Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1977-04-01
1979-05-22
Blum, Theodore M.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
343117R, 318649, H04B 700
Patent
active
041562410
ABSTRACT:
Satellite tracking apparatus for use on board ship as part of a maritime communications satellite terminal is disclosed. A directional antenna which is adapted to be trained in the direction of the satellite so as to be in communication therewith is mounted so as to be positioned about three axes, namely train, elevation, and cross-level axes. The mount also has a fourth axis which is parallel to or collinear with one of the other axes. This fourth axis may be a level axis which is movable with the antenna. A stable platform is movable with and rotatable about the level axis. Sensors on this platform provide outputs to servo controllers which rotate the antenna about the elevation and cross-level axes to maintain the platform stable. An azimuth sensor such as a gyro compass and sensors responsive to angular motion with respect to the train axis may also be mounted on the platform and provide outputs to a servo controller which controls the bearing or azimuth position of the antenna. An open loop control is provided for the level axis which establishes an equivalent angle between the stable platform and the true elevation line of sight (an angle equal to but opposite from the true elevation angle to the satellite). A mislevel is thereby created and sensed by the sensor for the elevation axis which provides an output that activates the elevation axis servo controller to reduce the mislevel to zero and null, thereby achieving the desired elevation of the antenna. The antenna is stabilized and decoupled from the motions (roll, pitch and yaw) of the ship and changes in the ship's heading, in that the sensors are mounted on the stable platform which moves with the antenna. The need for coordinate conversion computers responsive to sensors strapped down to the deck or other ship structure and for alignment of the antenna axes with the pitch or roll axis of the ship is also eliminated. The rotation of the antenna about its boresight axis is eliminated; thus avoiding misalignment between the polarization of the antenna and the satellite signals.
REFERENCES:
patent: 3305868 (1967-02-01), Kikuo et al.
patent: 3986092 (1976-10-01), Tijsma et al.
Mobley Joseph G.
Wilson Robert J.
Blum Theodore M.
Lukacher Martin
Scientific-Atlanta, Inc.
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