Charge for microwave circuit

Abstract

The invention relates to a metallic load (200) for terminating a waveguide (110) in a microwave circuit. The load is configured to form a plurality (221 to 236) of transmission lines of different lengths terminated by a short circuit at the end of the waveguide, the dimensions of the lines of the formed transmission lines being chosen so as to increase the intensity of the currents of the electromagnetic waves transported in the waveguide. The invention also relates to the manufacture of the load by an additive manufacturing method. Figure for abstract: Fig. 2d

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, that is to say 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, at the end of the waveguide, a plurality of transmission lines of different lengths, each terminated by a short circuit. The dimensions of the formed transmission lines are chosen so as to increase the intensity of the electromagnetic wave currents transported in the waveguide in the appropriate frequency range.

[0010] The load according to the invention is configured to attenuate signals in a frequency band of interest. The dimensions of each transmission line are adapted to resonate in a particular frequency sub-band of the frequency band of interest, so that jointly, the transmission lines make it possible to attenuate the entire frequency band of interest.

[0011] Advantageously, the transmission lines have lengths close to Xg / 4, with Xg the guided wavelength in the frequency band of interest, and less than Xg.

[0012] Advantageously, the transmission line(s) formed have a section smaller than the section of the waveguide in at least one direction.

[0013] In one embodiment of the invention, the plurality of transmission lines of different lengths terminated by a short circuit are arranged radially.

[0014] In one embodiment of the invention, the transmission lines are formed hollow in the load.

[0015] Advantageously, the load can then be configured to fit into the waveguide, and the transmission lines can be positioned inside the waveguide.

[0016] Advantageously, the load may further comprise coils configured to allow the circulation of a cooling liquid.

[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, such as titanium or Inconel™.

[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.

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

[0024] [Fig.2a] [Fig.2a] represents an embodiment of a load according to the invention comprising a plurality of parallel slots.

[0025] [Fig.2b] [Fig.2b] represents the current density in a slot of a charge as described in [Fig.2a].

[0026] [Fig.2c] [Fig.2c] represents a perspective view of an embodiment of a charge according to the invention comprising a plurality of parallel slots.

[0027] [Fig.2d] [Fig.2d] represents an embodiment of a load according to the invention comprising a plurality of radial slots.

[0028] [Fig.2e] [Fig.2e] represents a finalized charge according to the invention with 16 slots radial, transparent and after being dressed in material.

[0029] [Fig.2f] [Fig.2f] represents a finalized charge according to the invention with 8 parallel branches, in transparency and after having been dressed in material.

[0030] [Fig.2g] [Fig.2g] shows the measured performance of a load according to the invention.

[0031] [Fig.2h] [Fig.2h] represents an embodiment of a load according to the invention.

[0032] [Fig.2i] [Fig.2i] represents an embodiment of a load according to the invention.

[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 a transmitting or receiving device and 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 therefore 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 proposes a load designed and dimensioned so as to amplify the losses. For this, the load according to the invention is configured to form several transmission lines terminated by a short circuit (in English stub) positioned at the end of the waveguide to be terminated. The transmission lines formed by the load according to the invention have a reduced height relative to the waveguide to be terminated, 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 the reflection of electromagnetic waves.

[0039] [Fig.2a] represents an embodiment of a load according to the invention. The arrows represent the amplitude of the electric field.

[0040] In this embodiment, the load 200 comprises a plurality (five in the example of [Fig.2a]) of short-circuited transmission lines 201 to 205, each in the form of a waveguide of width L, height A' and length 11&15 terminated by a partition forming a short circuit. Each waveguide has a different length. They are positioned so as to form a set of slots parallel to the major axis of the section of the waveguide to be terminated.

[0041] The load 200 does not include a device allowing the adaptation of the impedance of the waveguide to be terminated with the impedance of the waveguides 201 to 205. This involves dividing the received wave by a set of slots, so that the wave propagates in a maximum of small waveguides of short lengths. The device “splits” the electric field into elementary sub-fields associated with different frequency bands, and which evolve in the waveguides 201 to 205 tuned to their frequency band.

