EP2658032A1 - Corrugated horn antenna - Google Patents

Abstract

The guide has a grid (21) placed in vicinity of an opening (14) and comprising a frame (210) surrounding strips (211-213) extending longitudinally and continuously from a small side (250a) of the frame to another small side (250b) of the frame so as to form a linear polarization filter attenuating a cross-polarization component of electric field of electromagnetic wave. The component is orthogonal to an axis (y) orthogonal to a longitudinal axis (z). The strips include corrugations (22) sized and positioned to reinforce attenuation of the component. An independent claim is also included for a method for testing a radiofrequency equipment.

Description

The invention relates to a horn radiating a radio wave, coming from an input waveguide, comprising a gate disposed at the opening of the horn. It applies in particular to the field of reflector antennas. The invention also relates to a satellite antenna provided with this horn.

Conventionally, an antenna for transmitting and receiving an electromagnetic wave can be achieved by associating a waveguide with a radiating element which can, for example, take the form of a horn. A waveguide in the shape of a horn, more simply called a horn, has a rectangular cross section (ie perpendicular to the direction of propagation of the wave) that grows progressively towards the opening. Such a waveguide makes it possible to favor the propagation, along its longitudinal axis, of an electromagnetic wave polarized along an axis orthogonal to the longitudinal axis of the horn. The electric field of the electromagnetic wave can be decomposed into a component parallel to the smaller-dimension sides of the aperture, and into a component parallel to the larger-dimension sides of the aperture. The first component is called the main component or the co-polarization component. The other component is called the cross-polarization component. In the context of certain applications, it is desirable to minimize the amplitude of the cross-polarization component. One solution is to have a grid at the opening of the horn. A grid is generally made of a metallic material, for example aluminum. It is formed of a set of blades arranged parallel to the longer sides of the opening of the waveguide. The grid makes it possible to let the copolarization component pass through and to filter the cross-polarization component of an electromagnetic wave. For a relatively directional horn, for example with a gain greater than 25 dBi, equipped with a grid, it is possible to obtain a cross-polarization component whose amplitude is approximately 40 to 45 dB below the amplitude of the co-polarization component. However, the effectiveness of the filtering decreases very clearly or completely when the horn is less directive. That is in particular the case for the test horns used for the microwave deaf chambers. Also, the filtering is effective only on a weak band of frequencies. With the increasing demand for better antenna performance, it becomes useful to develop horns with a cross-polarization attenuation of at least 40 dB relative to the co-polarization component over extended frequency bands. for example of the order of 40% to 50%.

An object of the invention is in particular to provide a horn having improved filtering properties of the cross-polarization component of the electric field of an electromagnetic wave, both in terms of amplitude of the cross-polarization component and in terms of bandwidth. For this purpose, the subject of the invention is a waveguide comprising a horn-shaped section, an inlet, an opening and a gate disposed in the vicinity of the opening, at least one linearly polarized electromagnetic wave being suitable propagating between the inlet and the opening along a first axis; the grid having a frame surrounding a plurality of blades extending longitudinally and continuously from a first small side of the frame to a second small side of the frame, so as to form a linear polarization filter attenuating the cross-polarization component of the electric field of the electromagnetic wave, said cross-polarization component being orthogonal to a second axis orthogonal to the first axis. The blades comprise corrugations sized and positioned to enhance the attenuation of said cross-polarization component.

The invention has the particular advantage of being able to adapt to any type of horn, including pyramidal horns and trifurcated, better known under the name Anglo-Saxon "trifurcated homs". These cones are relatively light, and relatively simple to design and manufacture. Compared to a corrugated horn, a pyramidal or trifurcated cornet has a diminished mass of about half. Also, the invention has the advantage of improving the stationary wave ratio and the gain of the horn.

The invention can be used in test equipments of radiofrequency deaf chambers to thereby provide more accurate and reliable measurement results on the cross-polarization levels and the orientation of the main bias of the tested equipment. With better cross-polarization levels and thanks to its simplicity of manufacture and its favorable mass, it will also be possible to use the invention for satellite antenna applications.

The corrugations consist for example of rectangular slots open in the opposite direction to the entrance of the waveguide.

