FR3110030A1 - Method of manufacturing a waveguide and waveguide manufactured by the process - Google Patents

Abstract

A waveguide device (300) includes a body having side walls with external and internal surfaces, the internal surfaces defining a waveguide channel and being covered with a layer of conductive metal, a plurality of through-holes being arranged on at least one side wall of the body, the holes being arranged in a periodic arrangement on each wall. Figure 3a

Description

Process for manufacturing a waveguide and waveguide manufactured by the process

Field of application

The invention relates to the field of electromagnetic waveguides and more specifically to methods of manufacturing such guides.

The invention relates in particular to waveguides defined by hollow metal channels in which the radiofrequency signals propagate. The invention applies to the manufacture of waveguides but also of devices comprising such waveguides such as, for example, filters or antennas.

Issue Raised

A particular problem to be solved in the field of the manufacture of waveguides concerns the electrolytic metallization of the internal surfaces of the guide. In particular for waveguides operating at high frequencies, the dimensions of the internal cavities of a waveguide are very small, which makes the metallization step complex. For example, for waveguides operating in the E band (60-90 GHz), the dimensions of the waveguides are of the order of a few millimeters.

More generally, whatever the targeted frequency, the metallization of the internal surfaces of the guide constitutes an important step in the manufacture of a waveguide.

Prior art

A suitable metallization technique for waveguides is to use a chemical deposition method. This method consists of immersing the part to be metallized successively in one or more baths containing reactive fluids which trigger chemical reactions leading to the deposition of a chosen metallic material. This material can be copper, gold, silver, nickel or any other conductive metal.

A first drawback of this type of method concerns the appearance of air bubbles in the waveguide channel which can influence the metallization process. These air bubbles can in particular prevent contact between the reactive agents and the surface of the walls to be metallized.

A second disadvantage concerns the evacuation of reactive fluids out of the waveguide. Indeed, a stagnation of these fluids can cause a stoppage of the deposition reaction and metallization defects on certain surfaces.

A specific disadvantage of electrolysis metallization methods is that the metal deposition is not uniform, which makes it difficult to metallize the inside of the waveguide cavity. Indeed, during the electrolysis process, the metal deposit may not penetrate sufficiently inside the guide.

To solve these drawbacks, it is known, in particular from reference document [1], to provide drainage holes in the walls of the waveguide to improve the drainage of reactive fluids during the metallization step.

French patent FR3048556 describes the general principle of introducing drainage holes in the walls of a waveguide so as to allow fluid communication between the channel and the outside of the waveguide during the step. metallization of the internal walls of the guide.

However, a drawback of this method is that it has a potentially significant impact on the radio performance of the waveguide. Indeed, depending on the dimensions and the positioning of the holes, these can degrade the propagation of the wave inside the guide and cause a reduction in the transmission parameter, mismatches or other disturbances.

Answer At issue And bring solution

The present invention makes it possible to solve the drawbacks of the solutions of the prior art by proposing a specific dimensioning and positioning of the drainage holes provided in the walls of the waveguide, this dimensioning being provided to optimize the performance of the waveguide. in terms of transmission and reflection and thus have the least possible influence on the propagation of the waves and the proper functioning of the waveguide.

The subject of the invention is thus a waveguide device comprising a body comprising side walls with external and internal surfaces, the internal surfaces defining a waveguide channel and being covered with a layer of conductive metal, a plurality of through holes being provided on at least one side wall of the body, the holes being arranged in a periodic arrangement on each wall.

According to a particular aspect of the invention, the maximum distance between two consecutive holes along the propagation axis of the waveguide is less than λg/2, with λg the guided wavelength.

According to a particular aspect of the invention, the guided wavelength λg is taken at the maximum operational frequency of the device.

According to a particular aspect of the invention, the maximum distance between two consecutive holes along the propagation axis of the waveguide is between (2K-1)*λg/2 and K*λg, with K a natural integer not null and λg the guided wavelength.

