The waveguide below-cutoff attenuation standard

A semitutorial review of the history, development, and application of waveguide below-cutoff (WBCO) attenuation standards is presented. A brief summary of the electromagnetic (EM) theory is followed by descriptions of the various designs implemented over a span of 60 years. Designs range from simplistic to elaborate electromechanical creations that stretch the toolmaker's art yet are ultimately dependent upon the primary standard of length.