The feed cone is the physical structure that houses the feed horns of the various receivers. The feed horns are sealed to prevent moisture from getting into the horns. The plastic seal is transparent to radio frequencies.
Over the 2.3 GHz [13cm] feed there is a grate. This is a dichroic reflector. This grate will allow the 2.3 GHz [13cm] signals to pass through, but reflect 8.4 GHz [4cm] over to a secondary reflector. This secondary reflector (the metal disc) then bounces the 8.4 GHz [4cm] signal into the 8.4 GHz feed. This allows simultaneous observation at two frequencies.
Around the higher frequency feeds there are feed heaters. When turned on, these heaters pump out infrared radiation to help evaporate moisture on the feed horn covers. While radio astronomy can take place in virtually any type of weather, moisture in the form of rain, snow, ice, and condensation on the feeds of the higher frequencies (8.4 GHz and up) cause the signal to degrade.