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  Electronically scanning direction finding antenna systemUSPTO Application #: 20060125704Title: Electronically scanning direction finding antenna system Abstract: An electronic scanning radio direction finding system for accurate direction finding of radio frequency signals using singly or doubly flared cylindrical reflectors surrounded by a circular array of inwardly facing feed horns. The array is operated as a phased array to determine the direction of origin of received signals. The feed horns can also be used to transmit RF signals on very narrowly controlled beams with minimal side lobes. The flared cylindrical reflector and its circular feed horn array may be paired with circular log periodic arrays operable at similar frequency ranges or different frequency ranges to provide more precise direction finding and direction finding of signals at frequencies beyond the range of the flared cylindrical reflector and its circular feed horn array. (end of abstract)
Agent: Crockett & Crockett - Laguna Hills, CA, US Inventors: Arsen Melconian, David Steward, Gregory Lackmeyer, John Longyear, Paul Crane USPTO Applicaton #: 20060125704 - Class: 343779000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060125704. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of U.S. application Ser. No. 10/826,442 filed Apr. 15, 2004, now U.S. Pat. No. 6,987,489, which claims the benefit of U.S. Provisional Application No. 60/463,168, filed Apr. 15, 2003. FIELD OF THE INVENTIONS [0002] The inventions described below relate the field of radio frequency direction finding. BACKGROUND OF THE INVENTIONS [0003] Radio frequency direction finding antenna systems are useful in a number of applications which require accurate determination of the direction from which a radio transmission originates. Communication systems that depend on mobile transmitters or receivers, or satellites, use direction finding to determine proper orientation of a receiving antenna. Surveillance, intelligence, and military targeting systems are primarily concerned with accurate location of a radio frequency source. [0004] The most prevalent radio direction finding systems include a paraboloid off-set antenna which comprises a reflector having the shape of a parabolic section, a feed horn fixed at the focal point of the reflector, a motor for rotating the reflector and feed horn together as a unit (and position indicators for communicating the exact orientation of the reflector and feed horn), and associated electronics for controlling the motor, processing received signals, and generating an output indicating the direction of a radio frequency signal of interest. While the reflector and feed horn are rotated together, associated signal processing systems analyze detected RF signals to determine the direction from which RF signals of interest originate. The direction of a received signal is determined by comparing the position information of the antenna and feed horn with the peak beam strength of the incoming signal. [0005] Non-rotating direction finding antenna systems have been proposed, and these operate as phased arrays. These systems comprise a number of antennae located in fixed relationship to each other, and associated electronics for processing received signals, and generating an output indicating the direction of a radio frequency signal of interest. These systems entail relatively large arrays, and are generally planar, and provide coverage over limited spans. SUMMARY [0006] The systems and methods disclosed below provide for accurate direction finding of radio frequency signals without moving parts. The resolution of the system is 0.08 degrees. The system operates on a broad frequency range of 0.4 to 50 gigahertz, with a gain of 10 to 20 dBi, depending on the frequency. The system comprises a central, outwardly convex (in the horizontal or azimuth plane) cylindrical reflector which is surrounded by a circular array of inwardly facing feed horns. The reflector is preferably outwardly concave in the elevational plane, and its shape approximates a surface of revolution of parabolic sections about the axis perpendicular to the beam plane, forming a flared cylinder. [0007] The array of feed horns comprises feed horns fixed at the focal points of the cylindrical reflector, or the focal plane of the flared cylindrical reflector, thus forming a ring of feed horns surrounding the flared cylindrical reflector, directed inwardly toward the flared cylindrical reflector. The feed horns are adapted to operate with the system as broadband receivers. The array is operated as a phased array, and associated electronics, signal processors and computers are used to analyze the signals received at each feed horn to determine the direction of origin of received signals. The feed horns can also be used to transmit RF signals on very narrowly controlled beams with minimal side lobes. [0008] The flared cylindrical reflector and its circular feed horn array may be paired with circular log periodic arrays operable at similar frequency ranges or different frequency ranges to provide more precise direction finding and direction finding of signals at frequencies beyond the range of the flared cylindrical reflector and its circular feed horn array. BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 shows the reflector and feed array of the direction finding antenna system. [0010] FIG. 2 shows the reflector and feed array of the direction finding antenna system, adapted to provide above-the-horizon coverage. [0011] FIG. 3 shows the reflector and feed array of the direction finding antenna system, adapted to provide above-the-horizon coverage over 180.degree. of azimuth. [0012] FIGS. 4a and 4b illustrate a feed horns adapted for use with the reflector. [0013] FIGS. 5 and 6 illustrate the adjustment of reflector shape which provides for localization of RF signals in elevation. [0014] FIG. 7 shows the reflector and feed array mounted on a turntable to provide a direction finding antenna system adapted to provide azimuth and elevation localization. [0015] FIG. 8 is cutaway view of the system of FIG. 7. [0016] FIG. 9 shows the reflector and feed array of the direction finding antenna system, modified with the addition of an inwardly hyperboloid sub-reflector. [0017] FIG. 10 shows the reflector and feed array of the direction finding antenna system, with orthogonally disposed reflector assemblies. [0018] FIGS. 11 and 12 show the reflector and feed array of the prior Figures paired with broadband log periodic active feed arrays. [0019] FIGS. 13 and 14 show a cylindrical array of antennas in an electronically scanning direction finding system. DETAILED DESCRIPTION OF THE INVENTIONS Continue reading... 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