Quasi-Optics

Beam wave-guide optics is used to relay received signal to the receiver system. It consists of four metal mirrors made of aluminum (M3 not shown in the picture). The optics trains needs to be precisely aligned before their installation in the antenna. All these optics are overly sized to minimize truncation loss. This set of mirrors is located near the ceiling of the cabin. The mirrors form a beam wave-guide system to direct the incoming signal into the receiver system.

For interested reader, the paper by Dr. S. Paine et al, of SAO would be a good reference.
S. Paine et al, "Beam Waveguide and Receiver Optics for the SMA", in the Proceedings of 5th Int. Symp. Space Terahertz Tech. pp.811-823, March 1994