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A 4:1 transmission-line impedance transformer for broadband superconducting circuits



Leonardo M. Ranzani, Lafe F. Spietz, Jose A. Aumentado, Zoya Popovic


We present a 4 : 1 superconducting transmission-line impedance transformer for cryogenic applications. The device transforms 25 {Ω} in the coplanar waveguide to 6.25 {Ω} in the microstrip and is designed to operate at 20 mK. Calibrated measurements in a dilution refrigerator demonstrate a -3 dB bandwidth from 1.6 to 13 GHz. In a modified Ruthroff design, a small capacitor is integrated at the input as a direct-current block, making it suitable for biasing and matching to low-impedance active circuits, such as superconducting quantum interference device (SQUID) amplifiers.
IEEE Transactions on Applied Superconductivity


Superconducting microwave devices, impedance matching, transformers


Ranzani, L. , Spietz, L. , Aumentado, J. and Popovic, Z. (2012), A 4:1 transmission-line impedance transformer for broadband superconducting circuits, IEEE Transactions on Applied Superconductivity, [online], (Accessed July 23, 2024)


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Created October 1, 2012, Updated November 10, 2018