Abstract: A telecommunications system antenna for communicating, in transmission and in reception, with a large area whose position relative to the antenna varies. The antenna has motors (80, 82) for pointing the antenna towards the area and radiating elements (74, 76) associated with a control device for modifying the antenna's radiation pattern according to the relative position of the antenna and the area. When the antenna is installed on a telecommunications satellite, as the antenna moves, the antenna can remain constantly in communication with an area of the Earth covering several hundred kilometers.

Abstract: The invention concerns a telecommunications system in which the Earth is divided into areas (26) within which communications are effected by means of transmit and receive means on a spacecraft, such as a satellite, allocated to communication for a plurality of areas. Areas (2610, 2611, 2612) of a first category (28) are allocated signals having respective polarizations (PD, PG) and carrier frequencies (&Dgr;F1, &Dgr;F2) such that two adjacent areas of the first category are allocated signals having different polarizations or carrier frequencies. Each area of a second category (30) is allocated signals having all the available polarizations and all the available carrier frequencies.

Abstract: A radiating structure, or antenna, includes an exciter patch which receives an excitation signal and a plurality of secondary patches which radiate the waves received from the exciter patch. The structure includes a reflective surface in the vicinity of the exciter patch and the secondary patches constitute semi-reflective surfaces. The combination is such that the waves radiated by the secondary patches are substantially in phase. The distance between the reflective surface and the secondary patches is substantially equal to half the wavelength to be transmitted. The structure maintains the purity of circular polarization over a wide angular sector.

Abstract: A microwave resonant antenna includes a ring whose peripheral length determines the wavelength guided in the antenna. The ring incorporates meanders or crenellations. These have substantially radial parts so that, overall, they do not produce any field interfering with the circular polarization of a signal to be transmitted. An antenna of this kind lends itself to miniaturization. It is omnidirectional over a wide angle with a high degree of purity of circular polarization.

Abstract: An antenna includes a radiating resonant member for transmitting polarized microwaves. A first diffracting system radiates waves at an angle greater than the transmission angle of the radiating member. A second diffracting system corrects the purity of polarization of the waves for some directions at least.

Abstract: A system with two concentric antennas for two bands of microwave frequencies includes between the two concentric antennas a system for eliminating or attenuating propagation of waves from the inner antenna to the outer antenna.