According to a particular aspect of the invention, the maximum distance between two consecutive holes along the propagation axis of the waveguide is between (2K-1)*λg(Fmin)/2 and K*λg (Fmax), with K a non-zero natural number, λg(Fmin) the guided wavelength taken at the minimum operating frequency of the device and λg(Fmax) the guided wavelength taken at the maximum operating frequency of the device.

According to a particular aspect of the invention, the holes are arranged on two opposite walls of the body.

According to a particular aspect of the invention, the period of the holes is identical for the two opposite walls.

According to a particular aspect of the invention, the holes of a wall are arranged so as not to be opposite with the holes of the opposite wall.

According to a particular aspect of the invention, the holes of a wall are arranged so as to face each other with a wall section between two holes of the opposite wall.

According to a particular aspect of the invention, the holes are arranged along one or more lines in the direction of propagation of the waveguide.

According to a particular aspect of the invention, the diameter of a hole is less than or equal to 0.37λ, preferably 0.3λ, with λ the wavelength in free space at the maximum operational frequency of the device.

1. fabriquer un corps comportant des parois latérales avec des surfaces externes et internes, une pluralité de trous traversants étant aménagée sur au moins une paroi latérale du corps, les trous étant disposés selon un agencement périodique sur chaque paroi,
2. déposer une couche de métal conducteur sur les surfaces internes, par immersion dans un bain chimique.

The invention also relates to a process for manufacturing a waveguide device comprising the following steps:

1. fabricating a body having side walls with outer and inner surfaces, a plurality of through holes being provided on at least one side wall of the body, the holes being arranged in a periodic arrangement on each wall,
2. deposit a layer of conductive metal on the internal surfaces, by immersion in a chemical bath.

1. Recevoir un fichier numérique comprenant des instructions de code pour le contrôle d’un dispositif de fabrication additive, lorsque les instructions de code sont exécutées par un processeur,
2. Contrôler le dispositif de fabrication additive à partir du fichier numérique pour fabriquer ledit corps

In a variant embodiment, the method according to the invention further comprises the steps of:

1. Receive a digital file comprising code instructions for controlling an additive manufacturing device, when the code instructions are executed by a processor,
2. Control the additive manufacturing device from the digital file to manufacture said body

1. Recevoir un fichier numérique représentant un modèle 3D dudit corps,
2. Contrôler un dispositif de fabrication additive pour fabriquer ledit corps selon le modèle 3D spécifié dans le fichier numérique.

In a variant embodiment, the method according to the invention further comprises the steps of:

1. Receive a digital file representing a 3D model of said body,
2. Control an additive manufacturing device to manufacture said body according to the 3D model specified in the digital file.

Other characteristics and advantages of the present invention will appear better on reading the following description in relation to the following appended drawings.

FIG. 1 represents a waveguide model comprising two drainage holes on either side of the guide, facing each other,

FIG. 2a represents a curve of the transmission parameter S21 of the waveguide of FIG. 1 as a function of the operating frequency, for different diameters of the drainage holes,

FIG. 2b represents a curve of the reflection parameter S11 of the waveguide of FIG. 1 as a function of the operating frequency, for different diameters of the drainage holes,

FIG. 3a represents a waveguide model comprising several drainage holes arranged periodically,

FIG. 3b represents a view in longitudinal section of the waveguide of FIG. 3a in the case where the drainage holes of the two opposite faces of the guide are opposite each other,

FIG. 3c represents a curve of the transmission parameter S21 of the waveguide of FIG. 3b as a function of the operating frequency, for different values of the number of pairs of drainage holes,

FIG. 3d represents a curve of the reflection parameter S11 of the waveguide of FIG. 3d as a function of the operating frequency, for different values of the number of pairs of drainage holes,

FIG. 4a represents a view in longitudinal section of the waveguide of FIG. 3a in the case where the drainage holes of the two opposite faces of the guide are not facing each other,

FIG. 4b represents a curve of the transmission parameter S21 of the waveguide of FIG. 4a as a function of frequency, for different values of the number of pairs of drainage holes,

FIG. 4c represents a curve of the reflection parameter S11 of the waveguide of FIG. 4a as a function of frequency, for different values of the number of pairs of drain holes.

