EP2058896A1 - Process for manufacturing a thick plate electroformed monobloc microwave source - Google Patents

Abstract

The method involves fixing a side (C) of an outlet of wave guide such that a chosen fundamental mode is within a bandwidth of a microwave source. Other sides (A, B) of the wave guide are set such that a guide section does not propagate the fundamental mode in the bandwidth. An arbitrary side (D) of the wave guide is set. Height (h1, h2, h3, h4) and/or length of a thick lamination of the source are determined to obtain performance of the source set by a given application. An independent claim is also included for a thick plate electroformed monobloc microwave source comprising a thick lamination.

Description

The present invention relates to a method for manufacturing a monobloc microwave source by electroforming and thick-plate polarizer better known as thick septum.

It finds its application in the field using sets of microwave sources / antennas. It can be implemented for satellite communications applications.

Circularly polarized space telecommunication antennas often use waveguide structures when a strict criterion of polarization purity is specified. Among them, the quadrature-powered four-port polarization system, the septum polarizer and the orthomode tee coupled to a screw polarizer remain the most used. However, the size and the mass of these systems disadvantage their use in certain applications and in particular in the low bands of telecommunications frequencies (bands L, S, C).

Antenna level intermodulation has been a known problem for communications satellite manufacturers for many years. This problem also exists in the case of GSM antennas (abbreviated Anglo-Saxon Global system for Mobile).

In the case of terrestrial satellite stations, the use of certain bands in multicarrier mode imposes to solve technical problems related to the metallic contacts appearing during the realization of the antenna and the source. Among the technical problems, there are adjustments by screws / plungers, flange-type interfaces, patches. It is known from the prior art that one of the best approaches is to achieve a minimum of parts and use an electroforming technology for the construction of microwave sources. One of the constraints to respect is then that the electrical design of the microwave source is adapted to allow its realization in this particular method.

Another disadvantage encountered in the field of microwave structures is that they lead to relatively large device sizes. Thus, a solution given in the patent is to manufacture an assembly formed of an antenna and a set of horns commonly known in Anglo-Saxon "horn".

The patent US 6,861,997 describes a polarizer for use in antennas associated with waveguides. The idea implemented in this patent consists in using two waveguides having a common wall. The shape of the central wall consists of several teeth whose shape and dimensions allow the septum to transform the linear polarization of a wave into a circular polarization and reciprocally.

However, the devices of the prior art generally consist of connecting two rectangular guides to form a single square section guide through a blade generally cut into steps. This process works well if the blade is very thin, as for example in the patent US 5,305,001 , for which the blade has a thickness of about 0.76 mm.

The figure 1 represents a block diagram of an X-band circular polarization satellite communication station. The emission signal passes through an emission amplifier 1 and then into a transmission filter 2 before the polarizing orthomode 3 whose function is to transform the transmission signal. initial polarization, for example, a linear polarization into a circular polarization, and then is emitted through the horn 4 of the reflector antenna. The signal is then received by the antenna before passing through the orthomode polarizer 3, then by a reception filter 5 and a low noise amplifier 6. Practice shows that the filtering is necessary but not sufficient to eliminate the problems of intermodulation encountered in the microwave field. Indeed, other nonlinearities are present along the chain. They come in particular from all contacts between metals introduced by the assembly of the source at the focus of the antenna. These contacts for example, the flanges of the connecting guides, the plungers with filter adjustment screws.

When the frequency plan used in a satellite communication system includes very similar reception and transmission frequencies, for example the 7.25-7.75 GHz range for reception and the 7.9-8.4 GHz transmission interval, for example when a station transmits several carriers (from 2 carriers, for example), there may be additional frequencies generated. For frequencies between 8.0 GHz and 8.4 GHz, any non-linearity of the transmission system will create additional frequencies, the most powerful of which are 7.6 and 8.8 GHz. The frequency 7.6 GHz is located in the reception band, which will lead to be particularly demanding on the quality of linearity of the system so as not to cause self-jamming.

The software known to those skilled in the art, for example, the software having as registered trademark MICIAN for microwavewizard to synthesize and simulate different structures.

