EP0228742A1 - Plane microwave antenna with suspended strip lines, and method for its production - Google Patents

Abstract

Flat multi-element microwave antenna for the reception of satellite television made up of at least two metal sheets (156, 157) on which are screened spacers (4, 19) and on which at least one block (50) is attached ) waveguides (2), the assembly of two such sheets constituting a sandwich enclosing a printed circuit (195) carrying microwave lines which open into the waveguide.

Description

The present invention relates to a planar microwave antenna composed of a plurality of radiating elements (receivers or, according to the principle of reciprocity of antennas, transmitters), having at least one network of planar lines arranged on a dielectric sheet of the "lines" type. with completely suspended substrate "enclosed between at least locally metallic or metallized devices in which recesses placed facing one another are drilled to form elementary open or closed waveguides, the ends of the central conductors of the planar lines being arranged inside these waveguides so as to constitute probes which carry out a coupling allowing the reception (or the emission) of microwave signals, and pads being provided to hold the dielectric sheet at a certain distance from said devices .

The present invention further relates to a method for manufacturing an antenna component.

Such antennas are used in particular for the reception of television broadcasts by satellite, at a frequency of approximately 12 GHZ.

A microwave plane antenna comprising a plurality of such elements has been described in the French patent application ^No. 2544920. It is described including an arrangement for maintaining transmission lines component or the antenna feed networks. Each of the microwave line networks consists of a printed circuit deposited on a thin sheet of dielectric serving as a substrate sandwiched between two metal plates or in metallized dielectric. Each network is arranged so that the ends of the central conductors of the lines are located opposite square recesses drilled respectively in each of the plates which enclose it so as to achieve coupling between the lines and the recesses. Each dielectric sheet carrying the network of central conductors printed with microwave lines is held between the plates which enclose it by positioning studs located on the faces of these plates, facing each other and on either side of this sheet, these pads being further disposed relative to this sheet, in spaces devoid of printed circuits.

Such an antenna has the disadvantage that the plates, constituting both the main framework of the antenna and the waveguide system, must have good rigidity and high dimensional accuracy. Metal plates with such a complex structure are expensive and also very heavy. Metallized plastic plates have thermal expansion characteristics which are unsuitable for producing a large antenna which must operate as well at -40 ° as in direct summer sun.

To overcome these drawbacks, the antenna according to the invention is particularly remarkable in that the "plates" are replaced there by composite devices each consisting of a thin sheet of metal pierced with recesses, on one side of which is applied to the at least one block constituting a plurality of waveguides, and on the other face of which the spacing pads are located, and in that all of the sheets are held by a single rigid frame.

Thus the thin and pierced sheet has a very simple shape and can therefore be produced economically, for example by punching. The block constituting a plurality of waveguides is attached to this sheet and held by it, it is therefore not subject to severe mechanical precision requirements and can therefore be produced in an eco-friendly manner. nomique. The term “thin sheet” is understood to mean the fact that it has a thickness that is too small to ensure sufficient rigidity by itself. It is relatively flexible, and is held in position by the chassis, which therefore constitutes a kind of marble to keep the sheets flat. There is therefore now a single rigid part: the chassis, which holds several sheets, instead of the plurality of complex self-supporting plates of the prior art. The antenna according to the prior art also has the disadvantage that, the pads can only be placed in positions where the sheet has no printed circuit, we are subject to the following alternative: or else we use a large number of small-sized studs, which is expensive because a mold for molding such a part is difficult to produce, or else few studs are used, with the disadvantage that the surface of the sheet parts suspended between the studs is important and therefore it is not well maintained everywhere in an ideal position: in the presence of unfavorable climatic conditions, the sheet can expand in significant proportions vis-à-vis the support devices, and the resulting displacement degrades the performance of the antenna.

This problem is completely solved by the antenna according to the invention which, in a preferred embodiment, has spacing pads constituted by areas of dielectric material deposited by screen printing, the design of which represents, practically, outside surfaces corresponding to the recesses of the sheets, a design similar, but in negative, to that of the network of lines, in which the latter would be enlarged.

