Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RADIO-FREQUENCY COMPONENT COMPRISING SEVERAL WAVEGUIDE DEVICES
WITH RIDGES
Technical domain
[0001] The present invention relates to a radiofrequency component
comprising a
plurality of waveguide devices provided with ridges.
Background art
[0002] Passive radiofrequency waveguide devices are already known in the
prior art,
which allow to propagate and manipulate radiofrequency signals without using
active
electronic components. Passive waveguides can be divided into three distinct
categories:
= Devices based on guiding waves inside hollow metal channels, commonly
called
waveguides.
= Devices based on guiding waves inside dielectric substrates.
= Devices based on guiding waves by means of surface waves on metallic
substrates
such as PCBs, microstrips, etc.
[0003] The present invention relates in particular to components provided
with devices
according to the first category above. Examples of such devices include
waveguides as such,
filters, polarizers, antennas, mode converters, etc. They may be used for
signal routing,
frequency filtering, signal separation or recombination, transmission or
reception of signals
in or from free space, etc.
[0004] For example, the device may consist of a compact antenna, a
polarizer, a
waveguide, or a set of such elements connected in series.
[0005] Antennas are elements that are used to transmit or receive
electromagnetic
signals in free space. Simple antennas, such as dipoles, have limited
performance in terms of
gain and directivity. Parabolic antennas allow higher directivity, but are
bulky and heavy,
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making them unsuitable for use in applications such as satellites, for
example, where weight
and volume must be reduced.
[0006] In order to improve these parameters, it is known to group several
such
waveguide devices together to form a radio frequency component. Thus, direct
radiating
antennas (DRA) generally combine several radiating elements (elementary
antennas) out of
phase in order to improve gain and directivity. The signals received on or
emitted by the
different radiating elements are amplified with variable gains and phase-
shifted between
them in order to control the shape of the array's receive and transmit lobes.
At high
frequencies, for example microwave frequencies, the different radiating
elements are each
connected to a waveguide which transmits the received signal towards the radio
frequency
electronic modules, respectively which feeds this radiating element with a
radio frequency
signal to be emitted. The signals transmitted or received by each radiating
element can also
be separated according to their polarization by means of a polarizer.
[0007] Such an arrangement with multiple waveguide devices is also used
for example
in electronically controlled antennas, array-fed reflector antennas, compact
fixed multi-
beam antennas, etc.
[0008] Such components consisting of many array antenna devices, however,
pose
particular difficulties of realization. For example, it is desirable to avoid
interference
between signals transmitted or received by adjacent antennas.
[0009] It is also sometimes desirable to reduce the amplitude of
undesirable
transmission or reception side lobes ("grating lobes").
[0010] It is also sometimes desirable to improve the performance of an
antenna array
in terms of cross-polarization, gain, return loss and/or isolation.
[0011] The parameters available to the designer of such a component in
order to avoid
these perturbations between antennas and side lobes are few. For example, it
is sometimes
made use of closely adjacent antennas, with a distance d between antennas less
than the
wavelength X of the signal to be transmitted or received, or even less than
X/2, which
allows to reduce the side lobes. However, such close proximity requires a
miniaturization of
all parts of the component which is difficult to achieve.
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[0012] Waveguide devices with one or more ridges on their internal
surface are also
often used; for example, double ridged antennas, quadruple ridged antennas,
etc. are called
"double ridged antennas", "quadruple ridged antennas", etc. to designate
antennas with
two ridges and four ridges respectively. Such ridges make it possible, for
example, to adapt
the impedance of the devices to that of the other devices of the component, to
manufacture more compact and therefore lighter devices with equivalent
performance, to
control the modes of transmission of electromagnetic signals in the ridged
device, and, for
example, to avoid the transmission of undesirable modes or those generating
significant
interference with adjacent devices.
[0013] However, the desired arrangement of the ridges downstream of the
device is
not always desired upstream, and vice versa.
[0014] W02015/134772 discloses in particular a sub-array of a
radiofrequency
component comprising several waveguide devices. This sub-array may comprise
sixteen
waveguide devices, which include sixteen septum polarizers, split waveguide
ports and
radiating elements. The sixteen waveguide devices in the sub-array are
arranged in four
rows. The septum polarizer of the waveguides of the first and third row have
the same first
and same orientation, while the septum polarizer of the waveguides of the
third and fourth
row have the same orientation but rotated 1800 from the first orientation.