As far as the Applicant is aware, the performances obtained by the devices according to the prior art do not however make it possible to maintain the desired performances while increasing the thickness of the blade beyond 2 mm.

The idea of the invention is based on a new approach which consists in carrying out all the microwave functions in the form of a single piece. The microwave source is a monoblock source. In fact, the phenomena of non-linearity are non-existent or negligible.

The invention relates to a microwave and polarizer source characterized in that it is formed of an electroformed monobloc comprising a septum or thick blade, greater than 1 mm thick.

The source comprises at least the following elements: a horn, an orthomode / polarizer a transmission band pass filter, a transmission band stop filter, a reception bandpass filter, a reception band stop filter.

The blade or septum comprises, for example, a number of steps and a widening D at the level of the access guides, said widening being disposed in an intermediate position along the blade.

• ○ utiliser un procédé d'électroformage,
• ○ fixer la côte C du guide de sortie afin que seul un mode fondamental choisi, du guide de la cote C soit dans la bande passante utile de la source hyperfréquence,
• ○ fixer la cote A correspondant sensiblement à la moitié de la largeur du guide d'onde pris dans sa partie élargie au moyen d'un décrochement D et B la hauteur du guide d'ondes afin que le guide de section (2*A+H, B) ne propage que le mode fondamental dans la bande passante,
• ○ fixer une côte arbitraire pour le décrochement D,
• ○ déterminer la hauteur et/ou la longueur des marches de la lame épaisse, afin d'obtenir des performances de la source hyperfréquence fixées par une application donnée,
• ○ modifier la côte D et réitérer les étapes précédentes afin d'optimiser le résultat des performances.

The invention also relates to a method for manufacturing a thick-plate polarizer microwave source characterized in that it comprises at least the following steps:

• ○ use an electroforming process,
• ○ set the coast C of the output guide so that only a chosen fundamental mode, the guide of the dimension C is in the useful bandwidth of the microwave source,
• ○ fix the dimension A corresponding substantially to half the width of the waveguide taken in its widened portion by means of a recess D and B the height of the waveguide so that the section guide (2 * A + H, B) propagates only the fundamental mode in the bandwidth,
• ○ set an arbitrary scale for the offset D,
• ○ determine the height and / or the length of the steps of the thick plate, in order to obtain performance of the microwave source fixed by a given application,
• ○ modify the D-side and repeat the previous steps to optimize the performance result.

The mode used is for example the TE10 mode.

The selected frequency band is the 7.25 GHz and 8.4 GHz frequency band.

• La figure 1, un synoptique d'une station de communication par satellite en polarisation circulaire,
• La figure 2, un schéma rappelant brièvement le procédé par électroformage,
• La figure 3, un exemple de lame ou septum selon l'art antérieur,
• La figure 4, un schéma d'une source monobloc selon l'invention,
• La figure 5, un détail du polariseur à lame épaisse selon l'invention.

Other features and advantages of the present invention will appear better on reading the description of an exemplary embodiment given by way of illustration and in no way limiting attached to the figures which represent:

• The figure 1 , a synoptic of a circular polarization satellite communication station,
• The figure 2 , a diagram briefly recalling the process by electroforming,
• The figure 3 an example of a blade or septum according to the prior art,
• The figure 4 , a diagram of a monoblock source according to the invention,
• The figure 5 , a detail of the thick-film polarizer according to the invention.

The figure 2 is a reminder of the electroforming process. This process consists in depositing a metal, for example copper, by electrolysis on an aluminum mandrel. At the end of this deposition, the mandrel is dissolved and a hollow piece of copper of "waveguide" type is obtained. Certain characteristics of the process impose to respect geometrical rules, such as, the relation between the width of a hollow and its depth. On the figure 2 the piece 10 is an aluminum piece on which is made a copper deposit 11 of thickness e. The minimum width I of the hollow is imposed according to the depth p.

On the figure 3 is recalled the very thin blade described in the patent US 5,305,001 wherein the source is formed of two rectangular cavities 20, 21 and a very thin blade 22 or "septum" whose thickness is of the order of 0.7 mm.

