Charge for microwave circuit

Abstract

A load for terminating a waveguide (110) in a microwave circuit is provided. The load is configured to form a transmission line (211) terminated by a short circuit at the end of the waveguide, the dimensions of the transmission line being chosen so as to increase the intensity of the electromagnetic wave currents carried from the waveguide to the load. The load further comprises a non-uniform height transmission line (202) configured to perform impedance matching between the waveguide and the transmission line (211). The transmission line is folded back on itself. The invention also relates to the manufacture of the load by an additive manufacturing method. Figure for abstract: Fig. 2b

Description

Title of the invention: Charge for microwave circuit Technical field

[0001] The invention lies in the field of microwave frequencies, and relates more particularly to the production of a load, i.e. a component intended to be fixed at the end of a waveguide, and whose function is to absorb the RF energy delivered to it and to transform it into thermal energy. Prior art

[0002] Loads (or termination loads) are microwave components designed to transform electromagnetic energy transmitted to them into thermal energy in order to dissipate it. They are used to make signals of no interest disappear. For example, they are frequently found in association with couplers, in order to orient the signal power, or with circulators configured to act as isolators.

[0003] The most widespread state-of-the-art solution for a microwave load consists of inserting into a short-circuited waveguide portion an absorbent material such as silicon carbide (SIC) or Eccosorb™rEccosorb™ being a rigid material composed of magnetically charged epoxy bars or sheets.

[0004] [Fig.l] represents a guided load according to the state of the art. The load 100 comprises a flange 101, by which it is connected to the waveguide 110 of which it is to serve as a termination, hereinafter called “waveguide to be terminated”. The flange 101 could be replaced by any holding means. For example, the load 100 could be welded to the waveguide. It then comprises two distinct parts: a waveguide part 102, made of aluminum, and an absorbent part 103, made of silicon carbide or Eccosorb™.

[0005] This solution, however, has several flaws: - the machining of the absorbent part 103 is complex, as is the precise assembly of the absorbent part 103 with the waveguide 102. The manufacture of the load 101 is therefore complex and costly, - absorbent materials, particularly silicon carbide, exhibit temperature instability. The load performance is therefore not stable over time, - communicating the heat from the absorbing material 103 to the metal of the waveguide 102 to dissipate it is complex, which can lead to limitations on the application cases depending on the power of the absorbed signals, - manufacturing times are long.

[0006] An aim of the invention is therefore to propose a microwave load which is not very complex and inexpensive to manufacture, without absorbent material, and which has good performance, so that it can be used instead of loads based on absorbent material.

[0007] Furthermore, some equipment, such as satellite antennas, can contain several hundred charges. Another aim of the invention is therefore to propose a compact solution that can be easily integrated into the design of radiocommunications equipment. Summary of the invention

[0008] To this end, the present invention relates to a load configured to maximize signal dissipation by exploiting surface current losses of the waveguides. The proposed load is entirely metallic, which allows it to be manufactured very simply, and to be easily integrated into the design of equipment.

[0009] It describes a load for terminating a waveguide in a microwave circuit. The load is configured to form a transmission line terminated by a short circuit at the end of the waveguide. The dimensions of the transmission line are chosen so as to increase the intensity of the electromagnetic wave currents carried from the waveguide to the load in the appropriate frequency range.

[0010] The load according to the invention further comprises a transmission line of non-uniform height configured to perform impedance matching between the waveguide and the transmission line. In the invention, the transmission line is folded back on itself.

[0011] Advantageously, the transmission line has a section smaller than the section of the waveguide in at least one direction.

[0012] Advantageously, the transmission line has a length greater than ten times the wavelength of signals transported by the waveguide.

[0013] In one embodiment of the invention, the transmission line terminated by a short circuit is formed by a waveguide.

[0014] Advantageously, the load according to the invention comprises a flange by which it is intended to be connected to a flange of the waveguide to be loaded. The end of the transmission line is open, the open end being housed in the flange so as to form a short circuit by fixing the flange of the load to the flange of the element to be loaded.

[0015] Advantageously, the load according to the invention further comprises coils configured to allow the circulation of a coolant.

[0016] In another embodiment of the invention, the transmission line terminated by a short circuit is formed by a coaxial cable.

[0017] Advantageously, the load according to the invention is entirely metallic. It can then advantageously be produced by additive manufacturing.

[0018] Advantageously, it is formed in a metal whose conductivity is lower than the conductivity of the waveguide.