Advantageously, the corrugations have dimensions that vary according to their position along the direction in which the blades extend longitudinally between the first and second short sides of the frame, as a function of the frequency of the electric field of the electromagnetic wave presenting locally. the greatest amplitude at the level of the respective corrugations. Filtering can thus be optimized over a wide frequency band.

The depth of the slots is, for example, substantially equal to a quarter of the wavelength corresponding to the frequency of the electric field having locally the greatest amplitude at the respective slots, and being oriented substantially along the second axis. The depth of the slots is, in another example, substantially equal to one quarter of the wavelength corresponding to a frequency of an operating frequency band of the waveguide, the electromagnetic wave emitted on said frequency band of operation having an electric field oriented substantially along the second axis. On the other hand, the higher the frequency, the smaller the width of the slots. Still with the aim of optimizing the filtering over a wide frequency band, the difference between two adjacent corrugations according to the direction in which the blades extend longitudinally is substantially equal to one quarter of the wavelength corresponding to the frequency of the electric field of the electromagnetic wave locally having the greatest amplitude at the respective slots. The difference between two adjacent corrugations according to the direction in which the blades extend longitudinally, is alternatively substantially equal to a quarter of the wavelength corresponding to a frequency of an operating frequency band of the waveguide, the electromagnetic wave emitted on said operating frequency band having an electric field oriented essentially according to the second axis.

Advantageously, in order to optimize the attenuation, the frame includes corrugations. Advantageously, in order to optimize the attenuation, the frame comprises corrugations extending over the entire thickness of at least one side of the frame in a direction perpendicular to the first axis.

Advantageously, the frame comprises corrugations extending over the entire thickness of at least one side of the frame along the second axis and / or corrugations extending over the entire thickness of at least one side of the frame according to a third axis orthogonal to the first axis and the second axis.

According to a particular embodiment, the corrugations are aligned in sets along the second axis, the corrugations of the same set having identical dimensions.

Still according to a particular embodiment, the gate is disposed at a non-zero distance from the opening of the waveguide along the first axis.

In order to reinforce the filtering of the cross-polarization component, the waveguide may comprise at least one additional gate, the gates being spaced two by two along the first axis by a distance between the corresponding wavelength substantially at a central frequency of an operating frequency band of the waveguide, and the eighth of this wavelength. One or more of the additional grids may be placed parallel to the grid disposed in the vicinity of the opening. In addition, one or more of the additional grids may each include corrugations. Each additional grid may be substantially identical to the grid disposed in the vicinity of the opening.

According to a particular embodiment, the grid comprises a frame substantially conforming to the periphery of the opening of the waveguide, the frame comprising projecting portions extending in a plane orthogonal to the first axis. The protruding parts form for example a sawtooth profile. The protruding portions may extend inwardly and / or outwardly of the frame.

Advantageously, the blades extend longitudinally in a direction substantially parallel to a third axis orthogonal to the second axis and orthogonal to the first axis.

Advantageously, so as to obtain a better attenuation, the blades extend longitudinally in a direction forming, with a third axis orthogonal to the second axis and orthogonal to the first axis, an angle of between 0.05 ° and 5 ° around the first axis. .

Advantageously, the waveguide is intended to operate over an operating frequency band, the blades have a height along the axis z substantially equal to half a wavelength corresponding to a frequency included in the band of operating frequencies of the waveguide.

The invention also relates to a satellite antenna comprising a waveguide as described above.

Finally, the subject of the invention is a method for testing a radio frequency equipment in which a waveguide as described above is used.

• la figure 1 représente, dans une vue en perspective, un exemple de guide d'onde terminé en forme de cornet et comprenant une grille simple proche de l'ouverture ;
• la figure 2 représente, dans une vue en perspective, un exemple de réalisation d'un guide d'onde terminé en forme de cornet et comprenant une grille selon l'invention proche de l'ouverture ;
• les figures 3A et 3B représentent, respectivement dans une vue de dessus et dans une vue de côté, l'exemple de grille selon la figure 2 dimensionnée pour une bande de fréquences donnée ;
• les figures 4A, 4B et 5 illustrent, par des graphiques, l'impact de la grille selon l'invention sur les performances du guide d'onde ;
• la figure 6 représente une forme particulière de réalisation d'un guide d'onde selon l'invention.

