A distributed lumped-element SIS mixer with very wide instantaneous bandwidth

A novel type of distributed superconducting mixer with very low output capacitance has been designed for a 330-420 GHz waveguide mixer. In this design, a pair of lumped element Superconductor-Insulator-Superconductor junctions is connected in series to form the unit cell of a composite transmission line. The mixer utilizes two cascaded cells. Using an intermediate frequency (IF) of 5 GHz, we have measured Double-side-band (DSB) receiver noise temperatures of 90-120 K between 360 and 410 GHz. This mixer design offers very wide instantaneous bandwidth. The measured IF bandwidth is in excess of 18 GHz. At a Local Oscillator frequency of 384 GHz, the Y-factor measured at an IF frequency of 18 GHz is 2.1, compared to a Y-factor of 2.2 measured at an IF of 5 GHz. The mixer also has a high dynamic range. The 1-dB input compression point is only reached with an input black body load of 30,000 K.