• ○ cornet 30
• ○ orthomode/polariseur 31
• ○ filtre passe bande émission 32
• ○ filtre stop bande émission 33
• ○ filtre passe bande réception 34
• ○ filtre stop bande réception 35.

The figure 4 represents a monobloc X-band source according to the invention, the size of the object being approximately 1 m. The monoblock source includes the following functions:

• ○ cornet 30
• ○ orthomode / polarizer 31
• ○ transmit band pass filter 32
• ○ stop filter band emission 33
• ○ reception bandpass filter 34
• ○ reception band stop filter 35.

The entire one-piece structure according to the invention is designed so that there is no sharp angle of small sizes, but also that the steps of the blade are rounded as shown in FIG. figure 5 . This avoids these sharp and small angles that are poorly reproduced by the electroforming process including this piece whose geometry must be very precise.

The method according to the invention comprises, for example, the following steps:

An extension of the access guides is created in an intermediate position along the blade, represented by the recess D on the figure 5 . This enlargement or recess has the particular function of compensating for the thickness of the thick blade obtained in the end. The thick leaf or septum is at least 1 mm for example.

According to an exemplary embodiment, by referencing the different sides with respect to the wavelength used, the polarization orthomode according to the invention has for example the following characteristics: AT ~ Λ / 4 11.5mm B ~ Λ / 2 23.5 VS ~3λ / 4 32mm H side of the blade or septum 5mm D (2A + H -B) / 2 2.25mm I1 ~ Λ / 6 8mm (rounded) 12 ~ Λ / 3 15mm (rounded) 13 ~ Λ / 3 15mm (rounded) 14 ~ Λ / 3 15mm (rounded) h1 ~ Λ / 4 12mm (rounded) h2 ~h1 / 2 6mm (rounded) h3 ~h2 / 2 3mm (rounded) h4 ~h3 / 2 1.5mm (rounded)

With A corresponding to half the width of the waveguide taken in its enlarged part,
B height of the waveguide,
C the width of the waveguide at the input output of the wave,
H the width of the blade,
D the offset chosen to compensate for the thickness of the blade, I1, I2, I3, I4 the length of the 4 steps of the thick blade,
h1, h2, h3, h4 the corresponding height of the 4 steps, the height being measured relative to a reference corresponding to the inner wall of the waveguide in contact with the steps.

• ○ Fixer la cote C du guide de sortie pour que seul le mode fondamental TE10 du guide de coté C soit dans la bande passante utile de la source hyperfréquence, par exemple en bande X (7.25-8.4GHz),
• ○ Fixer les cotes A et B pour que le guide de section (2*A + H, B) ne propage que le mode fondamental TE10 dans la bande passante de la source hyperfréquence,
• ○ Fixer une cote D arbitraire,
• ○ Optimiser la hauteur et la longueur des marches de la lame pour obtenir les performances voulues qui dépendent de l'application et sont, par exemple, : le TOS de chaque entrée, l'isolation entre entrée 1 et entrée 2, le rapport axial de l'onde en sortie de C et pour chaque entrée 1 ou 2,
• ○ Modifier la cote D et réitérer les étapes précitées.
  En suivant ces étapes, le procédé selon l'invention permet d'obtenir une source hyperfréquence monobloc électroformée à polariseur à lame épaisse.

From data set at startup, the method then comprises the following steps:

• ○ Fix dimension C of the output guide so that only the fundamental mode TE10 of the side guide C is in the useful bandwidth of the microwave source, for example in X band (7.25-8.4 GHz),
• ○ Fix the dimensions A and B so that the section guide (2 * A + H, B) only propagates the fundamental mode TE10 in the bandwidth of the microwave source,
• ○ Set an arbitrary D dimension,
• ○ Optimize the height and length of the steps of the blade to achieve the desired performance depending on the application and are, for example: the TOS of each input, the insulation between input 1 and input 2, the axial ratio of the wave output from C and for each input 1 or 2,
• ○ Modify dimension D and repeat the above steps.
  By following these steps, the method according to the invention makes it possible to obtain an electroformed monobloc microwave source with a thick-plate polarizer.

