FULL-WAVE ANALYSIS OF SUPERCONDUCTING MICROSTRIP LINES ON ANISOTROPICSUBSTRATES USING EQUIVALENT SURFACE IMPEDANCE APPROACH

A computationally efficient full-wave technique is developed to analyz e single and coupled superconducting microstrip lines on anisotropic s ubstrates. The optic axis of the dielectric is in the plane of the sub strate at an arbitrary angle with respect to the propagation direction . A dyadic Green's function for layered, anisotropic media is used to formulate an integral equation for the current in the strips. To incre ase the efficiency of the method, the superconducting strips are repla ced by equivalent surface impedances which account for the loss and ki netic inductance of the superconductors. The validity of this equivale nt surface impedance (ESI) approach is verified by comparing the calcu lated complex propagation constant and characteristic impedance for su perconducting microstrip lines on an isotropic substrate to measured r esults, and to numerical results by the more rigorous volume-integral equation method. The results calculated using the ESI approach for per fectly conducting coupled lines on an anisotropic substrate agree with the results by the finite-difference time-domain method. This efficie nt ESI technique is then used to study the effects of the optic axis o rientation and the strip width on the characteristics of single and co upled superconducting microstrip lines on M-plane sapphire. The effect s of the line separation and operating temperature on the coupled line s are also investigated.