[0019] Advantageously, it is treated in such a way as to degrade the porosity of the metal which composes it.

[0020] The invention also relates to a method of manufacturing a load by additive manufacturing, the method comprising the steps of: - obtaining an electronic file representing a geometry of a load according to the invention, and - control of an additive manufacturing device to manufacture the load according to the geometry specified in said electronic file.

[0021] Finally, the invention relates to a computer program product comprising computer-executable instructions which, when executed by a processor, make it possible to control an additive manufacturing device for manufacturing a load according to the invention. Brief description of the drawings

[0022] The invention will be better understood and other characteristics, details and advantages will appear more clearly on reading the description which follows, given without limitation, and thanks to the appended figures which follow, given by way of example, among which:

[0023] [Fig.l] [Fig.l] represents a guided load according to the state of the art;

[0024] [Fig.2a] [Fig.2a] represents the principles inherent in a load according to the invention.

[0025] [Fig.2b] [Fig.2b] represents an embodiment of a load according to the invention comprising a long waveguide folded back on itself.

[0026] [Fig.2c] [Fig.2c] represents an embodiment of a load according to the invention comprising a very long waveguide folded back on itself.

[0027] [Fig.2d] [Fig.2d] represents a longitudinal sectional view of an embodiment of the invention comprising a very long waveguide folded back on itself.

[0028] [Fig.2e] [Fig.2e] represents a view showing all the edges of the load of [Fig.2d].

[0029] [Fig.2f] [Fig.2f] gives an example of the absorption performance of a load according to an embodiment corresponding to that of [Fig.2d].

[0030] [Fig.3a] [Fig.3a] represents the principles related to another embodiment of a load according to the invention comprising a very long metallic coaxial cable.

[0031] [Fig.3b][Fig.3b] represents a perspective view of a load terminated by a coaxial cable.

[0032] [Fig.3c] [Fig.3c] represents an embodiment of a load according to the invention comprising a very long coaxial cable folded back on itself.

[0033] Identical references are used in different figures when the designated elements are the same. Description of the embodiments

[0034] A waveguide is a metallic tubular device for guiding electromagnetic waves while keeping them confined. They are therefore used as transmission lines, typically to link transmitting or receiving equipment to its antenna. Waveguides can have round or oval sections, but most often have rectangular sections and are hollow.

[0035] Inside a waveguide, the propagation of electromagnetic waves is done by reflections. The way in which electromagnetic waves propagate varies according to the format of the waveguide: the size of the waveguides is chosen according to the frequency band of the signals to be transmitted. For a waveguide with a rectangular section, L will denote the width of the waveguide and h the height of its section, with L > h. The height h of the waveguide influences the intensity of the currents which propagate there, which increases when the height of the guide decreases. Most waveguides have a height equal to half their width, because this configuration is optimal in terms of propagation.

[0036] Subsequently, the invention is illustrated by embodiments aimed at terminating a rectangular waveguide since this is the most widespread type of waveguide. However, the principles set out also apply to waveguides having circular, oval, or other sections.

[0037] The invention proposes to produce a load, not by inserting an absorbent material into a metal waveguide, but by exploiting the losses inherent in a transmission line, by passing the electromagnetic wave through an environment unfavorable to its propagation. The load according to the invention can be entirely metallic, which makes it possible to machine it in a simple manner, such as for example by additive manufacturing.

[0038] The invention describes a load designed as a transmission line sized to maximize losses. For this, the load according to the invention is configured to form a transmission line terminated by a short circuit (in English stub) positioned at the end of the waveguide to be terminated. The transmission line formed by the load according to the invention has a reduced height compared to the height of the waveguide to be completed, which has the effect of increasing the intensity of the voltages and currents transported in the waveguide, and consequently the losses due to heating of the support during reflection of the electromagnetic wave.

[0039] [Fig.2a] represents the principles inherent in a charge 200 according to the invention. The vertical arrows represent the amplitude of the electric field.

