Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2002-08-01
2004-03-09
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S372000, C342S378000, C342S380000, C342S383000, C343SDIG002, C343S881000
Reexamination Certificate
active
06703970
ABSTRACT:
The invention relates to an antenna on board a spacecraft, such as a geosynchronous satellite, adapted to receive and/or transmit radio frequency signals such as radio communication signals or radar signals.
BACKGROUND OF THE INVENTION
A geosynchronous satellite comprising a transmit antenna and a receive antenna, each of which has a reflector associated with a multiplicity of radiating elements, also known as sources, is used to provide communications over an extended territory, for example a territory the size of North America. To enable re-use of communication resources, especially frequency sub-bands, the territory to be covered is divided into areas and resources are allocated in such a way that adjacent areas are allocated different resources.
Each area, which has a diameter of the order of several hundred kilometers, for example, is of such a size that it must be covered by a plurality of radiating elements, in order to provide a high gain and so that the radiation from the antenna is sufficiently homogeneous over the area.
FIG. 1
shows a territory
10
′ covered by an antenna on board a geosynchronous satellite and n areas
12
′
1
,
12
′
2
, . . . ,
12
′
n
. In this example, four frequency sub-bands f
1
, f
2
, f
3
, f
4
are used.
The area
12
′
i
is divided into a plurality of sub-areas
14
′
1
,
14
′
2
, etc., each of which corresponds to one radiating element of the antenna.
FIG. 1
shows that some radiating elements, for example the element
14
′
3
at the center of the area
12
′
i
, correspond to only one frequency sub-band f
4
, whereas others, for example those at the periphery of the area
12
′
i
, are associated with a plurality of sub-bands (the sub-bands allocated to the adjacent areas).
FIG. 2
shows a prior art receive antenna for the above kind of telecommunication system.
The antenna has a reflector
20
and a plurality of radiating elements
22
1
, . . . ,
22
N
in the vicinity of the focal plane of the reflector. The signal received by each radiating element, for example the signal coming from the element
22
N
, passes first through a filter
24
N
for eliminating the transmit frequency (which is at a high power) followed by a low-noise amplifier
26
N
. At the output of the low-noise amplifier
26
N
, a divider
30
N
divides the signal into a plurality of portions, possibly with coefficients that can differ from one portion to another; the object of this division is to enable a radiating element to contribute to the formation of a plurality of beams. Thus an output
32
1
of the divider
30
N
is allocated to an area
34
p
and another output
32
i
of the divider
30
N
is allocated to another area
34
q
.
The dividers
30
1
, . . . ,
30
N
and the adders
34
p
, . . . ,
34
q
for constituting the areas are part of a system
40
as a beam forming network (BFN).
In the beam forming network
40
shown in
FIG. 2
, each output of each divider
30
i
is provided with a combination of a phase-shifter
42
and an attenuator
44
. The phase-shifters
42
and the attenuators
44
modify the radiation diagram, either to correct it if the satellite has suffered an unwanted displacement or to modify the distribution of the terrestrial areas.
Each low-noise amplifier
26
N
is associated with another low-noise amplifier
26
′
N
which is identical to it and whose function is to replace the amplifier
26
N
should it fail. To this end, two switches
46
N
and
48
N
are provided to enable such replacement. It is therefore necessary to provide telemetry means (not shown) for detecting such failure and telecontrol means (also not shown) to effect such replacement.
For existing satellite “mobile” services (for example satellite mobile telephony services) to grow without competition from terrestrial networks, it is necessary for the terminals used for these services to have the same overall size as those used for terrestrial networks. The only parameter of the link balance that is still open to modification in order to reduce terminal size and power is the figure of merit of the satellite, in the uplink direction, and the equivalent isotropically radiated power (EIRP) transmitted by the antenna of the satellite, in the downlink direction. To increase the EIRP of the satellite, it is possible to find a compromise between the size of the antenna and the power of the satellite amplifiers. However, a compromise is not possible for the figure of merit, because the noise temperature is fixed by natural constraints. Improving the figure of merit must therefore be achieved by increasing the size of the antenna.
A large antenna, i.e. an antenna having a large surface area for picking up or radiating electromagnetic signals, has the benefit of a high gain (its gain is proportional to its surface area) and a corresponding resolution (its resolution is proportional to its largest dimension). The great majority of space applications, such as radio communications, eavesdropping, and electromagnetic remote sensing, require the use on board spacecraft of antennas with a very high gain and a very high resolution. This is why, at present, space applications use antennas with a very large reflector (having a diameter of the order of 12 to 15 meters).
However, producing antennas with a diameter greater than 15 meters gives rise to numerous technical and practical problems, in particular stowage in the nose-cone of the launch vehicle, deployment from the spacecraft in orbit, and various mechanical and electrical constraints associated with objects in zero gravity and a vacuum, such as structural stiffness, mechanical strength, mechanical vibration, expansion and contraction.
One solution to these problems is to use “active” antennas with arrays of deployable radiating elements.
One such antenna, described in U.S. Pat. No. 5,430,451, is an array antenna for spacecraft including a plurality of sub-arrays connected together by a mechanism with joints. In this way, the antenna can occupy a folded configuration (referred to as the stacked configuration) during launch of the spacecraft and a flat, unfolded configuration (referred to as the unstacked configuration) after the spacecraft is launched.
However, establishing coherence of the signals from the sub-arrays does not take account of mechanical deformation relative to each other of the panels supporting the sub-arrays.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to eliminate the drawbacks previously cited. The invention has the particular object of providing a simple way to obtain a wide active array antenna comprising a plurality of deployable sub-arrays of radiating elements.
To this end, the invention provides a beam forming network adapted to cooperate with an active array antenna of a spacecraft, the antenna including:
a plurality of sub-arrays of radiating elements, and
a plurality of support panels for supporting respective sub-arrays, which panels are able to move from a folded configuration in which the panels at least partially overlap to a deployed configuration in which the panels are substantially coplanar,
said beam forming network including means for establishing the coherence of respective signals received by the plurality of sub-arrays by weighted summation of said signals as a function of the expected angle of incidence (&thgr;) on the sub-arrays of the respective signals and the expected relative phase-shifts due to signal propagation time-delays between the sub-arrays, and said beam forming network further comprising means for estimating information representative of a deformation (&agr;) of the relative positions of the panels compared to an expected predetermined configuration, and said summation of said signals is also effected as a function of said information representative of deformation.
Establishing coherence of the signals received by the sub-arrays entails weighted summation of the signals. The weighting applied to each signal is calculated as a function of the required angle of incidence of the signal
Caille Gerard
Gayrard Jean-Didier
Martin Laurent
Alcatel
Blum Theodore M.
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