[0042] In practice, the length of the waveguides (or stubs) 201 to 205 is close to Xg / 4, with Xg the guided wavelength in the frequency band of interest. Each waveguide 201 to 205 is adapted for a frequency sub-band among the total frequency band considered by adjusting its length. Each slot therefore resonates for a given sub-band, and absorbs the energy on this sub-band in the manner of a load. It therefore dissipates the power of the signal on a frequency sub-band only. By choosing different lengths of waveguides, the device resonates for several distinct sub-bands, which may overlap. The number of slots, their heights and lengths are therefore chosen according to the total frequency bandwidth of interest, the conductivity of the medium, the targeted matching and the coupling between the slots, so that together the slots attenuate the power in the entire frequency band of interest.

[0043] The different waveguides 201 to 205 act as short-circuited resonators for neighboring frequency bands, the joint response of which makes it possible to adapt the frequency band to attenuate a frequency band of interest, and to adapt the quality factor of the load. Depending on the embodiment, the height of the waveguides 201 to 205 can vary, which makes it possible to adapt the intensity of the currents in the waveguides. However, the use of waveguides of the same heights makes it possible to select the height maximizing the ratio between the intensity of the currents (and therefore the losses) and the design feasibility.

[0044] In [Fig.2a], the waveguides 201 to 205 are straight. However, the same results can be obtained with waveguides of any shape (for example folded, wound, etc.).

[0045] 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).

[0046] [Fig.2b] represents, by gray levels, the current density in a waveguide at the origin of the losses associated with a frequency sub-band. The current intensity, and therefore the losses, increases sharply at the end of each of the transmission lines.

[0047] [Fig.2c] represents a perspective view of an embodiment of a load according to the invention. In this embodiment, the load comprises a wall 210 in which are housed 8 slots 211 to 218 each corresponding to a short-circuited waveguide tuned to a distinct frequency sub-band.

[0048] The load according to the embodiments presented in figures 2a and 2c is very compact, which allows it to be easily integrated into any equipment design. Its weight and size are very reduced compared to known loads of the state of the art. It requires precise knowledge of the parameters and models for its design, and sufficiently careful production so that the electrical timing of the waveguides corresponds to expectations.

[0049] The load according to the embodiments shown in Figures 2a and 2c can be easily integrated into a design since it does not extend beyond the section of the waveguide to be terminated. However, the number of waveguides positioned in parallel is limited by the height of the waveguide to be terminated, and consequently the performance of the load is also limited.

[0050] [Fig.2d] shows another embodiment of a load according to the invention, in which the waveguides 221 to 236 are positioned radially, parallel to the major axis of the section of the waveguide to be terminated, unlike Figures 2a and 2c, where the waveguides terminating the load start at the same level. This embodiment makes it possible to densify the number of waveguides (it is doubled compared to the embodiment described in [Fig.2c]), and therefore to improve the performance of the load or to increase the width of the operating frequency band of the load, at the cost of a slightly larger footprint.

[0051] Generally, the waveguides resonating so as to absorb the power transmitted in the waveguide to be terminated are distributed regularly on the end of the waveguide, for example on a plane (Figures 2a and 2c), on a rounded end ([Fig.2d]) or on a slope.

[0052] [Fig.2e] represents a finalized load according to the invention, in transparency (A) and after having been dressed in material (B), in the case of a waveguide in technology WR22 (L = 5.68 mm, h = 2.84 mm) with 16 radial slots. The load here includes a flange 241 allowing it to be fixed to the waveguide to be terminated.

[0053] [Fig.2f] represents a finished load according to the invention, in transparency (A) and after having been dressed in material (B), in the case of a waveguide in WR51 technology with 8 parallel slots. The load here comprises a flange 242 allowing it to be fixed on the waveguide to be finished.

[0054] Figures 2e and 2f show the compactness of the load according to the invention, which is much greater than that of the loads according to the state of the art.

[0055] [Fig.2g] shows the measured performances of a load according to the invention. The measurements were made for four different slot arrangements Ai to A4, without the application of any chemical treatment. The Ai arrangement involves a load with a set of 8 parallel slots, as shown in [Fig.2c], while the A2 to A4 arrangements involve loads with a set of 16 radial slots, as shown in [Fig.2d]. An average matching of about 12 dB is observed over the entire 17 GHz - 21.5 GHz frequency band. The matching is more homogeneous over the band for the 16 radial slot arrangements.

[0056] If this result is satisfactory to a certain extent, the simulations show that a more precise realization of the load should make it possible to achieve attenuations of the order of 25 dB.

