Simulations of Microwave Planar Transmission Lines and Passive Devices on Anisotropic Substrate (Sapphire)

Sapphire is known as a very good dielectric material with extremely low microwave dielectric loss (tan δ=10^-7-10^-8) and high thermal conductivity (κ = 10³ W/m·K) at T=78 K. Sapphire is successfully used as a substrate for high quality YBCO film growing. The use of high-Tc superconducting (HTS) films on sapphire for microwave applications provides a realization of passive devices of higher performance. The anisotropy of sapphire presents the considerable challenge to designing and manufacturing MMICs and particularly YBCO filters on sapphire substrate. Account must be taken of a development of software tools for simulation of planar transmission lines on anisotropic substrate. The goal of this paper is to present a closed form model of propagation characteristics of the planar transmission lines on the anisotropic substrate. The model was verified experimentally and by a comparison of the results of simulation of single HTS microstrip line and coupled HTS microstrip lines on r-cut and m-cut sapphire using this model and the results of full-wave analysis. A good agreement between the measured and simulated data was observed.