This embodiment is easily implemented since the sheets, relatively thin and of constant thickness, are easily introduced into a common screen printing machine, and it makes it possible to obtain without difficulty a large number of pads of complex shape. In addition, these dielectric pads little disturb the characteristic impedance. only lines that pass nearby.

It is quite difficult to find enough space to accommodate a sufficient density of pads for good maintenance of dielectric sheets. This is why it is advantageous to make the recesses of the sheets with a circular or cross shape, so as to save space in the corners for accommodating studs, a place which does not exist with art squares. prior.

The dielectric material is advantageously charged with particles, themselves made of dielectric material, these particles being for example possibly hollow beads made of glass or plastic. Thus the studs resist crushing better and their dielectric constant is lower. In addition, the rheological characteristics of the material are better suited to deposits of significant thickness, and the material is cheaper (the particles are much cheaper than their binder).

Advantageously, the particles are transparent. This facilitates the penetration of light when using a polymerizable material with ultraviolet rays.

To simplify the manufacturing tools and especially to eliminate problems of relative expansion, a waveguide block is advantageously subdivided into several blocks fixed independently of each other on the same pierced sheet. Each of these blocks itself constitutes a plurality of waveguides.

In an advantageous variant, a block constituting a plurality of waveguides consists of two series of flat walls, the two series being assembled to form a matrix of cells.

This arrangement makes it possible to significantly reduce the cost of the waveguide blocks, while maintaining correct performance.

In an advantageous variant, blocks of closed waveguides are formed by recesses hollowed directly in one face of the frame applied to the face back. This arrangement simplifies the construction of the antenna since it saves the manufacture and assembly of the closed waveguide blocks.

In addition, the antenna being housed in a protective casing, the rear wall of this casing advantageously constitutes the above-mentioned chassis. This arrangement is economical since the same mechanical part fulfills two functions at the same time.

To facilitate the manufacture of the antenna and improve its performance, a preferred method for manufacturing a sheet provided with studs consists of screen printing the studs with a polymerizable dielectric material and only partially polymerizing it. Thus during the assembly of the components of the antenna, the material remains sticky and the components are fixed to each other as soon as they are assembled. Bonding the parts improves their mechanical strength and forces the dielectric sheets to "follow" the expanding sheets. This process is simpler than that according to which the material of the studs is traditionally polymerized and then deposits adhesive thereon.

• La figure 1 représente en coupe une partie d'une antenne comportant deux réseaux de lignes hyperfréquence, réa­lisée selon l'invention.
• La figure 2 représente une vue en plan de la même partie d'antenne.
• La figure 3 représente une variante de réalisa­tion des blocs constituant une pluralité de guides d'onde.
• La figure 4 représente un exemple d'un mode de fi­xation des constituants de l'antenne les uns aux autres.
• La figure 5 représente, partiellement en coupe, une antenne complète.

The description which follows, with reference to the appended drawings describing nonlimiting examples will make it clear how the invention can be implemented.

• FIG. 1 represents in section a part of an antenna comprising two networks of microwave lines, produced according to the invention.
• Figure 2 shows a plan view of the same antenna portion.
• FIG. 3 represents an alternative embodiment of the blocks constituting a plurality of waveguides.
• FIG. 4 represents an example of a method of fixing the components of the antenna to each other.
• Figure 5 shows, partially in section, a complete antenna.

Figure 1 which is a sectional view along line A of Figure 2 shows components of an antenna separated from each other for better clarity of the figure. The antenna is composed of a network of planar lines arranged on a dielectric sheet 195 and a second similar network arranged on a dielectric sheet 196, these networks are each sandwiched between devices made of metallic or metallized material. The lines carried by the sheets 195 and 196 are not shown, because their thickness on the scale is too small to make them visible. One of these devices comprises the elements referenced 50 and 156, another of these devices comprises the elements referenced 49 and 159. In all of these devices are recessed holes which constitute elementary waveguides 2, into which the ends open lines, as will appear more clearly from the description of Figure 2. Pads, 4, 14 are provided to hold the dielectric sheets 195, 196, at a certain distance from said devices.

