EP3306746B1 - Cavity radiating element and radiating network comprising at least two radiating elements - Google Patents

Description

The present invention relates to a new cavity radiating element architecture and a radiating network comprising at least two radiating elements. It applies in particular to the space domain and for single-beam or multi-beam applications.

A radiofrequency source used in an antenna consists of a radiating element coupled to an RF radiofrequency chain. In the low frequency bands, for example in C band, the radiating element often consists of a horn and the RF chain includes RF components intended to carry out the functions of transmission and reception in mono-polarization or in bipolarization. -polarization to cover user needs. The link with ground stations is generally bi-polarization.

The mass and size of the RF radiofrequency chains constitute a critical point in the field of space antennas intended to be installed on board satellites and in particular in the field of the lowest frequencies such as the C band. high, for example in Ka band or in Ku band, there are very compact radiating elements whose technology can be transposed to C band, but the radio frequency sources obtained remain bulky and massive and pose a problem of installation when they must be integrated into a focal network comprising a large number of sources.

There are cavity radiating elements which have the advantage of being compact, but these radiating elements are limited in terms of bandwidth and can only be used in mono-polarization and on a single operating frequency band or on two. very narrow frequency bands.

• US 2012/112977 A1
• RAWAT SANYOG ET AL, "Stacked elliptical patches for circularly polarized broadband performance", 2014 INTERNATIONAL CONFERENCE ON SIGNAL PROPAGATION AND COMPUTER TECHNOLOGY (ICSPCT 2014), IEEE, (20140712), doi:10.1 109/ICSPCT.2014.6884942, pages 232 - 235
• US 5 010 348 A
• WEILY A R ET AL, "Circularly Polarized Ellipse-Loaded Circular Slot Array for Millimeter-Wave WPAN Applications", IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, (20091001), vol. 57, no. 10, doi:10.1109/TAP.2009.2029305, ISSN 0018-926X, pages 2862 - 2870
• KOUTSOUPIDOU MARIA ET AL, "A microwave breast imaging system using elliptical uniplanar antennas in a circular-array setup", 2015 IEEE INTERNATIONAL CONFERENCE ON IMAGING SYSTEMS AND TECHNIQUES (IST), IEEE, (20150916), doi:10.1109/IST.2015.7294522, pages 1 - 4
• US 2012/062440 A1
• XIN ZHANG ET AL, "Design of circularly polarized stacked microstrip antennas", ANTENNAS, PROPAGATION AND EM THEORY, 2008. ISAPE 2008. 8TH INTERNATIONAL SYMPOSIUM ON, IEEE, PISCATAWAY, NJ, USA, (20081102), ISBN 978-1-4244-2192-3, pages 11 - 14
  WO2017/100126 A1

The following documents disclose radiating elements of the state of the art:

• US 2012/112977 A1
• RAWAT SANYOG ET AL, "Stacked elliptical patches for circularly polarized broadband performance", 2014 INTERNATIONAL CONFERENCE ON SIGNAL PROPAGATION AND COMPUTER TECHNOLOGY (ICSPCT 2014), IEEE, (20140712), doi:10.1 109/ICSPCT.2014.6884942, pages 232 - 235
• US 5,010,348 A
• WEILY AR ET AL, "Circularly Polarized Ellipse-Loaded Circular Slot Array for Millimeter-Wave WPAN Applications", IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, (20091001), vol. 57, no. 10, doi:10.1109/TAP.2009.2029305, ISSN 0018-926X, pages 2862 - 2870
• KOUTSOUPIDOU MARIA ET AL, "A microwave breast imaging system using elliptical uniplanar antennas in a circular-array setup", 2015 IEEE INTERNATIONAL CONFERENCE ON IMAGING SYSTEMS AND TECHNIQUES (IST), IEEE, (20150916), doi:10.1109/IST.2015.7294522, page 1 - 4
• US 2012/062440 A1
• XIN ZHANG ET AL, "Design of circularly polarized stacked microstrip antennas", ANTENNAS, PROPAGATION AND EM THEORY, 2008. ISAPE 2008. 8TH INTERNATIONAL SYMPOSIUM ON, IEEE, PISCATAWAY, NJ, USA, (20081102), ISBN 978-1-4244 -2192-3, pages 11 - 14
  WO2017/100126 A1

The object of the invention is to remedy the drawbacks of the known radiating elements and to produce a new compact radiating element having a sufficiently wide passband to allow operation in two disjoint frequency bands respectively for transmission and reception in bands of low frequencies including the C band and also allowing operation according to two orthogonal circular polarizations, respectively right and left.

