Multibeam antenna

Abstract

An antenna capable of generating multiple beams that are close together and have side lobes of low level includes optics comprising a single main reflector and a set of primary sources, each source suitable for generating a beam taken up by the optics that transmits it, or suitable for receiving a beam picked up by the optics of the antenna. The main reflector has an aperture of diameter D as a function of the center wavelength of the frequency band of the beams and the half-power beam width of the beams coming from the main antenna element, and a dimensionless number lying in the range 1.5 to 4. The optics present a profile that is modified relative to conventional optics comprising a parabolic main reflector by a correction that imparts an amplitude and phase distribution that is preferably circularly symmetrical, and compliant with a relationship for enlarging the reflected beams.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood on reading the following description given by way of non-limiting example, and with reference to the drawings, in which:

FIG. 1 shows an antenna having the third of the above-mentioned types of configuration;

FIGS. 2 a and 2b show two ways of embodying an antenna of the invention, respectively with and without an auxiliary reflector, and FIG. 2c, in which the right-hand portion shows a reflector in face view and the left-hand portion shows the analytic distribution of amplitude for γ=2 and α=0.2, shows the parameters a, D, α, and ρ;

FIGS. 3 a and 3b show an example of transmission distribution (or radiation patterns) E(θ) and of surface corrections Δz(x,y) for a circular aperture with D=3 meters (m) and N=7, for the embodiment of FIGS. 2a or of FIG. 2b;

FIGS. 4 a and 4b show two embodiments of the invention in the form of a Cassegrain type structure having an offset focus, with FIG. 4c showing the parameters f, D, φ₀, and ψ₀; and

FIGS. 5 a and 5b show an example of transmission distribution (or radiation pattern) E(θ) and of correction of the main reflector profile with D=3 m and N=7, for the embodiment of FIG. 4a or of FIG. 4b.

Claims

1. An antenna for transmitting and/or receiving multiple beams, wherein: the antenna includes optics comprising a main antenna element having at least one reflector or lens and optionally a secondary antenna element comprising at least one reflector or lens, together with a set of primary sources, each primary source transmitting or receiving one of said beams via the optics of the antenna;the main antenna element has an aperture of nominal diameter D, such that: D=70Bλ/HPBW λ designating the center wavelength of the frequency band of the beams;HPBW standing for half-power beam width (expressed in degrees) of the beams coming from the main antenna element; andB being a dimensionless number lying in the range 1.5 to 4; andthe optics present a profile modified by a profile correction giving it a distribution obeying a relationship suitable for enlarging the reflected beam relative to conventional optics comprising a parabolic main reflector and optionally at least one secondary reflector of conical type.

2. An antenna according to claim 1, wherein the profile correction corresponds to an aperture phase distribution relationship φ(ρ).

3. An antenna according to claim 2, wherein the aperture phase distribution relationship φ(ρ) corresponds to a cubic interpolation over (N+1) pairs of values (ρi, φi) so as to generate first and second derivatives of φ(ρ) that do not vary discontinuously.

4. An antenna according to claim 2, wherein the aperture phase distribution relationship φ(ρ) corresponds to constant phase values δn in N adjacent and successive annular zones of the antenna (n being an integer lying in the range 0 to N−1).

5. An antenna according to claim 2, wherein the aperture phase distribution relationship φ(ρ) corresponds to slopes βn of the phase δn that are constant in N adjacent and successive annular zones of the antenna (n being an integer lying in the range 0 to N−1).

6. An antenna according to claim 3, wherein N lies in the range 4 to 30, and more particularly in the range 4 to 20.

7. An antenna according to claim 1, presenting an aperture amplitude distribution relationship having amplitude of circular symmetry.

8. An antenna according to claim 1, presenting an aperture amplitude distribution relationship having an analytic function of the form:

9. An antenna according to claim 1, presenting an imported aperture amplitude distribution relationship f(ρ) in the form, for at least one frequency, of a numerical table having M+1 pairs of values (ρj, fj), fj=f (ρj) designating the complex aperture field for p=ρj, and j varying from 0 to M.

10. An antenna according to claim 1, wherein the main antenna element presents said profile correction.

11. An antenna according to claim 1, wherein the optics also present at least one said secondary antenna element for receiving the beams emitted by the primary sources and delivering them towards the main antenna element, and/or for taking the beams received by said main antenna element and directing them towards the primary sources.

12. An antenna according to claim 9, wherein the optics are of the Cassegrain type having an offset focus (FFOC, SFOC).

13. An antenna according to claim 1, wherein the optics present solely said main antenna element.

14. An antenna according to claim 1, wherein the main antenna element is a single lens or a reflector, and wherein said profile correction is a surface correction.

15. An antenna according to claim 1, wherein the main antenna element is a reflector array, and wherein said profile correction is a surface correction and/or a phase shift correction applied to phase shifter elements of the reflector array.

16. An antenna according to claim 1, wherein said distribution is circularly symmetrical.

17. A method of calculating a profile correction for an antenna according to claim 1, the method optimizing the radiation pattern E(θ) from an amplitude function f(ρ) to which a phase distribution criterion is applied in N annular zones, or by interpolation over N+1 points so as to obtain an optimum phase distribution φ(ρ), and calculating a surface correction (Δz) from said optimum phase distribution φ(ρ)