Full-wave analysis of lossy transmission line incorporating the metal modes

A full-wave mode-matching analysis of a unilateral finline with finite conductivity, metallization thickness, and holding grooves is presented. A novel class of metal modes exists in the metallized region for the most part and decays sharply in the air region. The relative convergence criterion for a lossless waveguide is also observed for the finline with good metal coating. A criterion is given in order to determine the relative numbers of air and metal modes needed in the mode-matching formulation. It is shown that there exist the so-called metal modes in each metallized region with finite conductivity. For the particular case studied, the omission of the metal modes results in an inaccurate propagation constant, of which the attenuation constant can be two orders of magnitude smaller than that obtained by including the metal modes.<>