6.1 Antenna, Subreflector, & Feeds

The antenna and subreflector concentrate the radio frequency (RF) radiation. The feed couples free-space electromagnetic waves into waveguides for transmission to the receiver system. Feeds at observing bands above 1 GHz are located on a ring at the offset Cassegrain focus, and are selected by rotation of the subreflector with a maximum transition time of about 20 seconds. A dichroic system enables simultaneous 2.3/8.4 GHz observations. The 330 and 610 MHz feeds are crossed dipoles mounted on the subreflector near prime focus; simultaneous 330/610 MHz observations are possible.