FIG. 5 represents an alternative embodiment of the waveguide of FIG. 4a.

FIG. 1 diagrams a model of electromagnetic waveguide 100 formed of a structure 101 comprising external and internal walls, the internal walls defining a cavity 102 which constitutes the wave propagation channel.

The structure 101, which constitutes the body of the waveguide, is made of a non-conductive material, for example ceramic. This structure can be manufactured by any additive manufacturing technique, for example by 3D printing, or by a plastic molding technique or more generally by any suitable manufacturing technique.

The dimensions of the structure 101 and of the cavity 102 depend on the operating frequency of the device and the desired mode of transmission.

The internal walls which define the cavity 102 are covered with a layer of conductive material, for example copper, silver, gold or nickel. The deposition of the conductive material is carried out by a chemical or electrochemical process which notably comprises a step of immersing the guide 100 in one or more baths consisting of one or more reactive fluids.

As indicated in the preamble, drainage holes are provided on the walls of the guide to improve the evacuation of air bubbles and the circulation of fluids.

These holes are not without consequence on the electromagnetic performances of the waveguide. One objective of the invention is to determine the most optimal dimensioning of the drainage holes to limit their impact on the propagation in the guide.

For this, the performance of a waveguide is simulated, for example by means of structural analysis software adapted to the simulation of the propagation of electromagnetic waves. The simulations are carried out by varying various parameters of dimensioning and number of drainage holes.

The invention can also be applied to waveguides whose structure 101 is made of metal, for example aluminum, and whose internal surfaces of the cavity 102 are covered with a finishing material to improve the conductivity. The finishing material is, for example, silver or gold. In this case, it is the layer of finishing material that is deposited by a chemical or electrochemical process.

Figure 1 schematizes an example of a waveguide comprising two identical drainage holes facing each other crossing two opposite walls of the guide.

Figure 2a plots the transmission parameter S21 of the waveguide in Figure 1 as a function of signal frequency for different radii of the drain holes. The transmission parameter S21 corresponds to a transmission coefficient of the wave between the input and the output of the waveguide. The performances of the guide in transmission are optimal when the transmission parameter S21 is closest to 0dB. In other words, the more the transmission parameter (expressed in dB) decreases, the more it means that parasitic reflection phenomena occur and that part of the wave will not be transmitted or propagated towards the output of the waveguide.

In the example illustrated in Figure 2a, the simulated frequencies are in the E band, i.e. [60; 90 GHz] for a 50mm long waveguide with a single pair of drain holes and a waveguide section of dimensions 3.1mm by 1.55mm.

Curves 201,202,203,204,205,206,207 correspond respectively to drain hole radii of 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm and 0.8mm. which corresponds to diameters varying from 0.12λ to 0.48λ at a frequency of 90 Hz.

It can be deduced from the results presented in FIG. 2a that the larger the diameter of the holes, the more significant the impact on the reduction in the transmission parameter, as can be observed for curve 207. In particular, in FIG. can observe that the parameter S21 decreases for a radius strictly greater than 0.5mm, which corresponds to a diameter of the hole equal to 0.3λ at 90GHz.

Figure 2b shows the waveguide reflection parameter S11 for the same parameters. The reflection parameter S11 corresponds to a wave reflection coefficient at the waveguide input.

The performances of the guide in reflection are optimal when the reflection parameter S11 is the lowest possible. In other words, the more the reflection parameter (expressed in dB) increases, the more it means that parasitic reflection phenomena occur and that part of the wave will not be transmitted or propagated towards the output of the waveguide.

Curves 211,212,213,214,215,216,217 correspond respectively to drain hole radii of 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm and 0.8mm.

It can be observed that the parameter S11, expressed in dB), increases with the increase in the radius of the hole, which also means that the part of the wave reflected at the input of the guide increases with the size of the hole. Otherwise expressed, the module |S11| of the reflection parameter increases with the increase in the radius of the holes.

