Hydrodynamic Techniques for Study of Wind Effects on Antenna Structures

The feasibility of operating a narrow beam tracking antenna without the environmental protection of a radome is dominated by the consideration of antenna tracking accuracy under the influence of wind-induced random disturbance torque. Although the wind power spectrum at a point may be quite variable and may depend somewhat upon the locality, for our purpose it is sufficient to assume a characteristic resembling a first order low-pass filter with a cut-off angular frequency wc in the range 0.12 to 3 radians per second.1'2,3 That is, we assume the variable component of wind velocity to have a two-sided power-density spectrum of the form: UCV1 fV -- -- (1) 7 U)c T w T where V is the standard deviation of the variational component of the wind velocity. It is assumed that a satellite communications antenna must survive winds of 100 mph velocity. For compressible flow, Bernoulli's theorem can be expressed as = 1339 , V 1 1340 T H E BELL SYSTEM TECHNICAL J O U R N A L , S E P T E M B E R 1905