Shrouded horn feed assembly

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.

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.

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.

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.

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.

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.