A broad-band microwave superconducting thin-film transformer

The design, construction, and testing of a broadband superconducting transformer based on a Dolph-Chebyshev distribution are described. The transformer is completely compatible with thin-film circuit topologies and allows access to 50-Ω coaxial launchers. The transformer is a taper that utilizes only one side of the substrate and features a coplanar waveguide to microstrip transition without the use of via holes. The taper provides a characteristic impedance transformation from 50 Ω to 2 Ω over a frequency range from 5 to 15 GHz. The taper provides a much larger bandwidth than a linear taper with the same length and impedance transformation