The invention will be better understood and other advantages will appear on reading the description which follows, made with reference to the attached drawings in which:

• the figure 1 represents, in a perspective view, an example of a horn-shaped waveguide and comprising a simple gate close to the opening;
• the figure 2 represents, in a perspective view, an exemplary embodiment of a waveguide terminated in the shape of a horn and comprising a gate according to the invention close to the opening;
• the Figures 3A and 3B represent, respectively in a view from above and in a side view, the example of a grid according to the figure 2 sized for a given frequency band;
• the Figures 4A, 4B and 5 illustrate, by graphs, the impact of the grid according to the invention on the performance of the waveguide;
• the figure 6 represents a particular embodiment of a waveguide according to the invention.

For the rest of the description, f _{0 is} the center frequency of the operating frequency band of an antenna, C _{0 is} the speed of light in the propagation medium considered, and λ _{0 is} the wavelength corresponding to the frequency λ ₀ (with λ ₀ = C ₀ / f ₀ ). f ₀ is the central frequency of the electric fields of the electromagnetic waves emitted on the operating band of the antenna. These electric fields are, even before their arrival on the grid, oriented essentially along the y axis.

The figure 1 is a perspective view of an exemplary horn-shaped waveguide for a reflector antenna. The waveguide is often called a horn in reference to its shape. The horn 10 comprises a first section 11 with a rectangular cross section (in the xy plane) and a second section 12 with a rectangular transverse section that regularly increases between the inlet 13 and the opening 14, that is to say according to its longitudinal axis z. For a given cross section, the largest dimension of this section is oriented along the x-axis, while the smaller dimension is oriented along the y-axis. The inlet 13 is generally connected to a rectangular waveguide, not shown, of the same cross section as that of the section 11. The horn 10 comprises a grid 15 disposed in the vicinity of the opening 14. By neighborhood, is meant a distance between the wavelength λ ₀ and the zero value, the grid 15 then being fixed on the periphery of the opening 14. The grid 15 comprises a frame 150 substantially around the periphery of the opening 14, and a set blades 151, 152 and 153. The frame supports the blades. The The blades 151-153 extend longitudinally and continuously along the x-axis from a first short side of the frame 150 to a second small side of the frame. This characteristic is essential to be able to attenuate the cross-component of the electric field of any wave emitted within the waveguide whatever its position on the grid.

On the realization of the figure 1 in a nonlimiting manner, the first small side 150a and the second small side 150b extend longitudinally parallel to the y axis. The frame also includes a first major side 150c and a second major side 150d orthogonal to the sides 150a, 150b. The frame is rectangular.

The two short sides of the frame are the two smaller sides of the frame, and two long sides of the frame are the two largest sides of the frame.

The blades 151-153 are arranged parallel to the xz plane on the embodiments of the figures. They are arranged to allow the passage of an electromagnetic wave whose electric field is polarized along the y-axis and the filtering of any electromagnetic wave whose electric field is not polarized along the y-axis. The gate 15 thus forms a linear polarization filter of axis y. By filtering is meant attenuation of the amplitude of the electric field. The gate 15 attenuates in particular the so-called cross-polarization component of the electric field of an electromagnetic wave, that is to say the component oriented along the x axis. In particular, it attenuates the cross-polarization components of the electric fields of the electromagnetic waves, the respective frequencies of which are included in the operating frequency band of the waveguide. The geometric properties of the gate 15 are essentially determined according to the operating frequency band of the antenna. The geometric properties having the most significant impact on the electromagnetic properties of the grid are the height of the grid 15 and the gap between the adjacent blades, as well as between the outer blades 151 and 153 and the inner edge of the frame Advantageously, the height of the grid 15 along the z axis is substantially equal to half the wavelength λ ₀ (λ _0/2 ). The gap between two adjacent blades, and between the outer blades 151 and 153 and the inner edge of the frame 150 is preferably substantially equal to one quarter of the wavelength λ ₀ (λ _0/4 ). Other geometrical properties have a secondary influence on the electromagnetic properties of the horn 10. These include the position of the grid 15 with respect to the opening 14. Advantageously, the grid 15 is placed at a distance from the plane xy of the opening 14 substantially zero. The thickness of the frame 150 along the x and y axes and that of the blades 151-153 along the y axis have little influence on the performance of the grid 15. The thickness of the blades 151-153 depends directly on the dimension the opening 14 of the horn along the y axis, the number of blades and the gap between blades. From an electromagnetic point of view, the thickness of the blades 151-153 can be very small. However, the blades 151-153 must be sufficiently thick to be manufacturable and to ensure their mechanical strength. For example, the thickness of the blades may be substantially equal to 1 mm. The thickness of the frame 150 is essentially determined so as to withstand the mechanical stresses experienced by the horn 10. In particular, the blades 151-153 being of relatively small thickness, the thickness of the frame 150 must be sufficient to avoid twisting. blades 151-153. For a horn intended for an antenna operating in the Ku frequency band, that is to say in the frequency band between 10.00 GHz and 15.00 GHz, the thickness of the frame 150 is for example between 2 and 10 mm.

