Third-order harmonic generation in high-temperature superconducting coplanar waveguides at microwave frequencies

We use third-harmonic measurements of coplanar waveguide (CPW) transmission lines to explore the behavior of nonlinearities in microwave devices fabricated from high-T-c superconductors. Our measurements focus on the effect of varying the CPW geometry, including center conductor linewidth, line length, and film thickness, on the nonlinearity of the transmission line circuit as measured by the third-order intercept. The third-order intercepts decrease (indicating more nonlinearity) with increasing line length for all geometries studied. Also, differences in the third-order intercepts between lines of different linewidth and film thickness can be explained quantitatively by appropriately scaling the incident microwave power. These observations demonstrate that the sources of nonlinearity in our CPW transmission lines are distributed along the line length, and depend on the detailed form of the current distribution within the superconductor. Published by Elsevier Science Ltd.