Prospects and challenges in developing the next generation astronomical sub-millimetre and terahertz heterodyne...

The development of next-generation astronomical receivers operating at millimetre (mm), sub-mm, and terahertz frequencies is essential to meet the increasing demand for wide-field, high-spectral-resolution observations. In this work, we examine the prospects and challenges associated with advancing heterodyne receiver technologies, with particular emphasis on superconductor-insulator-superconductor (SIS) mixers. We present a series of technological pathways aimed at enhancing receiver performance, including ultra-broadband RF and IF SIS mixer designs, compact sideband-separating (2SB) architectures enabled by planar superconducting circuit integration, and scalable focal plane array (FPA) concepts capable of supporting hundreds to thousands of pixels. These developments are motivated by the need to significantly improve mapping speed and survey efficiency for future facilities such as ALMA upgrades, AtLAST, LST, and next-generation space missions. Another key contribution of this work is the introduction of simultaneous observing multi-band receivers (SOMBRs), which enable concurrent multi-band 2SB observations through minimal additional hardware by reconfiguring conventional receiver architectures. This approach allows continuous spectral coverage while preserving phase information required for interferometric applications. We discuss the principal challenges in realising these systems, including bandwidth optimisation, impedance matching, local oscillator distribution, and scaling to large-format arrays. Overall, this work outlines a viable pathway towards highly integrated, ultra-broadband, and scalable heterodyne receiver systems, which are expected to play a critical role in enabling the next generation of astronomical discoveries.