Gain reduction of a shaped Cassegrain antenna due to lateral displacements

The response of a 32-m radio telescope to tilts and lateral displacements of its components was analysed in the design phase, and the results of the analysis have now been confirmed by measurements with the completed antenna. The same analysis yielded a simple procedure to minimise the resultant reduction in gain by making compensating adjustments to the position and tilt of the subreflector. For antennas whose reflectors are conic sections, only the lateral displacement of the subreflector will normally require adjustment. For shaped antennas, however, it may be important to adjust the tilt also. This procedure has been successfully implemented to correct for the effects of gravitational distortion of the 32-m telescope as it is driven in elevation