Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
1999-10-29
2001-08-28
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S753000, C343S909000
Reexamination Certificate
active
06281853
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a terminal and antenna system for transmitting and receiving data to and from non-geostationary satellites in low Earth orbit.
The terminal and antenna system is designed to be inserted into a system for transmitting data at high bit rates to and from a constellation of satellites for public or private, civil or military use.
A constellation of this kind comprises a large number of non-geostationary satellites in low or medium orbit around the Earth. In a standard configuration, the altitude is in the range from 800 km to 1500 km and the satellites are regularly spaced in a series of orbital planes, with eight satellites at 45° from each other, for example, in each of eight steeply inclined orbital planes around the Earth, so that any point on the globe is at all times in view of at least two if not three satellites. The choice of a low orbit for the satellites is motivated by the requirement for a high level of interactivity with a station centralizing access to networks, at high data bit rates and therefore with receivers that receive a high power level, which is not compatible with the propagation time via the geostationary orbit. However, this choice leads to fast movement of the satellites across the sky, a satellite in a 1500 km orbit remaining in view from a point on the ground for about 10 minutes only.
To reduce the number of satellites assuring continuity of calls with terminals on the ground, it is necessary for the terminals to be able to track the satellite for as long as possible, and therefore as far as possible towards the horizon. A second condition for these terminals is that they must be able to switch the stream of calls very quickly from a satellite reaching the horizon to a more visible satellite. Finally, the gain of the antenna must be in the order of 30 dBi for the transmit and receive beams.
Solutions to this problem have been proposed. A first solution uses an electronically scanned antenna, but the angular range to be covered is very wide (0° to 360° in azimuth, 10° to 90° in elevation), in which case this solution implies a prohibitive number of active elements: phase-shifters, low-noise receive amplifiers and transmit power amplifiers between the radiating elements and the phase-shifters to compensate for their losses and those of the splitters/combiners. Their cost is therefore much too high.
Another solution, originating in the military field, and for tracking a plurality of moving, over-the-horizon targets is disclosed in U.S. Pat. No. 3,755,815 and described in Microwave Journal (Oct. 75, pp. 31-34). It uses an array of active transmitter elements associated with a dome lens of dielectric material for deflecting the beam to the horizon and beyond. That solution has the major drawback of very high manufacturing cost because it requires an array of several hundred active elements.
There are other means for deflecting radio beams by using dielectric or waveguide lenses, for example as described by Lo and Lee in “Antenna Handbook”, but their technology restricts them to small deflection angles, of approximately 10° about the axis of the lens, and with no target tracking capability.
In the field of microwave antennas, the literature (see for example PCT WO 88/09066) describes antennas incorporating a plane array antenna associated with a focusing microwave lens and a horn source that can be positioned on a portion of a focal sphere depending on the direction required of the beam. Those antennas have the drawback that the radiating surface is a plane array so the directivity of the antenna falls off drastically at low elevations (approximately −7.6 dB for an elevation of 10°), whereas here the requirement is for constant directivity.
SUMMARY OF THE INVENTION
The invention is therefore aimed at a simple, compact system that is cheap to manufacture and that maintains calls at a high bit rate to and from a constellation of non-geostationary satellites.
To this end the invention proposes an antenna system for transmitting and receiving radio signals to and from a remote transceiver system moving in the space visible from said antenna, including a lens for focusing quasi-plane waves emitted by said remote transceiver, said means having a focal sphere S, at least one primary source for transmitting and receiving signals in the form of quasi-spherical wave beams, which source is mobile on a portion of the sphere S,
characterized in that it includes in combination:
a) a lens for deflecting the quasi-plane waves transmitted or received by the remote transceiver, and
b) means for slaving the position of each primary transmit/receive source to the known position of a remote transceiver.
The above combination of a focusing lens and a deflector lens produces a plane wave beam and deflects the beam practically to the horizon, the beam being emitted or picked up by a primary transmit/receive source disposed at a point on the focal sphere of the focusing lens corresponding to the position of the satellite at any given time.
The invention is aimed more particularly at a terminal and antenna system for transmitting and receiving radio signals to and from at least two remote transceiver systems at different points in the space visible from said terminal and antenna system, characterized in that it includes:
a) means for determining the position of said remote transceivers in view at a given time,
b) means for choosing a remote transceiver,
c) an antenna according to the above description, including at least two primary transmit/receive sources,
d) means for controlling movement of the primary transmit/receive sources over the focal sphere S adapted to prevent the primary sources colliding, and
e) means for switching between the primary sources.
Transfer of data with a constellation of non-geostationary satellites is therefore maintained continuously in this case. Reducing the number of primary transmit/receive sources to just two significantly reduces the overall cost of the antenna. Also, the system in this configuration is significantly smaller than the solution employing two Cassegrain antennas. A tool is therefore obtained which is much simpler than previous systems, can be installed on the roof of a house in the conventional way, and has a low manufacturing cost, making this type of antenna available to private individuals.
In one particular embodiment of the invention, the primary transmit/receive sources of signals in the form of quasi-spherical wave beams take the form of horn antennas which can be moved over a portion of the focal sphere of the focusing lens.
In a preferred embodiment of the invention, each primary transmit/receive source is moved by a pair of azimuth and inclination motors.
These features contribute to a low cost of manufacture through using standard components and a simple mechanical assembly.
In a preferred embodiment of the invention, the lens for focusing quasi-plane waves into quasi-spherical waves is a multi-focal convergent lens having a large scanning range.
More particularly, the scanning range is made to be greater than 30° relative to the axis of symmetry of revolution of the focusing lens by moving the primary transmit/receive wave sources over its focal sphere.
This feature makes it possible to achieve a wide scanning range with simple technology.
In a preferred embodiment of the invention, the focusing lens is a convex dielectric lens. In an advantageous embodiment of the invention, the focusing lens is a concave waveguide lens.
The above embodiments of the focusing lens based on cheap standard materials further reduce the cost of the system compared with the arrays of active components used in some prior art solutions.
In a preferred embodiment of the invention the lens for deflecting the quasi-plane waves is a dielectric dome lens. To be more precise, the dome lens has a generally hemispherical overall profile.
This embodiment of the lens can deflect beams practically to the horizon and it also provides a protective radome for the antenna.
In a preferred embodiment of
Caille Gerard
Pinte Béatrice
Alcatel
Phan Tho
Sughrue Mion Zinn Macpeak & Seas, PLLC
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