Design of compact transition from conical to coaxial transmission lines with a low return loss

Abstract

ABSTRACT In this paper, a simple design method for compact transition from conical to coaxial lines with a uniform impedance and low reflection in the standard ASTM D4935 jig for shielding measurement of planar materials is introduced. The proposed structures with even a short conical line exhibit a more uniform impedance and lower return loss and consequently expand the measurable frequency range. By two-port network analysis using a full-wave numerical simulator, the proposed structures are examined and validated in terms of the voltage standing wave ratio that indicates the reflection of the coaxial and conical junction. In addition, a time-domain reflectometry analysis is performed using the simulated S-parameters. Through this, the distributed characteristic impedances at the conical and coaxial lines are calculated and the difference from the theoretical values is analysed. To verify the accuracy of simulation analysis, the simulation results are compared with the measurement results using a commercial ASTM jig.