Adjustable microstrip transformer for use with Josephson devices in mm-wave ICs

A simple remotely adjustable cryogenic impedance transformer employing superconducting inverted microstrip circuits is described. The scheme is particularly suitable for efficiently coupling low impedance (0.1¿5 ¿) thin-film devices (e.g. Josephson junctions) in planar microwave integrated circuits to waveguide or other superconducting and semiconducting devices at millimetre wavelengths. Preliminary results obtained at 8 mm are presented.