EP0651458B1 - Method for manufacturing a planar antenna - Google Patents

Description

Technical area

The present invention relates to process for producing a planar antenna.

State of the art

The invention is part of the large market for Telecommunications. In fact, we have been witnessing for several years unprecedented take-off of a new Telecommunications service, that of connections with mobile terminals commonly called "mobile". These connections are to be considered both for fixed system and mobile connections as for the connections between mobiles.

Such connections are made possible by the enormous advances in electronics, particularly integrated components (M.M.I.C.), and that of energy sources (batteries).

In a link equipment, the antenna is the sub-assembly the most visible and often the most bulky exterior. She must have always better performance, for ever greater discretion, and an ever lower cost.

After intensive research work conducted among academics as among industrialists from the most developed countries, it is appeared that the so-called "printed" or "flat" antennas represented the best possible solution.

Antenna performance depends on technology chosen. The realization of flat antennas involves the use of supports exhibiting low losses, and the lowest possible dielectric constant. These supports can be made of organic materials having such characteristics. Particularly advantageous organic materials are those in expanded form or "foam". The constant dielectric of these is very close to that of air and their weak losses allow a significant improvement in antenna performance, particularly for frequencies around the GHz, or a few GHz. For other frequency ranges, the use of organic supports unexpanded is also possible.

• de diélectrique ;
• de radôme ;
• de rigidificateur.

Up to now, the different available foams have been used as an interface between several conductive planes and mechanically maintained to serve:

• dielectric;
• radome;
• stiffener.

But such achievements involve a number of constraints, due to the constituents which must be assembled with precision, and which do not not necessarily allow great ease of integration.

Also, currently, antenna designers wish have a technology in which the conductive planes would be directly associated with the foam, and selectively deposited.

The invention aims to solve such a problem.

We will analyze below various art documents prior.

WO 93/09577 describes different types of terrestrial antennas capable of transmitting and receiving radio signals directly to or from from satellites with low Earth orbit and in particular an antenna formed of elements each comprising conductive layers arranged in on either side of a layer of foam.

US-A-4937585 describes an antenna which comprises a polyethylene foam substrate, a plane mass on one face of the substrate and of the radiating elements deposited on a plastic layer, which can be made of polypropylene, and which adheres to the surface of the substrate. The deposit of the elements radiant is done on the plastic layer by a screen printing method, the layer then being reported on the foam substrate.

Statement of the invention

The invention relates to a method for producing an antenna. called plane, according to claim 1.

In certain exemplary embodiments, the support can be previously shaped.

It is possible to transfer onto at least one of the faces of the antenna, a (or more) layer (s) of metallized support materials by interposing one (or several) sheet (s) of adherent organic material The layer of material adherent organic can be polypropylene or a copolymer of polypropylene. The layers are juxtaposed by pressing or calendering, hot.

Advantageously, the foam is an imide foam of polymethylmethacrylate.

The antenna of the invention can comprise on at least one of its faces one (or more) layer (s) of metallized support materials, in interposing one (or more) sheet (s) of adherent organic material.

The antenna of the invention may include electrical connections, between conductive planes, made using conductive paste, or by any other type of conductive material.

Advantageously, the radome is a layer of foam organic, or a layer of polypropylene or polypropylene copolymer, or a protective varnish.

Brief description of the drawings

• Figures 1 to 7 illustrate different characteristics of the invention;
• Figures 8A and 8B, 9A and 9B illustrate examples useful for understanding of the invention.

Detailed description of embodiments

• sur une mousse organique ;
• sur un polymère non expansé ;
• sur un stratifié associant mousse et polymère non expansé.

The method of the invention relates to the production of printed antennas by selective deposition of a conductive layer, namely:

• on an organic foam;
• on an unexpanded polymer;
• on a laminate combining foam and unexpanded polymer.

The method of the invention also includes the production of antennas multilayer circuits by association of elements defined above, as well as making connections between conductive layers located in planes different. It makes it possible to create antennas by directly associating a protective radome or any other element, such as a polarizer, under a homogeneous shape.

According to the invention, the technique used to carry out these antennas consists of a deposit on a support material of metallic products, directly defining the geometry of the conductive parts of the circuits. This deposit is generally followed by a transformation operation of these products intended to make them adhere to the support materials and good drivers. It can be done by screen printing, stamping, spraying, or by any other method of deposit. Processing intended to give the deposit all its conductivity, for example heat treatment, exposure with different radiations: infrared, ultraviolet ..., can also be realized.

In the following description, the deposit will be made, as example, by screen printing followed by heat treatment.