[0015] All septum polarizers are combined by a series of combiners in a
common input.
.. The rotation of the septum polarizers allows to have adjacent ports of the
same
polarization, thus simplifying the combiners.
[0016] A major disadvantage of W02015/134772 is that the single mode
bandwidth is
limited.
Brief summary of the invention
[0017] An aim of the present invention is to provide a radio-frequency
component, for
example a passive radio-frequency component to form the passive part of an
antenna array
or direct radiating array (DRA), which provides more freedom to the designer
to reduce the
performance limitations of known radio-frequency components.
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[0018] Another aim of the present invention is to provide a radio-
frequency component
with a higher bandwidth.
[0019] Another aim of the present invention is to provide a compact
radiofrequency
component.
[0020] Another aim of the present invention is to propose a radio-frequency
component that allows to discriminate more easily between the fundamental mode
of
transmission and the first higher order mode.
[0021] According to the invention, these aims are achieved in particular
by means of a
radiofrequency component comprising several waveguide devices, for example
antennas or
polarizers, arranged in an array and intended to transmit and/or receive
electromagnetic
signals, the radiofrequency component comprising several ridges, each
waveguide device
having:
at least one inner wall ;
an upstream opening in the direction of propagation of said emitting signals ;
a downstream opening in said direction of propagation of said emitting
signals,
linked to said upstream opening so that said emitting signals are transmitted
from said
upstream opening to said downstream opening, and/or vice versa in reception;
and wherein the arrangement of ridges in the downstream opening of each
waveguide device comprises not more and not less than three ridges.
[0022] The use of ridges allows the transmission of a preferred mode of
transmission in
a compact device.
[0023] Surprisingly, the use of three ridges in the downstream openings
significantly
increases the single-mode bandwidth of each waveguide device.
[0024] In a preferred embodiment, the arrangement of the ridges in the
openings
upstream of the RF component is different from the arrangement of the ridges
in the
openings downstream of the RF component.
[0025] The possibility to provide different upstream and downstream
ridges offers
additional freedom when designing the component, for example to change the
polarization
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and/or phase shift of the signal within a device, or between different devices
of the same
component.
[0026] The component can be a polarizer with a septum, for example a
septum of
variable height forming stair steps.
[0027] For example, the septum can be used to create a circular
polarization. Septums
can also be used to combine two orthogonal polarizations.
[0028] The arrangement of the different upstream and downstream ridges
allows to
maintain this circular polarization in a stable way and in a compact
waveguide.
[0029] The arrangement of the ridges in the downstream openings of the
different
devices may be different.
[0030] For example, if the devices have antennas, the arrangement of the
upstream
ridges can be arranged in such a way as to facilitate the coupling with the
active electronic
circuits.
[0031] The arrangement of the downstream ridges may be different between
the
different antennas, in order to reduce the mutual coupling between signals
transmitted or
received by the different antennas.
[0032] The number of ridges upstream of at least one device may be
different from the
number of ridges in the downstream opening of that device. For example, the
component
may include one or more waveguides that are ridged downstream but not
upstream.
[0033] The angular space between the different ridges of the upstream
opening of a
device can be different from the angular space between the ridges of the
downstream
opening of this device. For example, the component may comprise one or more
waveguides
whose upstream ridges are spaced at an angle a and whose downstream ridges are
spaced
at an angle p different from a.
[0034] The component may comprise one or more devices with a curved ridge.
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[0035] A curved ridge, for example, allows the position of the ridges to
be rearranged in
such a way that the ridges are positioned differently between upstream and
downstream.
[0036] At least one of the curved ridges may have two curved walls that
are
nevertheless parallel to each other.
[0037] The height of at least one of the ridges may be constant.
[0038] The height of at least one of the ridges can be variable. The
height of at least one
of the ridges of at least one said device may vary progressively over at least
a portion of the
length of that ridge.
[0039] At least one of the curved ridges may lead into said downstream
opening and
into said upstream opening in radial planes.
[0040] The radial position of the ridge(s) of the upstream opening of at
least one said
device may be different from the radial position of the three ridges of the
downstream
opening of that device.
