Experimental spherical near-field antenna test facility. Volume 5: Antenna positioner servo system

The design of a programmable dual axis digital servo system for the antenna positionner of an experimental spherical near field antenna test facility is described. The main specifications of the system include. Full computer programmability of speed and acceleration, speed in the range 0.1 - 20 deg/sec (1 hour/rev - 18 sec/rev), acceleration in the range 0.01 - to 2 deg/S sq, and microstepping for precision alignment. The servo system employs dc pancake motors powered by Class AB transistor amplifiers as the driving elements and optical incremental encoders as velocity feedback elements. The servo system is designed as a velocity servo, but closing the loop through a microprocessor converts the system to a position servo employing position feedback from synchro transmitters and at a later stage from inductosyns.