An antenna tracking method for land‐mobile satellite communications system

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Abstract
A new satellite‐tracking method is proposed for a directional antenna installed on a car for L‐band land‐mobile satellite communication. This method uses both a fiber optic gyroscope (FOG) and a magnetic compass (MC) with an open‐loop control algorithm, which com pensates for the disadvantages of individual sensors. Since FOG can detect the angular velocity precisely but cannot detect the absolute azimuthal direction, this type of sensor has inherent errors due to accumulating the angular velocities necessary to obtain the azimuthal direction. Cumulative errors caused mainly by a disagreement between the FOG axis for measuring rotation and the vertical axis during turning curves can be compensat ed by MC. the disadvantage of MC is that errors due to magnetic disturbance are caused by magnetized bridges and trucks. In the proposed method, the occurrence of a magnetic disturbance is detected from a statistical analysis of MC acquired data and FOG is used to control the antenna direction when a car turns either right or left. According to an analysis of the three‐dimensional motions of cars, it was determined that only azimuthal antenna tracking can provide the precise control required to obtain good tracking performance, even when using an 91 L‐band directional antenna with an antenna gain of ap proximately 13 dBi.

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