FR2780319A1 - Antenna element, especially a 3-D antenna or associated microwave circuit, energy dissipater or screening box for communication systems - Google Patents

Abstract

An antenna element production process involves direct metal and/or graphite coating of a synthetic foam block of acidic pH from a coating bath. An antenna element is produced by direct metal and/or graphite coating of a synthetic foam block of pH below 7 from a coating bath. An Independent claim is also included for an antenna element produced by the above process and comprising a foam block having a directly contacting metal layer, preferably one or more metallized portions and one or more graphite coated portions. Preferred Features: The block may have an irregular shape with one or more non-planar faces and optionally with one or more holes (of \-0.2 mm diameter) and/or slits. The entire foam block is immersed in the metal and/or graphite coating bath for 10-20 min. Alternatively, one surface of the block is dipped in a metallization bath and another surface is dipped in a graphite bath. Parts of the foam block may be temporarily covered with masking elements or the metal coating may be removed from parts of the metallized block. The metal coating consists of copper, nickel, gold, silver or titanium. The block may be chemically and/or physically pretreated to improve deposition of metal and/or graphite and, after metallization, may be electroplated.

Description

Foam coating process for manufacturing antenna elements.

  The invention relates to the field of manufacturing antenna elements.

  It will be noted that, in the present description, the term "elements" means

  antennas ", both the antennas themselves, the microwave circuits (such as the waveguides in particular) associated with them, the energy dissipators and the shielding boxes associated with such antennas and such microwave circuits. The present invention finds particular application for the

  creation of three-dimensional antennas.

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

  having a relative dielectric constant of the order of 2 to 3.

  The increase in bandwidth required for many high speed communication systems can be done by increasing the thickness of the dielectric layer. This solution is however not technically satisfactory for conventional polymers, insofar as part of the energy is guided by surface waves, which leads to a reduction in yield and an increase in the weight of the assembly. It has therefore already been proposed in the prior art to use for the production of the antennas a foam of cellular synthetic material, since such a material has a dielectric constant which avoids surface waves and which allows the assembly to stay light. It was also envisaged to place several metal pellets

  separated by insulating layers and thereby increase the bandwidth.

  However, until now, foams have been mainly used as wedges

  thick or rigidification support for circuits.

  Furthermore, despite the interest presented by the use of such foams for

  the production of antennas, such use is limited to planar antennas.

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

  The main objective of the present invention is to present a method which allows the easy production of three-dimensional antennas. Such antennas in

  three dimensions indeed find many applications.

  Another objective of the present invention is to describe such a process which also allows the deposition of graphite layers on blocks of foam, in order to form coatings which can be used as charges for adaptation or dissipation of the residual energy d 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 large

  reproducibility, and according to simple implementation steps.

  These various objectives are achieved thanks to the invention which relates to a method of manufacturing an antenna element characterized in that it comprises at least one step consisting in bringing into direct contact at least a part of a block of foam. of synthetic material having a pH below 7 with at least one metallization bath and / or a graphite bath for a time sufficient to coat the entire portion of the surface of said foam block with a layer

of metal and / or graphite.

  The invention therefore proposes to dip all or part of a block of foam in a metallization bath and / or a graphite bath allowing the deposition of the metal.

  and / or graphite on a given surface of the block.

  Metallization baths and / or graphite baths which can be used are known from the state of the art and conventionally used for metallization

  and / or the deposition of a graphite coating on metallic supports.

  It will be noted that these baths exhibit a basic behavior which implies the need to use a foam of alveolar synthetic material having a pH below 7, therefore of acid behavior, for the implementation of 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 specified above, the method according to the present invention very particularly finds its application for the production of antennas in three dimensions. Consequently, according to a preferred variant of the invention, the method comprises a step consisting in fully dipping said block of foam of synthetic material in said bath of

  metallization and / or said graphite bath.

  The soaking time of the foam block in the metallization bath and / or 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 time of

  soaking will generally be between 10 minutes and 20 minutes.

  As already specified above, the process will find its particular

  interest in making three-dimensional antennas, especially when these

  these will have a complex shape. According to an interesting variant of the process, the foam block therefore has an irregular shape including at least one non-planar face. According to another variant, this block of foam will have at least one hole and / or a slot which may, thanks to the process, be entirely metallized or coated with graphite. Such holes will 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 produce antenna elements having certain metallized surfaces and certain surfaces coated with graphite. This is why, according to an advantageous variant of the method, it comprises at least one step consisting in dipping at least part of a surface of a block of foam in a metallization bath and at least one step consisting in dipping in at least part of a surface of said foam block in

a graphite bath.

  According to a variant of the method, the method according to the invention comprises a preliminary step consisting in coating one or more parts of the surface of said block of foam with one or more elements forming cover (s) and in removing the or

  said elements forming cover (s) after said soaking step.

  It will thus be possible to manufacture antenna elements of which certain parts will not be metallized, in particular for coating these non-metallized parts

later graphite.

  According to another variant, the method comprises a step consisting in removing said layer of metal deposited on one or more parts of the surface of said block of foam. This step of removing part of the metal layer on one or more parts of the surface of the foam block can be carried out by removing

  also part of this block of foam.

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

silver, titanium.

