Millimeter-Wave Mixing on NbN Superconducting Tunnel Junctions Integrated in a Linear-Array Configuration

NbN(base)/insulator/Pb(counter) tunnel junctions integrated in a linear-array configuration were prepared and used in a millimeter-wave mixing experiment at 35 and 70 GHz. Each junction worked well on the basis of the quantum theory of mixing, though the conversion efficiency was still low due to insufficiently developed mount design and fabrication technology. Owing to the allowance of an optimum local power as large as 10 dB, the linear-array SIS junctions acted as a sensitive millimeter-wave image sensor: These junctions offered a field intensity distribution inside the waveguide at 35 GHz.