This object is solved by the object of the independent claim, preferred embodiments are defined by the dependent claims.

• figures 1a, 1b, 1c : trois schémas, respectivement en coupe axiale, en perspective, et en vue de dessus, d'un exemple d'élément rayonnant bi-polarisation, selon l'invention ;
• figure 1d : un schéma en coupe axiale d'une variante de réalisation de l'élément rayonnant, selon l'invention ;
• figure 2 : un graphique illustrant deux courbes du rayonnement de l'élément rayonnant de la figure 1, en fonction de la fréquence, correspondant respectivement à une première polarisation circulaire et à une deuxième polarisation circulaire, selon l'invention;
• figures 3a et 3b : deux schémas, respectivement en perspective et en vue de dessus, d'un premier exemple de réseau rayonnant comportant quatre éléments rayonnants, selon l'invention ;
• figures 4a et 4b : deux schémas, respectivement en perspective et en vue de dessus d'un deuxième exemple de réseau rayonnant comportant quatre éléments rayonnants, ne faisant pas partie de l'invention revendiquée.

Other particularities and advantages of the invention will appear clearly in the remainder of the description given by way of purely illustrative and non-limiting example, with reference to the appended diagrammatic drawings which represent:

• figures 1a, 1b , 1 C : three diagrams, respectively in axial section, in perspective, and in top view, of an example of a dual-polarization radiating element, according to the invention;
• figure 1d : a diagram in axial section of an alternative embodiment of the radiating element, according to the invention;
• picture 2 : a graph illustrating two radiation curves of the radiating element of the figure 1 , as a function of frequency, corresponding respectively to a first circular polarization and to a second circular polarization, according to the invention;
• figures 3a and 3b : two diagrams, respectively in perspective and in plan view, of a first example of a radiating network comprising four radiating elements, according to the invention;
• figures 4a and 4b : two diagrams, respectively in perspective and in plan view of a second example of a radiating network comprising four radiating elements, not forming part of the claimed invention.

où n est un entier naturel et a_n, a_n-1, a₁, a₀ sont des coefficients réels de la fonction polynomiale f.The radiating element 10 represented on the figures 1a, 1b , 1 C comprises a cavity 11 with symmetry of revolution around an axis Z, a core central metal 12 extending axially at the center of the cavity 11 and N different metal planar elements 131, 132,..., 13N, stacked one above the other, parallel to each other and parallel to a lower metal wall 14 of the cavity 11, also called bottom of the cavity, N being an integer greater than 2, the N metal planar elements being centered in the cavity and integral with the central core 12. The central core 12 comprises a lower end 15 fixed to the lower metal wall 14 of the cavity and an upper end 16 free. Each metallic planar element 131, 132,..., 13N, called an elliptical planar element, has an elliptical outline whose orientation and dimensions are defined by the orientation and dimensions of the major axis and the minor axis of the ellipse corresponding. For each of the elliptical planar elements 131, 132,..., 13N, the dimensions of the major axis and of the minor axis of the same elliptical outline are different, the ratio between the length of the minor axis and the length of the major axis being preferably less than 0.99, and advantageously less than 0.9. The N elliptical planar elements 131, 132,..., 13N are regularly spaced along the central core 12 and have monotonically decreasing dimensions between the lower end 15 and the upper end 16 of the central core. . Preferably, the monotony of the decrease is strict. As a variant, the dimensions of certain elliptical planar elements may be equal, the elliptical planar elements not all being able to have the same dimensions. According to one embodiment, the dimensions of the N elliptical planar elements are exponentially decreasing, namely decreasing according to the exponential function. As a variant, the dimensions of the N elliptical planar elements are decreasing according to a polynomial function. By decrease according to a polynomial function, we mean that the dimensions of the N elliptical planar elements can be determined by a monotonic part of a function f of type: $$f\left(x\right)={\mathrm{To}}_{\mathrm{not}}{x}^{\mathrm{not}}+{\mathrm{To}}_{\mathrm{not}-1}{x}^{\mathrm{not}-1}+\cdots +{\mathrm{To}}_1{x}^1+{\mathrm{To}}_0{x}^0$$

where n is a natural number and a _n , a _n-1 , a ₁ , a ₀ are real coefficients of the polynomial function f.