[0041] The external section of at least one of said devices may be
identical upstream
and downstream.
[0042] In an embodiment, each device comprises a single upstream opening
and a
single downstream opening.
[0043] The radiofrequency component comprises a plurality of said
devices, the
upstream openings of the different devices being in one plane, the downstream
openings of
the different devices being in a second plane parallel to the first plane.
[0044] The radio-frequency component comprises a plurality of said
devices, each
device comprising a waveguide and an antenna with an opening linked to this
waveguide
and intended to transmit and/or receive electromagnetic signals,
each antenna defining a said downstream aperture,
each antenna has at least one inner wall with three ridges at the downstream
opening,
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the orientation of the three ridges between adjacent antennas being phase-
shifted.
[0045] This phase shift allows, for example, to control interference
between signals
transmitted or received by adjacent antennas.
[0046] According to one aspect, an object of the invention is also a
radiofrequency
component comprising an array of antennas, each antenna being at least
partially
surrounded by a rim in order to minimize mutual coupling between antennas.
[0047] According to one aspect, an object of the invention is also a
radiofrequency
component comprising an antenna array, said antennas progressively widening in
the
downstream direction by forming several steps. This improves the performance
of the array
in terms of return losses and bandwidth.
[0048] According to one aspect, an object of the invention is also a
radiofrequency
component comprising a ridged antenna array, the height of said ridges
progressively
reducing in the downstream direction by forming several steps. This improves
the
performance of the array in terms of return losses and bandwidth.
Brief description of the figures
[0049] Examples of implementation of the invention are indicated in the
description
illustrated by the annexed figures in which:
= Figure 1 schematically illustrates the downstream side of a component
comprising an
antenna array with different orientations.
= Figure 2 illustrates a component with an array of antennas with circular
openings,
each antenna being ridged.
= Figure 3 illustrates a component with an array of antennas with square
openings,
each antenna being ridged.
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= Figure 4 illustrates a section of a waveguide device according to an
aspect of the
invention, having a square or rectangular cross-section and forming two ridged
waveguides
upstream converging into a single waveguide with four ridges downstream.
= Figure 5 illustrates a section of a waveguide device according to an
aspect of the
invention, having an octagonal cross-section and forming two upstream ridged
waveguides
converging into a single downstream waveguide with four ridges.
= Figure 6 illustrates a section of a waveguide device according to an
aspect of the
invention, having a circular cross-section and forming two upstream ridged
waveguides
converging into a single downstream waveguide with four ridges.
= Figure 7 illustrates a section of a waveguide device according to an
aspect of the
invention, having a square or rectangular cross-section, and forming two
upstream ridged
waveguides converging into a single downstream waveguide with three ridges.
= Figure 8 illustrates a section of a waveguide device according to an
aspect of the
invention, having a hexagonal cross-section, and forming two upstream ridged
waveguides
.. converging into a single downstream waveguide with three ridges.
= Figure 9 illustrates a section of a waveguide device according to an
aspect of the
invention, having an octagonal cross-section, and forming two upstream ridged
waveguides
converging into a single downstream waveguide with three ridges.
= Figures 10 to 12 illustrate different views of a waveguide device with a
rearrangement of ridges and a different number of ridges upstream and
downstream, with
the ridges gradually disappearing.
= Figures 13 to 15 illustrate different views of a waveguide device with a
rearrangement ridges and a different number of upstream and downstream ridges,
with the
ridges being curved.
= Figure 16 illustrates an example of a component according to the
invention, with
radiating elements spaced further apart than the entry ports.
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= Figure 17 illustrates an example of a component according to the
invention, with
radiating elements less spaced than the entry ports.
= Figure 18a illustrates the evolution of the cut-off frequency of the
fundamental
mode and of the first higher order mode in a cylindrical waveguide without
ridges,
respectively with 3 ridges, as a function of the height of the ridge.
= Figure 18b illustrates the relative single mode bandwidth (defined as the
ratio
between the cut-off frequency of the fundamental mode and that of the first
higher order
mode) in a cylindrical waveguide without ridges, respectively with 3 ridges,
as a function of
the ridge height.
= Figure 19a illustrates the evolution of the cut-off frequency of the
fundamental
mode and of the first higher order mode in a cylindrical waveguide without
ridges,
respectively with 4 ridges, as a function of the ridge height.