The figure 2 represents, in a perspective view, an exemplary embodiment of a horn according to the invention. The horn 20 is different from the horn 10 of the figure 1 by its gate 21. The grid 21 also comprises a frame 210 disposed in the vicinity of the opening 14 of the horn 20, and a set of blades 211, 212 and 213 arranged parallel to the plane xz on the embodiments of the figures. The frame supports the blades. The blades 211-213 extend longitudinally between the two sides of the frame 150. Specifically, the blades extend longitudinally and continuously from a first small side 250a of the frame to a second small side 250b of the frame 250. On the embodiment of the figure without limitation, the first side 250a and the second side 250b extend longitudinally parallel to the y axis. The frame also includes a first large side 250c and a second large side 250d. The sides 250c and 250d are orthogonal sides 250a, 250b, the frame being rectangular on the figure 2 .

The geometrical properties of the grid 21 are determined identically to those of the grid 15 of the figure 1 . The gate 21 differs from the gate 15 in that it comprises corrugations 22. The gate 21 is said corrugated. The corrugations 22 consist for example of slots, notches or crenellations. Mechanically, they can be likened to grooves made along the y-axis on the outer face of the frame 210 and / or blades 211-213. By external face is meant the surface oriented in the opposite direction to the inlet 13 of the horn 20. Corrugations 22 advantageously have a rectangular shape or U in a plane xz. In practice, the corrugations 22 can be performed both by machining and by molding the gate 21. The corrugations 22 improve the attenuation of the amplitude of any non-polarized electric field along the y axis with respect to a simple grid such as that grid 15 of the figure 1 . In particular, they make it possible to improve the filtering, that is to say the attenuation of the cross-polarization components of the electric fields of the electromagnetic waves emitted in the operating frequency band of the waveguide. This means that the filtering will be better, and more uniform, in the operating frequency band of the waveguide. They also make it possible to achieve cross-component attenuation over a wider frequency band than the attenuation device of the figure 1 . As a reminder, the electric fields of the electromagnetic waves emitted in the waveguide are preferably oriented substantially in the y direction even before the passage of the gate. The passage of the grid further improves this orientation by limiting the cross-polarization components. The electric fields at the output of the waveguide are therefore necessarily oriented substantially along the y direction.