The cavity 11 is delimited by the lower metal wall 14 and by the side metal walls 17 and is filled with air. The radiating element 10 further comprises at least one power source consisting of a coaxial line 18 connected to the first elliptical planar element 131 located closest to the lower end 15 of the central core 12. Thus, only the first elliptical planar element 131 is powered directly by coaxial line 18. The first elliptical planar element 131 radiates a radiofrequency wave which propagates in the cavity and generates currents on the surface of the other elliptical planar elements 132,..., 13N which are then coupled step by step by induced electromagnetic coupling. The first elliptical planar element 131 is therefore an exciting planar element.

The major axes of the elliptical shapes corresponding to the various elliptical planar elements can all be oriented in a single common direction or in different directions. The N elliptical planar elements can all be accommodated inside the cavity as illustrated in the figures 1a, 1b , 1 C , but it is not obligatory and alternatively, some elliptical planar elements corresponding to the smallest dimensions and the highest frequencies, can protrude from the cavity as represented on the figure 1d .

When the radiating element comprises a single coaxial supply line 18, the various elliptical planar elements 131, 132,..., 13N are progressively shifted in rotation with respect to each other, around the central core 15, as represented, for example, on the figure 1b . The major axes of the elliptical shapes corresponding to the various elliptical planar elements are then oriented in different directions. The offset of the various elliptical planar elements in rotation makes it possible to obtain radiation from the radiating element in circular polarization. The radiation axis of the radiating element corresponds to the Z axis.

The graph of the figure 2 shows the two curves 21, 22 of the radiation of a radiating element according to the invention, as a function of the frequency, the radiating element being fed by a single coaxial line and comprising elliptical planar elements progressively offset in rotation from each in relation to others as to figures 1a, 1b , 1c, 1d . The rotational offset between the first and N ^th elliptical planar elements is approximately 90°.

The first curve 21 corresponds to the radiation from the radiating element according to a first circular polarization in the forward direction and the second curve 22 corresponds to the radiation from the radiating element according to a second circular polarization in the opposite direction.

As these two curves show, with a single feed line, the radiating element operates in two very wide different bandwidths between 3.7GHz and 6.4GHz and in each bandwidth, the polarizations are different and inverted. In each passband, the cross-polarization gain levels are less than -15dB relative to the gain levels of the corresponding operating bias.

This radiating element therefore allows operation in two distinct different frequency bands, for example transmission and reception, with different polarizations and a good level of gain.

These two curves 21, 22 show that the association of the cavity with a plurality of elliptical planar elements of different dimensions allows radiation of the radiating element in a much wider bandwidth than conventional radiating elements. This is due to the fact that the elliptical planar elements having the largest dimensions participate in the radiation of the radiating element in low frequencies while the elliptical planar elements of smaller dimensions participate in the radiation of the radiating element in higher frequencies. . The gradual decrease in the dimensions of the elliptical planar elements along the central core 12 makes it possible to obtain continuous radiation in a wide band of frequencies. In addition, the operation in double circular polarization is due to a particularly remarkable natural effect corresponding to a natural inversion of the direction of the polarization in the highest frequency bands.

This natural inversion of the direction of the polarization, in the band corresponding to the highest operating frequencies, for example the reception band, is a new effect which has never been encountered in conventional radiating elements and is due to a coupling between the elliptical planar exciter element 131 and the bottom of the cavity 14 formed by the lower wall of the cavity. The reflection, on the bottom of the cavity 14, of the radiofrequency waves, emitted by the elliptical planar element exciter 131 and corresponding to the highest operating frequencies, has the effect of reversing the direction of the polarization.

The electric field corresponding to the highest frequencies is reflected by the lower wall 14 of the cavity and is re-emitted towards the top of the cavity after reversal of the direction of the polarization. On the contrary, the electric field corresponding to the low frequencies is directly emitted towards the top of the cavity without reflection and without inversion of the direction of the polarization.

It is possible to assemble several identical radiating elements 10 to form a two-dimensional planar radiating network of large dimensions as illustrated for example in the figures 3a and 3b on which four radiating elements of the network are represented. In the radiating network, the different radiating elements are arranged side by side and their respective cavities are interconnected by a common metal support plate 30 forming a metal ground plane. Of course, the radiating network is not limited to four radiating elements, but can comprise any number of radiating elements greater than two. However, the radiating elements having an aperture reduced to a half central operating wavelength, at the bottom of the transmission frequency band, the radiating elements couple together with significant field levels which have the effect of d alter the polarization purity. To solve this problem, according to the invention, absorbent elements 31 made of a dielectric material have been added between the adjacent radiating elements, and fixed to the metal support plate 30. The absorbent elements are volumes of dielectric which can have a any shape, and can be positioned at junction points between four adjacent radiating elements, as shown in the figures 3a and 3b . The height of the absorbing elements can vary according to their position in the network and according to the frequency of the parasitic coupling to be eliminated. The dielectric material may for example consist of a material such as silicon carbide SiC.

