Microwave antenna system having enhanced band width and reduced cross-polarization
First Claim
1. A microwave antenna system for producing when energized by a source of microwave signals, first and second simultaneously propagating beams of microwave radiation, said first beam being of left-hand circularly polarized radiation, said second beam being of right-hand circularly polarized radiation, comprising in combination:
- a curvilinear microwave-reflective surface defining a focal region within which parallel beams of microwave electromagnetic radiation impinging on said surface are brought to focus;
and disposed within said focal region, a microwave feed array, said feed array comprising a plurality of waveguide feed elements disposed mutually adjacent to one another and commonly aligned to propagate microwave energy toward, and receive microwave energy from said reflective surface, each of said waveguide feed elements comprising a circular waveguide terminating in a circular aperture facing toward said reflective surface;
and disposed about each of said circular apertures, inductive tuning means to selectively reduce mutual coupling between said adjacent feed elements, and to minimize cross-polarization between adjacent feed elements, whereby adjacent feed elements can be energized with signals of alternate polarization sense while substantially avoiding cross-polarization;
said inductive tuning means comprising an inductive stub of generally U-shape, including a first leg, a second leg spaced from said first leg and generally parallel thereto, and a root portion extending between and interconnecting said first and second legs, at least one of said legs being of trapezoidal shape, having a greater width near the portion thereof adjacent said root portion and a lesser width at a tip portion thereof.
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Accused Products
Abstract
The antenna system employs a parabolic reflector fed by an offset feed array of circular wave guides located substantially at the focus of the parabolic reflector, but offset from the axis thereof. A plurality of aperture tuning mechanisms disposed at the mouths of the circular waveguides of the waveguide feed array, and having physical lengths much shorter than one wavelength at the frequencies involved, are provided to reduce cross-polarization and mutual coupling between adjacent feeds. The short resonant length of these tuning mechanisms, and their shape which is chosen to generate the TM11 mode E-field contour line ensures that they are effective over a broad bandwidth of as much as 20% or more. Within this bandwidth, they act as inductive suppressors to control both cross-polarization and mutual coupling between adjacent feeds.
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Citations
15 Claims
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1. A microwave antenna system for producing when energized by a source of microwave signals, first and second simultaneously propagating beams of microwave radiation, said first beam being of left-hand circularly polarized radiation, said second beam being of right-hand circularly polarized radiation, comprising in combination:
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a curvilinear microwave-reflective surface defining a focal region within which parallel beams of microwave electromagnetic radiation impinging on said surface are brought to focus; and disposed within said focal region, a microwave feed array, said feed array comprising a plurality of waveguide feed elements disposed mutually adjacent to one another and commonly aligned to propagate microwave energy toward, and receive microwave energy from said reflective surface, each of said waveguide feed elements comprising a circular waveguide terminating in a circular aperture facing toward said reflective surface; and disposed about each of said circular apertures, inductive tuning means to selectively reduce mutual coupling between said adjacent feed elements, and to minimize cross-polarization between adjacent feed elements, whereby adjacent feed elements can be energized with signals of alternate polarization sense while substantially avoiding cross-polarization; said inductive tuning means comprising an inductive stub of generally U-shape, including a first leg, a second leg spaced from said first leg and generally parallel thereto, and a root portion extending between and interconnecting said first and second legs, at least one of said legs being of trapezoidal shape, having a greater width near the portion thereof adjacent said root portion and a lesser width at a tip portion thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A microwave feed array for propagating microwave energy toward, and receiving microwave energy from, a microwave reflective surface, comprising a plurality of circular waveguide feed elements disposed mutually adjacent to one another and axially in alignment with one another along the axis of microwave energy propagation of said array, each of said circular waveguides terminating in a circular aperture, said circular apertures lying generally in a plane orthogonal to said axis of microwave energy propagation, and a plurality of generally U-shaped inductive tuning stubs disposed within and projecting from each of said apertures, each of said inductive stubs having an outer leg in contact with an inner wall of said waveguides, an inner leg generally parallel to said outer leg, and a root portion joining said inner and outer legs within said aperture, said inner and outer legs each being tapered from a width b1 at said root portion to a width b2 at the tip of each of said legs, where b1 >
- b2, said outer legs each having a length h1, said inner legs each having a length h2, where h1 >
h2. - View Dependent Claims (14, 15)
- b2, said outer legs each having a length h1, said inner legs each having a length h2, where h1 >
Specification