Shrouded horn feed assembly

• US 5,793,334 A
• Filed: 08/14/1996
• Issued: 08/11/1998
• Est. Priority Date: 08/14/1996
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Baird, Joseph Mark, Anderson, Bryant Ford, Gartside, Paul Johann, Harrison, Douglas Melville
• Primary Examiner(s): Le, Hoanganh T.
• Assistant Examiner(s): Ho, Tan
• Application Number:
  US08/698,234
• Time in Patent Office: 727 Days
• Field of Search: 343/766, 343/772, 343/776, 343/785, 343/786, 333/21 A, 333/126, 333/106, 333/108, 333/135
• US Class Current: 343/786
• CPC Class Codes: H01Q 13/02 Waveguide horns
• CPC Class Codes: H01Q 19/08 for modifying the radiation pattern of a radiating horn in which it is located corrugated horns H01Q13/0208; producing a circular polarisation H01Q13/0241
• CPC Class Codes: H01Q 25/04 Multimode antennas corrugated horns H01Q13/0208
• CPC Class Codes: H01Q 5/47 with a coaxial arrangement of the feeds

Abstract

A feed system for an antenna has a set of inner and outer coaxial waveguides which apply, respectively, both higher and lower frequency radiations to a common radiating aperture provided by a horn and shroud which envelops radiating apertures of the individual feed waveguides. Each of the feed waveguides carries signals having a bandwidth of an octave. Lower frequency radiation to be transmitted by the outer coaxial feed waveguide is applied thereto by a set of four waveguides of a launcher which launches a wave with a desired propagation mode into the outer feed waveguide. Each of the launch waveguides is initially a rectangular double-ridged waveguide for increase bandwidth. The ridging is reduced to a condition of no ridging in the outer feed waveguide by a transition to a single inner ridge which terminates in a tapered star-shaped combination ridge within the outer feed waveguide. Impedance matching rings are slidable within the space between the inner and outer surfaces of the coaxial waveguide for development of a desired standing wave ratio for accurate generation of a desired beam pattern. A dielectric rod is disposed in a forward end of the tube of the inner feed waveguide and protrudes therefrom into the horn for shaping a beam of the higher frequency radiation. A single common phase center is provided for all bands with radiation simultaneously at plural bands.

Claims

1. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam; and

wherein a radiating aperture of said outer feed waveguide is an annulus, said inner feed waveguide carrying a larger spectral band of electromagnetic signals than a spectral band carried by said outer feed waveguide.

2. A system according to claim 1 further comprising an impedance matching ring disposed in said outer feed waveguide.

3. A system according to claim 2 wherein a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn, said impedance matching ring being within said horn.

4. A system according to claim 3 wherein a central portion of said outer feed waveguide on a side of said horn opposite the radiating aperture of said outer feed waveguide joins with said horn by a series of steps of increasing diameter of said outer feed waveguide.

5. A system according to claim 3 wherein a spectral region of said lower frequency radiation is contiguous a spectral region of said higher frequency radiation, and said inhibiting means comprises a neck of reduced diameter at the radiating aperture of said inner feed waveguide.

6. A system according to claim 3 wherein a ratio of said reduced diameter of said neck to a diameter of said inner feed waveguide is approximately 5/4.

7. A system according to claim 5 wherein an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn, said system further comprising a dielectric rod held within said neck and extending outward into a region of said shroud.

8. A system according to claim 7 wherein said dielectric rod has a dielectric constant approximately double the dielectric constant of a wave propagation medium within said inner feed waveguide.

9. A system according to claim 8 wherein said wave propagation medium within said inner feed waveguide is air.

10. A system according to claim 8 wherein said dielectric rod extends inwardly into said inner feed waveguide beyond a region of said neck.

11. A system according to claim 7 wherein said shroud has a back wall recessed from said radiating aperture of said outer feed waveguide, said back wall extending radially from said horn, there being a reentrant cavity in said back wall facing said radiating aperture of said outer feed waveguide.

12. A system according to claim 11 wherein said reentrant cavity has a flat bottom which extends in a plane transverse to said outer feed waveguide.

13. A system according to claim 1 further comprising a plurality of impedance matching rings disposed in said outer feed waveguide at differing distances from said radiating aperture of said outer feed waveguide.

14. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam;

an impedance matching ring disposed in said outer feed waveguide;

wherein a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn, said impedance matching ring being within said horn;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn, said system further comprising a dielectric rod held within said neck and extending outward into a region of said shroud;

said dielectric rod has a dielectric constant approximately double the dielectric constant of a wave propagation medium within said inner feed waveguide; and

said dielectric rod has a conically shaped cavity opening toward a rear of said rod in a direction opposite from the radiating aperture of said inner feed waveguide, said conical cavity and said reduced diameter of said neck inhibiting egress of any portion of said lower frequency radiation having entered said inner feed waveguide.

15. A system according to claim 14 wherein said dielectric rod has a cylindrical cavity opening at a front end of said rod at the radiating aperture of said inner feed waveguide, and being coaxial with said inner feed waveguide, said cylindrical cavity inhibiting a reflection of the higher frequency radiation back into said inner feed waveguide.