According to the invention these devices consist of a flat sheet 156 and pierced with holes 6, on one side of which is applied a block 50 constituting a plurality of waveguides 2, and on the other side of which are located spacers 4. Another of these devices is similarly formed by the sheet 159 pierced with holes. 6, the block 49, constituting wave guides, and separation pads 14.

In the example described here, the antenna further comprises two additional sheets 157, 158, each provided with spacing pads 19, 20. If it were desired to space the two dielectric sheets 195, 196 it would be easy to have between the sheets 157, 158 of the additional waveguide blocks similar to the blocks 50, which would then constitute a third device according to the invention. The sheets 156, 157, 158, 159 are made of aluminum and have a thickness of 1 mm, the blocks 49, 50 are molded, for example in thermoplastic plastic material, called "ABS" and metallized, and the dielectric sheets carrying the line networks are made from a 70 micron "mylar" sheet thick covered with a copper sheet of 35 microns which is engraved to constitute the lines. It is possible to use even smaller thicknesses for the dielectric sheet, with the aim of further reducing the losses; one could use for example a sheet of Kapton of 25 microns, but the latter is more expensive than the sheet of mylar. The material used to form the pads is advantageously charged with particles of dielectric material; these particles are for example possibly hollow beads made of glass or plastic. The screen-printed spacers 4, 14, 19, 20 have a thickness of 0.8 mm. They are produced by screen printing using a screen of adequate thickness; the screen consists of a mesh fabric wide enough to let the above balls pass, covered with one or more layers providing the desired thickness, in photo-sensitive material, and the patterns of the studs are obtained, by means of 'photographic processing, on this screen.

Figure 2 shows the same components as Figure 1, but without the upper sheet 156 to reveal the network of lines 1. The latter generally have a width of 1.8 mm. They have narrower parts at the "T" connections to adapt the impedance. The screen-printed studs 19, 29 of the sheet 157 can be seen by transparency through the sheet of mylar 195.

The recesses 6 have the shape of a cross, while the waveguides 2 are of square section. References 7 and 8 respectively indicating a point on the perimeter of the waveguide and a point on the perimeter of the recess show how they are placed relative to each other. One can also make recesses of circular shape. However, the cross shape is more advantageous in the case of a wave with two orthogonal polarizations. The spacing studs 19, seen through the sheet 195 are represented by hatched zones surrounded by dotted lines. The drawing of the beaches silk-screened constituting these studs practically represents in negative a drawing similar to that of the network of lines, drawing in which the latter would be widened there. By the words "negative" is meant that the material is absent where the lines are present. Such a drawing can be easily obtained by means of computer-assisted drawing equipment. With this equipment, it is possible to draw bands having the same center line as the microwave lines, but wider, and to add the network of cross recesses. In the absence of such equipment, it is possible to make the same drawing. It is then necessary to use a cliché of transparent lines on a black background, and to make a negative counter-type by moving the cliché in all directions during the exhibition. The amplitude of this displacement is of course equal to the desired enlargement for the lines. This gives a black drawing of the enlarged lines, which then suffices to superimpose the black drawing of the recesses. In FIG. 2, the drawing of the studs comprises a blank corridor along the block 50, to its left and at the top: this is due to the fact that there is a line, hidden under the edge of the block 50.

The reference 3 indicates the end of a line of the network carried by the sheet 195, end which opens into the waveguide 2 to produce a coupling probe allowing the reception of microwave waves; the reference 30 indicates in the same way a probe of the network carried by the dielectric sheet 196. When the recesses have a cross shape as here, the width of the probes must be slightly increased compared to that of the lines. It is about 2.5 mm.

The references 29 indicate studs placed in angles of recesses, studs which it would have been impossible to place with square recesses.

The interval between two rows of recesses in both directions is 23 mm.

In the figure only a block of waveguides 50 has been shown, so as to leave visible next to this block the network of lines. It is quite obvious that other blocks of waveguides analogous to block 50 must be mounted over the entire surface of the antenna; these blocks are separated from each other which makes it possible to reduce the effect of the different expansions of the plastic material of these blocks on the one hand and of the aluminum constituting the sheets on the other hand. The waveguide blocks 50 are provided with pins such as 5 in FIG. 1, which allow the blocks 50 to be fixed on the sheets. Holes 17, intended to receive these lugs, are visible in FIG. 2.

