Propagation Constant of a Coaxial Transmission Line With Rough Surfaces

This paper describes the accurate calculation of the propagation constant of a precision coaxial transmission line with rough plated conductors. The results are compared with previous publications and with traceable measurements of 2.4- and 1.85-mm air lines. In contrast to all tested existing procedures the present algorithm's results agree simultaneously with the real and imaginary part of the measured propagation constant. In the new algorithm, the effects of roughness and plating are represented by perturbed material parameters of a smooth coaxial line problem. A highly accurate multiple multipole field solver is used for the computation of the perturbed material parameters. The differences between the predicted and the measured propagation constant of 1.85-mm air lines are less than 0.01% at 67 GHz. Such high-precision computations are needed for the specification of offset short standards for vector network analyzer calibration.