LNF-xxxxC4_12A is an ultra-low insertion loss cryogenic dual junction isolator/circulator operating in the 4‑12 GHz frequency range. It has been designed from ground up to meet the strict requirements of ultra-low temperature physics research. The gold plated OFHC copper body ensures minimum loss and that this loss reaches the lowest possible temperature to minimize thermal noise. The isolator/circulator is packaged in a slim coaxial module using industry standard SMA connectors. The module measures 44.7×24.6×10.2 mm excluding the connectors.