The strengthening of the attenuation of the electromagnetic waves whose electric field is not polarized along the y axis, in particular the attenuation of the cross-polarization components, is obtained by the geometric properties of the corrugations 22, namely by their dimensions and their positioning. These geometric properties of corrugations 22 are determined according to the operating frequency band of the antenna. The geometric properties having the most significant impact on the electromagnetic properties of the grid are the depth of the corrugations and the difference between adjacent corrugations along the x axis. The depth of a corrugation 22 is defined as the distance along the z axis between, on the one hand, the outer surface of the frame 210 or blades 211-213 and, on the other hand, the bottom of the slot 22 considered . The depth of the corrugations is advantageously dimensioned in "quarter wave trap". In other words, it is substantially equal to a quarter of the wavelength λ ₀ (λ _0/4 ). However, in order to maintain optimal filtering over the entire width of the frequency band, it is possible to consider several particular frequencies in the frequency band. Indeed, the signals at low frequencies tend to disperse more on the edges of the grid than in the center, while the higher frequency signals are more directional and therefore focus more in the center of the grid. This property can be used to dedicate different parts of the grid to the filtering of particular distinct frequencies. In the example of the figure 2 , four particular frequencies are considered. Each particular frequency corresponds to a wavelength and is associated with a set of corrugations 22. Each particular frequency thus gives a distinct depth of corrugation from the others. As visible on figures 2 , 3A, 3B the dimensions of the corrugations vary between the first side 250a and the second side 250b of the frame. Since the operation of the horn 20 is symmetrical with respect to the plane yz, the corrugations 22 can be made symmetrically with respect to the plane yz passing through the center of the grid. In the particular embodiment of the figure 2 a first set 221 of corrugations 22 is made on the frame 210 and the blades 211-213 so that the corrugations are aligned along the y axis passing through the center of the larger sides of the frame 210, sets of corrugations 222A-222B, 223A-223B, and 224A-224B being made symmetrically on either side of the first assembly 221. The difference between adjacent corrugations along the x axis constitutes the main criterion for optimizing the filtering character of the corrugations 22 The difference between two adjacent corrugations 22 is defined as the distance along the x axis between the contiguous edges of these corrugations 22 or, if appropriate, between the edge However, since the width of the corrugations is relatively small relative to the difference between corrugations, this difference can also be defined as the distance between the centers of the corrugations. The difference between adjacent corrugations 22 is advantageously substantially equal to one quarter of the wavelength λ ₀ (λ _0/4 ). However, similar to the depth of the corrugations, it is possible to consider several particular frequencies in the operating frequency band. Due to the symmetrical operation of the horn, the differences between corrugations are normally symmetrical with respect to the plane yz passing through the center of the grid 21. The width of the corrugations has a secondary influence on the electromagnetic properties of the grid 21. dimension is conditioned by the dimensions of the opening 14 of the horn 20 along the x axis, the number of corrugations along each axis x, as well as the differences between the corrugations. The width of the corrugations must nevertheless be sufficient to carry out their machining or the molding of the grid 21. By way of example, the width of the corrugations may be substantially equal to 1 mm. Preferably, the higher the particular frequency considered, the smaller the width. Thus, the width of the corrugations increases from the center towards the frame and in particular towards the edges of the frame 210.

The Figures 3A and 3B represent, respectively in a view from above and in a side view, an example of a grid according to the figure 2 sized for a frequency band between 10.3 GHz and 14.75 GHz. We denote H the height of the gate 21 along the axis z, of the gap between adjacent blades along the y axis, e _c the thickness of the frame 210 along the axes x and y, e _the thickness of the blades along the y axis, h ₁ to h _4, the depth of the corrugations 22 of the respective sets 221 to 224 along the z axis. Also note ₁₂ the gap between the corrugations along the x axis of the first set 221 and those of the assembly 222A (222B respectively) of ₂₃ the gap between the corrugations of the assembly 222A (222B respectively) and those of the set 223A (respectively 223B), d ₃₄ the difference between the corrugations of the set 223A (respectively 223B) and those of the set 224A (respectively 224B), and d ₄₀ the difference between the corrugations of the assembly 224A (respectively 224B) and the contiguous inner edge of 250b (respectively 250a) side of the frame 210. Finally, we note e ₁ to e ₄ the width of the corrugations 22 along the x axis of the respective sets 221 to 224.

The following frequencies are considered: f ₀ = 12.5 GHz, f ₁ = 14.75 GHz, f ₂ = 14.25 GHz, f ₃ = 12.75 GHz and f ₄ = 11.7 GHz. Each frequency f ₁ to f ₄ is associated with a set of corrugations 221, 222A-222B, 223A-223B or 224A-224B. These frequencies make it possible to define the depths h ₁ to h ₄ of the corrugations of the respective assemblies 221 to 224. With C ₀ = 3.10 ⁸ m / s, the wavelengths associated with the frequencies f0 to f4 are respectively λ ₀ = 24 mm, λ ₁ = 20.34 mm, λ ₂ = 21.05 mm, λ ₃ = 23.53 mm and λ ₄ = 25.64 mm.

• ■ H=12 mm, dimensionnée en λ₀/2 ;
• ■ d=8,25 mm ;
• ■ e_c=7,0 mm ;
• ■ e_l=1,0 mm ;
• ■ h₁=5,08 mm ; h₂=5,26 mm ; h₃=5,88 mm ; h₄=6,41 mm ;
• ■ d₁₂=5,17 mm ; d₂₃=5,46 mm ; d₃₄=6,00 mm ; d₄₀=7,28 mm ;
• ■ e₁=0,75 mm ; e₂=1,0 mm ; e₃=1,25 mm ; e₄=1,5 mm.

