Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PASSIVE RADIO FREQUENCY DEVICE WITH AXIAL FIXING APERTURES
Technical field
[0001] The
present invention relates to a radio frequency device comprising axial fixing
apertures.
State of the art
[0002]
Passive radio frequency devices are used to propagate or manipulate radio
frequency signals without using active electronic components. Passive RF
devices include for
example passive waveguides based on guiding waves within hollow metal
channels, filters,
antennas, mode converters, etc. Such devices can be used for signal routing,
frequency
filtering, signal separation or recombination, transmission or reception of
signals into or from
free space, etc.
[0003] Conventional waveguides used for radio frequency signals have
internal apertures
of, for example, rectangular or circular cross-section. They allow the
propagation of
electromagnetic modes corresponding to different electromagnetic field
distributions along
their cross-section.
[0004]
Radio frequency devices are used, for example, in aerospace (aircraft,
helicopters,
drones), to equip a spacecraft in space, on a ship at sea or on a submarine,
on devices
operating in the desert or in high mountains, in each case in hostile or even
extreme
conditions. In these environments, radio frequency devices are exposed to:
extreme pressures and temperatures that vary significantly, leading to
repeated
thermal shocks;
mechanical stress, as the waveguide is integrated into a machine that is
subjected
to shocks, vibrations and loads that impact the
waveguide;
hostile weather and environmental conditions in which waveguide-equipped
vehicles operate (wind, frost, humidity, sand, salt, fungi/bacteria).
[0005] In
addition, weight-related requirements are often critical for space or
aeronautical applications.
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[0006] In order to meet these constraints, waveguides formed by
assembling previously
machined metal plates are known, which make it possible to manufacture
waveguides
suitable for use in hostile environments. However, the manufacture of these
waveguides is
often difficult, costly and not easily adaptable to the manufacture of light
and complex shaped
waveguides.
[0007] Waveguides manufactured in this way by assembling plates of
aluminium, copper,
titanium, etc., with or without surface treatments, are therefore often made
as standardised
parts which must then be assembled together. On the other hand, it is often
useful to be able
to connect together two or more passive radio frequency devices, for example a
waveguide
with an antenna or several waveguide portions, in order to create various
types of
configurations. These connections are most often made by means of flanges or
clamps in
order to achieve the desired system. The presence of these connection elements
increases
the weight of the system, which is particularly problematic for applications
in aeronautics or
space.
[0008] For example, W02018029455 describes a waveguide connector comprising
a
flange and a plurality of ports. The flange includes means for coupling to
another waveguide
connector, each port of the plurality of ports being configured to interface
with a respective
waveguide. The volume of the flange and its weight are substantial relative to
the connector.
[0009] As an example, the dissertation by Huilin LI, "Waveguide flange
design and
characterization of misalignment at submillimeter wavelengths", May 2013,
pages 4, 22, 23,
24, 26, 62, 152, describes various embodiments of waveguide connectors, e.g.
flanges with
complementary holes and pins, flanges with complementary male/female profiles,
or flanges
with an interlocking alignment ring.
[0010] Examples of such flanges are shown in Figures la, lb and lc
herein. It can be seen
that known interfaces use flanges of large dimensions and masses compared to
the useful
part of the waveguides. In order to make connections with great rigour, with
rigorous
alignments and durable fixings, the flanges occupy particularly large
surfaces.
[0011] W02017/192071 discloses a waveguide interconnect system that
provides fast
and reliable interconnection with minimal interconnections. The interconnect
system
comprises a flange adapter element adapted to be disposed between two flanges
of two
waveguides. The connection of the two waveguides therefore requires an
additional part to
connect the waveguides which increases the complexity and cost of waveguide
assembly.
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[0012] Recent work has demonstrated the possibility of realizing passive
radio frequency
devices, including antennas, waveguides, filters, converters, etc., using
additive
manufacturing methods, for example 3D printing. In particular, the additive
manufacturing of
waveguides comprising both a core of non-conductive material, such as polymers
or ceramics,
and a shell of conductive metal is known.
