On the Attenuation of Guided Waves in the Limit of High Frequencies

The conventional formulas for the attenuation of waves due to the wall losses in uniform waveguides are based on the two assumptions that the wall currents are the same as the loss-free currents and that the surface resistance of the highly conductive walls is isotropic. In the limit of high frequencies the former assumption remains valid whereas the latter assumption breaks down. As the frequency is increased the surface resistance becomes anisotropic in the sense that it assumes different values depending on whether the wall current is longitudinal or transverse. In this paper new attenuation formulas are derived, which take into account the high-frequency anisotropy of the surface resistance and hence yield accurate results for all frequencies