EP3306746A1 - Cavity radiating element and radiating network comprising at least two radiating elements - Google Patents

Abstract

The radiating element (10) comprises a cavity (11) with a symmetry of revolution about a Z axis, a central core (12) extending axially in the center of the cavity and N elliptical planar elements (131, 132, Successive successive metallic ones, stacked one above the other, parallel to the lower wall (15) of the cavity, the central core having a lower end attached to the lower metal wall of the cavity and a upper end (16) free, each elliptical metallic planar element being centered in the cavity and integral with the central core, the N elliptical planar elements being regularly spaced and having monotonically decreasing dimensions between the lower end and the end superior of the central soul, where N is an integer greater than 2.

Description

The present invention relates to a novel cavity radiating element architecture and a radiating network having 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 radio frequency chain. In the low frequency bands, for example in the C band, the radiating element is often constituted by a horn and the RF chain comprises RF components intended to perform the transmission and reception functions in mono-polarization or bi-direction. -polarization to cover the needs of users. The link with ground stations is usually bi-polarization.

The mass and bulk of the RF radio frequency chains is a critical point in the field of space antennas intended to be installed on satellites and in particular in the lower frequency domain such as the C-band. In the frequency domains high, for example Ka-band or Ku-band, there are very compact radiating elements whose technology can be transposed into C-band, but the radiofrequency sources obtained remain cumbersome and massive and pose a problem of implantation when they have to be integrated in a focal network with 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 single-polarization and on a single operating frequency band or in two very narrow frequency bands.

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

For this, the invention relates to a radiating element comprising a rotationally symmetrical cavity around a Z axis and a power source, the cavity being delimited by lateral metal walls and a lower metal wall. The radiating element further comprises a central metal core extending axially in the center of the cavity and N different successive metallic elliptical planar elements, stacked one above the other, parallel to the lower wall of the cavity, the core center comprising a lower end fixed to the lower metal wall of the cavity and a free upper end, each elliptical metallic planar element being centered in the cavity and integral with the central core, the N elliptical planar elements being regularly spaced and having dimensions monotonically decreasing between the lower end and the upper end of the central core, where N is an integer greater than 2.

Advantageously, the N planar elliptical elements have exponentially decreasing dimensions.

According to a variant, the N planar elliptical elements have decreasing dimensions according to a polynomial function.

Advantageously, the power source may consist of a coaxial line connected to the first elliptical planar element located closest to the lower end of the central core and the N successive elliptical planar elements may be progressively staggered in rotation. compared to others, around the central soul.

Alternatively, the power source may consist of two coaxial lines connected, at two different connection points, to the first elliptical planar element located closest to the lower end of the central core, the two connection points being respectively placed in two directions of the first planar element elliptical, perpendicular to each other, and the N elliptical planar elements may all be aligned in a common direction.

The invention also relates to a radiating network comprising at least two radiating elements.

Advantageously, the radiating elements of the radiating network can be arranged next to each other on a common support plate.

Advantageously, the adjacent radiating elements of the radiating network may be arranged spatially so that their respective elliptical planar elements are respectively oriented in two directions orthogonal to each other.

Advantageously, the radiating network may further comprise absorbing dielectric elements disposed between two adjacent radiating elements.

• 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, selon l'invention.

Other features and advantages of the invention will become clear in the following description given by way of purely illustrative and non-limiting example, with reference to the attached schematic drawings which represent:

