Radio antenna having blades and having a controlled angle of attack, and method of 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. Figure for abstract: Fig. 1.

Description

Title of the invention: Radioelectric antenna having blades and having a controlled angle of attack, and method of manufacturing such an antenna

[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 desired 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 certain cases, its gain is insufficient. It is then appropriate to use a horn with simple linear polarization, associated with a polarizer at the antenna output. It is also possible to use a horn with double linear polarization, associated with a wide-band hybrid coupler upstream of the antenna.

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

[0004] A better solution consists of modifying the structure of the horn antenna itself so that said structure alone allows circular polarization to be generated. To do this, ridged antennas are known, comprising blades (or ''ridges'') twisted around a longitudinal axis. The blades form an angle with the longitudinal axis, called the angle of attack.

[0005] Although the solutions of the prior art (ridged antennas) 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 an optimal production yield with a preferred manufacturing process which is additive manufacturing. Additive manufacturing of the Laser Powder Bed Fusion (or LPBF) type requires indeed the control of the angle of attack of the antenna. 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 2ir.

[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 improve the manufacturing yield. 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 manufacturing of the antenna, in particular when this manufacturing 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 said twist is the same along the radio antenna.

[0012] The maximum angle is predefined depending on the manufacturing material of the radio antenna.

[0013] The radio antenna is made of metal. The maximum predefined angle is equal to 45.

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

[0015] The housing 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 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 comprises at least two blades twisted along and 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: - [Fig.l] is a perspective view of a radio antenna according to one embodiment of the invention; - [Fig.2] is a perspective view of blades of the radio antenna of [Fig.l]; - [Fig.3] is a perspective view of a radio antenna according to another embodiment of the invention; - [Fig.4] represents the projection of a logarithmic spiral onto a cone; - [Fig.5] represents a projection of the antenna on a longitudinal plane; - [Fig.6] shows two radiation pattern graphs for comparison, one graph relating to a prior art radio antenna and another graph relating to the radio antenna according to the invention; and - [Fig.7] shows for comparison two graphs of radiation patterns relating to the radio antenna according to two variants of the invention.

[0023] [Fig.l] 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 an alloy of aluminum, 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 [Fig.l] and removed in [Fig.2] to show the blades 3 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 may have a conical, truncated cone, cylindrical or truncated pyramid shape. The radio antenna 1 is then a horn antenna. In the example shown, the housing 2 has a truncated cone shape.

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

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

[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 2ir.

[0033] Each twist 30 forms with the longitudinal axis Al an angle called the angle of attack [3.

[0034] The distance Lt along the longitudinal axis Al between each twist 30 and a twist 30 adjacent (i.e. consecutive) to said twist 30 is chosen so that the angle of attack [3 between the twist 30 and the longitudinal axis Al is less than a predefined maximum angle [3max (or maximum angle of attack |3max).

[0035] Advantageously, the angle of attack [3] is the same along the entire length of the radio antenna 1.

[0036] Alternatively, the angle of attack [3 can vary along the antenna, i.e. along the longitudinal axis AL the angle of attack [3 must nevertheless remain lower than the maximum angle [3max.

[0037] The predefined maximum angle [3max is imposed in particular by the manufacturing process of the radio antenna. The maximum angle [3max is particularly critical when the radio antenna is manufactured by additive manufacturing. In particular, the maximum angle [3max 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 [3max makes it possible to guarantee good control of the geometry (and therefore the radiated performances). If the maximum angle [3max is not respected, the antenna can be degraded locally. This degradation can, by propagation of defects during manufacturing, alter the entire antenna. Ultimately, this can lead to a partial collapse of the antenna. An alteration of the mechanical properties of the antenna thus manufactured can also be observed.

[0038] During additive manufacturing of the Powder Bed Laser Fusion type, the maximum angle [3max] also depends on the material used for the powder as well as the granularity of said powder. The maximum angle [3max] can also depend on the machine used for manufacturing and possibly on the additive printing parameters.

[0039] When the radio antenna 1 is manufactured from metal, in particular using metal powder (such as aluminum alloy) by additive manufacturing, the predefined maximum angle [3max is for example equal to 45°.

[0040] In the example shown in Figures 1 and 2, the radio antenna 1 comprises two blades 3. This number can of course vary and can for example be equal to one, two, three, four, etc. [Fig. 3] shows, as non-limiting examples, the radio antenna 1 comprising respectively three blades 3 and four blades 3.

[0041] Furthermore, the radio antenna 1 described above comprises a housing 2. The electromagnetic radiation takes place in this case in the longitudinal axis AL Alternatively, the radio antenna 1 may not have a housing 2. In other words, the radio antenna 1 may be devoid of a housing 2. The electromagnetic radiation then takes place orthogonally to the longitudinal axis AL

[0042] As visible in [Fig.4], the intersection of each blade 3 with the housing 2 forms a curve called a 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 Al is a logarithmic spiral.

