The optical system is shown in Figure 2a and 2b. The telescope beam emerges
from the elevation flange and is reflected downwards by a wire grid.
The beam then reflects off a flat mirror and passes through a Mylar
beamsplitter into the dewar where it is focused into the mixer feedhorn
by a polyethylene lens. The system is configured so that the focal plane
of the telescope is coincident with the cooled polyethylene lens.
During the receiver commissioning, we measured a main beam efficiency
( 
) of 
on Mars and 
on Saturn.