Multiple beam antenna system and method

• US 6,018,316 A
• Filed: 05/21/1997
• Issued: 01/25/2000
• Est. Priority Date: 01/24/1997
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: AIL Systems, Inc. (L3Harris Technologies, Inc.)
• Inventors: Rudish, Ronald M., McVeigh, Peter J., Levy, Joseph S.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US08/861,358
• Time in Patent Office: 979 Days
• Field of Search: 342/363, 342/366, 342/368, 342/361, 342/81, 342/154, 342/354
• US Class Current: 342/361
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 25/008 lens fed multibeam arrays

Abstract

A satellite based signal transmission and reception system which generates multiple beams with low side lobes and minimal crossover losses. The system includes a focusing device and an array of signal generator elements coupled to feed radiator elements. The feed radiator elements are assigned into overlapping beam sub-arrays characterized by a frequency and radiated beam polarization. Each overlapping sub-array generates a transmission beam signal which is orthogonally polarized with respect to the beam generated by the other overlapping sub-array. The use of beam orthogonality provides for physically overlapping beam sub-arrays without the use of analog combining networks which are inherently lossy structures. This allows beams to be generated having a highly tapered amplitude distribution to simultaneously achieve low side lobe levels and low beam cross over losses. By employing multiple signal generators driving the transmission elements of the beam sub-arrays, the transmission system is able to step the transmit signals along the feed radiator array to compensate for satellite motion without the use of complex RF switching networks. In an analogous fashion, antenna elements in an array receive multiple transmission beam signals which are incident upon a focusing device. The antenna elements are dynamically assigned to overlapping receive beam sub-arrays which are orthogonally polarized. The multiple beam receiving system is able to step the received signal sub-arrays along the array to compensate for satellite motion.

Claims

1. An array antenna for forming multiple, overlapping, transmission beam signals in response to transmission signals from an external signal source, the array antenna comprising:

a plurality of overlapping beam subarrays, each subarray comprising;

a plurality of antenna feed radiators, each antenna feed radiator having a first signal input, a second signal input and a radiator aperture, each antenna feed radiator radiating a first signal applied to the first signal input with a first polarization and radiating a second signal applied to the second signal input with a second polarization, the second polarization being orthogonal to the first polarization, whereby each antenna feed radiator can support two radiating signals from a common radiator aperture to allow orthogonally polarized subarrays to overlap; and

beam focusing means, the beam focusing means receiving the radiated signals from the plurality of antenna feed radiators and inducing required focal properties to the signals to establish a plurality of shaped transmission beam signals.

2. A multiple beam array antenna, as defined by claim 1, wherein the beam focusing means comprises a lens.

3. A multiple beam array antenna, as defined by claim 1, wherein each of the plurality of antenna feed radiators comprises a waveguide, the waveguide comprising:

a substantially hollow conductive body having a first end, a second end and a substantially square interior cross-section, the first and second ends defining a length; and

an electrically conductive partition, the partition substantially bisecting the interior cross-section of the waveguide body along a portion of the length from a point proximate to the first end, whereby the first end comprises first and second rectangular waveguide sections and the second end comprises a square waveguide section, the first and second rectangular waveguide sections corresponding to the first and second signal inputs, the second end corresponding to the radiator aperture.

4. A multiple beam array antenna, as defined by claim 2, wherein the lens is formed with astigmatism to achieve the required focal properties.

5. A multiple beam array antenna, as defined by claim 4, wherein the required focal properties imparted by the lens astigmatism provide for a substantially circular beam projected in a nadir direction and progressively compressed elliptically shaped beams for those beams projected off the nadir direction.

6. A multiple beam array antenna, as defined by claim 2, wherein the lens is symmetrical and the antenna feed radiators are selectively positioned with respect to the lens to establish the plurality of shaped transmission beam signals.

7. A multiple beam array antenna, as defined in claim 2, wherein the lens is spherically symmetrical and the antenna feed radiators are selectively grouped in sub-arrays sized and shaped to achieve a substantially circular beam projected in a nadir direction and progressively compressed elliptically shaped beams for those beams off the nadir direction.

8. A multiple beam transmission system for generating a plurality of overlapping transmission beam signals, the system comprising:

a digital processor;

a plurality of antenna feed radiators, each antenna feed radiator having a first signal input, a second signal input and a radiator aperture, each antenna feed radiator radiating a first signal applied to the first signal input with a first polarization and radiating a second signal applied to the second signal input with a second polarization, the second polarization being orthogonal to the first polarization, whereby each antenna feed radiator can support two radiating signals from a common radiator aperture;

a plurality of signal generators, each signal generator having an output terminal, the output terminal being electrically coupled to at least one of the plurality of antenna feed radiator signal inputs, the signal generators being responsive to the digital processor and generating transmit beam signals in response thereto; and

beam focusing means, the beam focusing means receiving the radiated signals from the plurality of antenna feed radiators and inducing required focal properties to the signals to establish a plurality of transmission beams.

9. A multiple beam transmission system, as defined by claim 8, wherein each of the plurality of signal generators comprises a direct digital synthesizer.