The repetitive configuration of the line network makes it easy to reconstruct the rest of the antenna which is not shown in the figure. An antenna can be constituted for example by sixteen blocks 50 each comprising sixteen waveguides 2 arranged in a rectangle of eight on two blocks. The drawing of the network of lines carried by the sheet 196 is different from that shown in FIG. 2, so that the lines emerge perpendicular to those of the sheet 195. The drawing of this network (not shown) can be easily imagined from the drawing shown. In addition, schematic examples of these two drawings are given in the patent application cited in the introduction.

As it appears in FIG. 1, the antenna according to the present example comprises two arrays of lines, each of them corresponding to a direction of polarization of the wave, so that the antenna can operate with two different polarizations. One of them is constituted by the dielectric sheet 195 carrying lines, placed between 2 identical drilled sheets 156, 157 sheets provided with spacers on their internal faces. The second network is constituted in the same way by the elements 158, 196, 159.

It is easy to understand that the spacers 4 and 19 or 20 and 24 could also have been deposited by serigraphy on both sides of each sheet 195, 196 instead of being deposited on the metal sheets 156 to 159. However, the deposit on the sheets is much easier.

The manufacture of an antenna according to the invention is facilitated by the fact that a polymerizable dielectric material is used for the pads, and that it is only partially polymerized before assembling the components of the antenna. Thus this material remains sticky when the sheets are brought into the desired position on either side of the dielectric sheets 195, 196 and then pressed against one another by clamping the dielectric sheets, which secures the various layers together. Of course a complete anaerobic polymerization is obtained thereafter, possibly accelerated by an addition of heat. In addition, it is possible to provide additional mechanical means for perfecting this fixing. The dielectric material is, for example, an adhesive which can be polymerized by ultraviolet light, sold under the trade name Framet, reference LI 553. A charge of transparent glass beads is added thereto.

FIG. 3 represents an alternative embodiment of the blocks constituting a plurality of waveguides. According to this variant, the blocks are formed by mounting the two series of walls. A first series of walls 9 is located, perpendicular to the plane of the antenna, between each line of recesses and a second series of walls 10 is located in the same way between each column of recesses.

The two series thus assembled form a matrix of cells, each cell 12 of which constitutes a waveguide and corresponds to a recess 6 of the sheets. The walls 9 carry cutouts 11 on half their height and the walls 10 have similar cutouts on the other half of their height in order to allow their assembly in the manner of internal separators of cardboard packaging.

The walls 9, 10 are made of aluminum. As a result, the matrix of cells can cover the entire surface of the antenna at one time, since its coefficient of expansion is the same as that of the sheets 156 to 159.

The fixing of this matrix of cells can be carried out by means of tongues, 13, cut during the manufacture of the walls. To receive these tongues, the holes 17 in FIG. 2 are advantageously replaced by rectangular holes (not shown), corresponding to the section of the tongues 13 and into which the latter are introduced, then twisted. The matrix can also be glued to the sheet 156.

Figure 4 shows in detail the assembly means of the antenna. There are the four sheets 156, 157, 158 and 159, respectively provided with spacing pads 4, 19, 20 and 14 and enclosing the sheets 195 and 196. The lug 18, belonging to the block of open waveguides upper is fixed in a hole of the sheets 156 and 157. The lug 5 belonging to the block of closed waveguides lower is fixed in a hole of the sheets 159 and 158. The sheet 157 is applied directly against the sheet 158. The the antenna assembly is mounted on a chassis, a small portion of which is shown hatched at 22. A pin 21 is fixed in the material of this chassis and the stack constituting the antenna, provided with suitable holes, is fixed to the chassis at using such pins and clips 23 forcibly pressed onto the pins.

FIG. 5 represents a complete antenna: the two parts in section each represent an alternative embodiment. It goes without saying that in practice these two variants would not be present together in the same antenna!

At the bottom left, the variant is the same as that described in FIGS. 1 and 4. There are the same references 22 for the chassis, 49 and 50 for the waveguide blocks. The reference 15 includes the stacking of the sheets previously referenced 156 to 159. The antenna is housed in a protective case, the rear wall 22 of which constitutes the above-mentioned chassis.