[0013] In particular, waveguides comprising ceramic or polymer walls
manufactured by
an additive method and then covered with a metal plating have been suggested.
The internal
surfaces of the waveguide must indeed be electrically conductive to operate.
The use of a
non-conductive core allows on the one hand to reduce the weight and the cost
of the device,
and on the other hand to implement 3D printing methods adapted to polymers or
ceramics
and allowing to produce high precision parts with low roughness.
[0014] As an example, the article by Mario D'Auria et al, "3-D PRINTED
METAL-PIPE
RECTANGULAR WAVEGUIDES", 21 August 2015, IEEE Transactions on components,
packaging
and manufacturing technologies, Vol. 5, No. 9, pages 1339-1349, describes in
paragraph III a
process for manufacturing the core of a waveguide by fused deposition modeling
(FDM).
[0015] For example, waveguides made by additive manufacturing are known,
comprising
a non-conductive core manufactured for example by stereolithography, by
selective laser
melting, by selective laser sintering, or by another additive process. This
core typically has an
internal opening for the propagation of the radio frequency signal. The
internal walls of the
core around the aperture may be coated with an electrically conductive
coating, for example
a metal plating.
[0016] Additive manufacturing of passive radio frequency devices allows
the production
of complex shaped devices that would be difficult or even impossible to
produce by
machining. However, additive manufacturing has its own constraints and does
not allow the
manufacture of certain shapes or large parts.
[0017] The need to make effective connections between multiple parts is
therefore
recurrent.
[0018] 0018] US2012/0084968A1 describes a process for manufacturing
passive
waveguides in multiple parts made by 3D printing and then metallized before
being
assembled. The multi-part manufacturing process makes the process more
flexible and allows
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for complex shaped parts that would be impossible to print in a single
operation. However,
this process creates discontinuities in the metal layer at the junction
between the different
metallized parts, which disrupt the signal transmission in the waveguide. On
the other hand,
the precise fit of the individual parts is difficult to ensure, and can hardly
be improved by
polishing or adjusting the metal layer, which is usually too thin.
[0019] The same problems of flange weight and bulk are also found in
active RF
equipment, e.g. semiconductor equipment such as low noise amplifiers, power
amplifiers,
filters, etc., where such equipment must be connected to waveguides.
Brief summary of the invention
[0020] An aim of the present invention is to provide a passive or active
radio frequency
device free of or minimizing the limitations of known devices.
[0021] In particular, an aim of the invention is to provide a radio
frequency device, for
example a passive device, for example a waveguide, which is easily connectable
to other
elements, for example other waveguides, antennas, polarizers, etc.
[0022] A further aim of the invention is to provide an easily assembled
radio frequency
device of reduced mass, suitable for uses where mass reduction is a critical
objective.
[0023] According to the invention, these aims are achieved in particular
by means of a
radio frequency device comprising at least: a tube through which a channel
passes, a front
face and/or a rear face forming a bearing surface through which the channel
passes, said
bearing surface forming an annular frame around one end of the tube and
integral with the
tube, said bearing surface comprising a plurality of axial fixing apertures
passing through the
bearing surface and opening outside said channel in order to allow the device
to be fixed, the
width of said frame being greater at the level of, and in the immediate
vicinity of, the axial
fixing apertures than at a distance from these axial fixing apertures.
[0024] The front and/or rear face thus forms a lightened flange.
[0025] The term "annular" and the term "annular frame" refer to any
closed, non-full
shape, including for example a rectangular, square, circular, oval, elliptical
ring, etc. The shape
of the outer circumference may be different from the shape of the aperture.
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[0026] The bearing surface(s) allow the device to be aligned and pressed
against another
device attached by means of the axial fixing apertures.
[0027] At least one of the axial fixing apertures may be reinforced.
