Reduction of wind induced antenna pointing errors using structural analysis and testing

A finite element model of the antenna was built in order to predict and study the structural characteristics which caused pointing errors. The entire antenna was modelled including reflector, supporting structure and elevation and azimuth jacks. The finite element model was solved to predict the lowest 5 modes of vibration. It was considered likely that these two lowest frequency modes were causing the problems because wind energy tends to be low frequency. In addition, the modeshapes are ideal contenders for being excited and causing problems due to the rotational motion of the entire reflector. To confirm this opinion, it was decided to embark upon a programme of testing, initially preliminary, to be followed by more comprehensive tests if successful. The objectives of testing were as follows: correlate frequencies and modeshapes predicted by finite element analysis; determine absolute deflections; and measure wind velocities.<
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