Top right, the waveguide block is constituted by the walls 9, 10 described with reference to FIG. 3. The closed waveguides placed at the rear of the stack 15 are constituted by recesses 23 dug directly into the face of the frame 22, which is here the rear wall of the case, applied to the rear face of the rear sheet of the stack 15.

In front of the previously described components is placed a depolarizer 25 intended to allow the antenna to operate in circular polarization and which is not part of the invention, and a cover 24 for closing the case, cover obviously transparent to electromagnetic radiation. , for example in polyurethane.

The case is made by molding. It can be metallic, but it is more advantageous to make the same material as the cover 24, which makes it possible to economically make a sealed assembly with the latter by bonding. In this case, the parts constituting the closed rear waveguides 23 must be made conductive on the surface, for example by means of a conductive paint (charged with conductive particles) deposited for example by spraying. These conductive particles are grounded simply by their contact with the rear sheets of the stack.

It goes without saying that the combinations of variants shown are not exclusive, and that it is equally possible to use subdivided blocks 50 with rear waveguides 23 incorporated in the housing, or a front block based on plane walls 9, 10 with a rear block 49. This rear block can also be produced on the basis of flat walls similar to those of FIG. 3, the closing of the guides then being ensured by the face of the chassis on which they are applied.

Of course, the present invention is not limited to an antenna with two networks of microwave lines. If one wants to have a planar antenna intended to receive or transmit microwave signals of a single type of polarization, said antenna can be obtained from that which has been described previously, by simply omitting the superfluous constituents.

Finally, it is clear that the application of the invention to the reception of 12 gigahertz television signals retransmitted by satellites is not limiting. On the one hand, the invention is applicable to all kinds of purely terrestrial microwave transmission networks, and on the other hand, the choice of an example of application at the frequency of 12 gigahertz is not exclusive of any other operating frequency, in the microwave range, linked to another envisaged application. The dimensions of the waveguides and their intervals should then of course be modified.

Claims (11)

1) microwave planar antenna composed of a plurality of radiating elements, having at least one network of planar lines disposed on a sheet of dielectric sandwiched between at least locally metallic or metallized devices in which recesses are drilled to form guides open or closed elementary wave into which the ends of lines open, studs being provided to hold the dielectric sheet at a certain distance from said devices, characterized in that these devices each consist of at least one thin sheet of metal pierced with recesses, on one side of which is applied at least one block constituting a plurality of waveguides, and on the other side of which are located the spacing pads, and in that all of the sheets are held by a unique rigid chassis. 2) Antenna according to claim 1, characterized in that the spacing pads consist of areas of dielectric material deposited by screen printing. 3) Antenna according to claim 2, characterized in that the design of the screen-printed areas constituting the spacers represents, practically, outside the surfaces corresponding to the recesses of the sheets, a design similar, but in negative, to that of network of lines, in which the latter would be extended. 4) According to one of the preceding claims, characterized in that the recesses in the sheets have a circular or cross shape. 5) An antenna according to any one of claims 2 to 4 characterized in that the dielectric material of the pads is charged with particles of dielectric material. 6) Antenna according to claim 5, characterized in that the particles are transparent. 7) Antenna according to any one of the preceding claims, characterized in that on the same rigid pierced sheet are applied several separate blocks constituting each killing a plurality of waveguides. 8) Antenna according to any one of claims 1 to 7 characterized in that at least one of the above blocks constituting a plurality of waveguides consists of two series of planar walls, the two series being assembled to form a matrix alveoli. 9) Antenna according to any one of the preceding claims, characterized in that closed waveguides are formed by recesses hollowed directly in one face of the frame, applied to the rear face of the rear sheet. 10) Antenna according to any one of the preceding claims, housed in a protective case, characterized in that the chassis is constituted by the rear wall of this case. 11) Method for manufacturing an antenna according to any one of the preceding claims, characterized in that a dielectric polymerizable material is used for the pads and in that it is only partially polymerized before assembling the components of the antenna .

Images