Conductor profile effects on the propagation constant of microstrip transmission lines

We experimentally show that the increase in conductor loss due to roughness is larger than the factor of two predicted by the most widely used roughness factor models. This is consistent with a recent numerical study of the effect of random roughness on conductor loss. The data also show that, for thin substrates, increasing the conductor profile substantially slows the effective velocity of propagation and also increases dispersion, independent of the composition of the dielectric material. Measurements are compared with results from a new conductor model as used in a 3-D planar EM analysis that includes an excess inductance related to the conductor profile. It is shown that this accounts quantitatively for both the insertion loss and phase constant effects.