Adiabatic Design for a Coaxial Transmission Line

This paper proposes an air-gap applied adiabatic line for a coaxial transmission line. The adiabatic characteristics with excellent microwave transmission were simulated in terms of the S-parameter and the heat transfer of coaxial lines with a finite-element-method-based tool for the adiabatic microwave design. The detailed design scheme of the air-gap adiabatic line is presented and its performance is evaluated. The adiabatic efficiency associated with microwave feature was analyzed by a resistive equivalent circuit model of the line. We made a stainless steel air-gap adiabatic line that had about 11 times greater thermal resistance than that of a gapless coaxial line, a beryllium copper line, with the increment of just 0.4-dB insertion loss. We also propose a solution to improve the low-frequency transmission of an air-gap adiabatic line with a tunable ground wire for broad-band feature.