= Figure 19b illustrates the relative single mode bandwidth (defined as the
ratio
between the cut-off frequency of the fundamental mode and that of the first
higher order
mode) in a cylindrical guide without ridges, respectively with 4 ridges, as a
function of the
ridge height.
Example(s) of embodiments of the invention
[0050] Figure 16 shows an example of a component 1 comprising several
waveguide
devices 2. In this example, the component 1 is a passive RF module intended to
form the
passive part of a direct radiating array (DRA).
[0051] The RF module 1 comprises a plurality of devices, each device
comprising for
example four layers from the top to the bottom of the figure.
[0052] Among these layers, the first layer at the top of the figure
consists of a radiating
element 30 (antennas) for emitting electromagnetic signals into ether,
respectively for
receiving the received signals. This layer is downstream of the component.
[0053] The second layer comprises a waveguide 40.
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[0054] The third layer is optional; it can also be integrated into the
second layer. When
present, the third layer includes an element such as a polarizer or a section
adapter.
[0055] The fourth layer at the bottom of the figure (upstream) comprises
a waveguide
port 60. Each port 60 is an interface to an active element of the DRA, such as
an amplifier
and/or a phase shifter, which is part of a beamforming array. One port thus
allows a
waveguide to be connected to an electronic circuit, in order to inject a
signal into the
waveguides or in the opposite direction to receive electromagnetic signals in
the
waveguides.
[0056] This module 1 is intended for use in a multi-beam environment. The
radiating
elements are preferably close together, as shown in Figure 17 in particular,
so that the pitch
p1 between two adjacent radiating elements is smaller than the wavelength at
the nominal
frequency at which the module 1 is intended to be used. This reduces the
amplitude of the
transmission and reception side lobes.
[0057] In Fig. 16, the pitch p1 between two adjacent radiating elements
is larger than
the pitch between two waveguide ports 60, which allows to create a module with
large
antennas. It is also possible to use a module in which the pitch p1 between
two adjacent
radiating elements is equal to or smaller than the pitch between two waveguide
ports 60, as
in Figure 17, in order to bring the radiating elements closer to each other
without having to
use miniaturized active electronics on the ports 60.
[0058] The different devices 2 form an array, for example a grid.
[0059] The invention aims to optimize each device 2 as such, and to
optimize the
component 1 by minimizing the disturbances between devices and/or by
preventing the
defects of the different devices from adding up.
[0060] Figure 1 schematically illustrates a component 1 seen from the
downstream
side, i.e. from the radiating elements (antennas) as waveguide devices 2. This
component
can be used, for example, as a passive part of an DRA antenna similar to the
one illustrated
in Figure 16.
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[0061] The individual devices 2 are arranged in a plane and form a grid
array or with
position shifts between lines as shown in Figure 1. The distance between
adjacent devices is
preferably less than the nominal wavelength of the signal to be transmitted.
[0062] The antenna devices shown in this example have a circular
downstream
opening. Their inner face 3 is provided with three ridges 23 angularly spaced
by 1200 and
parallel to the direction of signal propagation.
[0063] Unexpectedly, the use of three ridges in a waveguide with a
circular, square or
rectangular section has the advantage of favoring the transmission of the
fundamental
transmission mode, by accentuating the frequency difference between the
fundamental
mode and the first higher order mode.
[0064] Figure 18a illustrates the evolution of the cut-off frequency of
the fundamental
mode and of the first higher order mode in a cylindrical waveguide without
ridges,
respectively with 3 ridges, as a function of the ridge height. The x-axis
scale represents the
normalized ridge height and the y-axis scale represents the normalized
frequency. The
upper curve (dotted line with solid squares) represents the frequency of the
first upper
mode as a function of the ridge height h in a waveguide with three ridges. The
solid line
curve with solid squares represents the frequency of the fundamental mode as a
function of
the ridge height h. The dotted curve with white circles represents the
frequency of the first
higher mode in a non-ridged waveguide. The solid line curve with white circles
represents
the frequency of the fundamental mode in a non-ridged waveguide. As can be
seen, the
difference in frequency between the fundamental mode and the first higher mode
is much
larger in a cylindrical waveguide with three ridges than in a cylindrical non-
ridged
waveguide, making it easier to filter modes other than the fundamental mode.
