Autotrack Control Systems for Antenna Mounts with Non-Orthogonal Axes

The use of non-orthogonal, or conic, mounts for steerable antennas introduces some control system design problems not present in the more conventional orthogonal mounts. These problems result from both the geometrical and the mechanical cross-coupling which occurs between the two non-orthogonal axes of motion. This paper presents a general analysis and design of the control system for the open cassegrain antenna which can be readily applied to other nonorthogonal antenna structures. The form of the feedback controller for approximately non-interacting control of each axis is developed. Also described is a supplementary control strategy for providing tracking near the zenith region without excessively high slewing rates. A computer simulation o1 the system has verified the basic control strategy for non-orthogonal mounts and established the feasability of operating compact antenna structures such as the open cassegrain design under severe wind conditions without a radome.