1. a) La source hyperfréquence à réaliser est décomposée en différents éléments.
2. b) Chaque élément est réalisé en négatif (un guide d'onde creux devient une pièce pleine) dans un type défini d'aluminium par un procédé mécanique qui peut être soit de l'usinage soit de la découpe au fil. Ces éléments sont appelés mandrins.
3. c) Les différents mandrins sont assemblés par un procédé de tenon-mortaise de sorte que toutes les parties métalliques d'interconnexion soient étroitement en contact afin de garantir une bonne continuité électrique de l'ensemble mécanique, continuité nécessaire au procédé d'électroformage.
4. d) Par électrolyse, un dépôt de cuivre d'environ 3mm d'épaisseur est crée sur cet assemblage.
5. e) L'ensemble des mandrins en aluminium est finalement dissous dans une solution alcaline, la partie en cuivre étant inerte vis-à-vis de cette solution.
6. f) La source hyperfréquence monobloc en cuivre est ainsi obtenue après nettoyage des oxydes de cuivre résiduels.

Since electrical performance is related to the absence of discontinuities (separation or contact zones between different metals) over the entire surface of the sources, the method of producing the mandrel is chosen so that:

1. a) The microwave source to be produced is broken down into different elements.
2. b) Each element is made of a negative (a hollow waveguide becomes a solid part) in a defined type of aluminum by a mechanical process that can be either machining or cutting the wire. These elements are called mandrels.
3. c) The different mandrels are assembled by a tenon-mortise process so that all the interconnecting metal parts are closely in contact in order to ensure good electrical continuity of the mechanical assembly, continuity necessary for the electroforming process.
4. d) By electrolysis, a copper deposit about 3mm thick is created on this assembly.
5. e) The set of aluminum mandrels is finally dissolved in an alkaline solution, the copper part being inert with respect to this solution.
6. f) The copper monoblock microwave source is thus obtained after cleaning the residual copper oxides.

Claims (5)

- A method for manufacturing a thick-plate polarizer monoblock microwave source characterized in that it comprises at least the following steps: ○ using an electroforming process to form the source and the thick-plate orthopolarizer comprising a waveguide, ○ said thick blade consisting of at least four steps of width I1, I2, I3 and I4 and of height respectively h1, h2, h3 and h4, said blade having a width H, D being a setback chosen to compensate for the thickness said blade, ○ said waveguide having a coast C corresponding to the output of the waveguide, a rib A corresponding substantially to half the width of the waveguide taken in its enlarged part, a rib B corresponding to the height of said waveguide; waveguide, ○ set the coast C of the output guide so that only a chosen fundamental mode, the guide of the dimension C is in the useful bandwidth of the microwave source, ○ fix the dimension A by means of a step D and B the height of the waveguide so that the section guide (2 * A + H, B) propagates only the fundamental mode in the bandwidth, ○ set an arbitrary scale for the offset D, ○ determine the height and / or the length of the steps of the thick plate, in order to obtain performance of the microwave source fixed by a given application, ○ modify the D-side and repeat the previous steps to optimize the performance result. - Method according to claim 1, characterized in that the electroforming step comprises at least the following steps: ○ Each element of the microwave source is made of negative, these elements are called mandrels, ○ The different mandrels are assembled by a tenon-mortise process so that all the interconnecting metal parts are closely in contact in order to guarantee a good electrical continuity of the mechanical assembly, By electrolysis, a copper deposit approximately 3 mm thick is created on this assembly, ○ The set of aluminum mandrels is finally dissolved in an alkaline solution, the copper part being inert with respect to this solution in order to obtain the monoblock copper microwave source. - Method according to claim 1, characterized in that it uses the TE10 mode. - Method according to one of claims 1 or 2, characterized in that the selected frequency band is the frequency band 7.25 GHz and 8.4 GHz. - Microwave source and electroformed monobloc polarizer having a septum or thick blade, characterized in that it is obtained by performing the steps of the method according to one of claims 1 to 4.

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