Communications: radio wave antennas – Antennas – Antenna components
Reexamination Certificate
1999-11-30
2001-05-08
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Antenna components
C343S753000
Reexamination Certificate
active
06229500
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a multilayer focusing spherical lens which can be incorporated in a transceive antenna of a terminal of a remote transceiver system.
The invention also relates to a transceive antenna including a lens of the above kind and a terminal for transmitting and receiving radio signals to and from at least two remote transceiver systems moving at different points in the field of view of said terminal, the terminal including an antenna of the above kind.
The invention applies in particular to systems for transmitting data at a high bit rate to and from a constellation of satellites for public or private, civil or military use, but this application is not limiting on the invention.
More generally, the invention relates to any application requiring a lens of simple structure with which a compact antenna can be obtained.
One solution to the problem of simplifying the structure of the lens in an antenna is to use a single-layer focusing spherical lens, of the kind shown in FIG.
1
. Such lenses have the advantage that they are easy to manufacture because they comprise only one layer, and possibly also an index matching layer, as shown.
However, for a given overall size, such lenses have relatively low gain, yielding an antenna efficiency of less than 50%. In the example shown in
FIG. 1
, even though the various parameters of the lens have been optimized, such as the refractive index, the diameter and the losses by reflection limited by the index matching layer, the gain is still low because of the convergent rays, which represent a loss of energy and disturb the radiation pattern of the antenna in the form of raised secondary lobes. Experience shows that reducing the refractive index increases the focal length and therefore increases the overall volume of the antenna, whereas increasing the refractive index increases ohmic losses without improving the focusing of the lens.
One solution to that problem would be to increase the overall size of the lens to obtain satisfactory gain, for example gain of the order of 31 dB in the applications in question. However, this is not acceptable because it leads to overall size and additional weight which are incompatible with minimizing the overall size and weight of a transceive terminal.
A second solution uses a multilayer Luneberg lens, as shown in FIG.
2
. Such lenses comprise a plurality of concentric spherical layers of dielectric constant that decreases continuously from the center towards the edge of the lens. That type of lens has the advantage of total spherical symmetry, which is ideal for producing an antenna with a very wide field of view.
However, for given overall size, such lenses also have relatively low gain, yielding an antenna with efficiency of 50% to 60%.
FIG. 2
shows divergence of many rays despite relatively fine sampling of the theoretical law stated by Luneberg. To obtain high efficiency it is necessary to increase the number of layers considerably, which is totally prohibitive in terms of manufacturing cost, especially for mass-market applications.
Finally, U.S. Pat. No. 4,307,404 describes a planar and spherical multilayer antenna design and refers to a spherical artificial structure.
However, the problem addressed in the above document is concerned with interference between different frequencies. Consequently, the beam is deflected for certain frequencies only and the antenna described is therefore not a particularly broadband antenna: the beam is swept mechanically in the same direction for all frequencies compatible with the radiating source.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome the aforementioned disadvantages.
The invention consists in a focusing spherical lens whose structure is simple and compact and whose manufacturing cost is small compared to that of prior art lenses.
The invention further consists in a lens of the above kind whose performance, and in particular whose efficiency, is better than that of prior art lenses.
To this end, in a first aspect, the invention proposes a multilayer focusing spherical lens adapted to be mounted in a transceive antenna device of a terminal of a remote transceiver system and having a concentric focal sphere, characterized in that it has a central layer and a peripheral layer having different dielectric constants, each dielectric constant value being determined so that the lens focuses parallel microwave beams towards the focal sphere concentric with the lens.
The two-layer structure of the lens improves focusing and therefore assures a simple structure whilst reducing the volume of the lens compared to that of prior art lenses. Of course, this presupposes that the two dielectric constant values, the intermediate radius, and the position of the source have all been optimized. This achieves efficiency of 70% to 80%, which is entirely satisfactory for the applications concerned.
In one embodiment of the invention, the lens includes an index matching layer adapted to reduce losses by reflection at the lens dielectric/air interface.
The index matching layer reduces losses and coupling generated by reflection phenomena at the surface of the spherical lens.
In another embodiment of the invention the values of the dielectric constants of the two layers are in the range from 2 to 5.
In a second aspect, the invention proposes an antenna for transmitting and receiving radio signals to and from at least one remote transceiver system moving in the field of view of said antenna, characterized in that it includes a focusing spherical lens as previously mentioned.
In a third aspect, the invention proposes a terminal for transmitting and receiving radio signals to and from at least two remote transceiver systems moving at different points in the field of view of said terminal, characterized in that it includes means for determining the position of said remote transmitters/receiver in view at a given time, means for choosing a remote transceiver, an antenna having one primary source (
23
,
24
) for transmitting and receiving signals in the form of quasi-spherical wave beams which is mobile over a portion of the focal sphere (S), and means (
10
) for slaving the position of each primary transceive source to the known position of a remote transceiver system, including at least two primary transceive sources, means for controlling movement of the primary transceive sources over the focal sphere adapted to prevent the primary sources colliding and means for switching between the primary sources.
In an embodiment of the terminal, each primary source, mounted on a support, is moved by at least one pair of motors so that each source is moved over at least the lower half of the focal sphere.
In a first variant, each primary source is moved by a pair of azimuth/elevation motors.
In a second variant, each primary source is moved by an X/Y motor pair, the first motor rotating each primary source about a horizontal primary axis Ox and the second motor rotating each primary source about a secondary axis Oy orthogonal to said primary axis at all times and moved relative to the primary axis by the first motor.
In a third variant, a first primary source is moved by an azimuth/elevation motor pair and the second primary source is moved by an X/Y motor pair, the azimuth motor of the first primary source also driving the antenna as a whole.
In a fourth variant, each primary source is moved by a pair of motors with oblique rotation axes.
REFERENCES:
patent: 3914769 (1975-10-01), Andrews
patent: 4307404 (1981-12-01), Young
patent: 4333082 (1982-06-01), Susman
patent: 5145973 (1992-09-01), Newman et al.
patent: 5677796 (1997-10-01), Zimmerman et al.
patent: 5748151 (1998-05-01), Kingston et al.
patent: 5781163 (1998-07-01), Ricardi et al.
patent: 5900847 (1999-05-01), Ishikawa et al.
patent: 6081239 (2000-06-01), Sabet et al.
patent: 0 632 522 A1 (1995-01-01), None
patent: WO 93/10572 (1993-05-01), None
Caille Gerard
Martin Laurent
Pinte Béatrice
Alcatel
Nguyen Hoang
Sughrue Mion Zinn Macpeak & Seas, PLLC
Wong Don
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