les courbes d'adaptation en impédance d'une telle antenne ;
• la figure 5 représente une vue en perspective d'une antenne-pastille métallisée selon le procédé de l'invention ;
• la figure 6 montre le diagramme d'adaptation d'une telle antenne ;
• la figure 7 montre une vue en perspective d'un "té-magique", constituant un circuit hyperfréquence, réalisé selon le procédé selon l'invention.

The invention, as well as the various advantages which it presents, will be more easily understood thanks to the nonlimiting description which will follow from a description of its realization, with reference to the drawings, in which:

• FIG. 1 represents a perspective view of a metallized 3D antenna according to the method of the invention;
• Figures 2 and 3 show the impedance matching curves of such an antenna;
• Figure 4 shows the impedance matching curves of such an antenna;
• FIG. 5 represents a perspective view of a metallized antenna-patch according to the method of the invention;
• Figure 6 shows the adaptation diagram of such an antenna;
• Figure 7 shows a perspective view of a "magic tee", constituting a microwave circuit, produced according to the method according to the invention.

According to the method according to the invention, blocks of foam different sizes and shapes have been metallized and in some cases, provided on some of their faces with graphite. In the present embodiment, a foam marketed was used under the name DIVINYCELL marketed by the company Divinycell international, 18 allée des Moissons, 94263 Fresnes Cedex, France.

Initially, these foam blocks were pre-treated aimed at preparing their surfaces for the action of a metallization.

All the products mentioned in the following two paragraphs are marketed by the company Shipley - 2 rue Pierre Josse - ZA Les Bordes -91921 EVRY Cédex 9, France)

The pre-treatment consisted of dipping the blocks in a degreaser (reference 813) for 4 min then in an acid bath sulfuric at 3% for 2 minutes neutralizing the degreasing product. The blocks of foam were then rinsed with tap water for 2 minutes before being soaked for 3 minutes in a conditioning bath "Circuposit catalyst 3344" consisting of a colloidal tin-palladium system allowing metallization by catalysis. Blocks of foam were then rinsed with tap water for 2 min and then soaked in an accelerator bath "19H" for 2 min promoting the start of the metal depot.

After rinsing again with tap water for 2 min, the blocks thus prepared were soaked in a metallization bath to copper base and marketed under the trade name "CH 251" for 20 minutes depending on the case. This bath is a stabilized bath at EDTA, the formulation of which makes it possible to obtain a copper deposit uniform.

After metallization, a first rinse was carried out with water city for 3 minutes then a second rinse with distilled water for 2 min. The metallized blocks were then dried in the oven for 30 min at 45 ° C.

The block shown in Figure 1 thus metallized has a section 1 in V and a hole 2 metallized. At the angle of the V, the metal layer deposited was removed by scraping (the use of a protective tape during metallization could also have been used) to form a feed slot 3.

The adaptation diagrams of such an antenna are shown in Figures 2 and 3 while Figure 4 shows the diagram of radiation from such an antenna in an H plane.

The metallized block shown in Figure 5 constitutes an antenna patch and shows a U-shaped slot 4 and a connector coaxial feed 5.

The adaptation of such an antenna is shown in Figure 6.

The metallized block constituting a "magic t" shown in part to FIG. 4 constitutes a microwave power supply device which feeds two antennas either in phase (Sum 6 channel) or in phase opposition (Difference channel 7).

In order to charge channel 7, two waveguides in phase opposition, the end of the track was first cut according to a V shape then dipped in a graphite bath sold by the company Shipley. The V shape is an example and allows improves energy absorption and therefore improves load performance.

The embodiments of the invention described here are not no limiting cases. The foam blocks treated according to the invention may therefore have different sizes and shapes from those indicated without departing from the scope of the invention. Other metallization or graphite baths may also be used.

Claims (11)

1. Process for manufacturing an antenna element, characterised in that it comprises:

   at least one chemical and/or physical-chemical stage of preparation of the surface finish of a block of polyvinyl-chloride-based foam, intended to enhance the metal and graphite deposition on said block, said stage of preparation including a stage consisting in dipping said block in an acid bath;

   at least one stage consisting in dipping at least one part of one surface of said block of foam in a metallisation bath and at least one stage consisting in dipping at least one part of one surface of said block of foam in a graphite bath for a time that is adequate to coat at least one part of said block of foam with a layer of metal and graphite.
2. Process according to Claim 1, characterised in that it comprises one stage consisting in fully dipping said block of polyvinyl-chloride-based foam in said metallisation bath.
3. Process according to any one of Claims 1 or 2, characterised in that said dipping time of said block of foam in said metallisation bath and said graphite bath is between 10 minutes and 20 minutes.
4. Process according to any one of Claims 1 to 3, characterised in that said block of foam has an irregular shape integrating at least one non-plane face.
5. Process according to any one of Claims 1 to 4, characterised in that said block of foam has at least one aperture and/or one slot.
6. Process according to Claim 5, characterised in that said aperture has a diameter greater than or equal to 0.2 mm.
7. Process according to any one of Claims 1 to 6, characterised in that it comprises a preliminary stage consisting in coating one or more parts of the surface of said block of foam with one or more elements forming mask(s) and removing said element or elements forming mask(s) after said dipping stage.
8. Process according to any one of Claims 1 to 6, characterised in that it comprises a stage consisting in eliminating said layer of metal deposited on one or more parts of the surface of said block of foam.
9. Process according to any one of Claims 1 to 8, characterised in that said metal is chosen from the group made up of copper, nickel, gold, silver, titanium.
10. Process according to any one of Claims 1 to 9, characterised in that it comprises a subsequent stage of deposition of a metal by electrochemistry on the part of said block of foam previously metallised.
11. Antenna element realised by means of the process according any one of Claims 1 to 10, characterised in that it comprises at least one metallised part and at least one part coated with a layer of graphite.

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