Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-03-16
2001-03-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S772000, C343S775000, C343S7810CA
Reexamination Certificate
active
06208309
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to horn antennas, and, more particularly, to horn antennas capable of operating at two or more separate frequencies and capable of providing equalized E and H plane patterns at each of the frequencies.
In the communication field, a number of systems exist which require antenna systems to be capable of operating at two or more separate frequencies. For example, in military and commercial satellite systems, it is common for the uplink signal from a ground station to the satellite to have a first frequency while the downlink signal from the satellite to the ground station has a second frequency. Commercial and military Ka-Band communication satellites are one example of this where the uplink frequency is 20 GHz and the downlink frequency is 30 GHz.
In the past, communication satellite systems such as those mentioned above have handled the two frequencies by using reflector antenna systems in the satellite which are designed with an antenna feed (for example, a feed horn) and a reflector system (generally using a primary reflector and a sub-reflector). In such an arrangement, separate horn antennas are often used as the feeds, with one horn antenna provided for each frequency to be covered. On the other hand, various systems have been developed using a single horn operating at dual frequencies. U.S. Pat. No. 3,938,159, U.S. Pat. No. 4,785,306 and U.S. Pat. No. 5,003,321 are three examples of such dual frequency feed horns that can be used in a satellite communication system. However, these arrangements are somewhat complicated to construct, and are not readily adaptable to equalizing the E and the H plane patterns at the different frequencies.
In their studies, the inventors considered the possibility of using a corrugated horn operating at two or more separate frequencies such as the above-noted 20 GHz and 30 GHz frequencies in the Ka-Band. Corrugated horns (i.e., horns where corrugated recesses are provided which each have a depth extending radially to the central axis of the horn) have an advantage in being able to readily provide antenna patterns that are equal in the E and H planes by effectively terminating substantially all of the current parallel to the inner wall of the horn (so that the horn will have the same boundary conditions that exist for the E field perpendicular to the wall). To this end, the inventors designed and studied a corrugated horn such as shown in FIG.
1
.
In the arrangement shown in
FIG. 1
, a corrugated horn
10
has a plurality of corrugated recesses
12
that gradually increase in depth and width from an inner portion of the horn to an outer portion. By virtue of the different depths, the center frequency of each of the recesses
12
will be slightly different than that of the adjacent recess
12
. Typically, the depth is set at &lgr;/4 to tune to the desired frequency. The width of each corrugation recess
12
determines the bandwidth of that particular recess around the center frequency. Thus, by properly designing the depth and the width of each of the recesses
12
, the horn of
FIG. 1
can provide continuous coverage of a desired frequency band. Also, by properly setting the depth and width of the corrugation recesses, equalized E and H plane patterns can be provided within that frequency band, as noted above.
In further considering this structure, the inventors studied the possibility of providing two or more groups of corrugation recesses
12
in a horn such as
FIG. 1
, to thereby construct a horn which would operate at two distinct frequency bands (e.g., centered around 20 GHz and 30 GHz, for example), while providing equalized E and H plane patterns at each of these separate frequency bands. However, after considering this, the inventors noted a fundamental problem which would exist with such an arrangement. Specifically, as shown in
FIG. 1
, the electrical aperture of the corrugated horn
10
would be limited to the inner diameter of the horn. Because of the corrugation recess construction, this inner diameter will be substantially smaller than the actual maximum physical diameter of the horn. In other words, the corrugated horn
10
of
FIG. 1
has a significantly larger physical aperture than its electrical aperture. This can be a serious drawback, particularly in terms of size and weight considerations which are involved in construction of a satellite antenna. Also, the relatively large physical diameter of such a horn could serve as a significant constraint in reflector systems used in satellites wherein a plurality of feed horns might be located adjacent to one another to provide multiple coverage beams from a single reflector system.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a horn capable of operating at two or more separate frequencies.
It is a further object of the present invention to provide a horn antenna capable of operating at two or more separate frequencies while providing substantially equalized E and H plane patterns at each of the different frequencies.
It is a further object of the present invention to provide an antenna horn capable of operating at two or more separate frequencies and providing substantially equalized E and H plane patterns, wherein the electrical aperture of the horn is close in size to the physical aperture.
It is a further object of the present invention to provide a horn antenna capable of operating at two or more frequencies which is easy to construct, compact in size and capable of providing equal E and H plane patterns at multiple separate frequencies.
To achieve this and other objects, a horn antenna is provided which is capable of operating at a plurality of separate frequencies, and which includes a coupling portion to permit coupling of the horn antenna to a communication device. An inner portion is coupled to the coupling portion, and includes a first choke having a depth which extends substantially parallel to a central longitudinal axis of the antenna and a width which extends in a radial direction of the antenna. The depth and the width of the first choke are set so that the first choke will operate at the first frequency. An outer portion is coupled to the inner portion, wherein the outer portion has a maximum diameter in the radial direction which is greater than the maximum diameter in the radial direction of the inner portion. The outer portion comprises a second choke which also has a depth to extend substantially parallel to the central longitudinal axis of the antenna, and a width which extends in the radial direction.
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patent: 3924237 (1975-12-01), Fletcher et al.
patent: 3938159 (1976-02-01), Ajioka et al.
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patent: 4442437 (1984-04-01), Chu et al.
patent: 4477816 (1984-10-01), Cho
patent: 4658258 (1987-04-01), Cook
patent: 4680558 (1987-07-01), Ghosh et al.
patent: 4785306 (1988-11-01), Adams
patent: 4847574 (1989-07-01), Gauthier et al.
patent: 5003321 (1991-03-01), Smith et al.
patent: 5258768 (1993-11-01), Smith
patent: 5486839 (1996-01-01), Rodeffer et al.
patent: 5546097 (1996-08-01), Ramanujam et al.
patent: 5552797 (1996-09-01), Cook
patent: 5812096 (1998-09-01), Tilford
patent: 144319 (1981-11-01), None
Chandler Charles W.
Em Makkalon
Nguyen Hoang
TRW Inc.
Wong Don
Yatsko Michael S.
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