• Figures 1a, 1b , 1 C three diagrams, respectively in axial section, in perspective, and in plan view, of an example of a bi-polarization radiating element, according to the invention;
• figure 1d : an axial sectional diagram of an alternative embodiment of the radiating element, according to the invention;
• figure 2 : a graph illustrating two curves of the radiation of the radiating element of the figure 1 as a function of frequency, respectively corresponding to a first circular polarization and a second circular polarization according to the invention;
• Figures 3a and 3b : two diagrams, respectively in perspective and in top view, of a first example of 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, according to the 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 about an axis Z, a central core 12 extending axially in the center of the cavity 11 and N different metallic planar elements 131, 132,..., 13N, stacked at each above the others, parallel to each other and parallel to a lower metal wall 14 of the cavity 11, also called the bottom of the cavity, N being an integer greater than 2, the N planar metal elements being centered in the cavity and integral with the central core 12. The central core 12 has a lower end 15 fixed to the lower metal wall 14 of the cavity and an upper end 16 free. Each planar metallic element 131, 132, ..., 13N, called an elliptical planar element, has an elliptical contour whose orientation and dimensions are defined by the orientation and the 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 the minor axis of the same elliptical contour 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 preferably less than 0.9. The N planar elliptical 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 decay is strict. Alternatively, the dimensions of some elliptical planar elements may be equal, the elliptical planar elements can not all have the same dimensions. According to one embodiment, the dimensions of the N planar elliptical elements are exponentially decreasing, namely decreasing according to the exponential function. Alternatively, the dimensions of the N planar elliptic elements are decreasing according to a polynomial function. Decaying according to a polynomial function means that the dimensions of the N planar elliptical elements can be determined by a monotonic part of a function f of type: $$f\left(x\right)={\mathrm{at}}_{\mathrm{not}}{x}^{\mathrm{not}}+{\mathrm{at}}_{\mathrm{not}-1}{x}^{\mathrm{not}-1}+\cdots +{\mathrm{at}}_1{x}^1+{\mathrm{at}}_0{x}^0$$

where n is a natural integer and _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 lateral metal walls 17 and is filled with air. The radiating element 10 further comprises at least one power supply constituted by 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 planar elliptical element 131 is fed directly by the 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 a planar exciter element.

The major axes of the elliptical shapes corresponding to the different elliptical planar elements can all be oriented in a single common direction or in different directions. The N elliptical planar elements can all be housed inside the cavity as illustrated on the Figures 1a, 1b , 1 C , but this is not mandatory and alternatively, some elliptical planar elements corresponding to the smallest dimensions and the highest frequencies, may protrude from the cavity as shown in FIG. figure 1 d.

When the radiating element comprises a single coaxial feed line 18, the various elliptical planar elements 131, 132,..., 13N can be progressively shifted in rotation relative to one another, around the central core 15, as represented for example on the figure 1b . The major axes of the elliptical shapes corresponding to different planar elliptical elements are then oriented in different directions. The offset of the different elliptical planar elements in rotation makes it possible to obtain a radiation of the radiating element in circular polarization. The radiating 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 having elliptical planar elements progressively offset in rotation, some by compared to others as to Figures 1a, 1b , 1c, 1d . The shift in rotation between the first and ^N-th elliptic planar members is about 90 °.

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

As shown by these two curves, with a single power 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 reversed. In each bandwidth, the cross-polarization gain levels are less than -15 dB relative to the gain levels of the corresponding operating bias.

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

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

This natural inversion of the direction of 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 excitatory planar element 131 and the bottom of the cavity 14 constituted by the lower wall of the cavity. The reflection, on the bottom of the cavity 14, radiofrequency waves, emitted by the excitatory elliptical planar element 131 and corresponding to the highest operating frequencies, has the effect of reversing the direction of polarization.

The electric field corresponding to the highest frequencies is reflected by the lower wall 14 of the cavity and is reemitted to the top of the cavity after inversion of the direction of polarization. On the contrary, the electric field corresponding to the low frequencies is directly transmitted 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 to form a large two-dimensional planar radiating network, as illustrated, for example, in FIGS. Figures 3a and 3b on which four radiating elements of the network are represented. In the radiating network, the different radiating elements are arranged next to one another 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 may have any number of radiating elements greater than two. However, since the radiating elements have an opening reduced to half a central wavelength of operation, at the bottom of the emission frequency band, the radiating elements couple with each other with large field levels which have the effect of alter the purity of polarization. To solve this problem, according to the invention, absorbent elements 31 made in a dielectric material, have been added between the adjacent radiating elements, and fixed on the metal support plate 30. The absorbent elements are dielectric volumes that can have any shape, and can be positioned at junction points between four adjacent radiating elements as shown on Figures 3a and 3b . The height of the absorbent elements may vary according to their position in the network and the frequency of parasitic coupling to be eliminated. The dielectric material may for example consist of a material such as silicon carbide SiC.

