Broadband RF-coupling to thin-film Josephson and SIS devices

The fabrication of a planar fin-line circuit for rf-coupling to Josephson tunnel junctions and SIS devices is reported. E-field coupling is achieved by means of tapered transitions from a rectangular waveguide to a fin-line and from this line to the active device. Its low impedance can be matched by an antipodal fin-line with a fin-separation in the μm-range. Circuit parameters have been determined for Nb-Pb-devices mounted in a split Ka-band waveguide. Measurements were performed in the frequency range from 33 GHz and 38 GHz. Mismatches as low as 10 dB have been observed.