Design and analysis of an all-NbN SIS mixer using a tuning circuit with two half-wavelength distributed junctions

We have designed an all-NbN superconductor-insulator-superconductor mixer with a broadband tuning circuit for the terahertz band, which enables the use of junctions with a lower current density. It uses the reactance compensation efficiently produced by two half-wavelength distributed junctions connected by a half-wavelength microstripline. Based on the design and simulated noise performance, a tuning circuit using NbN junctions with a current density of 25 kA/cm² should be able to cover the 780-950 GHz band with an SSB receiver noise temperature below 4hfk_B.