10. A multiple beam transmission system, as defined by claim 9, wherein the first signal input of each antenna feed radiator is operatively coupled to a corresponding first direct digital synthesizer and the second signal input of each antenna feed radiator is operatively coupled to a corresponding second direct digital synthesizer.

11. A multiple beam transmission system, as defined by claim 8, wherein the beam focusing means comprises a lens.

12. A multiple beam transmission system, as defined by claim 11, wherein the lens is formed with astigmatism to achieve the required focal properties.

13. A multiple beam transmission system, as defined by claim 12, wherein the required focal properties imparted by the lens astigmatism provide for a substantially circular beam projected in a nadir direction and progressively compressed elliptically shaped beams for those beams projected off the nadir direction.

14. A multiple beam transmission system, as defined by claim 8, wherein each of the plurality of antenna feed radiators comprises a waveguide, the waveguide comprising:

a substantially hollow conductive body having a first end, a second end and a substantially square interior cross-section, the first and second ends defining a length; and

an electrically conductive partition, the partition substantially bisecting the interior cross-section of the waveguide body along a portion of the length from a point proximate to the first end, whereby the first end comprises first and second rectangular waveguide sections and the second end comprises a square waveguide section, the first and second rectangular waveguide sections corresponding to the first and second signal inputs, the second end corresponding to the radiator aperture.

15. A multiple beam transmission system, as defined by claim 11, wherein the lens is symmetrical and the antenna feed radiators are selectively positioned with respect to the lens to achieve a required shape for each of the plurality of transmission beams.

16. A multiple beam transmission system, as defined by claim 11, wherein the lens is spherically symmetrical and the antenna feed radiators are selectively grouped in sub-arrays sized and shaped to achieve a required shape for each of the plurality of transmission beams.

17. A multiple beam transmission system, as defined by claim 8, wherein the plurality of signal generators further comprise:

a plurality of beam generators, each beam generator generating a digital signal representative of one of a plurality of transmission beam signals;

a digital switch matrix, the digital switch matrix being responsive to the digital signal from each of the plurality of beam generators and routing each digital signal to at least one of a plurality of beam signal outputs; and

a plurality of conversion means, each of the plurality of conversion means being operatively coupled to one of the plurality of beam signal outputs, the conversion means converting each digital signal to an analog transmit beam signal.

18. A multiple beam transmission system, as defined by claim 8, wherein each of the plurality of antenna feed radiators is operatively coupled to first and second conversion means, the first conversion means providing the first signal, the second conversion means providing the second signal.

19. A multiple beam transmission system, as defined by claim 17, wherein the system includes one beam generator for each of the plurality of transmission beams.

20. A multiple beam transmission system, as defined by claim 17, wherein each beam generator further comprises:

a phase accumulator, the phase accumulator generating an address signal; and

a sine read only memory (ROM), the sine ROM being responsive to the address signal and generating the digital signal.

21. A method of generating overlapping transmission beams in an array of transmission elements with low crossover loss and high side-lobe suppression, the method comprising the steps:

a) generating a first beam from a sub-array of transmission elements, the first beam having a first polarization; and

b) generating a second beam from a second sub-array of transmission elements, the first and second sub-arrays sharing at least one transmission element, the second beam having a second polarization which is orthogonal to the first polarization.

22. A method of stepping multiple transmit signals to a sequence of beams generated in a non-geosynchronous satellite based signal transmission array and projected onto a target, the transmission array having a plurality of antenna feed radiators, the method comprising the steps of:

a) assigning frequency and polarization characteristics of each transmit signal to the antenna feed radiators to establish a plurality of overlapping beam sub-arrrays which generate a plurality of transmission beams; and

b) reassigning the frequency characteristics of the antenna feed radiators to reposition the transmit signals to different beam sub-arrays, the repositioned transmit signal characteristics being re-located on the array to compensate for satellite motion such that the plurality of transmission beams provide substantially stationary target illumination for an extended time period.

23. An array antenna for receiving multiple, overlapping, transmission beam signals, the array antenna comprising:

a plurality of overlapping beam sub-arrays, each sub-array comprising;

a plurality of antenna feed elements, each antenna feed element having a first signal output, a second signal output and an antenna aperture, each antenna aperture responsive to a first signal applied with a first polarization and a second signal applied with a second polarization, the second polarization being orthogonal to the first polarization, whereby each antenna feed element can receive two overlapping, transmission beam signals with a common antenna aperture; and

beam focusing means, the beam focusing means receiving the transmission beam signals and inducing required focal properties to direct the transmission beam signals onto a selected plurality of antenna feed elements forming the beam sub-arrays.

24. A multiple beam array antenna, as defined by claim 23, wherein the beam focusing means comprises a lens.

25. A multiple beam array antenna, as defined by claim 23, wherein each of the plurality of antenna feed radiators comprises a waveguide, the waveguide comprising:

a substantially hollow conductive body having a first end, a second end and a substantially square interior cross-section, the first and second ends defining a length; and

an electrically conductive partition, the partition substantially bisecting the interior cross-section of the waveguide body along a portion of the length from a point proximate to the first end, whereby the first end comprises first and second rectangular waveguide sections and the second end comprises a square waveguide section, the first and second rectangular waveguide sections corresponding to the first and second signal inputs, the second end corresponding to the antenna aperture.