For the different zones of the grid 21 situated between the corrugations, the following frequencies are considered: f ₁₂ = 14.5 GHz, f ₂₃ = 13.75 GHz, f ₃₄ = f ₀ = 12.5 GHz and f ₄₀ = 10 , 3 GHz. They make it possible to define the differences between adjacent corrugations. The wavelengths associated with these frequencies are respectively λ ₁₂ = 20.69 mm, λ ₂₃ = 21.82 mm, λ ₃₄ = 24.00 mm, and λ ₄₀ = 29.13 mm. For these frequencies, the dimensions of the grid 21 are for example the following:

• ■ H = 12 mm, dimensioned in λ _0/2 ;
• ■ d = 8.25 mm;
• ■ e _c = 7.0 mm;
• _I = 1.0 mm;
• ■ h ₁ = 5.08 mm; h ₂ = 5.26 mm; h ₃ = 5.88 mm; h ₄ = 6.41 mm;
• D ₁₂ = 5.17 mm; d ₂₃ = 5.46 mm; d ₃₄ = 6.00 mm; d ₄₀ = 7.28 mm;
• ■ e ₁ = 0.75 mm; e ₂ = 1.0 mm; e ₃ = 1.25 mm; e ₄ = 1.5 mm.

In other words, the dimensions and / or the gaps between the respective slots are defined by the wavelength corresponding to the frequency of the electric field having locally the greatest amplitude at the gate 21, and in particular at the respective slots 22.

As visible on the figure 2 , the large sides 250d and 250c of the frame include corrugations. These corrugations are spaced along the longitudinal direction of the sides. They extend advantageously over the entire thickness of these sides in a direction perpendicular to the z axis. The corrugations formed on each long side extend over the entire thickness of the long side in a direction perpendicular to the longitudinal direction on the big side. In this way they open on both sides of this side. On the realization of the figure 2 the corrugations extend over the entire thickness of the respective long sides along the y direction. The corrugations formed on one side have, for example as visible on the figure 2 , the shape of a channel extending longitudinally in a direction perpendicular to the longitudinal direction of said side and have a rectangular section in the xz plane.

In a variant not shown or in addition to corrugations of the long sides, the short sides 250a and 250b of the frame comprise corrugations extending over all their respective thicknesses in a direction perpendicular to the z axis. The corrugations of each small side extend over the whole thickness of the short side perpendicular to the longitudinal direction of the short side. In this way they open on both sides of this side. In the case where the short sides extend longitudinally along the y axis, the corrugations extend over all their respective thicknesses in the x direction. The corrugations formed on one side have, for example, the shape of a channel extending longitudinally in a direction perpendicular to the longitudinal direction of said side (direction y) and have a rectangular section in the plane yz.

Advantageously, at least one of the sides of the frame comprises corrugations extending over its entire thickness.

The Figures 4A, 4B and 5 illustrate, by means of graphs, the improvement of the performances of a C-band horn due to the presence of a grid according to the invention with respect to the same non-grided horn, and with respect to the same horn provided with a simple grid (without corrugations).

On the graphs of Figures 4A and 4B , the amplitudes A, in dB, of the co-polarization and cross-polarization components of the electric field of an electromagnetic wave are plotted as a function of the angle of elevation φ, and for a single frequency. The elevation angle corresponds to the angle formed between the z axis and the direction of propagation of the electromagnetic wave. Typically, we are mainly interested in angles of site between 0 ° and 30 to 40 °. On the graph of the Figure 4A a curve 41 represents the amplitude of the co-polarization component for a gateless horn, a curve 42 represents the amplitude of the cross-polarization component for a gateless horn, and a curve 43 represents the amplitude of the component cross-polarization for a horn with a simple grid. On the graph of the Figure 4B curves 41 and 42 are reproduced, and a curve 44 represents the amplitude of the cross-polarization component for a horn provided with a grid comprising corrugations according to the invention. The Figures 4A and 4B show amplitude maxima of the cross-polarization component substantially 30 dB below the maximum amplitude of the co-polarization component for a horn without a grid, 35 dB for a horn with a simple grid, and 45 dB for a horn provided with a grid according to the invention.

