Formula Derivation of Characteristic Impedance of Substrate Integrated Coaxial Line

A closed-form formula for the characteristic impedance of substrate integrated coaxial line (SICL) is proposed in this paper. The central inner conductor of the SICL is sandwiched between two grounded dielectric substrate layers and shielded by two rows of metallic via holes. Thickness of the inner conductor in SICL has a significant effect on its characteristic impedance, which is investigated in the paper. The formula of the characteristic impedance of the SICL is derived with taking the thickness effect of inner conductor into account. Besides, the conductor loss of the SICL can be calculated based on the proposed characteristic impedance formula. Calculation results from the proposed formula show good agreements with simulation results under different processes.