26. A multiple beam array antenna, as defined by claim 24, wherein the lens is formed with astigmatism to achieve the required focal properties.

27. A multiple beam array antenna, as defined by claim 26, wherein the required focal properties imparted by the lens astigmatism provide for reception of substantially circular beams incident on the lens in a nadir direction and progressively compressed elliptically shaped beams incident on the lens off the nadir direction.

28. A multiple beam array antenna, as defined by claim 24, wherein the lens is symmetrical and the antenna feed elements are selectively positioned with respect to the lens to achieve focusing required for each received transmission beam signal.

29. A multiple beam array antenna, as defined in claim 24, wherein the lens is spherically symmetrical and the antenna feed elements are selectively grouped in sub-arrays sized and shaped to receive substantially circular beams incident on the lens from a nadir direction and progressively compressed elliptically shaped beams for those beams incident on the lens off the nadir direction.

30. A multiple beam antenna system for receiving a plurality of overlapping transmission beam signals, the system comprising:

a digital processor;

a plurality of antenna feed elements, each antenna feed element having a first signal output, a second signal output and an antenna aperture, each antenna feed element being responsive to a first transmission beam signal applied to the antenna aperture with a first polarization and a second transmission beam signal applied to the antenna aperture with a second polarization, the second polarization being orthogonal to the first polarization, whereby each antenna feed element can receive two overlapping transmission beam signals from a common antenna aperture;

a plurality of signal receivers, each signal receiver having an input terminal, the input terminal being electrically coupled to at least one of the plurality of antenna feed clement signal outputs, the signal receivers providing signals to the digital processor in response thereto; and

beam focusing means, the beam focusing means responsive to the transmission beam signals incident upon the beam focusing means and inducing required focal properties in the transmission beam signals to direct the transmission beam signals onto a selected plurality of antenna feed elements forming beam sub-arrays.

31. A multiple beam antenna system, as defined by claim 30, wherein the beam focusing means comprises a lens.

32. A multiple beam antenna system, as defined by claim 31, wherein the lens is formed with astigmatism to achieve the required focal properties for each transmission beam signal.

33. A multiple beam antenna system, as defined by claim 32, wherein the required focal properties imparted by the lens astigmatism provide for reception of a substantially circular beam incident upon the lens in a nadir direction and progressively compressed elliptically shaped beams for those beams incident upon the lens off the nadir direction.

34. A multiple beam antenna system, as defined by claim 30, wherein each of the plurality of antenna feed elements comprises a waveguide, the waveguide comprising:

a substantially hollow conductive body having a first end, a second end and a substantially square interior cross-section, the first and second ends defining a length; and

an electrically conductive partition, the partition substantially bisecting the interior cross-section of the waveguide body along a portion of the length from a point proximate to the first end, whereby the first end comprises first and second rectangular waveguide sections and the second end comprises a square waveguide section, the first and second rectangular waveguide sections corresponding to the first and second signal inputs, the second end corresponding to the antenna aperture.

35. A multiple beam antenna system, as defined by claim 31, wherein the lens is symmetrical and the antenna feed elements are selectively positioned with respect to the lens to receive and focus transmission beams incident upon the lens from a plurality of angles.

36. A multiple beam antenna system, as defined by claim 31, wherein the lens is spherically symmetrical and the antenna feed elements are selectively grouped in sub-arrays sized and shaped to achieve the required focal properties.

37. A multiple beam antenna system, as defined by claim 30, wherein the plurality of signal receivers further comprise:

a plurality of analog to digital (A/D) converters, each analog to digital converter being responsive to one of the first and second transmission beam signals from one of the plurality of antenna feed elements, each A/D converter providing a digital receive signal to the digital processor; and

wherein the digital processor is a digital beam forming processor which mathematically combines the digital receive signals received from a select plurality of AID converters to form received beam sub-arrays.

38. A method of receiving multiple, overlapping transmission beams in an array of antenna elements, the method comprising the steps:

a) receiving a first transmission beam from a sub-array of antenna elements, the first beam having a first polarization; and

b) receiving a second transmission beam from a second sub-array of antenna elements, the first and second sub-arrays sharing at least one of the plurality of antenna feed elements, the second beam having a second polarization which is orthogonal to the first polarization.

39. A method of receiving multiple transmission beam signals in a non-geosynchronous satellite based signal reception array, the reception array having a plurality of antenna feed elements, the method comprising the steps of:

a) assigning frequency and polarization characteristics to each antenna feed element to establish a plurality of overlapping beam sub-arrays which receive a plurality of transmission beams, and

b) reassigning the frequency characteristics of the antenna feed elements to reposition the beam sub-arrays, the repositioned sub-arrays being relocated on the array to compensate for satellite motion such that the plurality of transmission beams are received for an extended time period.