In addition, since the networking can cause an increase in the cross-polarization levels, the adjacent radiating elements are arranged spatially so that their respective elliptical planar elements are respectively oriented parallel to two orthogonal directions X, Y between each other. that is, the directions of the major axes of their respective elliptical planar elements are orthogonal to each other, as illustrated in FIG. figure 3b . Thanks to the superposition of several orthogonal field ellipses with one another, this sequential spatial arrangement of the successive radiating elements makes it possible to improve the purity of the two circular polarizations generated by the different radiating elements of the grating and to significantly reduce the levels of cross polarization in the the radiation axis of the network.

According to a second embodiment of the invention, the different 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 direction.

In this case, for an operation of the radiating element in two polarizations orthogonal to each other, 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 FIG. the central soul. The two coaxial supply lines 18, 28 are respectively connected at 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, perpendicular to each other, the two directions that correspond for example to the directions of the major axis and the minor axis of the elliptical shape of the first elliptical planar element 131. Thus, only the first elliptical planar element is fed directly by the two coaxial lines in two orthogonal polarizations. In this case, the radiating element 10 can only operate in a single frequency band and bi-polarization because it is not possible in this case to select both a frequency band and a single polarization. According to this second embodiment, for operation on transmission and reception, it is then necessary to produce radiating elements of different dimensions adapted respectively to either an operating frequency band dedicated to the transmission, or to an operating frequency band dedicated to the reception. The Figures 4a and 4b illustrate an example of a network comprising radiating elements according to this second embodiment of the invention. As shown in figure 4b the adjacent radiating elements are arranged spatially so that their respective elliptical planar elements are respectively oriented in two directions X, Y orthogonal to one another, that is to say that the directions of the major axes of their respective elliptic planar elements are orthogonal between them.

Although the invention has been described in connection with particular embodiments, it is obvious that it is not limited thereto and that it includes all the technical equivalents of the means described and their combinations if they are within the scope of the invention. In particular, the networks of radiating elements are not limited to four radiating elements but may have a number of radiating elements greater than two.

Claims (9)

Radiant element (10) comprising a cavity (11) with a symmetry of revolution around a Z axis and a power source, the cavity (11) being delimited by lateral metal walls (17) and a lower metal wall ( 14), characterized in that it further comprises a central core (12) extending axially in the center of the cavity (11) and N successive elliptical planar elements (131, 132, ..., 13N) different metallic successive , stacked one above the other, parallel to the bottom wall (14) of the cavity, the central core (12) having a lower end (15) fixed to the lower metal wall (14) of the cavity and a upper end (16) free, each elliptical planar element (131, 132, ..., 13N) being centered in the cavity (11) and integral with the central core (12), the N elliptical planar elements being regularly spaced and having decreasing dimensions of mani re monotonous between the lower end (15) and the upper end (16) of the central core (12), where N is an integer greater than 2. Radiant element according to claim 1, characterized in that the N planar elliptical elements have exponentially decreasing dimensions. Radiant element according to claim 1, characterized in that the N planar elliptical elements have decreasing dimensions according to a polynomial function. Radiant element according to one of Claims 1 to 3, characterized in that the power source consists 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 in that the N successive elliptical planar elements (131, 132, ..., 13N) are progressively offset in rotation relative to one another, around the central core ( 12). Radiant element according to one of Claims 1 to 3, characterized in that the power source consists of two coaxial lines (18, 28) connected at two different connection points to the first elliptical planar element (131) situated closest to the lower end of the central core (12), the two connection points being respectively located in two directions of the first elliptical planar element, perpendicular to each other, and in that the N planar elliptical elements (131, 132, ..., 13N) are all aligned in a common direction. Radiant network characterized in that it comprises at least two radiating elements (10) according to one of the preceding claims. Radiant network according to claim 6, characterized in that the radiating elements (10) are arranged next to one another on a common support plate (30). Radiant network according to claim 7, characterized in that the adjacent radiating elements are arranged spatially so that their respective elliptical planar elements (131, 132, ..., 13N) are respectively oriented in two directions orthogonal to each other. Radiant network according to claim 8, characterized in that it further comprises absorbing dielectric elements (31) arranged between two adjacent radiating elements (10).

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