[0040] The load 200 according to the invention comprises a transmission line 201 implemented in the form of a waveguide of width L, height A' and length l. The waveguide 201 is terminated by a partition, which creates a short circuit at the end of the transmission line. The height A' of the waveguide 201 is less than the height h of the waveguide to be terminated. The lower the height A', the greater the intensities of the currents and voltages, and consequently the losses due to heating of the waveguide. The height A' and the length l of the waveguide 201 are therefore chosen according to the adaptation sought by the load, the adaptation being the capacity of the load to absorb energy, taking into account the operating frequency and the conductivity of the metal used for the waveguide.Measuring the losses induced by a waveguide is a common practice for those skilled in the art, whether theoretically, using a simulation tool or by experimentation. In any event, the waveguide 201 will have a length much greater than the wavelength X of the signals received from the waveguide, for example greater than ten times the wavelength, and advantageously greater than fifteen times the wavelength.

[0041] The load 201 also comprises a variable height transmission line 202, better known by the English term taper, configured to carry out the impedance matching between the waveguide to be terminated and the waveguide 201. Indeed, without impedance matching between the two guides of different heights, part of the electromagnetic waves would be reflected by the load, which would then not play its role as a power absorber.

[0042] Depending on how the load is to be connected to the waveguide to be terminated, it may or may not be equipped with a fixing means such as a flange (not shown).

[0043] In the case of a waveguide to be terminated having an elliptical section, the invention can be implemented by connecting this waveguide to an ellipsoidal waveguide whose dimension is reduced along at least one axis (the width of the waveguide to be terminated having to be maintained over the entire path of the wave so that it propagates).

[0044] Advantageously, in this embodiment and the following ones, the totally metallic load 200 can be made of a metal or metal alloy having high conductivity losses, such as for example titanium or Inconel™. Indeed, the waveguides are generally made of aluminum, which has good conductivity properties and a low weight. The propagation losses increase when the conductivity of the support decreases. By using a metal whose conductivity is lower than that of aluminum, the losses of the load according to the invention are therefore increased. For example, for an equal level of performance, the size l of the waveguide 201 in a load according to the invention is divided by two between an aluminum waveguide (electrical conductivity of 36.9 MSiemens / m) and a titanium guide (electrical conductivity of 2.4 MSiemens / m).

[0045] Advantageously again, in this embodiment and the following ones, the load 200 can be designed in a metal treated so as to degrade the porosity. For example, the load can be designed by an additive manufacturing technique. Additive manufacturing is the design of three-dimensional metal parts from successive thin layers of metal powder melted by a laser beam coupled to a CAD model of the part to be produced. The part is then built layer by layer, unlike machining, which proceeds by removing material. This is the equivalent of 3D printing for metal. Additive manufacturing makes it possible to quickly and easily design metal parts having degraded porosity (Ra), with conductivity typically reduced by a factor of 5 to 10.This degradation of the porosity of the charge reduces the equivalent conductivity of the metal used to carry out the charge, which further increases the losses and corresponds to the desired objective.

[0046] The porosity of the filler can also be artificially degraded by additive manufacturing, or by any other method, such as for example by using chemical treatments.

[0047] The implementation of this embodiment to terminate a waveguide in WR51 technology (waveguide to be terminated with a width L = 12.954 mm and a height h = 6.477 mm) shows that an adaptation of 25 dB is achievable with an additive titanium load (porous) whose transmission line 201 has a height A' = 0.3 mm and a length between 10 and 20 times the wavelength of the signals transmitted by the waveguide to be terminated.

[0048] The load 200 according to the invention therefore meets the expressed need to thermally dissipate the electromagnetic energy supplied to it. Rather than absorbing it, the energy is directly dissipated by a metal waveguide exhibiting significant losses. However, the size of the load, mainly linked to the length of the waveguide 201, does not allow simple use of the load.

[0049] [Fig.2b] represents a first embodiment of the invention, comparable to that of [Fig.2a], but in which the waveguide 211 is folded back on itself so as to form meanders. The arrangement of the waveguide 211 makes it possible to reduce the dimensions of the load 200. The waveguide 211 still has a length l when unfolded, but the folds allow it to occupy only a length equivalent to the lower one. This embodiment is therefore equivalent to that of [Fig.l] in terms of performance, while being more compact.

[0050] [Fig.2c] shows another embodiment of a load according to the invention. This differs from the embodiment shown in [Fig.2b] in that the waveguide 221 is folded back on itself and occupies the spaces freed up above the variable height transmission line 202. This embodiment makes it possible to further reduce the length l” occupied by the waveguide 221. Indeed, the folding of the waveguide 221 is not governed by any particular rule, which allows the waveguide 221 to be arranged in unused areas of the equipment.