[0028] An axial aperture is, for example, said to be reinforced if the
bearing surface uses
more material in the vicinity of the axial fixing apertures than between the
axial fixing
apertures.
[0029] An axial aperture is for example said to be reinforced when the
bearing surface
forms an annular surface around the channel and the width of this annular
surface is greater
at the aperture than between two apertures. For example, the aperture is said
to be
reinforced when this axial aperture is provided in a lug or other prominent
portion around
the annular surface surrounding the channel.
[0030] An axial aperture is also said to be reinforced when the bearing
surface forms an
annular surface around the axial channel, which bearing surface comprises,
except for a
portion, for example a ring, around the axial aperture.
[0031] The reinforcement of the bearing surface at the axial fixing
apertures allows for a
comparatively lighter bearing surface between these fixing apertures, which
ultimately
results in a lighter bearing surface.
[0032] The bearing surface may be provided with an aperture corresponding
to said
channel, and an annular surface around said aperture.
[0033] The radial apertures pass through this bearing surface and open out
at the rear of
the bearing surface, but outside the channel.
[0034] The width of the bearing surface may be wider at and in close
proximity to the
axial fixing apertures than at a distance from the axial fixing apertures.
[0035] The bearing surface may be made thinner between the axial fixing
apertures.
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[0036] The bearing surface may be provided with recesses between the
axial fixing
apertures.
[0037] Advantageously, all or part of the bearing surfaces of the front
or rear faces
comprise a lattice structure. The use of such a structure, which is easy to
produce by additive
manufacturing, makes it possible to lighten the bearing surfaces, in
particular between the
lugs or the fixing apertures, in order to reduce the mass still further while
maintaining
sufficient rigidity of the bearing portions.
[0038] In one aspect, at least one of the bearing surfaces comprises a
plurality of fixing
lugs, each of the lugs comprising at least one said axial fixing aperture.
[0039] The reinforced lugs prevent deformation of the device when attached
to another
device by means of screws or pins engaged in the axial fixing apertures.
[0040] Each of the lugs may be independent and disjointed from the
others, thus forming
material-free inter-lug spaces, thereby lightening the structure of the
device.
[0041] The device may have exactly three axial fixing apertures on one or
more sides to
allow isostatic fixing.
[0042] The device may have exactly three lugs per bearing surface,
defining an attaching
plane in an isostatic manner.
[0043] However, it is also possible to have two fixing points, four
fixing points, or another
number of fixing points.
[0044] The devices may be secured together by at least one screw or pin
engaged in each
axial fixing aperture. The screw or screws may be metallic or made of other
materials.
[0045] The device may be a waveguide, more particularly a satellite
antenna waveguide.
[0046] Advantageously, the bearing surface is flat. The fixation of two
elements with flat
faces allows for a simple, reliable and quickly installed fixation.
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[0047] According to another advantageous embodiment, the bearing surface
is in a plane
perpendicular to the axis of the channel. In this way, devices with standard
profiles, with
aligned lugs, can be easily produced for easy and rigorous assembly.
[0048] Also advantageously, the bearing surface may be manufactured in
one piece with
the device. The one-piece construction simplifies the manufacturing process,
and facilitates
obtaining regular and precise dimensions.
[0049] According to a further advantageous embodiment, the device and its
bearing
surfaces are produced by additive manufacturing. This manufacturing method is
particularly
advantageous for producing customized or standard parts with a regular
quality.
[0050] The channel may comprise a non-conductive core and a conductive
shell around
said core, said core and said conductive shell extending into said bearing
surface.
[0051] The thickness of the metallic conductive layer is advantageously
at least five times
the skin depth 8, preferably at least twenty times the skin depth 8. This
large thickness is not
necessary for signal transmission, but contributes to the rigidity of the
device, which is thus
guaranteed by the metal shell despite a potentially less rigid multi-piece
core than a
monolithic core, and despite a reduced flange bearing surface.