[0043] In this configuration, the angle of attack [3 is constant along the entire length of the radio antenna 1. The distance Lt between the consecutive twists 30 varies along the radio antenna 1. In particular, the distance Lt increases while progressing from a first end 21 of the housing 2 towards a second end 22 opposite the first end 21.

[0044] The Cartesian parameterization of the conical helix is ​​as follows: ' x = aektcost y = aektsïnt . z = aektcosa

[0045] with k = sinacos / ï and where a corresponds to the half-angle at the apex of the cone and P to the angle between the helix and the generatrices of the cone.

[0046] The angle P as defined in the above equation 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 the angle P of the above equation to be less than the maximum angle [3max. The structure of the radio antenna can thus be optimized by parameterizing the geometry of the blades.

[0047] The conical helix solution makes it possible to guarantee a constant angle of attack P over the entire antenna and configurable, based on the use of a logarithmic spiral as a generator.

[0048] [Fig.5] shows the parameters of the truncated cone-shaped housing. Certain 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 level of the second end 22) or output radius Rout determined by the desired gain for the antenna. The housing 2 has for example a radius at its apex (i.e. at the level of the first end 21) or input radius Rin determined in part by the desired bandwidth.

[0049] A preferred means of implementation consists of fixing the output radius Rout and the input radius Rin. The remaining optimization parameters are then the length of the antenna Lhorn, the number of turns NtUm of the conical helix in the length Lhorn, and 0< [3max.

[0050] According to the geometry of the truncated cone, it is possible to write: . 1 / ^ouT^Ih \ « = tan iT--- X ^'horn <

[0051] The number of turns NtUmpensures that and [3< [3max through the following equation: & = an«)= sinacos / î

[0052] It is thus possible to parameterize the angle of attack P so as to guarantee < [3max, where [3max 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 truncated, 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 term circumscribed cone refers to the mathematical object and does not constitute a physical part of the radio antenna 1.

[0054] In an exemplary embodiment not shown, the distance Lt 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 circular helix. If the radio antenna 1 comprises a housing 2, the distance Lt may be constant from the first end 21 of the housing 2 to the second end 22. The housing 2 may, for example, in this case have a cylindrical shape. Whether or not the radio antenna 1 comprises a housing 2, the angle of attack may then be kept constant along the radio antenna 1 while being less than the maximum angle [3max.

[0055] In this document, the term "blade" means 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 conventionally called a "ridge" in the antennal domain.

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

[0057] When manufacturing the antenna, the blade(s) obtained then follow a profile according to a conical helix. The blade(s) can first be manufactured by having a solid surface and are then hollowed out according to a particular progressive profile. The progressive profile is chosen to ensure 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] [Fig.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 the left polarization and the right polarization is also observed in both cases (prior art and example according to the invention).

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

[0061] [Fig.7] represents for comparison radiation patterns obtained at 16 GHz: in a) the pattern represented in b) of [Fig.6] and in which the number of turns Nturn of the conical helix is ​​equal to 2.6, and in b) the pattern obtained for the same example of embodiment of the conical helix of the invention but with a number of turns NtUrnequal to 4. Comparison of the patterns 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 lower than the predefined maximum angle of attack.

[0063] The invention makes it possible to greatly simplify the design phase: the proposed parameterization makes it possible to simply launch an optimization in dedicated software, constrained by the attack value [3 lower than that of the predefined maximum attack angle [3max 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 print parameters (and which would require re-optimization to satisfy the radiated performance) and so on.

Claims

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10. Claims Radio antenna comprising at least one blade (3) twisted along and around a longitudinal axis (Al) 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 2ir, said radio antenna (1) being characterized in that the distance (Lt) along the longitudinal axis (Al) between each twist and a twist adjacent to said twist is chosen so that the angle (|3) between the twist (30) and the longitudinal axis (Al) is less than a predefined maximum angle (|3max). Radio antenna according to claim 1, wherein the angle (|3) between each twist and the twist adjacent to said twist is the same along the radio antenna (1). Radio antenna according to claim 1 or claim 2, wherein the maximum angle (|3max) is predefined depending on the manufacturing material of the radio antenna (1). Radio antenna according to claim 3, made of metal and in which the predefined maximum angle (|3max) is equal to 45°. Radio antenna according to one of claims 1 to 4, further comprising a housing (2), the blade (3) extending inside the housing (2). Radio antenna according to claim 5, in which the housing (2) has a truncated cone shape. Radio antenna according to claim 6, in which the intersection of the blade (3) with the housing (2) 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. Radio antenna according to claim 5, wherein the housing (2) has a cylindrical shape, the distance (Lt) along the longitudinal axis (Al) between each twist and a twist adjacent to said twist being identical all along the radio antenna (1). Radio antenna according to one of claims 5 to 8, wherein the radio antenna (1) is a horn antenna. Radio antenna according to one of claims 1 to 9, comprising at least two blades (3) twisted along and around the longitudinal axis (Al).

11. A method of manufacturing a radio antenna according to one of claims 1 to 10, wherein the manufacturing is carried out by additive manufacturing.

12. Manufacturing method according to claim 11, in which the additive manufacturing is of the Powder Bed Laser Fusion type.

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