On the graph of the figure 5 , the maximum amplitude A _max of the cross-polarization components of the electric field of an electromagnetic wave for an angle of elevation between -10 ° and + 10 ° are plotted as a function of the frequency f. These amplitude maxima are considered in decibels with respect to the maximum amplitude of the copolarization component calculated for an angle of elevation between -180 ° and + 180 °, ie on the total sphere of radiation of the 'wave. A curve 51 represents the maximum amplitude, for an angle of elevation between -10 ° and + 10 °, of the cross-polarization component for a gateless horn. A curve 52 represents this maximum, for an angle of elevation between -10 ° and + 10 ° and for a cone equipped with a simple grid, and a curve 53 represents this maximum for an angle of elevation between -10 ° and + 10 ° and for a cornet provided with a grid comprising corrugations. The lowest attenuation of the cross-polarization component over the operating frequency band for a horn provided with a gate according to the invention is substantially equal to -44 dB, whereas it is approximately equal to -40 dB for a horn with a simple grid and -34 dB for a horn without grid.

The corrugated gate according to the invention also has the advantage of improving the stationary wave ratio by about 1 to 5 dB, as well as than the gain of the horn of a few tenths of decibels. It makes it possible to obtain amplitude maxima of the cross-polarization component 40 dB below the amplitude maximums of the copolarization component with pyramidal horns.

In the example of figures 2 , 3A and 3B , the horn 20 is pyramidal, that is to say it comprises a section 12 whose dimensions in the transverse plane increase linearly along the axis of propagation of the electromagnetic wave. The invention nevertheless applies to any other form of horn, in particular so-called "trifurcated" horns and corrugated horns.

Furthermore, a horn according to the invention may comprise a plurality of grids in addition to the grid 21 disposed in the vicinity of the opening 14 of the horn 20. These additional grids also have corrugations on their blades and / or on the edges of the horn. their setting. The grids are for example spaced regularly from each other (two by two) by a distance between the wavelength λ ₀ and the eighth of this wavelength. The additional grids may or may not be identical to the grid 21.

The figure 6 represents a particular embodiment of a waveguide according to the invention. The horn 30 is different from the horn 20 of the figure 2 in that the frame 310 of the grid 31 comprises projecting parts 320 extending in a plane xy, that is to say in a plane orthogonal to the z axis. These projecting portions 320 are for example arranged on the smaller sides of the frame 310, as shown in FIG. figure 6 . However, the protruding portions may also be disposed all around the frame 310, or only on the larger sides. On the other hand, the projecting parts may extend either towards the inside of the frame 310 or towards the outside, as shown in FIG. figure 6 . The protruding parts may for example be like saw teeth or rectangular slots.

In the embodiment of the figures, the blades extend longitudinally in the direction substantially parallel to the x axis. The positioning and dimensions of the corrugations are defined according to and / or relative to this axis. In other words, the longitudinal direction of the blades forms an angle less than 0.05 ° with the x axis around the z axis.

In an advantageous variant, the blades extend longitudinally in a direction forming with the x axis, about the z axis, an angle at least equal to 0.05 ° and between 0.05 and 5 °. In this case, the positioning (for example the difference between the corrugations) and the dimensions of the corrugations (for example their width) are defined according to and / or with respect to the longitudinal direction of the blades. In some practical cases, this embodiment advantageously allows a better attenuation of cross-polarization components extending along the x axis.

In these two embodiments since the angle formed between the longitudinal direction of the blades and the x axis is at most equal to 5 °, it is assumed and said that the blades extend longitudinally globally along the x axis .

The blades generally form rectangular parallelepipeds having a side extending along the z direction.

We have previously described embodiments in which the depth of the corrugations, the difference between the corrugations or the height of the blade are equal to a fraction (quarter or half) of the wavelength of the central frequency. In a variant, these dimensions and positioning are equal to a fraction (one quarter or one half) of the wavelength of a frequency comprised in the operating frequency band of the waveguide.