[0052] The skin depth 8 is defined as:
6 = i 2
pi 27rf a
where is the magnetic permeability of the plated metal, f is the radio
frequency of the signal
to be transmitted and cr is the electrical conductivity of the plated metal.
Intuitively, this is
the thickness of the zone where the current is concentrated in the conductor,
at a given
frequency.
[0053] In particular, this solution has the advantage, compared to the
prior art, of
providing waveguides assembled by additive manufacturing which are more
resistant to the
stresses to which they are exposed (thermal, mechanical, meteorological and
environmental
stresses).
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[0054] The device core may be formed from a polymeric material.
[0055] The device core may be formed of a metal or alloy, for example
aluminum,
titanium or steel.
[0056] The device core may be formed of ceramic.
[0057] The device core may be formed by stereolithography, selective laser
melting or
selective laser sintering.
[0058] The metal layer forming the shell may optionally comprise a metal
selected from
Cu, Au, Ag, Ni, Al, stainless steel, brass or a combination thereof.
[0059] The strength of the device selected from tensile strength,
torsional strength,
bending strength or a combination thereof may be provided predominantly by the
conductive
layer.
[0060] According to an embodiment, the deposition of the conductive layer
on the core
is performed by electrolytic or galvanic deposition, chemical deposition,
vacuum deposition,
physical vapour deposition (PVD), printing deposition, sintering deposition.
[0061] In one embodiment of the process, the conductive layer comprises a
plurality of
successively deposited metal and/or non-metal layers.
[0062] The manufacture of the core comprises an additive manufacturing
step. By
"additive manufacturing" is meant any process for manufacturing parts by
adding material,
according to computer data stored on a computer medium and defining a model of
the part.
In addition to stereolithography and selective laser melting, the term also
refers to other
manufacturing methods such as liquid or powder curing or coagulation,
including but not
limited to binder jetting, DED (Direct Energy Deposition), EBFF (Electron beam
freeform
fabrication), FDM (fused deposition modeling), PFF (plastic freeforming),
aerosol, BPM
(ballistic particle manufacturing), powder bed, SLS (Selective Laser
Sintering), ALM (Additive
Layer Manufacturing), polyjet, EBM (electron beam melting),
photopolymerization, etc.
However, manufacturing by stereolithography or selective laser melting is
preferred because
it allows parts with relatively clean, low-roughness surfaces to be obtained.
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[0063] The manufacturing of the core may comprise an additive
manufacturing step by
stereolithography, by selective laser melting or by selective laser sintering.
[0064] In the context of the invention, the terms "conductive layer",
"conductive
coating", "metallic conductive layer" and "metallic layer" are synonymous and
interchangeable.
Brief description of the figures
[0065] Examples of the implementation of the invention are shown in the
description
illustrated by the attached figures in which :
= Figures la, 1b and lc illustrate examples of waveguides of the prior art,
comprising a
flange surrounding the waveguide and allowing two waveguides with compatible
flanges to
be fixed together;
= Figure 2 is a perspective view of two parts intended to be joined in a
plane
perpendicular to the direction of signal propagation to form a longer
waveguide;
= Figure 3 shows an enlarged view of a lug of a variant of the device in
which the fixing
lugs are made with a lattice structure;
= Figure 4 illustrates a front view of a front or rear face of a waveguide
device forming a
bearing surface (flange) provided with an opening corresponding to said
channel, said bearing
surface being made of a lattice structure and comprising four reinforced axial
apertures.
= Figure 5 shows a cross-sectional view of a device having a core covered
with a
conductive jacket on the inner and outer walls.
Example(s) of embodiment of the invention
[0066] Figures la to lc illustrate examples of flanges belonging to prior
art radio
frequency devices. These flanges are provided to facilitate the assembly
together of several
devices, for example several waveguide sections of identical or different
shapes. Fixing is
achieved by contacting the flanges provided at the ends of the waveguide
sections. The
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flanges have apertures for the insertion of fixing elements such as screws or
pins. The known
flanges are large and their surface area is significantly larger than the
surface area of a
waveguide section. The large surface areas provided allow high quality
assemblies to be
made, with precise alignments, without the risk of impairing the performance
of the
assembled elements. However, the large surface areas used make the parts
considerably
heavier, making them unsuitable for certain applications where mass is a
critical factor.
