Millimetre Wave Kinetic Inductance Parametric Amplification using Ridge Gap Waveguide

We present the design and simulation methodology of a superconducting ridge-gap waveguide (RGWG) as a potential basis for mm-wave kinetic inductance travelling wave parametric amplifiers (KI-TWPAs). A superconducting RGWG was designed using Ansys HFSS to support a quasi-TEM mode of transmission over a bandwidth of 20 to 120 GHz with its internal dimensions optimised for integration with W-band rectangular waveguide. A design of an impedance loaded travelling wave structure incorporating periodic perturbations of the ridge was described. A method to simulate the nonlinear kinetic inductance via user-defined components in Keysight's ADS was outlined, which yielded the power dependent S-parameters and parametric signal gain. A RGWG with a 30 nm NbTiN coating and 5 um conductor spacing, corresponding to a kinetic inductance fraction $\alpha \sim 60\%$ was used for the description of a KI-TWPA with 900 perturbations equivalent to a physical length 25 cm that achieved more than 10 dB of signal gain over a 75--110 GHz bandwidth via 4-wave mixing (4WM).