Corrections to the attenuation constants of piston attenuators

The modes existing in a circular waveguide with walls of finite conductivity are investigated and expressions derived for the corrections to the attenuation constant of a piston attenuator. The correction is negligible for E-modes but may be of importance in work of the highest accuracy when H-modes are used. Similar corrections are derived for the effect of an oxide layer on the inner surface of the attenuator.