A radio antenna with blades and a controlled angle of attack, and a 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 an adjacent 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 the abstract: Fig. 1.

Description

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

[0001] The invention relates to the field of radio antennas, that is to say, devices for radiating and / or receiving electromagnetic waves. The invention is 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 simple linearly polarized horn, coupled with a polarizer at the antenna output, should be used. It is also possible to use a dual linearly polarized horn, coupled with a wideband 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 (dual linear polarization horn) requires the use of a hybrid coupler for circular polarization, which necessarily generates losses.

[0004] A better solution is to modify the structure of the horn antenna itself so that this structure alone generates circular polarization. Ridged antennas with blades (or "ridges") twisted around a longitudinal axis are known for this purpose. The blades form an angle with the longitudinal axis called the angle of attack.

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

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

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

[0008] According to the invention, the distance along the longitudinal axis between each twist and an adjacent twist to said twist is 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 parameterized to enable both electromagnetic functions and improved manufacturing efficiency. 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 fabrication of the antenna, especially when this fabrication 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 according to the material from which the radio antenna is made.

[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 an adjacent twist being identical all along the radio antenna.

[0018] The radio antenna is a horn antenna.

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

[0020] The invention also relates to a method for 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 Fusion type.

[0022] Other features and advantages of the invention will become apparent in the following description with reference to the accompanying drawings, given by way of non-limiting examples: - Fig. 1 is a perspective view of a radio antenna according to one embodiment of the invention; - [Fig.2] is a perspective view of the blades of the radio antenna of [Fig.1]; - [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 onto a longitudinal plane; - Figure 6 shows two radiation pattern graphs for comparison, one graph relating to a prior art radio antenna and the other graph relating to the radio antenna according to the invention; and - Fig. 7 shows for comparison two radiation diagram graphs relating to the radio antenna according to two variants of the invention.

[0023] Fig. 1 represents an example of an 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 Al, in particular a median longitudinal axis.

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

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

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

[0029] The housing 2 may have a conical, frustoconical, cylindrical, or truncated pyramidal shape. The radio antenna 1 is then a horn antenna. In the example shown, the housing 2 has a frustoconical 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 as a single 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 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 all along 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 less 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 especially 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 Fusion type. Indeed, the reliability of such manufacturing is subject to the design rules of such manufacturing. The maximum angle [3max] ensures good control of the geometry (and therefore of the radiated performance). If the maximum angle [3max] is not respected, the antenna may be locally degraded. This degradation can, through the propagation of defects during manufacturing, alter the entire antenna. Ultimately, this can lead to partial sagging of the antenna. An alteration of the mechanical properties of the antenna thus manufactured may also be observed.

[0038] During additive manufacturing using Powder Bed Fusion, the maximum angle [3max] also depends on the material used for the powder and its particle size. The maximum angle [3max] may also depend on the manufacturing machine and possibly the additive printing parameters.

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

[0040] 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 one, two, three, four, etc. Figure 3 shows, by way of non-limiting example, the radio antenna 1 having three blades 3 and four blades 3, respectively.

[0041] Furthermore, the radio antenna 1 described above includes a housing 2. In this case, electromagnetic radiation occurs along the longitudinal axis AL. 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 occurs orthogonally to the longitudinal axis AL

[0042] . As can be seen in [Fig. 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 the shape of a conical helix. 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 L between the consecutive twists 30 varies along the radio antenna 1. In particular, the distance L increases as it progresses from a first end 21 of the housing 2 to a second end 22 opposite to the first end 21.

[0044] The Cartesian parameterization of the conical helix is ​​as follows: ' X = ae^COSÙ with k = sinctcos / ? and where a corresponds to half the angle at * y = a^sint ,z = ae kt cosa apex of the cone and fi at the angle between the helix and the generatrices of the cone.

[0045] The angle fi as defined in the above equation also corresponds to the angle of attack between each twist 30 and the longitudinal axis Al of the radio antenna 1. It is therefore possible to impose on the angle fi 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.

[0046] The conical helix solution makes it possible to guarantee a constant angle of attack fi over the entire antenna and configurable, based on the use of a logarithmic spiral as a generator.

[0047] Figure 5 shows the parameters of the frustoconical housing. Some parameters of housing 2 are fixed by physical constraints. Housing 2 has, for example, a radius at its base (i.e., at the second end 22), or output radius Rout, determined by the desired gain for the antenna. Housing 2 has, for example, a radius at its apex (i.e., at the first end 21), or input radius Rin, determined in part by the desired bandwidth.

