Towards a Producible ALMA2030-Ready Sideband-Separating Band 9 Receiver

In the last quarter of 2022, the NOVA Sub-mm Instrumentation Group (University of Groningen) finalized an ESO-cofunded study on the possibility of upgrading the current ALMA double sideband (DSB) Band 9 (602-720GHz) receivers to a sideband-separating (2SB) architecture. Besides the 2SB conversion itself, several other enhancements in line with the ALMA2030 roadmap were studied, in particular aspects of the Wideband Sensitivity Upgrade (WSU). A proof-of-concept Band 9 2SB mixer with an IF band of 4-20 GHz was demonstrated. Compared to the 4-12 GHz IF of the existing DSB Band 9 receivers, this represents a fourfold increase in exported IF bandwidth (from 2 x 8 GHz to 4 x 16 GHz). Another subject that was studied was the possibility to enhance the polarimetric performance of Band 9; for this a straw-man design of an OMT-based architecture (rather than the current grid-based design) was presented. In the currently running follow-up study ``Towards a Producible ALMA2030-Ready Band 9 CCA'' (also co-funded by ESO, with Observatorio Astron\'omico de Yebes and Chalmers University as partners), we address the lessons learned in the former study with the goal of arriving at a reviewable 2SB Band 9 WSU-compliant receiver prototype with polarimetric performance (cross-polar and beam squint) on par with the other OMT-based ALMA bands. We present the up-to-date results of this study (started Oct 2024).