[0051] [Fig.2d] shows a longitudinal sectional view of an embodiment of the invention in which the load comprises a flange 232 for flange-to-flange attachment to the waveguide to be terminated. In this embodiment, the waveguide 231 is folded and occupies the free spaces under the variable-height transmission line 202. It ends at 233 at the flange 232, and does not have a final partition. The final partition of the waveguide 231, which short-circuits the transmission line, is formed by the flange of the waveguide to be terminated, when connecting the load.

[0052] This embodiment is particularly advantageous when the load is produced by additive manufacturing. Indeed, this manufacturing method can leave powder residues in the waveguide 231, which modify the propagation properties and therefore the performances, in uncontrolled proportions. The embodiment of [Fig.2d] makes it possible to evacuate these powder residues after manufacturing, for example by injecting air or a liquid under pressure through the variable height transmission line 202, the air or liquid passing through the entire waveguide 231 before being expelled through the orifice 233.

[0053] [Fig.2e] represents a view showing all the edges of the load of [Fig.2d]

[0054] [Fig.2f] gives an example of the absorption performance of a load according to a embodiment corresponding to that of [Fig.2d]. The results are measured in the case of a waveguide in WR51 technology on the Ka frequency band (measured here between 17.75 GHz and 21.25 GHz). The load is made of titanium, and includes a waveguide 231 of height A' = 0.2 mm and length 250 mm when unrolled. Once folded, the entire load measures 40 mm in length. The load is therefore very compact.

[0055] As indicated in [Fig.2f], the load according to the invention has an adaptation greater than 20 dB over the entire band.

[0056] The load according to the invention can be produced in a single piece, by additive manufacturing, which makes it inexpensive, not very complex to produce, and infinitely replicable. from a 3D file.

[0057] Furthermore, it can be easily integrated into the design of any component (for example a coupler or an antenna source), and be manufactured jointly with this component. Its shape can then be adapted to that of the component so as to occupy wasted spaces. Such joint manufacturing reduces the volume of the assembly, the manufacturing costs, and improves the reliability of the component.

[0058] Furthermore, additive manufacturing makes it possible to interweave coils dedicated to the circulation of a cooling liquid directly in the load (for example between the folds of the waveguide 211), in order to improve the dissipation of the thermal energy produced.

[0059] In Figures 2b to 2e, the load is folded back on itself by 180° bends. However, many other ways of folding the transmission line are possible, making it possible to achieve the same result of reducing the size of the load, for example by rolling it back on itself in the form of a spiral, or by arranging it so as to form a broken line forming alternately salient and re-entrant angles (zig-zag).

[0060] [Fig.3a] shows the principles related to another embodiment of a load according to the invention. In this embodiment, the load 300 comprises a transmission line 301 in the form of a metallic coaxial cable whose diameter is less than the height h of the waveguide to which the load is connected. The coaxial cable is terminated by a short circuit. The arrows represent the electric field.

[0061] The length l of the coaxial cable is chosen according to the desired level of adaptation and the conductivity of the coaxial cable. In a coaxial cable, the electric field extends between the core and the shielding of the cable. The coaxial cable is then advantageously chosen to have the smallest possible gap between the core and the shielding, in order to increase the intensity of the current and the voltages which propagate inside, and therefore the thermal losses. Advantageously, the core of the cable can be made of a low-conductivity material, such as titanium. Advantageously still, the coaxial cable does not have a dielectric material positioned between the core and the shielding, fixing means making it possible to ensure that the core is held in position and to avoid contact with the shielding. Satisfactory results have been obtained at 20 GHz with a coaxial cable of 0.2 mm radius and 300 mm length.

[0062] The load also includes a guide / coaxial transition device (TGC) 302 configured to allow the transition between guided propagation along a waveguide and coaxial propagation. This device further performs impedance matching between the two transmission lines, in order to avoid reflections of the electromagnetic waves. Such devices are well known to those skilled in the art and are available at low cost.

[0063] [Fig.3b] shows a perspective view of a load terminated by a coaxial cable.

[0064] Just like the embodiments shown in Figures 2a to 2e, the load of Figures 3a and 3b has the advantage of being able to be entirely metallic. However, its size can be significant.

[0065] [Fig. 3c] represents an embodiment of a load according to the invention, in which the transmission line is implemented by a coaxial cable. In order to limit the space occupied by the coaxial cable 303, the latter is folded back on itself, or wound, so as to form one or more meanders. This embodiment has the advantage of occupying less space than that of [Fig. 3a]. Particular attention must be paid to avoid short circuits between the core and the shielding of the coaxial cable, in particular in bends.