Creation of antennas on organic foam

In an example already known in the prior art, illustrated in FIG. 1, for use in the radiofrequency field, the choice of foam as the support material 10 is first dictated by the search for interesting electrical characteristics: a low dielectric constant, close to 1, and low losses, less than 10 ^-3 . The foam must be a rigid foam capable of withstanding temperatures at least equal to those of cooking pasta between 120 ° C and 200 ° C.

In some cases it is interesting, as illustrated in Figure 3, to give the foam a particular shape, before depositing selective conductive parts 11. The shaping of the foam can be obtained by cold or hot pressing thereof in a suitable mold, or by mechanical machining.

• il faut qu'en final le dépôt obtenu possède la meilleure conductibilité possible ;
• il faut que ses différents constituants soient compatibles avec la nature de la mousse.

The conductive paste 11 to be screen printed consists of metallic elements suspended in an organic vehicle. Its choice is made according to two essential criteria:

• in the end, the deposit obtained must have the best possible conductivity;
• its various constituents must be compatible with the nature of the foam.

Other factors may influence the choice of this dough conductive such as being able to get a good definition circuits made or good weldability, etc.

In an exemplary embodiment, the circuits are produced by serigraphy. However, in the case of circuits intended for high frequencies, certain precautions must be observed: obtain the best definition possible geometries and a good regularity of thickness is necessary. In the case of double-sided circuits, the alignment precision of the patterns of a facing the other side of the foam is important ....

By its very nature, the surface of a foam has often a relatively large roughness, which can affect accuracy conductors. As illustrated in the figure 2, an insulating paste is deposited forming a uniform layer 12 on one or two sides of the foam support material 10 before depositing the metallic products 11. Such a layer 12 has the effect of improving the state of area. The insulating paste must be chosen so as not to disturb, or disturb the electrical characteristics of the support as little as possible. he can be interesting to choose the organic vehicle constituting the conductive paste. After polymerization of this insulating layer, the realization of the antenna is done with the classic screen printing technique.

Antennas on foam - polymer laminates unexpanded thermoplastic

If given the performance required by the antenna, the condition foam surface is penalizing, and if the dielectric constants of unexpanded materials are too high, a compromise is found in performing a metallic deposition 11 on a laminate made of a foam 10 covered on one or both sides with an unexpanded thermoplastic polymer 17, as shown in FIG. 4. This laminate can be produced for example by a hot pressing operation.

The choice of foam is made according to the defined criteria previously. There is also an obligation, that of being able to bear pressures of a few bars at a temperature of 120 ° C or more.

The thermoplastic material is still chosen according to its low dielectric constant and its low losses. In addition its temperature softening must be lower than the deformation temperature under foam charge.

The choice of conductive paste is made according to two criteria defined above.

Realization of antennas with several dielectric levels of the same dielectric constant or of dielectric constants different

From circuits produced according to variants of the the invention defined above, it is possible, as illustrated in FIG. 5, to realize multilayer circuits in particular by hot pressing.

The connection between the different circuits is done through a thin thickness 13 thermoplastic film, chosen according to the selection criteria support material, as defined above. In addition, its temperature of softening should be less than that of the carrier materials previously defined. Its implementation cycle includes a temperature-pressure juxtaposition.

As illustrated in Figure 6, it is possible to make conductive links 15 between the different conductive levels 11. These connections can be made in different ways known to the man of art, for example by metallization using conductive pastes, or by inserts metal.

In many cases, printed antennas require protection against the environment by a radome 16. This can be made with a layer of organic material, expanded or not. Fixation of such a radome on the antenna which has just been described can be produced, as illustrated in FIG. 7, using the antenna production technique comprising several dielectric levels. previously described.

In an example useful for understanding the invention, an antenna present as a double-sided printed circuit, as illustrated in the figures 8A and 8B.

The support material 20 is made of polymethacrylate imide foam, with a density 51 Kg / m ³ , having the following characteristics provided by the manufacturer. Dielectric constant at 2.8 GHz and 20 ° C εr2 = 1.07 Tangent of the loss angle tgδ2 = 8.10 ^-4 Thickness h2 = 3 mm

The metal deposits 21 and 22 are produced by screen printing of a paste composed of an organic binder based on ethylcellulose charged with silver as described above. We have the following characteristics: Conductivity σ1 = σ3 = 50 mΩ / □ Average thickness h1 = h3 = 40 µm Dimensions of the ground plane L1 = W1 = 160 mm Dimensions of the radiating element L3 = W3 = 64 mm

This antenna is supplied by a coaxial probe 23 located on the median of the radiating element 21 at a distance of 10.25 mm of the Center.

