Radioelectric antenna having blades and having a controlled attack angle, and method for manufacturing such an antenna

Abstract

The invention relates to a radio antenna (1) comprising at least one blade (3) twisted along and around a longitudinal axis (A1) of the radio antenna (1), the blade (3) comprising several twists (30), each twist (30) corresponding to a portion of the blade having a polar angle of 2π. The distance along the longitudinal axis (A1) between each twist and a twist adjacent to said twist is chosen such that the angle (β) between the twist (30) and the longitudinal axis (A1) is less than a predefined maximum angle. The invention also relates to a method for manufacturing such a radio antenna, the manufacturing being carried out by additive manufacturing.

Description

[0001] The invention relates to the field of radio antennas, i.e. to devices for radiating and / or capturing electromagnetic waves. The invention is more particularly concerned with broadband circularly polarized antennas.

[0002] When circular polarization is required over a wide frequency band (typically greater than or equal to one octave), the preferred conventional solution is to use a spiral antenna. However, in some cases, its gain is insufficient. In such cases, a single linearly polarized horn should be used, combined with a polarizer at the antenna output. It is also possible to use a dual linearly polarized horn, combined with a wideband hybrid coupler upstream of the antenna.

[0003] With the first solution (the polarizer), it is very difficult to ensure good performance (especially in terms of polarization purity) over wide bandwidths. The second solution (dual linear polarization horn) requires the use of a hybrid coupler for circular polarization, this coupler necessarily generating losses.

[0004] A better solution is to modify the structure of the horn antenna itself so that the structure alone can generate circular polarization. To achieve this, ridged horns are known, the ridges of which (a kind of rib in the center of which the electric field is confined) are twisted around a longitudinal axis (the axis of the horn). The ridges form an angle with the longitudinal axis, called the angle of attack.

[0005] Although the prior art solutions (horn antennas with twisted ridges) are satisfactory in terms of electromagnetic radiation, they are not always satisfactory in terms of manufacturing. Indeed, the inventors realized that these solutions were not always compatible with certain manufacturing processes. In particular, the inventors realized that these solutions were not manufacturable, or at least not with optimal production yield, with a preferred manufacturing process which is additive manufacturing. Additive manufacturing of the Laser Powder Bed Fusion (or LPBF) type requires control of the antenna's angle of attack. More precisely, this type of manufacturing process requires that the angle of attack does not exceed a certain value depending on the type of manufacturing machine and the manufacturing material used.

[0006] The invention therefore aims to provide a radio antenna configured to convert a linearly polarized signal into a circularly polarized signal, making it possible to guarantee both the desired radiofrequency performance and proper compliance with technological manufacturing rules.

[0007] The invention proposes for this purpose a radio antenna comprising at least one blade twisted along and around a longitudinal axis of the radio antenna, the blade comprising several twists, each twist corresponding to a portion of the blade traveling a polar angle of 2π.

[0008] According to the invention, the distance along the longitudinal axis between each twist and a twist adjacent to said twist being chosen so that the angle between the twist and the longitudinal axis is less than a predefined maximum angle.

[0009] Thanks to the invention, the very structure of the antenna is configured to allow both the electromagnetic functions but also to guarantee the manufacturability of the antenna according to LPBF technology. The geometry of the antenna is optimized, in particular by controlling the distance along the longitudinal axis between each twist and an adjacent twist, to guarantee the manufacture of the antenna, in particular when this manufacture is carried out by additive manufacturing.

[0010] Particularly convenient preferred features of the antenna according to the invention are presented below.

[0011] The angle between each twist and the twist adjacent to that twist is the same along the radio antenna.

[0012] The maximum angle is predefined depending on the material the radio antenna is made of and the machine used for manufacturing.

[0013] The radio antenna is made of metal. The maximum preset angle is 45°.

[0014] The radio antenna further comprises a housing, the blade extending inside the housing.

[0015] The case has a truncated cone shape.

[0016] The intersection of the blade with the housing forms a curve called the blade curve, the projection of the blade curve onto any plane orthogonal to the longitudinal axis is a logarithmic spiral.

[0017] The housing has a cylindrical or conical shape, the distance along the longitudinal axis between each twist and a twist adjacent to said twist being identical along the entire length of the radio antenna.

[0018] The radio antenna is a horn antenna.

[0019] The radio antenna has at least two blades twisted around the longitudinal axis.

