Millimeter wave response of Josephson junction arrays using a waveguide to microstrip line converter

Abstract

High Tc weak-link Josephson junction (JJ) arrays are expected to be used as high-resolution, high frequency mixers. We have fabricated JJ arrays in the form of a 10 µm-width Eu1Ba2Cu3O7-x superconducting meander line on the grain boundary of a bi-crystal MgO substrate. The millimeter wave response of these arrays has been measured using the waveguide to microstrip line transition technique, which directly couples a waveguide with a 50Ω superconducting microstrip line. A JJ array consisting of junctions shows RSJ type I-V characteristics and evolves Shapiro steps in the presence of a millimeter wave transmission at 6.7 K at voltage intervals of 3VO (VO=hf/2e). The mixing output reaches its peak at bias voltages corresponding to the peaks of dV/dI characteristics in the millimeter wave region. The mixing conversion efficiency of a 3 JJ array is estimated to be -29.4 dB at an intermediate frequency of 2.045 GHz.