Band 1 optics design.
We present the design, implementation, and characterization of the optics of ALMA Band 1. Since the optics is the first subsystem of any receiver, low noise figure and maximum aperture efficiency are fundamental for best sensitivity. However, a conjunction of several factors makes extremely challenging to achieve these goals. To overcome these problems, the optics presented here includes two innovative solutions, a compact optimized-profile corrugated horn and a modified Fresnel lens.