Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2001-03-01
2002-11-12
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S761000, C343S762000, C343S776000, C343S786000, C343SDIG002
Reexamination Certificate
active
06480165
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an antenna for establishing communication with multiple transmitting and receiving sources, such as satellites. More particularly, the multibeam antenna of the present invention relates to an antenna for establishing communication with satellites which are located at geostationary positions that are in close angular proximity to each other.
BACKGROUND OF THE INVENTION
In recent years, there has been a significant increase in the amount and types of information that is transmitted via satellite communication. For instance, satellites now transmit telephone signals, television signals, and Internet data, etc. Due to the expanded use of satellites for data communication, there has also been an associated increase in the number of satellites placed in orbit about the earth. For instance, there are currently satellites that are dedicated to transmission of not only television signals in general, but are dedicated to transmission of only certain types of programming, such as movie channels, foreign language channels, local channel programming, or high definition television signals. Further, satellites have been deployed for Internet communication.
Due to the increasing amount of information and services that are offered via satellite communication, there exists a current need for an integrated antenna that can transmit and receive signals to and from different satellites each located at different geostationary positions, such that a user is not required to use multiple antennas. This, however, presents an increasing problem with the introduction of additional satellites into orbit for different types of data communication. As more satellites are introduced into orbit, the angular spacing between the satellites will decrease. In fact, currently there are several satellites that are positioned within a range of 5 degrees or less of arc with respect to each other. The proximity of these satellites to each other is somewhat problematic from the standpoint of using one antenna to establish individual communication links with both of these satellites.
Specifically, to communicate with multiple satellites, an antenna will typically include individual antenna elements, referred to as feeds or more generally, wave-guides, where each feed is dedicated to communicating with one of the satellites. Because of the closeness in angular proximity of some satellites, these wave-guides should be placed in close proximity to each other on the antenna to properly communicate with their respective satellites. The problem is that many conventional corrugated wave-guide designs cannot be used, because of the reduced spacing required between the phase centers of the wave-guides needed to receive from and transmit signals to the satellites is such that the conventional individual wave-guides would occupy overlapping space due to their size.
This problem is more clearly illustrated with reference to
FIGS. 1A and 1B
.
FIG. 1A
illustrates a typical satellite system
10
having two satellites,
12
and
14
, located at geostationary positions that are a particular arc distance
16
apart. The satellite system further includes either one or a plurality of ground-based antennas,
18
-
22
, for communication with these satellites. In particular, each of the ground-based antennas typically includes a reflector
22
directed toward the satellites. Each of the antennas also includes respective individual wave-guides,
24
and
26
, for establishing communication links with the individual satellites. The wave-guides are positioned with respect to the reflector so that signals
28
received from the satellite associated with the wave-guides are directed by the reflector to the wave-guides and signals from the wave-guides are directed by the reflector to the associated satellite. As the wave-guides are positioned with respect to the reflector to receive signals from and transmit signals to their associated satellite, problems occur when the satellites with which the individual wave-guides respectively communicate are located in close angular proximity to each other.
Specifically,
FIG. 1B
shows two signals,
30
and
32
, respectively transmitted by two individual satellites to an antenna
34
. In this illustration, the reflector
36
of the antenna is directed at a first satellite, and the signals
30
from this satellite are reflected by the reflector to a focal point
38
in front of the reflector. Further, the signals
32
received from the second satellite are directed by the reflector to a second point
40
in front of the reflector. In this instance, the wave-guide
42
associated with the first satellite is located at the focal point
38
, and the wave-guide
44
associated with the second satellite is located at the second point
40
to thereby establish respective communication links with the satellites.
As can be seen, there is an offset distance
46
between the wave-guides. This offset distance is determined by the angular difference between the geostationary positions of the satellites. If the satellites are located at geostationary positions that are farther apart angularly, then there will be a larger offset distance
46
between the wave-guides. However, the closer the satellites are positioned with respect to each other, the smaller the offset distance
46
becomes. At some point, typically when the satellites are spaced apart by an angular distance of 5° or less, the offset distance between the wave-guides becomes sufficiently small, such that many conventional corrugated wave-guide designs cannot be used. Specifically, the spacing required between the phase centers of the wave-guides to properly receive and transmit signals to the satellites is such that the conventional individual wave-guides would occupy overlapping space due to their size.
To address this problem, an antenna system has been designed to allow for more closely spaced receive feeds, as described in U.S. Pat. No. 5,812,096 to Tilford. With reference to
FIG. 2
, this antenna system
50
includes a reflector
52
and a feed system in which two conventional receive feeds,
54
and
56
, have been modified such that they may be spaced a reduced distance apart. This feed configuration is referred to as a siamese feed, in which a section of the housing for each conventional feed has been cutaway so that the feeds may be spaced closer together. The siamese feed allows for reception of signals,
30
and
32
, from two closely spaced satellites.
Although the siamese feed of this antenna system allows for communication with closely spaced satellites, it does have some drawbacks. For example, first the siamese feed does not use standard wave-guides. Instead, the wave-guides must be modified by removing a portion of their housing. This, in turn, may increase manufacturing time and cost.
Further, the siamese feed system does not provide a solution for antennas that establish two-way communication with satellites. This is a significant limitation of the siamese feed system. Specifically, certain commercial systems employ one satellite used for Internet communication and in close proximity to this particular satellite is another satellite used for transmission of high definition television. Since the siamese feed system only includes receive wave-guides, and not a bidirectional wave-guide for two-way communication, it would not be suitable for this antenna application.
An added problem with placement of wave-guides in close proximity to each other, besides physical size limitations, not addressed by the siamese feed system is signal isolation concerns. Specifically, in applications in which the antenna is used in a two-way communication application, signals transmitted from a bi-directional wave-guide to a satellite are also broadcast to the area surrounding the wave-guide. If a second wave-guide is positioned in close proximity to communicate with another closely angular spaced satellite, the transmission signals from the first wave-guide may be received by the second wave-guid
Moheb Hamid
Robinson Colin Michael
Alston & Bird LLP
Prodelin Corporation
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