[0057] [Fig.2h] shows another embodiment of a load according to the invention. This load 250 has the characteristics of the load of [Fig.2a]. However, rather than extending outwards from the load, the transmission lines 251 to 255 are formed hollow in the load. This embodiment has the advantage of being very compact. It is also compatible with a radial arrangement of the short-circuited transmission lines.

[0058] [Fig.2i] shows another embodiment of a load according to the invention, in which the load 260 is reentrant, that is to say that it extends inside the waveguide to be closed 261. The transmission lines 271 to 275 are formed hollow in the load, so as to form a set of short-circuited slots positioned at the end of the waveguide 260.

[0059] In terms of size, this solution is particularly advantageous since the load is inserted into the waveguide.

[0060] The load 200 according to the invention has the advantage of being entirely metallic. It can thus 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 increased. For example, the length of a waveguide necessary to dissipate a signal is halved between an aluminum waveguide (electrical conductivity of 36.9 MSiemens / m) and a titanium waveguide (electrical conductivity of 2.4 MSiemens / m).

[0061] Advantageously, the load 200 can be designed in a metal treated so as to degrade its 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 with 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 with degraded porosity (Ra), with conductivity typically reduced by a factor of 5 to 10. This degradation of the porosity of the load reduces the equivalent conductivity of the metal used to produce the load, which further increases losses and corresponds to the desired objective.

[0062] The porosity of the filler can be artificially degraded by additive manufacturing, or by any other method, such as for example by using chemical treatments.

[0063] 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 dissipated by metal waveguides exhibiting significant losses in distinct frequency sub-bands.

[0064] Being entirely metallic, the load according to the invention can be produced from a single piece, and by additive manufacturing, which makes it inexpensive, not very complex to produce, and infinitely replicable from a 3D file.

[0065] It can take different forms, and thus be easily integrated into the design of any component (for example a coupler or an antenna source). It can possibly 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.

[0066] 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 waveguides 201 to 205), in order to improve the dissipation of the thermal energy produced.

[0067] 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, cost, time and manufacturing complexity. The invention can be arranged in different ways, each having particular performance characteristics, manufacturing complexity and compactness. Finally, the loads according to the invention can be further improved by using 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.

[0068] 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.

[0069] The method according to the invention comprises the steps of:

[0070] - obtaining an electronic file representing a geometry of a load according to the invention, and

[0071] - control of an additive manufacturing device for manufacturing the load according to the geometry specified in said electronic file.

[0072] 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 for example files of the Stereolithography or “Standard Tessellation Language” type (.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.

[0073] 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 formed sequentially 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.

[0074] 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) for terminating a waveguide (110) in a microwave circuit, characterized in that it is configured to form a plurality (201 to 205, 211 to 218, 221 to 236, 251 to 255, 271 to 275) of transmission lines of different lengths terminated by a short circuit at the end of the waveguide, the dimensions of the transmission lines formed being chosen so as to increase the intensity of the currents of the electromagnetic waves transported in the waveguide.

2. A load according to claim 1, configured to attenuate signals in a frequency band of interest, wherein the dimensions of each transmission line (201 to 205, 211 to 218, 221 to 236, 251 to 255, 271 to 275) are adapted to resonate in a particular frequency sub-band of the frequency band of interest, such that together, the transmission lines attenuate the entire frequency band of interest.

3. A load according to any preceding claim, wherein the transmission lines have lengths of Xg / 4, with Xg the guided wavelength in the frequency band of interest, and less than Xg

4. Load according to one of the preceding claims, in which the formed transmission lines have a section smaller than the section of the waveguide in at least one direction.

5. Load (200, 241, 242, 250, 260) according to one of the preceding claims, in which the plurality of transmission lines of different lengths terminated by a short circuit are arranged radially (221 to 236).

6. Load (200, 241, 242, 250, 260) according to one of the preceding claims, in which the transmission lines are formed in hollows (251 to 255, 271 to 275) in the load.

7. The load (260) of claim 6, configured to insert into the waveguide (261), wherein the transmission lines (271-275) are positioned within the waveguide.

8. A load (200, 241, 242, 250, 260) according to any preceding claim, further comprising coils configured to allow circulation of a cooling liquid.

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

10.

11. Load according to claim 9, produced by additive manufacturing. Load according to one of the preceding claims, formed in a metal whose conductivity is lower than the conductivity of the waveguide.

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

13. 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 12, and - controlling an additive manufacturing device to manufacture the load according to the geometry specified in said electronic file.

14. 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 12.

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