Satellite tracking antenna system

Abstract

A satellite tracking antenna system for use on board ship as part of a maritime communications satellite terminal is disclosed. The system has a directional antenna which is continually trained in the direction of the satellite so as to receive signals therefrom and transmit thereto in spite of the continual rolling, pitching and turning movement of the ship as it travels along its course, even in heavy seas. The system includes a platform which is adapted to be mounted at the head of the mast of the ship. A servo control unit receives position and angular rate signals from roll and pitch sensors mounted on the platform, and serves to drive stepper motors through drive units therefor which counteract pitch and roll without the need for gyroscopic stabilization means and without requiring tachometers or other feedback control in the drive units so that the platform always remains level regardless of the pitching and rolling of the ship. A heading input unit receives synchro information from the ship's gyrocompass or from its synchro or step repeaters by way of a gyrocompass converter which translates this information into digital form. The heading input unit also receives azimuth information regarding the position of the satellite as well as elevation data, also regarding the position of the satellite. Azimuth and elevation control servos which may include stepper motors and drive units similar to those used in the pitch and roll servos, are operated by control signals from the heading input unit train the antenna in azimuth and elevation so that it points in the direction of the satellite. Yawing or turning is counteracted by the heading input unit which modifies the azimuth control signal in accordance with the data as to the ship's heading from the gyrocompass converter. The direction of the pointing of the antenna, to accommodate slow changes in latitude and longitude as the ship moves along its course which causes a change in satellite position relative to the ship, is accommodated by either changing the elevation and azimuth data provided to the heading input unit or by means of an automatic satellite position update unit which changes the heading input data to the azimuth and elevation servos in accordance with changes in the strength of the signal received by the antenna from the satellite.

Dependencies are inferred from the claim text.