[0065] The use of waveguides with three ridges also makes it possible to
widen the
signal bandwidth in single mode. Figure 18b shows the normalized single mode
bandwidth
as a function of the normalized ridge height for a waveguide with three ridges
(curve with
solid squares) and for a waveguide without ridges (curve with white circles).
[0066] Figure 19a is comparable to Figure 18a, but illustrates the
comparison between
a cylindrical waveguide with four ridges (curved with black squares) and a
cylindrical
waveguide without ridges (curved with white circles). As can be seen, the
frequency
difference between the fundamental mode (solid curve) and the first higher
order mode
(dotted-line) is much smaller than in a waveguide with three ridges,
especially for large
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heights of ridge favorable to large bandwidths. The filtering of the first
higher order mode is
therefore easier in the case of a waveguide with three ridges than in a non
ridged or four
ridged waveguide.
[0067] The use of a waveguides with four ridges is also less favorable
than the use of
waveguides with three ridges in terms of single mode bandwidth. Figure 19b
shows the
normalized single-mode bandwidth as a function of the normalized ridge height
for a
waveguide with four ridges (curve with solid squares) and for a waveguide
without ridges
(curve with white circles). As can be seen, the bandwidth of a waveguide with
four ridges is
only marginally better than that of a non-ridged waveguide when the ridge
height is very
low; for higher ridge heights, the bandwidth is lower in single mode than that
of a non-
ridged cylindrical waveguide, and even significantly lower than that of a
waveguide with
three ridges as shown in Figure 18b.
[0068] Square, rectangular, hexagonal or octagonal section antennas can
also be used.
Similarly, the number of ridges can be different from three, although three
ridges is a
preferred embodiment in view of the advantages described above. In particular,
all the
antennas or waveguide devices described in the rest of this description can be
used instead
of the antennas shown in this figure.
[0069] According to one aspect of the invention, the different waveguide
devices 2 are
oriented differently, as can be seen with the position of the ridges 23. The
angles of rotation
between devices can be regular or more random as in this example. These
rotations make it
possible to add up the imperfections specific to each antenna, which
compensate each
other by adding up, preferably in a destructive way. This avoids multiplying
the
imperfections of each device 2 if they were all aligned identically.
[0070] Figures 2 and 3 illustrate another component 1 comprising several
waveguide
devices of the type of antenna 2, seen in perspective from the downstream
side. The
antennas 2 in Figure 2 have circular downstream openings 25 while those in
Figure 3 have
square openings. Other sections can be considered, for example rectangular,
hexagonal,
octagonal, elliptical, semi-circular, semi-elliptical, etc. The antennas are
arranged in an array
in a single plane, with a triangular arrangement; other arrangements, for
example grid
arrangements, may be considered.
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[0071] One or more ribs form a rim 20 that at least partially surrounds
each antenna.
This rim reduces the mutual coupling between antennas 2, thus improving the
performance
of the array.
[0072] Antennas 2 have an opening whose section widens progressively
towards the
downstream direction, forming one or more steps 21. These steps reduce return
losses and
improve performance in terms of bandwidth. The septum also forms the desired
downstream polarization.
[0073] Antennas 2 are provided with at least one septum 26 in order to
generate
respectively to discriminate between two signals with linear or circular
polarizations
orthogonal to each other.
[0074] Each antenna can be provided with several septa to create one or
two circular
polarizations, or to combine two linear polarizations, which allows for
example to protect
active antennas with linear polarizations. It is also possible to provide
antennas with several
septa to create elliptical polarizations.
[0075] Each antenna can be provided with one or more ridges, the height of
which is
progressively reduced in the downstream direction, forming one or more steps.
These steps
help to reduce return losses and improve performance in terms of bandwidth.
[0076] In Figure 2, the antennas are provided with two ridges, two of
which are curved,
i.e. they do not extend exclusively in radial planes.
[0077] Figures 4 to 6 illustrate sections of waveguide devices respectively
square,
octagonal and circular. Other sections, including hexagonal, elliptical,
semicircular oval, or
semi-elliptical sections may be used.
[0078] These devices 2 can constitute for example polarizers and be used
in isolation, or
in an array in a component 1 such as an DRA antenna for example.