[0066] The various embodiments presented of a load according to the invention achieve the desired objectives. By using high-loss transmission lines, they make it possible to manufacture a load without absorbent material, which is of significant interest in terms of temperature stability, stability over time, costs, time and manufacturing difficulties. The metal load according to the invention is either entirely metallic (case of figures 2b to 2g), or made from low-complexity consumer components ([Fig.3c]). The invention can be arranged in different ways, each having particular performance characteristics, manufacturing complexity and compactness.Finally, the charges according to the invention can be further improved by the use of low-conductivity metals, generally not considered for the manufacture of microwave materials, by producing them using additive manufacturing processes, or by subjecting them to chemical treatments intended to increase their porosity.

[0067] The invention also relates to a method for manufacturing a load by additive manufacturing. As indicated previously, additive manufacturing makes it possible to quickly and simply design metal loads having degraded porosity, which is usually problematic but proves advantageous in the context of a load since this degradation of the porosity reduces the equivalent conductivity of the metal used to make the load, which further increases the losses and corresponds to the desired objective.

[0068] The method according to the invention comprises the steps of: - obtaining an electronic file representing a geometry of a load according to the invention, and - control of an additive manufacturing device to manufacture the load according to the geometry specified in said electronic file.

[0069] More specifically, the electronic file can be obtained by software modeling (in English Computer Aided Design, or CAD) and / or by scanning the surface of the load to measure its surface configuration (in English scanning). Many file formats are possible, such as Stereolithography or “Standard Tessellation Language” files (.stl files), Additive Manufacturing File (.amf files), AutoCad (.dwg files), Blender (.blend files), Parasolid (.x_t files), 3D Manufacturing Format (.3mf files), Autodesk (3ds files), Collada (.dae files) and Wavefront (.obj files), among others.

[0070] Once obtained, the electronic file can be converted into a set of instructions executable by a processor, allowing it to control an additive manufacturing device in order to produce the load according to the geometric arrangement considered. The conversion can consist of converting the file into a set of layers to be sequentially formed by the additive manufacturing device. The additive manufacturing device (3D printer) executes the instructions transmitted to it to manufacture the load according to the invention.

[0071] The electronic file can be saved in different formats, and saved on a storage medium capable of being read by a computer.

Claims

Claims

1. Load (200, 300, 400) for terminating a waveguide (110) in a microwave circuit, said load being configured to form a transmission line (201, 301) terminated by a short circuit at the end of the waveguide, the dimensions of the transmission line being chosen so as to increase the intensity of the currents of the electromagnetic waves transported from the waveguide to the load, the load further comprising a transmission line of non-uniform height (202, 302) configured to perform impedance matching between the waveguide (110) and said transmission line, the load being characterized in that the transmission line is folded back on itself.

2. A load according to claim 1, wherein said transmission line has a section smaller than the section of the waveguide in at least one direction.

3. A load according to any preceding claim, wherein said transmission line has a length greater than ten times the wavelength of signals carried by the waveguide.

4. Load according to one of the preceding claims, wherein said transmission line terminated by a short circuit is formed by a waveguide (201).

5. A load according to claim 4, comprising a flange (232) by which it is intended to be connected to a flange of the waveguide to be loaded, and in which the end of the transmission line is open, the open end (233) being housed in the flange so as to form a short circuit by fixing the flange of the load on the flange of the element to be loaded.

6. A load according to one of claims 4 and 5, further comprising coils configured to allow the circulation of a cooling liquid.

7. Load according to one of claims 1 to 3, wherein said transmission line terminated by a short circuit is formed by a coaxial cable (301).

8. Load according to one of the preceding claims, entirely metallic.

9.

10. A charge according to claim 8, produced by additive manufacturing. A charge according to one of the preceding claims, formed in a metal whose conductivity is lower than the conductivity of the waveguide.

11. Charge according to one of the preceding claims, treated so as to degrade the porosity of the metal which composes it.

12. A method of manufacturing a load by additive manufacturing, the method comprising the steps of: - obtaining an electronic file representing a geometry of a load according to one of claims 1 to 11, and - controlling an additive manufacturing device to manufacture the load according to the geometry specified in said electronic file.

13. A computer program product comprising computer-executable instructions which, when executed by a processor, enable control of an additive manufacturing device for manufacturing a load according to one of claims 1 to 11.

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