Claims (22)

Waveguide comprising a horn-shaped section (12), an inlet (13), an opening (14), and a grid (21) arranged in the vicinity of the opening (14), at least one electromagnetic wave with linear polarization being able to propagate between the inlet (13) and the opening (14) along a first axis (z), the grid (21) comprising a frame (210) surrounding a set of blades (211-213) extending longitudinally and continuously from a first small side (250a) of the frame to a second minor side (250b) of the frame, thereby forming a linear polarization filter attenuating the cross-polarization component of the electric field of the electromagnetic wave, said cross-polarization component being orthogonal to a second axis (y) orthogonal to the first axis (z), the waveguide (20) being characterized in that the blades (211-213) comprise corrugations (22) dimensioned and positioned to enhance the attenuation of the said cross-polarization component. A waveguide according to claim 1, wherein the corrugations (22) are rectangular slots open in the opposite direction to the input (13) of the waveguide (20). Waveguide according to one of claims 1 and 2, wherein the corrugations (22) have dimensions varying according to their position along the direction in which the blades extend longitudinally between the first and second short side of the frame, as a function of the frequency of the electric field of the electromagnetic wave locally having the greatest amplitude at the respective corrugations (22). Waveguide according to claims 2 and 3, wherein the depth (h1-h4) of the slots (22) is substantially equal to one-quarter of the wavelength corresponding to the frequency of the electric field having the greatest amplitude locally at level of the respective slots (22), and being oriented substantially along the second axis (y). A waveguide according to claims 2 and 3, wherein the depth (h1-h4) of the slots (22) is substantially equal to one quarter of the wavelength corresponding to a frequency of an operating frequency band of the waveguide, the electromagnetic wave emitted on said operating frequency band having an electric field oriented essentially along the second axis (y). A waveguide according to claim 3 or 4, wherein the higher the locally higher amplitude frequency, the smaller the width (e1-e4) of the slots (22). Waveguide according to one of the preceding claims, wherein the difference between two corrugations (22) adjacent in the direction in which the blades extend longitudinally is substantially equal to one quarter of the wavelength corresponding to the frequency the electric field of the electromagnetic wave locally having the greatest amplitude at the respective slots (22). Waveguide according to the preceding claim, wherein the distance between two corrugations (22) adjacent in the direction in which the blades extend longitudinally is substantially equal to one quarter of the wavelength corresponding to a frequency of an operating frequency band of the waveguide, the electromagnetic wave emitted on said operating frequency band having an electric field oriented substantially along the second axis (y). Waveguide according to one of the preceding claims, wherein the frame (210) comprises corrugations (22). Waveguide according to the preceding claim, wherein the frame comprises corrugations extending over the entire thickness of at least one side of the frame in a direction perpendicular to the first axis (z). Waveguide according to the preceding claim, wherein the frame comprises corrugations extending over the entire thickness of at least one side of the frame along the second axis (y) and / or corrugations extending over the entire thickness of at least one side of the frame along a third axis (x) orthogonal to the first axis (z) and the second axis (y). Waveguide according to one of the preceding claims, wherein the corrugations (22) are aligned in sets (221, 222A-222B, 223A-223B, 224A-224B) along the second axis (y), the corrugations (22), ) of the same set having identical dimensions. Waveguide according to any one of the preceding claims, wherein the blades extend longitudinally in a direction substantially parallel to a third axis (x) orthogonal to the second axis (y) and orthogonal to the first axis (z). Waveguide according to any one of the preceding claims, wherein the blades extend longitudinally in a direction forming, with a third axis (x) orthogonal to the second axis (y) and orthogonal to the first axis (z), a angle between 0.05 ° and 5 ° around the first axis (z). A waveguide according to any one of the preceding claims, wherein the waveguide is adapted to operate over an operating frequency band, the blades having a height along the z-axis substantially equal to one-half of one wavelength corresponding to a frequency in the operating frequency band of the waveguide. Waveguide according to one of the preceding claims, wherein the gate (21) is arranged at a non-zero distance from the opening (14) of the waveguide (20) along the first axis (z). Waveguide according to one of the preceding claims, comprising at least one additional gate, the gates being spaced two by two along the first axis (z) by a distance between wavelength substantially corresponding to a central frequency of an operating frequency band of the waveguide (20), and the eighth of this wavelength. Waveguide according to the preceding claim, wherein one or more additional grids are placed parallel to the gate (21) disposed in the vicinity of the opening (14). Waveguide according to one of claims 17 to 18, wherein one or more additional grids each comprise corrugations. Waveguide according to one of claims 17 to 19, wherein each additional gate is substantially identical to the gate (21) disposed in the vicinity of the opening (14). Satellite antenna comprising a waveguide according to one of the preceding claims. A method of testing a radio frequency equipment in which a waveguide according to one of claims 1 to 20 is used.

Images