[0079] The devices of these figures having two inputs 24, for example two
upstream
inputs, separated by a vertical septum 26 on the figure and juxtaposed to the
left and right
of this septum at the back of the figure. Only one output 25 is provided, for
example one
upstream output, at the front of the figure. The inner face 3 of each of the
two inputs is
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provided with a single ridge 23. The output 25 at the front of the figure is
provided with
three ridges 23 and a septum 26 spaced 90 apart. The two inputs can
individually extend
into a waveguide with a rectangular cross-section with one ridge. The output
can extend
into a waveguide with a square section with four ridges, or be connected to a
waveguide
with this section. The device 24 allows to generate two signals which after
their passage
through the septum will have two distinct polarities, or conversely to join
two signals
corresponding to the two received polarities.
[0080] Figures 7 to 9 illustrate sections of waveguide device
respectively square,
hexagonal and circular. Other sections, including octagonal, elliptical,
semicircular oval or
semi-elliptical sections may be used.
[0081] These devices may constitute, for example, polarizers and be used
in isolation,
or as an array in a component of the type of DRA antenna for example.
[0082] The devices in these figures have two inputs 24, for example two
upstream
inputs, separated by a vertical septum 26 on the figure and juxtaposed to the
left and right
of the device at the back of the figure. Only one output 25 is provided, for
example one
upstream output, at the front of the figure. Each of the two inlets is
provided with a single
ridge 23. The output 25 at the front of the figure can be connected to a
waveguide with
three ridges spaced 90 apart. The two inputs can individually extend into a
waveguide with
a rectangular section with one ridge, or be connected to a waveguide with this
section. The
device thus constitutes a polarizer and allows to join two signals of distinct
polarity into a
single signal combining the two polarities, or conversely to separate a signal
into two signals
of distinct polarity, and to be connected to ridged waveguides.
[0083] Figures 10 to 12 show three views of a portion of a circular-
section waveguide
device; again, the section could be different and any of the other sections
described in this
application can also be implemented with this embodiment. The inner face 3 of
the device is
provided with a septum 26 in order to separate a signal into two
polarizations, and with
ridges 23 whose height progressively reduces from the downstream end, until it
disappears
completely before the upstream end. Other ridges 23 are formed between the
upstream
and downstream ends of the device, and their height gradually increases. This
configuration
makes it possible to replace an arrangement of ridges at the upstream end, for
example four
ridges spaced at 900, with another arrangement of ridges at the downstream
end, for
example three ridges spaced at 1200. In this way, the number of ridges and/or
their angular
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spacing between the two ends can be changed, in order to connect them to
waveguides or
other devices with suitable configurations of ridges.
[0084] Figures 13 to 15 show three views of a portion of a circular-
section waveguide
device; again, the section could be different and any of the other sections
described in this
application can also be implemented with this embodiment. The inner face 3 of
the device is
provided with a septum 26 in order to separate a signal into two
polarizations, and with
curved 23 ridges, i.e. ridges that instead of extending in a radial direction
as in most of the
examples described above, are curved. This curved ridge has two walls which
are non-planar
but nevertheless parallel to each other. It is also possible to have a similar
configuration but
with non-parallel ridge faces.
[0085] The same ridge can thus lead to different axial positions upstream
and
downstream, which makes it possible to modify the phases of the ridges, and/or
their
relative phase shifts.
[0086] The embodiments described above can be used independently or in
combination. For example, the devices 2 described individually in relation to
Figures 4 to 15
may all be used either individually or in connection with one or more
waveguide devices
connected upstream and/or downstream, and/or combined in a single component
with
several devices of the same or different types. These devices in Figures 4 to
15 may for
example be used as an antenna, polarizer or waveguide between the active part
of a
component grouping several antennas, and the individual antennas of this
component. In
addition, the features of these devices can be combined with each other; for
example, it is
possible to provide devices with curved ridges of variable height.
[0087] A radio-frequency component may, for example, be designed by
grouping
several devices according to one of Figures 4 to 15, or according to a
combination of these
devices, so as to transmit signals between the active components and the
radiating
elements. As shown in Figure 1, these different devices can be oriented
differently. In any
case, the orientation of the ridges 23 on the downstream openings 25 may be
different
between the different devices 2 of such a component 1.
Date Recue/Date Received 2021-03-31