The simulation results presented in Figures 2a and 2b lead to the conclusion that the performances in transmission and in reflection remain acceptable for a drainage hole having a diameter less than or equal to 0.3λ with λ the wavelength in free space at the highest target frequency.

The increase in the radius of the holes degrades both the adaptation (parameter S11) and the transmission (parameter S21), however the effects on the transmission are negligible for a hole diameter less than or equal to 0.3λ and the adaptation remains at a sufficiently low level (< - 25 dB).

In a second step, we seek to simulate the impact of several holes periodically arranged on two opposite walls of the guide as shown in Figure 3a.

FIGS. 3b and 4a represent a view in longitudinal section along a median plane perpendicular to the z axis, of the waveguide 300 for two layout configurations of the drainage holes. In the first configuration 301 represented in FIG. 3b, the holes are arranged opposite the holes of the opposite wall. In the second configuration 401 shown in Figure 4a, the holes are arranged in "staggered", that is to say they are vis-à-vis the wall between two adjacent holes of the opposite face of the guide of waves.

The waveguide of Figure 3b is an E-band guide, whose cross section has a width a=3.1mm and a height b=1.55mm and whose total length L is equal to 50 mm. The drainage holes have a radius of 0.5mm. The distance between two centers of two adjacent holes varies from 8.33mm (5 holes per face) to 1.22 mm (40 holes per face).

Figure 3c shows different simulation results of the transmission parameter S21 for the waveguide of Figure 3b as a function of frequency and for different numbers of holes. The respective curves 311,312,313,314,315,316,317,318 correspond to a number of pairs of holes respectively equal to N=5,N=10,N=15,N=20,N=25,N=30,N=35,N=40. A pair of holes corresponds to two holes arranged respectively on two opposite faces of the waveguide.

The curves in FIG. 3c make it possible to show a reduction in transmission for certain frequencies and certain numbers N. For example, for N=15 and a frequency of 67.5 GHZ, a drop in the transmission parameter of the order of -2dB.

By analysis, it can be deduced that a drop in the transmission parameter appears when the following relationship is respected:

λ _g /2 = L/(N+1) with L the total length of the guide, N the number of pairs of holes and λ _g the guided wavelength, i.e. the wavelength in the propagation channel. The term L/(N+1) corresponds to the distance d between two adjacent holes represented in FIG. 3b.

As a reminder, the wavelength of a signal propagating in a rectangular waveguide is expressed by:

Where m and n express the mode TE _mn of the guide, a the width and b the height of the guide, and the wavelength in free space:

where c is the speed of light and f is the frequency.

By limiting ourselves to the fundamental mode TE ₁₀ of the waveguide, the equation is simplified:

Thus the guided wavelength λ _g is dependent on the wavelength in free space, on the propagated mode (generally TE ₁₀ ) and on the dimensions of the guide.

Figure 3d shows the simulation results of the reflection parameter S11. An increase in the reflection parameter can be observed for the same pairs (frequencies, number of holes) as in Figure 3c.

In general, a drop in the transmission parameter or an increase in the reflection parameter appears when the following relationship is respected:

K*(λ _g /2) = L/(N+1)=d, with K a nonzero natural integer.

For example for N=5 we have L/(N+1) = 8.33 mm . For a frequency of 72.3 GHz, 3*λg/2 = 8.37 mm L/(N+1). For a frequency of 86.4 GHz we have 4*λg/2 = 8.38 mm L/(N+1).

Figure 4b shows different simulation results of the transmission parameter S21 for the waveguide of Figure 4a as a function of frequency and for different numbers of hole pairs.

The waveguide of Figure 4a is an E-band guide, whose cross section has a width a=3.1mm and a height b=1.55mm and whose total length L is equal to 50 mm. The drainage holes have a radius of 0.5mm. The distance between two centers of two adjacent holes varies from 8.33mm (5 holes) to 1.22 mm (40 holes). The distance between two adjacent holes is shown in Figure 4a, it is the distance between two consecutive holes regardless of the face on which the hole is arranged. In this case, d' = L/2*(N+1).