16. A system according to claim 15 further comprising a cover plate of nonconducting dielectric material, and a mounting ring of nonconducting dielectric material extending forward of said shroud and connecting with said cover plate.

17. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam;

wherein a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn;

said system further comprises a dielectric rod held within said neck and extending outward into a region of said shroud;

said dielectric rod has a dielectric constant approximately double the dielectric constant of a wave propagation medium within said inner feed waveguide;

said dielectric rod extends inwardly into said inner feed waveguide beyond a region of said neck; and

said dielectric rod has a conically shaped cavity opening toward a rear of said rod in a direction opposite from the radiating aperture of said inner feed waveguide, said conical cavity and said reduced diameter of said neck inhibiting egress of any portion of said lower frequency radiation having entered said inner feed waveguide.

18. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam;

wherein a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn;

said system further comprises a dielectric rod held within said neck and extending outward into a region of said shroud;

said dielectric rod has a dielectric constant approximately double the dielectric constant of a wave propagation medium within said inner feed waveguide;

said dielectric rod extends inwardly into said inner feed waveguide beyond a region of said neck; and

said dielectric rod has a cylindrical cavity opening at a front end of said rod at the radiating aperture of said inner feed waveguide, and being coaxial with said inner feed waveguide, said cylindrical cavity inhibiting a reflection of the higher frequency radiation back into said inner feed waveguide.

19. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam;

wherein a radiating aperture of said outer feed waveguide is an annulus, said inner feed waveguide carrying a larger spectral band of electromagnetic signals than a spectral band carried by said outer feed waveguide;

a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn;

a central portion of said outer feed waveguide on a side of said horn opposite the radiating aperture of said outer feed waveguide joins with said horn by a series of steps of increasing diameter of said outer feed waveguide;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn; and

said shroud has a back wall recessed from said radiating aperture of said outer feed waveguide, said back wall extending radially from said horn, there being a reentrant cavity in said back wall facing said radiating aperture of said outer feed waveguide.

20. A system according to claim 19 wherein said reentrant cavity has a flat bottom which extends in a plane transverse to said outer feed waveguide, said reentrant cavity having a depth of approximately one tenth of a wavelength at a midband frequency of radiation transmitted by said horn.

21. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam, said inhibiting means comprising a neck of reduced diameter at the radiating aperture of said inner feed waveguide;

wherein a radiating aperture of said outer feed waveguide is an annulus, said inner feed waveguide carrying a larger spectral band of electromagnetic signals than a spectral band carried by said outer feed waveguide;

a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn;

a spectral region of said lower frequency radiation is contiguous a spectral region of said higher frequency radiation;

said system further comprises a dielectric rod held within said neck and extending outward into a region of said shroud;

said dielectric rod extends inwardly into said inner feed waveguide beyond a region of said neck; and

a reentrant cavity is disposed on an outer surface of said neck and encircles both said neck and a portion of said dielectric rod.

22. A feed system according to claim 21 wherein said reentrant cavity on said neck has a depth in a range of one-quarter to one-half wavelength at a midband frequency of radiation transmitted by said horn.

23. A feed system for an antenna, the feed system comprising:

an inner electrically conducting tube and an outer electrically conducting tube, a space within the inner tube constituting an inner feed waveguide, and a space between the inner tube and the outer tube constituting an outer feed waveguide;

means for applying a higher frequency radiation to the inner feed waveguide, and a launcher for launching a wave of lower frequency radiation in the outer feed waveguide, said feed waveguides having coaxial radiating apertures for radiation of signals at the higher and the lower frequencies to produce higher and lower frequency beams from a common phase center;

means at the radiating aperture of said inner feed waveguide for inhibiting entry of the lower frequency radiation into said inner feed waveguide to insure a desired pattern to said lower frequency beam;

wherein a portion of said outer feed waveguide, contiguous its radiating aperture, has an enlarged diameter to form a horn;

an outer perimeter of a radiating aperture of said horn comprises a shroud enveloping a mouth of said horn and having a larger diameter than a portion of said horn set back from said radiating aperture of said horn;

a spectral region of said lower frequency radiation is contiguous a spectral region of said higher frequency radiation;

said system further comprises a dielectric rod held within said neck and extending outward into a region of said shroud;

said dielectric rod extends inwardly into said inner feed waveguide beyond a region of said neck;

a reentrant cavity is disposed on an outer surface of said neck and encircles both said neck and a portion of said dielectric rod;

a central portion of said outer feed waveguide on a side of said horn opposite the radiating aperture of said outer feed waveguide joins with said horn by a series of steps of increasing diameter of said outer feed waveguide;

said shroud has a back wall recessed from said radiating aperture of said outer feed waveguide, said back wall extending radially from said horn, there being a reentrant cavity in said back wall facing said radiating aperture of said outer feed waveguide; and

said reentrant cavity has a flat bottom which extends in a plane transverse to said outer feed waveguide, said reentrant cavity having a depth of approximately one tenth of a wavelength at a midband frequency of radiation transmitted by said horn.