[0067] An example of a device according to the invention is illustrated
in Figure 2. As
illustrated, the radio frequency device 1, here a passive radio frequency
device, for example
a waveguide, comprises a tube 2 of elongated shape along a longitudinal axis A-
A. A channel
3, for the transmission of the radio frequency signal, is also aligned along
the axis A-A, and
passes through the tube. In the example shown, the longitudinal opening 3 is
rectangular in
cross-section and defines a channel for the transmission of the radio
frequency signal. Other
channel shapes, including round, square, elliptical, semi-circular, semi-
elliptical, hexagonal,
octagonal, etc., can be used.
[0068] The cross-section of the opening is determined according to the
frequency of the
electromagnetic signal to be transmitted. The dimensions of this internal
channel and its
shape are determined according to the operational frequency of the device 1,
i.e. the
frequency of the electromagnetic signal for which the device is manufactured
and for which
a stable transmission mode and optionally with minimum attenuation is
obtained. The tube
2 may be made of metal, or by metallization of a core 2 of for example
polymer, epoxy,
ceramic, organic material or metal.
[0069] A front face 4 and/or a rear face 5 define bearing surfaces for
connecting two or
more devices 1 together along the axis A-A. The bearing surfaces of the front
4 and rear 5 are
in a plane perpendicular to the channel axis.
[0070] In order to fix two consecutive adjacent devices together, the front
and/or rear
faces of the device form an annular surface around the channel 3, this annular
surface
comprising a plurality of fixing lugs 6. The width of the annular surface is
therefore greater at
the lugs around the fixing points than between the lugs, thereby strengthening
the fixing
points. The contact face of each lug is coplanar with the adjacent face 4 or 5
of the channel.
Arrangements can be designed to maintain compatibility with existing flanges,
whether
standardized or not.
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[0071] In the illustrated examples, exactly three fixing points are
provided, thus enabling
isostatic fixing. These three fixing points are provided in three lugs 6
distributed around the
opening and thus creating an isostatic fixing plane. The lugs 6 are here
distributed with two
lugs in the lower corners and one in the middle area of the opposite edge.
Other
arrangements with lugs 6 in the corners and/or along the edges are possible.
[0072] 0072] The lugs have axial apertures 7, which are used to insert
fastening elements
such as screws, screw/nut assemblies, pins, etc. Other apertures may be
provided in the lugs
or bearing surfaces to reduce mass. Heat dissipation surfaces may also be
provided.
[0073] In order to best meet the desired objectives of reducing mass in
relation to the
.. use of flanges, the dimensions of the lugs 6 are greatly reduced in
relation to those of the
device 1. For example, the lugs 6 are dimensioned so that the total sum of the
footprints E is
less than one third and more preferably less than one quarter of the external
perimeter of
the core 2 of the device 1. By footprint is meant the width of the lug at the
level of the
intersection with the core 2 of the device, as illustrated for example in
Figures 2 and 4.
[0074] Figure 3 illustrates an alternative embodiment in which at least one
of the lugs 6,
and possibly the remainder of the annular surface around the channel, is made
of a lattice
structure, i.e. comprising beams separated by recesses. Such an architecture
further
contributes to the objectives of mass reduction, without affecting the
rigidity and/or
durability of the fixture.
[0075] Figure 4 illustrates a front view of an all-mesh bearing surface
(flange) 4 between
the four axial fixing apertures 7. The apertures are reinforced with a
reinforcing ring 70 which
is denser than the rest of the mesh around each aperture. This design allows
the size of the
bearing surface 4 to be increased, without significantly increasing its mass,
and thus ensures
a strictly flat bearing surface even after clamping against the corresponding
bearing surface
.. of an adjacent device. The density of the mesh may vary around the
periphery of the bearing
surface, and may be greater, for example, in the vicinity of the fixing
apertures 7 than at a
distance from them.