The respective curves 411,412,413,414,415,416,417,418 correspond to a number of pairs of holes respectively equal to N=5,N=10,N=15,N=20,N=25,N=30,N=35,N=40, in other words the number of holes on one face of the guide.

Figure 4c shows different simulation results of the reflection parameter S11 for the waveguide of Figure 4a as a function of frequency and for different numbers of holes.

The respective curves 421,422,423,424,425,426,427,428 correspond to a number of pairs of holes respectively equal to N=5,N=10,N=15,N=20,N=25,N=30,N=35,N=40, in other words the number of holes on one face of the guide.

The curves in figures 4b and 4c make it possible to deduce that the adaptation is strongly degraded when the following relation is respected:

K*λg/2= L/2*(N+1)=d'

For example for N=10 at 81.3GHz the guided wavelength is 4.59 mm and the distance in the direction of propagation between two successive holes is 2.27mm or λg/2.

For N=5 the distance in the direction of propagation between two successive holes is 4.16mm or λg/2 at 60.3GHz and λg at 86.8GHz.

The distance of = L/2*(N+1) corresponds to the distance between two consecutive holes in staggered rows on the two opposite faces. In other words, the distance d' corresponds to an offset between the row of periodic holes on the first face and the row of periodic holes on the second face, in a longitudinal section plane of the guide (the plane represented in FIG. 4a).

From the previous simulation results, it can be deduced that an optimal dimensioning for the distance D between two consecutive holes in the direction of wave propagation in the waveguide is D< λg/2. Depending on the case, the distance D is d or d'. Indeed, by respecting this rule, a degradation of the transmission or reflection parameters is avoided for all the lower frequencies and the number of holes is maximized, which makes it possible to improve the metallization process.

The minimum value of distance D depends on the one hand on the diameter of the holes and on the technological feasibility of making small-sized holes.

Without departing from the scope of the invention, intermediate configurations between 301 and 401 can be envisaged, that is to say configurations for which the holes arranged in a wall of the guide are arranged partially opposite the holes of the opposite wall and wall portions between two holes of the opposite wall.

Such an example is represented in FIG. 5. In this case, the rule to be observed is that the greatest distance d ₂ between two consecutive holes must be less than λg/2 (d ₂ <λg/2).

In all cases, the dimensioning rule to be respected in order to optimize the performance of the waveguide and the metallization process, is that the maximum distance between two consecutive holes along the propagation axis of the waveguide must be less than λg/2 at maximum frequency.

This maximum distance is equal to d in the case of figure 3b, to d' in figure 4a and to d ₂ in the case of figure 5.

Without departing from the scope of the invention, other dimensioning rules making it possible to obtain similar transmission performances are possible.

In fact, the simulation results described previously make it possible to conclude that, to avoid degradation of the transmission or adaptation (reflection) parameters, a general criterion to be respected is that the distance D (d, d' or d ₂ ) be different of K* λg/2, with K a nonzero natural integer, at all frequencies of interest.

In this case, we can set a general criterion defined by the following relationship:

K*λg > D > (2K-1)*λg/2

In particular, in the case where the guide is used to operate in a narrow frequency band, it is possible to define a distance D greater than λg/2 (of the maximum frequency of this band) without having parasitic reflection peaks, such as this has been demonstrated previously.

For example, for a frequency band of 70 to 75 GHz in the guide presented in figure 3a (a=3.1; b=1.55mm), i.e. a guided wavelength of 5.93mm to 5.23mm, if the periodicity of the holes is 4mm, parasitic reflection peaks are avoided.

In the case of a dimensioning provided for a frequency band [Fmin; Fmax] and not a single frequency, the dimensioning criterion to be respected becomes: K*λg (F _max ) > D > (2K-1)*λg (F _min ) /2, with λg (F _max ) the length of guided wave at frequency F _max and λg (F _min ) the guide wavelength at frequency F _min .