[0020] The invention also relates to a method of manufacturing a radio antenna having at least one of the preceding characteristics, and in which the manufacturing is carried out by additive manufacturing.

[0021] Additive manufacturing is, for example, of the Powder Bed Laser Fusion type.

[0022] Other features and advantages of the invention will become apparent in the description below with reference to the appended drawings, given as non-limiting examples: there figure 1 is a perspective view of a radio antenna according to one embodiment of the invention; figure 2 is a perspective view of the blades of the radio antenna of the figure 1 ; there figure 3 is a perspective view of a radio antenna according to another embodiment of the invention; figure 4 represents the projection of a logarithmic spiral onto a cone; figure 5 represents a projection of the antenna onto a longitudinal plane; the figure 6 shows two graphs of radiation patterns for comparison, one graph relating to a prior art radio antenna and another graph relating to the radio antenna according to the invention; and the figure 7 shows for comparison two graphs of radiation patterns relating to the radio antenna according to two variants of the invention. figure 8 illustrates the definition of the angle of attack.

[0023] There figure 1 represents an exemplary embodiment according to the invention of a radio antenna 1. The radio antenna 1 is configured to convert a linearly polarized signal into a circularly polarized signal.

[0024] The radio antenna 1 is preferably made of metal, for example aluminum alloy, copper, or titanium.

[0025] The radio antenna 1 has a longitudinal axis A1, in particular a median longitudinal axis.

[0026] The radio antenna 1 comprises at least one blade 3. In the example shown, the radio antenna 1 comprises two blades 3.

[0027] The radio antenna 1 further comprises here a housing 2 shown in figure 1 and removed in figure 2 to show the 3 blades alone.

[0028] The housing 2 may have a shape of revolution. The longitudinal axis A1 is in this case the axis of revolution of the housing 2.

[0029] The housing 2 preferably has a conical or truncated shape. The radio antenna 1 is then called a horn antenna. In the example shown, the housing 2 has a truncated shape.

[0030] The blades 3 extend inside the housing 2. The blades 3 are assembled to an inner wall 20 of the housing 2. Alternatively, the blades 3 are formed in one piece with the housing 2 and extend the inner wall 20 of the housing 2.

[0031] The blades 3 are twisted along and around the longitudinal axis A1.

[0032] Each blade 3 comprises several twists 30 or turns. Each twist 30 corresponds to a portion of the blade having traveled a polar angle of 2π. In the state-of-the-art solutions, the distance between each twist is identical. In the proposed invention, the distance between each twist varies progressively along the longitudinal axis.

[0033] Each twist 30 forms with the longitudinal axis A1 an angle called the angle of attack β which can also be defined as follows: Let P be a point belonging to the curve C defined by the intersection between the profile of the conical helix and the walls of the truncated cone, Let ez(P) be the normalized direction vector parallel to the longitudinal axis and passing through P, oriented towards the top of the helix Let ut(P) be the normalized direction vector tangent to C at P, oriented towards the top of the helix

[0034] Then the angle of attack β is the angle formed by the two vectors (ez(P), ut(P)) see the figure 8 .

[0035] The distance L t along the longitudinal axis A1 between each twist 30 and a twist 30 adjacent (i.e. consecutive) to said twist 30 is chosen so that the angle of attack β between the twist 30 and the longitudinal axis A1 is less than a predefined maximum angle β max (or maximum angle of attack β max ).

[0036] Advantageously, the angle of attack β is the same along the entire length of the radio antenna 1.

[0037] Alternatively, the angle of attack β can vary along the antenna, i.e. along the longitudinal axis A1. The angle of attack β must nevertheless remain lower than the maximum angle β max .

[0038] The predefined maximum angle β max is imposed in particular by the manufacturing process of the radio antenna and the machine used. The maximum angle β max is particularly critical when the radio antenna is manufactured by additive manufacturing. In particular, the maximum angle β max is critical when the additive manufacturing is of the Powder Bed Laser Fusion type. Indeed, the reliability of such manufacturing is subject to the design rules of such manufacturing. The maximum angle β max ensures good control of the geometry (and therefore radiated performance). If the maximum angle β max is not respected, the antenna may be degraded locally. This degradation can, by propagation of defects during manufacturing, alter the entire antenna. Ultimately, this can lead to partial collapse of the antenna. An alteration of the mechanical and / or radioelectric properties of the antenna thus manufactured may also be observed.

