Antenna system with plural reflectors

• US 6,049,312 A
• Filed: 02/11/1998
• Issued: 04/11/2000
• Est. Priority Date: 02/11/1998
• Status: Expired due to Term

• Current Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Original Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Inventors: Lord, Peter, Barkeshli, Sina, Brydon, Louis B., Luh, Howard, Zaine, Jeff
• Primary Examiner(s): Le, Hoanganh
• Assistant Examiner(s): NGUYEN, HOANG V
• Application Number:
  US09/021,926
• Time in Patent Office: 790 Days
• Field of Search: 343/781 P, 343/754, 343/755, 343/757, 343/758, 343/765, 343/781 R, 343/761
• US Class Current: 343/781.00P
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 19/195 wherein a reflecting surface acts also as a polarisation filter or a polarising device
• CPC Class Codes: H01Q 5/45 using two or more feeds in association with a common reflecting, diffracting or refracting device

Abstract

An antenna system having a front reflector and a rear reflector arranged in tandem, a front feed for illuminating the front reflector, and a rear feed for illuminating the rear reflector. Each of the reflectors has a generally dish-shaped configuration, and the feeds are located in positions offset from axes of the respective reflectors. The front reflector is reflective to a first radiation, while being substantially transparent to a second radiation except for a fraction of the power of the second radiation. The fractional part of the second radiation is reflected from the first reflector as an interfering beam, the interfering beam being scanned away from a coverage region of a beam of the first radiation by an offset between the feeds. The radiations may differ in polarization or in frequency. There may be a complete shading of the rear reflector by the front reflector from the radiation of the rear feed to produce uniform illumination of the rear reflector for greater accuracy in a formation of a beam from the rear reflector. Six degrees of freedom in positioning and orientation of the reflectors and their feeds provides maximum design flexibility for obtaining a compact antenna.

Claims

1. An antenna system for producing a plurality of beams including a first beam and a second beam, comprising:

a first element, a second element, a first feed and a second feed; and

wherein said first element and said first feed are positioned for propagation of radiation between said first element and said first feed for formation of said first beam reflected by said first element;

said second element and said second feed are positioned on opposite sides of said first element for propagation of radiation between said second element and said second feed for formation of said second beam reflected by said second element, said positioning of said second element and said second feed on opposite sides of said first element resulting in a set of interfering beams comprising at least one interfering beam;

said first element is substantially transparent to radiation of said second feed for illuminating said second element with the radiation of said second feed while reflecting a portion of the power of the radiation of said second feed as said one interfering beam;

said first element and said first feed constitute a first subsystem providing said first beam of said antenna system, said second element and said second feed constitute a second subsystem providing said second beam of said antenna system; and

said antenna system includes means for positioning each of said subsystems with three degrees of freedom of translation and three degrees of freedom of rotation to enable placement of said subsystems relative to each other to minimize the size of the antenna system while enabling a scanning of said interfering beams away from areas of coverage of the beams of said subsystems; and

said second feed is angled from said first feed to direct said one interfering beam away from an area of coverage of said first beam.

2. An antenna system according to claim 1 wherein a magnitude of coverage of said first beam is equal to a magnitude of coverage of said second beam.

3. An antenna system according to claim 1 wherein a magnitude of coverage of said first beam differs from a magnitude of coverage of said second beam.

4. An antenna system according to claim 1 wherein said first element is a first reflector and said second element is a second reflector, said first reflector being equal in size to said second reflector.

5. An antenna system according to claim 1 wherein said first element is a first reflector and said second element is a second reflector, said first reflector differing in size from said second reflector.

6. An antenna system according to claim 1 wherein said first element is a first reflector and said second element is a second reflector, at least one of said reflectors having a parabolic reflecting surface.

7. An antenna system according to claim 1 wherein said first element is a first reflector and said second element is a second reflector, at least one of said reflectors having a reflecting surface which is shaped to provide a desired coverage beam.

8. An antenna system comprising:

a first element, a second element, a first feed and a second feed; and

wherein said first element and said first feed are positioned for propagation of radiation between said first element and said first feed for formation of a first beam directed in a forward direction of said first element;

said second element and said second feed are positioned on opposite sides of said first element for propagation of radiation between said second element and said second feed for formation of a second beam directed in a forward direction of said second element;

said first element is operative to reflect radiation of said first feed having a first characteristic and to transmit radiation of said second feed having a second characteristic different from said first characteristic, each of said first and said second characteristics being a polarization or a frequency;

said second element reflects radiation of said second feed;

said first element is substantially transparent to radiation of said second feed for illuminating said second element with the radiation of said second feed while reflecting a portion of the power of the radiation of said second feed as an interfering beam in a forward direction of said first element;

said antenna system includes means for positioning each of said subsystems with three degrees of freedom of translation and three degrees of freedom of rotation to enable placement of said subsystems relative to each other to minimize the size of the antenna system while enabling a scanning of said interfering beams away from areas of coverage of the beams of said subsystems; and

said second feed is angled from said first feed to direct said interfering beam away from an area of coverage of said first beam.

9. An antenna system according to claim 8 wherein:

said first element and said first feed constitute a first subsystem of said antenna system, said second element and said second feed constitute a second subsystem of said antenna system; and

said antenna system includes means for positioning each of said subsystems with three degrees of freedom of translation and three degrees of freedom of rotation to enable placement of said subsystems relative to each other to minimize the size of the antenna system.

10. An antenna system according to claim 9 wherein said positioning means allows for independent positioning and orientation of said first subsystem relative to said second subsystem for scanning said interfering beam away from the area of coverage of said first beam while minimizing the size of the antenna system.

11. An antenna system according to claim 10 wherein said positioning means comprises a support which allows independent positioning and orientation of said first feed relative to said second feed.

12. An antenna system according to claim 8 wherein:

said first element casts a shadow upon said second element with respect to illumination of said second element by said second feed, said shadow constituting a reduction in the intensity of said radiation of said second feed; and

said first element extends in a direction transverse to rays of radiation of said second feed to enclose completely said second element within said shadow, thereby to attain a uniform illumination of said second element with radiation of said second feed.

13. An antenna system according to claim 8 wherein said first element comprises a grid of spaced-apart, parallel, linear, electrically conductive elements.

14. An antenna system according to claim 8 wherein said first element comprises a frequency selective surface.

15. An antenna system according to claim 8 wherein said first element comprises a grid of spaced-apart, parallel, linear, electrically conductive elements;

and

said first characteristic is vertical polarization and said second characteristic is horizontal polarization.

16. An antenna system according to claim 8 wherein said first element comprises a frequency selective surface;

and

said first characteristic is a first frequency and said second characteristic is a second frequency.