[0076] The tube and its bearing surfaces 6 are preferably produced by
additive
manufacturing, as described later. This method of manufacturing makes it
possible to
produce in a simple manner a device provided with bearing surfaces (flanges)
of complex
shape, for example a tube provided with lugs, and/or a lattice structure.
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[0077] Figure 2 illustrates two aligned devices 1, intended to be fixed
together.
[0078] The two devices are intended in this example to be juxtaposed one
after the other
in the direction of signal transmission, thus forming a continuous elongated
longitudinal
channel. The bearing surfaces intended to be brought into contact are flat and
perpendicular
to the direction of transmission of the radio frequency signal.
[0079] The front or rear face of the device may have a central area that
is very slightly
recessed so that it does not touch the face of the flange of the device or of
the connected
equipment, but is separated from it by a narrow gap. The recessed area is
bounded by a
deeper groove in the flange surface. This arrangement allows for short-circuit
operation. This
central recessed area can also be provided in the case of a lattice flange as
described above.
[0080] In the embodiment illustrated in Figure 5, the inner and outer
surface of the core
2 are covered with a conductive metal layer, for example copper, silver, gold,
nickel etc, plated
by chemical deposition without electrical current. The thickness of this layer
is for example
between 1 and 20 micrometers, for example between 4 and 10 micrometers. Figure
5
illustrates the device in which a layer formed by metal deposition forms a
conductive coating
8 on the inner surface 9 and on the outer surface of the core 2. The coating
may also be a
combination of layers, comprising for example a smoothing layer directly on
the core, one or
more bonding layers, etc.
[0081] In this example, the bearing surfaces (e.g. the lugs 6) also
comprise a core covered
by the outer conductive layer 8.
[0082] The thickness of this conductive coating 8 or 9 must be sufficient
for the surface
to be electrically conductive at the chosen radio frequency. This is typically
achieved by using
a conductive layer with a thickness greater than the skin depth 6.
[0083] This thickness is preferably substantially constant on all
internal surfaces in order
to achieve a finished part with accurate dimensional tolerances for the
channel.
[0084] In one embodiment, the thickness of this layer 8 or 9 is at least
five times and
preferably at least twenty times greater than the skin depth, in order to
improve the
structural, mechanical, thermal and chemical properties of the device. The
surface currents
are thus mainly, if not almost exclusively, concentrated in this layer.
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[0085] The application of a metallic coating on the external surfaces
does not contribute
to the propagation of the radio frequency signal in the channel 3, but does
have the advantage
of protecting the device from thermal, mechanical or chemical attack. In a non-
illustrated
embodiment, only the inner surface of the core, around channel 3, is covered
with a metal
jacket. The outer surfaces are bare, or covered with a different coating.
Additive manufacturing
[0086] The device 1 is advantageously manufactured by additive
manufacturing,
preferably by stereolithography, selective laser melting, selective laser
sintering (SLS) in order
to reduce surface roughness. The core material may be non-conductive or
conductive. The
.. wall thickness is for example between 0.5 and 3 mm, preferably between 0.8
and 1.5 mm.
[0087] The shape of the device may be determined by a computer file
stored in a
computer data medium and used to control an additive manufacturing device.
[0088] The deposition of conductive metal on the inner and possibly outer
faces is
achieved by immersing the core 2 in a series of successive baths, typically 1
to 15 baths. Each
bath involves a fluid with one or more reagents. The deposition does not
require the
application of a current to the core to be coated.
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Reference numbers used on figures
1 Passive radio frequency device
2 Core
3 Channel
4 Front side
Rear side
6 Lugs
7 Axial fixing aperture
70 Reinforcement ring
8 Inner conductive coating
9 External conductive coating
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