A LOW-NOISE MICROMACHINED MILLIMETER-WAVE HETERODYNE MIXER USING NB SUPERCONDUCTING TUNNEL-JUNCTIONS

A heterodyne mixer with a micromachined horn antenna and a superconduc tor-insulator-superconductor (SIS) tunnel junction as mixing element i s tested in the W-band (75-115 GHz) frequency range. Micromachined int egrated horn antennas consist of a dipole antenna suspended on a thin Si3N4 dielectric membrane inside a pyramidal cavity etched in silicon. The mixer performance is optimized by using a backing plane behind th e dipole antenna to tune out the capacitance of the tunnel junction. T he lowest receiver noise temperature of 30+/-3 K (without any correcti on) is measured at 106 GHz with a 3-dB bandwidth of 8 GHz. This sensit ivity is comparable to the state-of-the-art waveguide and quasi-optica l SIS receivers, showing the potential use of micromachined horn anten nas in imaging arrays. (C) 1996 American Institute of Physics.