Multibeam satellite communication antenna

• US 6,204,822 B1
• Filed: 05/20/1999
• Issued: 03/20/2001
• Est. Priority Date: 05/20/1998
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Cardiasmenos, Apostle G., Monk, Anthony D., Rhoades, Luther E., Sangiolo, John
• Primary Examiner(s): LE, HOANGANH T
• Application Number:
  US09/315,864
• Time in Patent Office: 670 Days
• Field of Search: H01/Q.312, 343/761, 343/757, 343/758, 343/766, 343/763, 343/764, 343/765, 343/781.P, 343/781.CA, 343/782, 343/839
• US Class Current: 343/761
• CPC Class Codes: H01Q 25/007 using two or more primary active elements in the focal region of a focusing device for operation on different wavebands H01Q5/22
• CPC Class Codes: H01Q 3/18 wherein the primary active element is movable and the reflecting device is fixed
• CPC Class Codes: H01Q 5/55 for horn or waveguide antennas

Abstract

A low-cost spherical reflector and a mechanically scanned antenna system utilizing such reflectors. The system employs one or more (substantially similar) primary spherical reflectors (each a truncated spherical surface), each having an associated moveable feed driven by a two-axis positioner mechanism that has few moving parts. The feed structure may preferably comprise a point source waveguide feed in combination with a shaped concave secondary reflector used in a Gregorian-like configuration to correct for spherical phase error. The positioner mechanism moves the waveguide feed and secondary reflector in tandem to shift the position of the far field beam direction in the sky. After phase correction by the secondary reflector, the resultant signal reflected from the primary aperture can simultaneously transmit and receive at two or more independent frequencies. With an assembly of multiple such spherical reflectors, each having a moveable feed driven by its own positioner mechanism, a compact arrangement is achieved. The assembly is mounted on a circular baseplate and preferably is covered by a radome.

Claims

1. An antenna system comprising:

at least a first antenna assembly each antenna assembly having a spherically-contoured primary reflector having a radius of curvature and a reflective surface toward the inside of the sphere; and

a feed assembly comprising;

(1) a spherical-aberration-correcting secondary reflector, and

(2) a feed element;

wherein the secondary reflector and feed element are placed such that their principal axes of symmetry are co-linear and lie upon a line passing through the center of a sphere corresponding to the spherical contour of the primary reflector, and the center of the secondary reflector; and

wherein the secondary reflector is positioned and shaped such that all possible ray paths starting from the feed and traveling to the secondary reflector from which they are reflected to the primary reflector become substantially the same lengths, such that a point source radiator illuminating the secondary reflector and therefrom the primary reflector produces a collimated quasi-plane wave.

2. The antenna system of claim 1, wherein the collimated quasi-plane wave is a TEM wave.

3. The antenna system of claim 1, wherein the feed radiates polarized radiation.

4. The antenna system of claim 1, wherein the feed is a point source dual frequency feed.

5. The antenna system of claim 4, wherein the feed radiates polarized radiation at both of said dual frequencies.

6. The antenna system of any of claims 3 or 5, wherein the polarization is either linear or circular.

7. The antenna system of claim 1, wherein the secondary reflector and the feed direct radiation towards said primary reflector surface parallel to any allowable Poynting vectors to illuminate the primary reflector for transmitting radiation or to receive radiation.

8. The antenna system of claim 1, further comprising

a positioner mechanism to position the feed assembly to transmit radiation to and receive radiation from a desired direction.

9. The antenna system of claim 8 wherein the primary reflector is mounted in a fixed position and the positioner mechanism supports and moves the feed assembly about an azimuthal bearing and an elevation bearing to provide azimuthal and elevational rotation of the feed assembly relative to the primary reflector to rotate and position the feed assembly such that radiation from the feed can be pointed to all directions in the set of allowable Poynting vector directions.

10. The antenna system of claim 9 further including

a support structure for supporting the positioner mechanism;

a transmitter waveguide routed along the support structure to the azimuthal bearing;

a first rotary waveguide joint attached to the support structure and having an input connected to the transmitter waveguide at the azimuthal bearing and having an axis and an output which rotate in the azimuthal plane;

a second rotary waveguide joint having an input and an output rotatable about the input in the elevational plane;

a connecting waveguide member having a first end connected to the output of the first rotary joint and a second end connected to the input of the second rotary joint;

a first motorized drive connected to and operable to effect rotation of the connecting waveguide member in the azimuthal plane;

the feed assembly connected to the output of the second rotary joint; and

a second motorized drive connected to and operable to effect rotation of the feed assembly in the elevational direction.

11. The antenna system of claim 10, further including a control computer operable to control the drive mechanisms to point the feed assembly so as to achieve a Poynting vector for radiation from the feed along any of the allowed Poynting vector directions.

12. The antenna system of claim 1, wherein the surface of the primary reflector spans less than a hemisphere.

13. The antenna system of claim 1 having at least two co-located antenna assemblies, wherein the system provides at least two simultaneous and independent transmitter or receiver, or transmitter and receiver, beams.

14. The antenna system of claim 13 wherein the beams together can point to substantially all possible directions in a hemisphere above a predetermined minimum elevation angle with respect to local horizon.

15. The antenna system of claim 14 including three co-located antennas and wherein the beams provided thereby together can point to all possible directions in the hemisphere above an elevation angle of about 15 degrees with respect to the horizon.

16. The antenna system of any of claims 1-15 further including interconnection and control circuits for switching between and controlling use of the apertures provided by the primary reflectors as satellites traverse the sky.

17. The antenna system of any of claims 1-15 further including a radome covering the antennas.

18. An antenna system comprising:

a plurality of spherically-contoured reflectors, each having a radius of curvature and an aperture of a size and a shape; and

exactly one electro-mechanically scannable feed per reflector, each having an azimuthal angle scan range and an elevational angle scan range;

wherein the radius of curvature of the reflectors and the aperture size of the reflectors are individually configured to

(1) achieve a desired gain and communications link margin, and

(2) cover the entire elevation and azimuthal angle scan ranges of the feeds, such that any Poynting vectors directed between a feed and a corresponding satellite in the sky is not obstructed by any portion of the reflector.