This second optimization criterion is suboptimal from the point of view of the metallization process because in this case the density of the holes is not maximum, but remains optimal from the point of view of the electromagnetic performance of the waveguide.

The invention also extends to configurations for which two or more rows of holes are made on each face of the guide.

As indicated in the preamble, the body of the waveguide comprising the drainage holes can be manufactured by an additive manufacturing technique, for example a stereolithography technique (SLA), a printing technique by digital light processing (Digital Light Processing DLP or Continuous Digital Light Processing CDLP), a printing technique by fused deposition modeling (Fused Deposition Modeling FDM), inkjet (binder jetting), DED (direct energy deposition), EBFF (electron beam freeform manufacturing), by BPM (ballistic particle manufacturing) aerosols, SLS (selective laser sintering) powder bed, ALM (additive layer manufacturing), this list is not exhaustive.

In the case of additive manufacturing, a 3D digital model, of the CAD file type, can be used to define the surface or the volume of the body including the drainage holes.

This 3D digital model is then transformed into an instruction file compatible with the chosen additive manufacturing technology to control an additive manufacturing device to produce the body of the waveguide.

References

[1] Reference document on the best available techniques, Surface treatment of metals and plastics, August 2006, European Commission.

Claims (14)

A waveguide device (300,301,401,501) comprising a body having side walls with outer and inner surfaces, the inner surfaces defining a waveguide channel and being covered with a layer of conductive metal, a plurality of through holes being arranged on at least one side wall of the body, the holes being arranged in a periodic arrangement on each wall. Waveguide device according to Claim 1, in which the maximum distance (d,d',d ₂ ) between two consecutive holes along the propagation axis of the waveguide (301,401,501) is less than λg/2, with λg the guided wavelength. A waveguide device according to claim 2 wherein the guided wavelength λg is taken at the maximum operating frequency of the device. Waveguide device according to Claim 1, in which the maximum distance (d,d',d ₂ ) between two consecutive holes along the propagation axis of the waveguide (301,401,501) is between (2K-1) *λg/2 and K*λg , with K a nonzero natural integer and λg the guided wavelength. Waveguide device according to Claim 4, in which the maximum distance (d,d',d ₂ ) between two consecutive holes along the propagation axis of the waveguide (301,401,501) is between (2K-1) *λg(Fmin)/2 and K*λg (Fmax), with K a non-zero natural number, λg(Fmin) the guided wavelength taken at the minimum operating frequency of the device and λg(Fmax) the length of guided wave taken at the maximum operating frequency of the device. Waveguide device according to one of the preceding claims, in which the holes are arranged on two opposite walls of the body. A waveguide device according to claim 6 in which the period of the holes is identical for the two opposite walls. Waveguide device according to one of Claims 6 or 7, in which the holes of one wall are arranged so as not to face each other with the holes of the opposite wall. Waveguide device according to one of Claims 6 or 7, in which the holes of one wall are arranged so as to face a wall section between two holes of the opposite wall. Waveguide device according to one of the preceding claims, in which the holes are arranged along one or more lines in the direction of propagation of the waveguide. Waveguide device according to one of the preceding claims, in which the diameter of a hole is less than or equal to 0.37λ, preferably 0.3λ, with λ the wavelength in free space at the maximum operational frequency of the device. Process for manufacturing a waveguide device comprising the following steps:

• fabricating a body having side walls with outer and inner surfaces, a plurality of through holes being provided on at least one side wall of the body, the holes being arranged in a periodic arrangement on each wall,
• deposit a layer of conductive metal on the internal surfaces, by immersion in a chemical bath.

A method of manufacturing a waveguide device according to claim 12 further comprising the steps of:

• Receive a digital file comprising code instructions for controlling an additive manufacturing device, when the code instructions are executed by a processor,
• Control the additive manufacturing device from the digital file to manufacture said body

A method of manufacturing a waveguide device according to claim 12 further comprising the steps of:

• Receive a digital file representing a 3D model of said body,
• Control an additive manufacturing device to manufacture said body according to the 3D model specified in the digital file.