  According to a variant of the invention, the method also comprises at least one chemical and / or physicochemical step for preparing the surface state of said

  foam block to improve the deposition of metal and / or 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.

  Different foams can be used to carry out the process according to the invention from the moment when it has a pH of less than 7. Such a foam can for example consist of certain foams based on

polyvinyl chloride.

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

direct contact with said foam.

  Preferably, said antenna element comprises at least one part

  metallized and at least part coated with a layer of graphite.

  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 my

  realization thereof, with reference to the drawings, in which: - Figure 1 shows a perspective view of a 3D antenna metallized 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; - Figure 5 shows 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 "t-magic", constituting

  a microwave circuit, produced according to the method according to the invention.

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

  aimed at preparing their surfaces for the action of a metallization bath.

  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 in dipping the blocks in a degreaser (reference 813) for 4 min then in a 3% sulfuric acid bath for 2 min neutralizing the degreasing product. The foam blocks were then rinsed with tap water for 2 minutes before being soaked for 3 minutes in a bath.

  "Circuposit catalyst 3344" conditioner consisting of a colloidal tin system

  palladium allowing metallization by catalysis. The foam blocks were then rinsed with tap water for 2 min and then soaked in an accelerator bath.

  "19H" for 2 minutes favoring the start of the metallic deposit.

  After rinsing again with tap water for 2 min, the blocks thus prepared were soaked in a metallization bath based on copper and sold under the trade name "CH 251" for 20 min depending on the case. This bath is a bath stabilized with EDTA whose formulation makes it possible to obtain

a uniform copper deposit.

  After metallization, a first rinse was carried out with tap water for 3 min and then a second rinse with distilled water for 2 min. The metallized blocks have

  then dried in an 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 layer of deposited metal was removed by scraping (the use of a protective strip during metallization would have

  could also be used) to form a feed slot 3.

  The adaptation diagrams of such an antenna are shown in FIGS. 2 and 3 while FIG. 4 shows the radiation diagram of such an antenna in an H plane. The metallized block shown in FIG. 5 constitutes a patch antenna and watch

  an adaptation U-shaped slot 4 and a coaxial power connector 5.

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

  The metallized block constituting a "magic tee" shown in part in FIG. 4 constitutes a microwave power supply device which makes it possible to supply two antennas either in phase (Sum channel 6) or in phase opposition (Difference channel 7). In order to carry out the loading of track 7, two waveguides in phase opposition, the end of the track was first cut in a V shape and then dipped in a graphite bath sold by the company Shipley. The V shape is an example and improves energy absorption and therefore improves

load performance.

  The embodiments of the invention described here are in no way limiting. 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 foams, other metallization or graphite baths

  can also be used.

Claims (14)

  1. A method of manufacturing an antenna element characterized in that it comprises at least one step consisting in bringing into direct contact at least part of a block of foam of synthetic material having a pH of less than 7 with at least a metallization bath and / or a graphite bath for a time sufficient to coat all of said part of the surface of said foam block with a layer of metal and / or graphite.   2. Method according to claim 1 characterized in that it comprises a step consisting in fully dipping said block of foam of synthetic material   in said metallization bath and / or said graphite bath.   3. Method according to any one of claims 1 or 2 characterized in that   that said soaking time of said foam block in said metallization bath   and / or said graphite bath is between 10 min and 20 min.   4. Method according to any one of claims 1 to 3 characterized in that   said block of foam has an irregular shape including at least one non-planar face.   5. Method according to one of claims 1 to 4 characterized in that said block   foam has at least one hole and / or slot.   6. Method according to claim 5 characterized in that said hole has a   diameter greater than or equal to 0.2 mm.   7. Method according to one of claims 1 to 6 characterized in that it comprises   at least one step of dipping at least part of a surface of a block of foam in a metallization bath and at least one step of dipping at least part of a surface of said block of foam in a bath of graphite.   8. Method according to any one of claims 1 to 7 characterized in that   that it comprises a preliminary step consisting in coating one or more parts of the surface of said block of foam with one or more elements forming cover (s)   and removing the at least one cover element (s) after said soaking step.   9. Method according to any one of claims 1 to 7 characterized in that   that it comprises a step consisting in eliminating said layer of metal deposited on   one or more parts of the surface of said foam block.   10. Method according to any one of claims 1 to 9 characterized in that   said metal is chosen from the group consisting of copper, nickel, gold, silver, titanium.   1 1. Method according to any one of claims 1 to 10 characterized in that   that it comprises at least one chemical and / or physico-chemical step of preparing the surface state of said block of foam aimed at improving the deposition of metal and / or graphite.   12. Method according to any one of claims 1 to 11 characterized in that   that it comprises a subsequent step of depositing a metal by electrochemistry on the   part of said block of foam previously metallized.   13. Method according to any one of claims 1 to 12 characterized in that   that said foam is a polyvinyl chloride-based foam.   14. Antenna element produced by the method according to any one of   Claims 1 to 13, characterized in that it consists of a block of foam   of which at least part of at least one of the faces is coated with a layer of   metal in direct contact with said foam.   15. An antenna element according to claim 14 characterized in that it comprises at least one metallized part and at least one part coated with a layer of graphite.