IEC 60154-4:2017 specifies the dimensions of flanges for circular waveguides for use in electronic equipment. It covers requirements for flanges drilled before or after mounting on waveguides. The aim of this document is to specify for waveguide flanges the mechanical requirements necessary to ensure compatibility and, as far as practicable, interchangeability as well as to ensure adequate electrical performance. This edition includes the following significant technical changes with respect to the previous edition: - revise the estimation for return loss at connection interface of waveguides; - add two type of waveguide flange for high frequency application, i.e. over 50 GHz; - expand the operation frequency range up to 3,3 THz; - rename the frequency band over R1200, i.e. R1.2K.