ALMA band 2+ (67–95 GHz) receiver optics

Recently, NRAO has successfully developed an ALMA band 2 (67-90 GHz) prototype receiver based on MIC low noise amplifiers (LNA). NAOJ collaborated in the receiver optics design and simulations. After some initial evaluation of the performance of new MMIC LNAs, it has been decided to extend the frequency coverage to 95 GHz to cover some additional science cases. In this paper, we describe the design of a new corrugated horn and dielectric lens to extend the receiver optics bandwidth up to 95 GHz. A new design target has been to ease fabrication. The new receiver optics has a fractional bandwidth of 35% and is fully compliant with ALMA specifications.