Furthermore, since networking can cause increased cross-polarization levels, the adjacent radiating elements are spatially arranged so that their respective elliptical planar elements are respectively oriented parallel to two mutually orthogonal X, Y directions, i.e. i.e. the directions of the major axes of their respective elliptical planar elements are orthogonal to each other, as shown in the figure 3b . Thanks to the superposition of several orthogonal field ellipses between them, this sequential spatial arrangement of the successive radiating elements makes it possible to improve the purity of the two circular polarizations generated by the various radiating elements of the network and to clearly reduce the levels of crossed polarization in the radiation axis of the network.

According to one example, not forming part of the claimed invention, the various elliptical planar elements of each radiating element are not offset in rotation with respect to each other, but the major axes of their respective elliptical shapes are all aligned in a common leadership.

In this case, for operation of the radiating element in two mutually orthogonal polarizations, each radiating element 10 comprises two coaxial supply lines 18, 28 connected to the first elliptical planar element 131 located closest to the lower end of the central soul. The two coaxial supply lines 18, 28 are respectively connected to two different connection points of the first elliptical planar element 131, the two connection points being placed in two different directions of the first elliptical planar element 131, mutually perpendicular, the two directions which can correspond, for example, to the directions of the major axis and of the minor axis of the elliptical shape of the first elliptical planar element 131. Thus, only the first elliptical planar element is supplied directly by the two coaxial lines according to two orthogonal polarizations. In this case, the radiating element 10 can only operate in a single frequency band and in bi-polarization since it is not possible in this case to select both a frequency band and a single polarization. According to this second embodiment, for transmission and reception operation, it is then necessary to produce radiating elements of different dimensions adapted respectively either to an operating frequency band dedicated to transmission, or to an operating frequency band dedicated to reception. THE figures 4a and 4b illustrate an example of a network, not forming part of the claimed invention, comprising radiating elements according to this second embodiment of the invention. As shown in figure 4b , the adjacent radiating elements are spatially arranged so that their respective elliptical planar elements are respectively oriented in two mutually orthogonal X, Y directions, that is to say that the directions of the major axes of their respective elliptical planar elements are orthogonal between them.

Claims (7)

1. A use of a dual circular polarisation radiating element (10), said radiating element (10) having a cavity (11) that is axially symmetric about an axis Z and a power source, the cavity (11) being bounded by lateral metal walls (17) and a lower metal wall (14), said radiating element (10) further having a metal central core (12) that extends axially at the center of the cavity (11) and N different successive metal elliptical planar elements (131, 132, ..., 13N) that are stacked on top of one another parallel to the lower wall (14) of the cavity, the central core (12) having a lower end (15) that is fastened to the lower metal wall (14) of the cavity and an upper end (16) that is free, each elliptical planar element (131, 132, ..., 13N) being centered in the cavity (11) and secured to the central core (12), the N elliptical planar elements being non-circular, regularly spaced apart and having dimensions that decrease monotonically between the lower end (15) and the upper end (16) of the central core (12), where N is an integer higher than 2, the power source consisting of a coaxial line (18) connected to the first elliptical planar element (131) located closest to the lower end (15) of the central core (12) and the N successive elliptical planar elements (131, 132, ..., 13N) being progressively offset rotationally with respect to one another, about the central core (12).
2. The use of a dual circular polarisation radiating element (10) according to claim 1, wherein the N elliptical planar elements have dimensions that decrease exponentially.
3. The use of a dual circular polarisation radiating element (10) according to claim 1, wherein the N elliptical planar elements have dimensions that decrease according to a polynomial function.
4. A use of a dual circular polarisation radiating array, said radiating array having at least two radiating elements (10) as defined according to one of claims 1 to 3.
5. The use of a dual circular polarisation radiating array according to claim 4, wherein the radiating elements (10) are arranged beside one another on a common carrier plate (30).
6. The use of a dual circular polarisation radiating array according to claim 5, wherein the radiating elements that are adjacent to one another are spatially arranged so that their respective elliptical planar elements (131, 132, ..., 13N) are respectively oriented in two directions that are orthogonal to each other.
7. The use of a dual circular polarisation radiating array according to claim 6, wherein the radiating array further has absorbent dielectric elements (31) placed between two adjacent radiating elements (10).

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