This memo presents a conceptual design for the optics of the ALMA front ends. The design is intended to be as simple as possible, under certain stated constraints, while achieving the major performance goals. Bands 1 and 2 use an in-line configuration consisting of a room-temperature lens and cold horn. Bands 3-10 have no room-temperature elements ahead of the window; each uses a pair of cold mirrors, one flat and one ellipsoidal, to re-focus the beam onto a cold horn. The performance of the design is analyzed with respect to aberrations, polarization beam squint, thermal load due to the windows, and ohmic losses. The results are preliminary, and some important implementation issues are not covered.
View a PDF version of ALMA Memo #324.
Last modified: September 26, 2000
alma-memos@nrao.edu