This antenna transmits in the L band around 2 GHz. The radio characteristics of this were measured and are collated in the following table: Resonance frequency 1.975 GHz Bandwidth at ROS <1.5 2.2% Gain 7.5 dB

These results, along with the radiation patterns, are quite comparable to those obtained with laboratory prototypes made using glued copper film.

In another example useful for understanding the invention an antenna with two coupled radiating elements is produced on a laminate combining foam and unexpanded polymer. The antenna is presented as a two-layer antenna produced as illustrated in FIGS. 9A and 9B.

Epaisseur h4 = 40 µm environ

Conductivité = 50 mΩ/□

L4 = W4 = 74 mm

The metal deposit 31 constituting the upper radiating element is produced by screen printing of a paste composed of an organic binder based on ethylcellulose charged with silver as described above:

Thickness h4 = about 40 µm

Conductivity = 50 mΩ / □

L4 = W4 = 74 mm

εr5 = 1.07

tgδ5 = 8.10^-4

h5= 10mm

The support material 30 is a polymethacrylate imide foam with a density of 51 Kg / m ³ having the following characteristics:

εr5 = 1.07

tgδ5 = 8.10 ^-4

h5 = 10mm

Layer 32 is a layer of highly expanded unexpanded polymer thin with thickness h6 = 20 µm and dimensions 200 x 200 mm.

εr7 = 2,2

Tfδ7 = 10^-4

h7= 1,6 mm

L7 = W7 = 200 mm

Layer 33 is a polypropylene layer, the characteristics of which are as follows:

εr7 = 2.2

Tfδ7 = 10 ^-4

h7 = 1.6 mm

L7 = W7 = 200 mm

L8 = W8 = 64 mm

L9 = W9 = 200 mm

The metal deposits 34 and 35 respectively constituting the second radiating element and the ground plane are produced using a copper strip 20 μm thick. Their respective dimensions are as follows:

L8 = W8 = 64 mm

L9 = W9 = 200 mm

The antenna is fed on the diagonal by a probe 36, at level of the lower conductor 34, at a distance of 41 mm from the center.

This antenna transmits in the L band around 1.5 GHz. Its characteristics have been measured and gathered in the following table: Resonance frequency 1,490 - 1,640 GHz Bandwidth at ROS <1.5 11.5% Gain 9.52 dB Opening to 3dB plans E and H 60 °

This type of antenna can be fully realized with all conductive levels obtained using screen-printed silver paste.

Claims (10)

1. Process for producing a flat-top antenna operating at a frequency of a few GHz and comprising at least one circuit layer, in which, for each circuit layer, a metallization takes place by the direct deposition of a conductive material layer (11) on all or part of at least one surface of an organic material support, defining the conductive portions of said circuit, characterized in that the support is formed prior to said direct deposition by a laminate constituted by a foam layer (10) covered on at least one of its two faces by an unexpanded, organic material layer (17), the deposition of the conductive material layer taking place on the unexpanded, organic material layer and in that the organic material has a dielectric constant below 2.5 and losses below 10^-3.
2. Process according to claim 1, wherein the conductive material is constituted by a conductive paste with an organic binder based on silver-filled ethyl cellulose.
3. Process according to either of the claims 1 and 2, wherein a transformation operation takes place on the conductive material layer (11) so as to make it adherent to the support and a good conductor.
4. Process according to one of the claims 1 to 3, wherein the organic material support is previously shaped prior to the selective deposition of the conductive material layer (11).
5. Process according to one of the claims 1 to 4, wherein to at least one of the faces of the antenna is connected one or more metallized support material layers (11) by intercalating one or more adherent, organic material sheets (13).
6. Process according to claim 5, wherein each adherent organic material layer is of polypropylene or polypropylene copolymer.
7. Process according to either of the claims 5 and 6, wherein the juxtapositioning of the layers takes place by hot calendering or pressing.
8. Process according to one of the claims 5 to 7, wherein electrical connections (15) between conductive planes (11) are produced with the aid of a conductive paste formed from an organic binder based on silver-filled ethyl cellulose.
9. Process according to one of the claims 1 to 8, wherein deposition takes place of a radome (16), formed from an organic foam, polypropylene, polypropylene copolymer or protecting lacquer layer adhering to one of the outer faces of the antenna.
10. Process according to one of the claims 1 to 9, characterized in that the foam is a polymethacrylate imide foam.

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