External Field Coupling to Superconducting Microstrip Transmission Line in Nonlinear Operation

Superconducting circuits, as the possible basis for a new generation of electronic devices, have been remarkably investigated due to high-speed operation in an electronically low-noise floor environment. It is, however, shown that coupling the external electromagnetic field to these circuits can nullify their performance. On the other hand, it is observed that at the moderate level of operating current, the superconducting microstrip transmission lines (SMTLs) show nonlinear behavior. This article focuses on external field coupling to SMTL in nonlinear operation, which has not been considered by the researchers. To tackle this issue, first, an equivalent model is proposed in which the superconducting film is replaced by a nonlinear impedance sheet. The boundary condition is then applied to the equivalent nonlinear impedance sheet. The mixed potential integral equation (MPIE) technique is employed through which a nonlinear integral equation is established. The analysis is performed under different settings of the amplitude of incidence wave and temperature. The results show that at amplitude above 1 kV/m, the induced current contains higher order wavenumber due to the nonlinear behavior of the superconductor. Further, our studies reveal that by decreasing the temperature, the SMTL exhibits less nonlinearity.