Effect on return loss of dimensional tolerances of the aperture of rectangular waveguide

The letter suggests a definition of a nominal characteristic impedance R0 for the dominant mode postulated for lossless rectangular waveguide in order to provide a basis for comparing reflection by waveguide components. The width a, height b and internal corner radius r enter into this defined R0, and the calculated limits of reflection?expressed as return loss normalised to this R0?are presented for some waveguides to British Standard Specifications together with others to tighter tolerances.