The present invention relates to microwave radio frequency waveguide feed systems, and more particularly to a high-isolation, broadband, and polarization diverse circular waveguide feed for reception of Direct Broadcast Satellite (DBS) television and Internet satellite downlink services that operate worldwide.
The widespread demand for high-quality video, audio, and data communications via satellite has resulted in the need for additional bandwidth and better cross polarization rejection as well as reduced interference from noise or adjacent frequency operation. As a result, satellite broadcast systems are operating over broader and higher frequency ranges and implementing sophisticated methods to reduce interference and improve the intelligibility of communication signals that limit their operating capability. However, the radio frequency apparatus that operate at higher frequencies and with broader bandwidth require considerable design attention and often result in multiple and complicated waveguide feeds in order to account for electric and magnetic field behavior that exists inside the microwave waveguides that propagate their signals.
Also, in order to maintain reliable communication, transmit and receive systems must possess polarization compatibility, which is that property of a radiated wave of an antenna that describes the shape and orientation of the electric field vector as a function of time. Polarization compatibility further complicates the waveguide feed design because electromagnetic energy may be transmitted in arbitrary linear, right-hand circular, left-hand circular, or elliptical polarization.
It is well known in the art that square waveguides produce mode patterns that allow high efficiency injection or removal of energy for linear polarized electromagnetic waves using probe coupling, which results in orthogonal linear polarizations of high-isolation needed to reduce noise and unwanted adjacent frequency interference. Satellite systems, however, typically operate with circular polarization, which propagates well in circular waveguides, but generates undesirable cross polarization components and poor isolation when using orthogonal probe coupling methods in planar orientation. To minimize cross polarization components that result in a circular waveguide from the two orthogonal polarizations that comprise the circular polarized wave, elaborate conversion methods are employed to transform circular polarized electromagnetic waves. Polarity converters and filters are methods used to condition the circular polarized wave, but have the disadvantage of being difficult to design and possessing high cost and large size.
The present invention is a microwave feed assembly of simple, elegant, and scalable design that incorporates the desirable characteristics of broadband operation, polarization diversity, high-isolation between the orthogonal linear polarizations, low insertion losses, small size, and applicability to a broad family of antennas.
The present invention relates to a high-isolation, broadband, and polarization diverse circular waveguide feed for microwave frequency antennas. In one aspect of the invention, the waveguide feed supports transmission or reception of any arbitrary linear, right-hand circular, left-hand circular, or elliptical polarized microwave signal while achieving desirable performance over a wide range of frequencies with small size. In another aspect of the invention, the waveguide feed incorporates high cross-polarization rejection of unwanted TE11 Mode components when operating in arbitrary linear mode. In yet another aspect of the invention, the waveguide feed employs high probe-to-probe isolation for rejection of undesired cross-polarization when operating in circular or elliptical polarization mode. A waveguide feed assembly is disclosed, which comprises a combination of symmetrical shaped conical frustrum waveguide and circular waveguide segments together with a novel arrangement of orthogonal and nonplanar electric field probes and radio frequency impedance posts to achieve high-isolation, broad bandwidth, and polarization diversity.
It is an object of the present invention to provide a microwave waveguide feed system that can transmit or receive arbitrary linear, right-hand circular, left-hand circular, or elliptically polarized electromagnetic waves.
It is another object of the present invention to provide a microwave waveguide feed system that will support operation over a broad range of frequencies.
It is yet another object of the present invention to provide a microwave waveguide feed system with cross polarization rejection greater than 20 dB.
It is yet another object of the present invention to provide a microwave waveguide feed system with probe-to-probe isolation greater than 30 dB when rejecting undesired linear cross polarization of the two orthogonal linear polarizations that comprise circular or elliptical polarized electromagnetic waves.
It is a feature of the present invention to provide a waveguide assembly that is polarization diverse for operation with arbitrary linear, right-hand circular, left-hand circular, or elliptically polarized electromagnetic waves.
It is yet another feature of the present invention to provide a compact, reliable, and simple to manufacture waveguide assembly that uses common materials and is suitable for reflector type antennas used to meet minimal radome swept volume applications by reducing the axial length of the waveguide assembly.
It is an advantage of the present invention to provide a waveguide assembly that is low cost, rugged, and applicable to a broad family of microwave antennas.
It is another advantage of the present invention to provide a microwave waveguide feed that can operate as a stand-alone microwave antenna system.
It is yet another advantage of the present invention to provide a waveguide assembly that incorporates design characteristics that are scalable to any frequency of microwave operation.
These and other objects, features, and advantages are disclosed in the specification, figures, and claims of the present invention.