[0048] A preferred embodiment is to fix the output radius Rout and the input radius Rin. The remaining optimization parameters are then the antenna length Lhorn, the number of turns Nturn of the conical helix in the length Lhorn, and fi < [3max.

[0049] According to the geometry of the frustoconical case, it is possible to write: cr = tan 1 (^^) \ ^horn t

[0050] The number of turns NtUmpermet allows us to ensure that and [3< [3max] through the following equation: * = = sina.cos / 3

[0051] It is thus possible to parameterize the angle of attack fi so as to guarantee < Pmax, where Pmax depends as explained above on the machine used for manufacturing, its parameterization, and the type of material used.

[0052] The blade curve is defined above as the intersection of each blade 3 with the frustoconical housing 2. In an example where the housing 2 has a shape other than frustoconical, or where 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 be the mathematical object and is not a physical part of the radio antenna 1.

[0053] In an example of an embodiment not shown, the distance Lt along the longitudinal axis Al between consecutive twists 30 can be identical along the entire length of the radio antenna 1. For example, each blade 3 would have the shape of a circular helix. If the radio antenna 1 has a housing 2, the distance Lt can be constant from the first end 21 of the housing 2 to the second end 22. The housing 2 can, for example, have a cylindrical shape in this case. Whether or not the radio antenna 1 has a housing 2, the angle of attack fi can then be kept constant along the radio antenna 1 while being less than the maximum angle [3max].

[0054] In this document, the term "blade" refers to a volume generated by scanning any section along the generatrix 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.

[0055] The radio antenna 1 is preferably manufactured by additive manufacturing.

[0056] During the manufacture of the antenna, the resulting blade(s) follow a profile based on a conical helix. The blade(s) may initially be manufactured with a solid surface and are subsequently hollowed out according to a specific progressive profile. The progressive profile is chosen to ensure broadband matching and controlled secondary lobes. Several implementation methods are possible for the progressive profile (tapering), for example an exponential profile or a Klopfenstein profile.

[0057] Figure 6 shows radiation patterns obtained at 16 GHz: a) the pattern obtained for the prior art antenna as described in US patent 2021 / 184359, and b) the pattern obtained for the exemplary embodiment of the conical helix of the invention. The antenna's native polarization (i.e., right-hand polarization) RHCP and orthogonal polarization (i.e., left-hand polarization) are shown. The patterns are plotted along three cross-sectional planes, for three values ​​of phi: 0°, 45°, and 90°.

[0058] Diagrams a) and b) are relatively similar. The diagrams are symmetrical in both cases. The on-axis gain is identical, and the cross-bias levels are of the same order of magnitude. A significant decoupling between left- and right-bias is also observed in both cases (prior art and the example according to the invention).

[0059] Comparison with the prior art in [Fig.6] shows that the structure of the radioelectric antenna according to the invention behaves nominally from the point of view of electromagnetic radiation.

[0060] Figure 7 shows, for comparison, radiation patterns obtained at 16 GHz: a) the pattern shown in b) of Figure 6, in which the number of turns Nturn of the conical helix is ​​equal to 2.6, and b) the pattern obtained for the same embodiment of the conical helix of the invention but with a number of turns Nturn equal to 4. The 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 radio antenna configuration according to the invention.

[0061] 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.

[0062] The invention greatly simplifies the design phase: the proposed parameterization allows for a simple optimization in dedicated software, constrained by the attack value [3] being lower than the predefined maximum attack angle [3max]. The resulting solution is then guaranteed to be manufacturable, particularly printable by additive manufacturing. This avoids the need for multiple electromagnetic or mechanical modifications, or adjustments to the geometry to meet printing parameters (which would require re-optimization to achieve radiated performance), and so on.

Claims

Demands

1. Radio antenna comprising a housing (2) within which extends 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 housing (2) has a frustoconical shape, • the distance (Lt) along the longitudinal axis (Al) between each twist and a twist adjacent to said twist 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 of attack (|3max). • the angle of attack (|3) between each twist and the twist adjacent to said twist is the same along the radio antenna (1).

2. Radio antenna according to claim 1 wherein the maximum angle (|3max) is predefined according to the material of manufacture of the radio antenna (1).

3. Radioelectric antenna according to claim 2, made of metal and in which the predefined maximum angle (|3max) is equal to 45°.

4. Radio antenna according to any one of the preceding claims, wherein 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.

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

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

7. A method for manufacturing a radio antenna according to any one of claims 1 to 6, wherein the manufacturing is carried out by additive manufacturing.

8. A manufacturing method according to claim 7, wherein the additive manufacturing is of the Powder Bed Laser Fusion type.

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