Circularly polarised radiating element making use of a resonance in a Fabry-Perot cavity
A circularly polarized radiating element includes at least one excitation aperture for a wave that is linearly polarized with what is referred to as an excitation first polarization, a frequency selective surface and a metasurface comprising a two-dimensional and periodic array of metasurface cells, the excitation aperture opening onto the metasurface, the metasurface cells all being oriented identically with respect to the excitation polarization and configured to: reflect an incident wave having the excitation polarization in order to form a reflected wave polarized with the excitation polarization, and depolarize and reflect the incident wave in order to form a reflected wave polarized with the orthogonal polarization, having a phase difference substantially equal to ±90° with respect to the reflected wave polarized with the excitation polarization, and having an amplitude substantially equal to the amplitude of a wave radiated by the frequency selective surface, generated from the reflected wave polarized with the excitation polarization.
1. A circularly polarized radiating element comprising:
at least one excitation aperture for a wave that is linearly polarized with what is referred to as an excitation first polarization; and
a frequency selective surface that partially reflects the excitation polarization and that is transparent to a second polarization, referred to as the orthogonal polarization, that is orthogonal to the excitation polarization and to the direction of propagation of the wave, said surface being placed in a plane defined by the excitation polarization and by the orthogonal polarization;
wherein it further comprises a completely reflective metasurface facing the frequency selective surface, and comprising a two-dimensional and periodic array of conductive planar elements forming metasurface cells, the excitation aperture opening onto the metasurface,
the frequency selective surface and the metasurface forming a resonant cavity for the excitation polarization,
the metasurface cells all being oriented identically with respect to the excitation polarization and configured to:
reflect an incident wave having the excitation polarization in order to form a reflected wave polarized with the excitation polarization, and depolarize and reflect the incident wave in order to form a reflected wave polarized with the orthogonal polarization, having a phase difference substantially equal to ±90° with respect to the reflected wave polarized with the excitation polarization, and having an amplitude substantially equal to the amplitude of a wave radiated by the frequency selective surface, generated from the reflected wave polarized with the excitation polarization.
2. The radiating element according to claim 1 , the metasurface comprising a ground plane on which are placed a substrate and the array of metasurface cells, which cells are arranged in rows, the centres center of each metasurface cell of a given row being aligned along an alignment axis, the alignment axis being oriented by a rotation angle (ψ) with respect to the excitation polarization, the rotation angle (ψ) being defined so as to make the matrix [S′] diagonal, where:
[
S
′
]
=
t
[
R
]
[
S
]
[
R
]
,
[S] being the scattering matrix of the metasurface (S 1 ), and [R] the rotation matrix of a rotation of angle ψ.
3. The radiating element according to claim 2 , the metasurface cells of a given row being coupled by a metasurface interconnect line that is elongate along the alignment axis.
4. The radiating element according to claim 3 , the rows being connected to one another by way of metasurface cells, forming with the metasurface interconnect lines a rectangular grid.
5. The radiating element according to claim 2 , the metasurface cells of a given row being mutually isolated.
6. The radiating element according to claim 2 , the metasurface cells of a given row all being periodically spaced.
7. The radiating element according to claim 2 , all the metasurface cells of the metasurface having the same dimensions.
8. The radiating element according to claim 1 , the frequency selective surface comprising an array of parallel metal wires that are periodically spaced and aligned with the excitation polarization.
9. The radiating element according to claim 1 , the frequency selective surface comprising a two-dimensional array of metal dipoles that are arranged periodically.
10. The radiating element according to claim 1 , the excitation aperture comprising at least one waveguide aperture opening into the resonant cavity.
11. The radiating element according to claim 10 , the excitation aperture comprising a dual feed formed by two waveguides that open symmetrically into the resonant cavity, and that are connected to an impedance matching network.
12. The radiating element according to claim 1 , the excitation aperture being a horn of a linear radiating aperture.
13. The radiating element according to claim 1 , comprising a plurality of excitation apertures, the excitation apertures being formed by an array of linear radiating apertures.
14. The radiating element according to claim 1 , comprising at least one second cavity arranged in cascade on the frequency selective surface.
15. The radiating element according to claim 1 , the metasurface cells being of rectangular shape.
16. An array antenna comprising at least one radiating element according to claim 1 .