[0039] In additive manufacturing such as Laser Powder Bed Fusion, the maximum angle β max also depends on the material used for the powder as well as the granularity of the powder. The maximum angle β max may also depend on the machine used for manufacturing and possibly the additive printing parameters.

[0040] When the radio antenna 1 is made of metal, in particular using metal powder (such as aluminum alloy) by additive manufacturing, the predefined maximum angle β max is for example equal to 45°.

[0041] In the example shown in figures 1 And 2 , the radio antenna 1 has two blades 3. This number can of course vary and can for example be equal to one, two, three, four, etc. The figure 3 shows, as non-limiting examples, the radioelectric antenna 1 comprising respectively three blades 3 and four blades 3.

[0042] Furthermore, the radio antenna 1 described above comprises a housing 2. In this case, the electromagnetic radiation takes place in the longitudinal axis A1. Alternatively, the radio antenna 1 may not have a housing 2. In other words, the radio antenna 1 may be without a housing 2. The electromagnetic radiation then takes place orthogonally to the longitudinal axis A1.

[0043] As visible on the figure 4 , the intersection of each blade 3 with the housing 2 forms a curve called the blade curve. The intersection is understood in the mathematical sense. The blade curve has a conical helix shape. The projection of the blade curve onto any plane orthogonal to the longitudinal axis A1 is a logarithmic spiral.

[0044] In this configuration, the angle of attack β is constant along the entire length of the radio antenna 1. The distance L t between the consecutive twists 30 varies along the radio antenna 1. In particular, the distance L t increases as it progresses from a first end 21 of the housing 2 towards a second end 22 opposite the first end 21.

[0045] The Cartesian parameterization of the conical helix is ​​as follows: x = ae kt cos t y = ae kt sin t z = ae kt cos α with k = sin α cos β and where α corresponds to the half angle at the apex of the cone and β at the angle between the helix and the generators of the cone.

[0046] The angle β as defined in the equation above also corresponds to the angle of attack between each twist 30 and the longitudinal axis A1 of the radio antenna 1. It is thus possible to impose on the angle βof the above equation to be less than the maximum angle β max. The structure of the radio antenna can thus be optimized by parameterizing the geometry of the blades.

[0047] The conical propeller solution ensures an angle of attack β constant over the entire antenna and configurable, based on the use of a logarithmic spiral as a generator.

[0048] There figure 5 shows the parameters of the truncated cone-shaped housing. Some parameters of the housing 2 are fixed by physical constraints. The housing 2 has, for example, a radius at its base (i.e. at the second end 22) or output radius R out determined by the desired gain for the antenna. The housing 2 has, for example, a radius at its top (i.e. at the first end 21) or input radius R in determined in part by the desired bandwidth.

[0049] A preferred way of realization is to fix the output radius R out and the input radius R in . The remaining optimization parameters are then the antenna length L horn , the number of turns N turn of the conical helix in the length Lhorn, and β < β max .

[0050] According to the geometry of the truncated cone, it is possible to write: α = tan − 1 R out − R in L horn

[0051] The number of turns N turn makes it possible to ensure that and β< β max through the following equation: k = 1 2 πN turn ln L tot R in tan α = sin α . cos β

[0052] It is thus possible to configure the angle of attack β in order to guarantee β < β max , where β max depends as explained above on the machine used for manufacturing, its parameterization, and the type of material used.

[0053] The blade curve is defined above as the intersection of each blade 3 with the truncated housing 2. In an example in which the housing 2 has a shape other than a truncated cone, or in which the radio antenna 1 has no blades, the blade curve would be defined by the intersection between the blade and the circumscribed cone. The circumscribed cone is understood to mean the mathematical object and does not constitute a physical part of the radio antenna 1.

[0054] In an exemplary embodiment not shown, the distance L t along the longitudinal axis A1 between the consecutive twists 30 may be identical all along the radio antenna 1. For example, each blade 3 would have the shape of a conical helix. If the radio antenna 1 comprises a housing 2, the distance L t may be constant from the first end 21 of the housing 2 to the second end 22. The housing 2 may, for example, have a cylindrical shape in this case. Whether or not the radio antenna 1 comprises a housing 2, the angle of attack β can then be kept constant along the radio antenna 1 while being less than the maximum angle β max.

