Communications: radio wave antennas – Antennas – With polarization filter or converter
Reexamination Certificate
1999-09-10
2001-09-04
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With polarization filter or converter
C343S909000
Reexamination Certificate
active
06285332
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to reflectors for use in electromagnetic antenna systems, and, more particularly, to reflectors capable of reflecting electromagnetic signals having two or more frequencies.
In the communication field, a number of systems exist which require antenna systems to be capable of operating at two or more frequencies. For example, in military and commercial satellites 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 satellites systems such as those mentioned above have handled the two frequencies by using reflector antenna systems in the satellites which are designed with an antenna feed (for example, a feed horn) and a reflector system (generally using a concave primary reflector and a sub-reflector). One technique in such systems has been to provide two antenna feeds with each one designed to shape the beam so that the uplink receiving beam of the satellite (for example, at 30 GHz) will have substantially the same beam width as the downlink transmitted beam from the satellite (e.g., at 20 GHz). Designing the feeds for this purpose is difficult, and they are sometimes not realizable within the practical constraints of the satellite environment. An alternative approach is to use a separate reflector for each frequency. This, of course, is not advantageous in a satellite system, given the limitations of size and weight which must be considered.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an improved reflector for an electromagnetic antenna system which is capable of reflecting two or more frequencies having substantial equal beam widths.
It is a further object of the present invention to provide such an improved reflector system without requiring specialized feed design and without requiring separate reflectors for each of the frequencies.
It is a further object of the present invention to provide an improved reflector for use in a satellite communication system which permits a single reflector to receive the uplink signal at one frequency and to transmit the downlink signal at a second frequency, wherein the beam widths of the receiving pattern for the uplink signal and the transmitting pattern for the downlink signal are substantially the same, and wherein these patterns overlap one another.
To achieve these and other objects in accordance with one aspect of the present invention, a frequency selective reflector is provided for receiving and reflecting electromagnetic waves, including an inner reflector portion and an outer reflector portion. The inner portion has a reflector surface which reflects electromagnetic waves having first and second frequencies. The outer portion reflector has a surface which will constructively reflect electromagnetic waves having the first frequency but will non-constructively reflect electromagnetic waves having the second frequency.
In accordance with another aspect of the present invention, a frequency selective reflector is provided having an inner portion which reflects electromagnetic waves having first and second frequencies, and an outer diffraction portion which diffracts electromagnetic waves having the first frequency in a direction to align them with the electromagnetic waves of the first frequency reflected from the inner portion, and which diverts electromagnetic waves of the second frequency in a direction different from the direction of the electromagnetic waves of the second frequency reflected from the inner portion.
REFERENCES:
patent: 4544928 (1985-10-01), Afifi et al.
patent: 5283591 (1994-02-01), Delmas
patent: 5606335 (1997-02-01), English et al.
patent: 5861860 (1999-01-01), Stanek et al.
Alemu Ephrem
Keller Robert W.
TRW Inc.
Wong Don
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