[0055] By "blade" is meant in this document a volume generated from the scanning of any section along the generator defined above in paragraph

[0044] . In the case of a circular section, for example, the "blade" represents a strand (or wire). In the case of a rectangular section, the blade forms what is classically called a "ridge" in the antennal domain.

[0056] The radio antenna 1 is preferably manufactured by additive manufacturing.

[0057] During antenna manufacturing, the blade(s) obtained then follow a profile according to a conical helix. The blade(s) can first be manufactured with a solid surface and are then hollowed out according to a particular progressive profile. The progressive profile is chosen to guarantee broadband adaptation and controlled secondary lobes. Several embodiments are possible for the progressive profile (taperization), for example an exponential profile or a Klopfenstein profile.

[0058] There figure 6 represents radiation patterns obtained at 16 GHz: in a) the pattern obtained for the prior art antenna as described in document US 2021 / 184359, and in b) the pattern obtained for the exemplary embodiment of the conical helix of the invention. The native polarization of the antenna (i.e. the right-hand polarization) RHCP as well as the orthogonal polarization (i.e. the left-hand polarization) are represented. The patterns are plotted along three cutting planes, for three phi values: 0°, 45° and 90°.

[0059] Diagrams a) and b) are relatively similar. The diagrams are symmetrical in both cases. The gain on the axis is identical, and the cross-polarization levels are of the same order of magnitude. A significant decoupling between left and right polarization is also observed in both cases (prior art and example according to the invention).

[0060] The comparison made with the prior art to the figure 6 shows that the structure of the radio antenna according to the invention behaves nominally from the point of view of electromagnetic radiation.

[0061] There figure 7 represents for comparison the radiation patterns obtained at 16 GHz: in a) the pattern represented in b) of the figure 6 and in which the number of turns N turn of the conical helix is ​​equal to 2.6, and in b) the diagram obtained for the same example of embodiment of the conical helix of the invention but with a number of turns N turn equal to 4. Comparison of the diagrams shows that the radiation is maintained even with a large number of turns, and that it is possible to achieve excellent polarization purities with the configuration of the radio antenna according to the invention.

[0062] The antenna according to the invention allows a higher manufacturing yield than that of the prior art by guaranteeing an angle of attack always lower than the predefined maximum angle of attack.

[0063] The invention allows to greatly simplify the design phase: the proposed parameterization allows to simply launch an optimization in a dedicated software, constrained by the attack value β lower than that of the predefined maximum attack angle β max. The solution obtained is then guaranteed to be manufacturable, in particular printable by additive printing. This avoids the multiplication of electromagnetic or mechanical modifications, or retouching of the geometry to satisfy the printing parameters (and which would require a re-optimization to satisfy the radiated performances) and so on (iterative approach).

Claims

1. Radio antenna comprising a housing (2) inside which extends at least one blade (3) twisted along and around a longitudinal axis (A1) of the radio antenna (1), the blade (3) comprising several twists (30), each twist (30) corresponding to a portion of the blade having a polar angle of 2π, said radio antenna (1) being characterized in that : - housing (2) has a truncated cone shape, - the distance (L t ) along the longitudinal axis (A1) between each twist and a twist adjacent to said twist is chosen so that the angle of attack (β) between the twist (30) and the longitudinal axis (A1) is less than a predefined maximum angle of attack (β max ),. - The angle of attack (β) of each twist is the same along the radio antenna (1).

2. Radio antenna according to claim 1 or claim 2, in which the maximum angle (β max) is predefined depending on the manufacturing material of the radio antenna (1).

3. Radio antenna according to claim 3, made of metal and in which the maximum angle (β max ) predefined is equal to 45°.

4. Radio antenna according to one of the preceding claims, in which the intersection of the blade (3) with the housing (2) forms a curve called the blade curve and the projection of the blade curve onto any plane orthogonal to the longitudinal axis is a logarithmic spiral.

5. Radio antenna according to one of the preceding claims, in which the radio antenna (1) is a horn antenna.

6. Radio antenna according to one of the preceding claims, comprising at least two blades (3) twisted along and around the longitudinal axis (A1).

7. Method for manufacturing a radio antenna according to one of claims 1 to 6, in which the manufacturing is carried out by additive manufacturing.

8. Manufacturing method according to claim 7, in which the additive manufacturing is of the Powder Bed Laser Fusion type.

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